Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31828 Publications
Multiphase flow imaging: Techniques and Applications
Schubert, M.; Hampel, U.;
Multiphase flows are omnipresent in many industrial sectors and engineering disciplines, such as petroleum and chemical engineering, nuclear engineering and thermal hydraulics, and fluid me-chanics and multiphase CFD.
Multiphase flows of gases, liquids, and/or solids are often highly dynamic and fully opaque, housed in pressurized and large vessels and thus, are hardly accessible with today’s commercial diagnostic tools and standard instrumentation. In turn, improvements in process efficiency, sustainability and safety depend on detailed insights – often at CFD-grade – at different scales.
The seminar will give an overview about recent developments in advanced multiphase flow sensors and imaging techniques for in-detail flow analyses, with a focus on measurement with high resolu-tion in space and/or time. Recently pioneered imaging techniques are the wire-mesh sensor, ultrafast X-ray tomography and high-resolution gamma-ray tomography.
In particular, the underlying principles of the techniques will be shown together with a variety of application examples, such as sand erosion in pipe flow, gas entrainment in centrifugal pumps and dispersive gas-liquid mixing in static mixers.
Keywords: imaging techniques, tomography, wire-mesh sensor, applications
  • Lecture (others)
    SABIC Process Seminar, 05.10.2015, Geleen, Niederlande

Publ.-Id: 22880 - Permalink

Hydrodynamics of Concurrent Gas-Liquid Flows in Inclined Rotating and Floating Packed Beds
Dashliborun, A. M.; Larachi, F.; Härting, H.-U.; Schubert, M.; Schleicher, E.;
The effects of floating vessel motions and reactor rotation on the hydrodynamic behaviour of multiphase flows in porous media were studied. For elucidating such effects, laboratory-scale packed bed systems with co-current gas-liquid flow were subjected to different types of motion by using a hexapod ship motion simulator and a hollow shaft rotary actuator. The hydrodynamic characteristics in terms of bed overall pressure drop, liquid saturation, gas-liquid segregation, and flow regime transition was experimentally studied. A capacitance wire mesh sensor (WMS) and a compact gamma-ray tomography system (CompaCT) were positioned firmly on, respectively, the floating packed bed and the inclined rotating packed bed to visualize the two-phase flow patterns in terms of local liquid saturation distribution. The response of pressure drop, liquid saturation, and flow regime transition to the bed motions was monitored and compared to those corresponding to the static upright and 15°-inclined configurations. The results indicated that the known characteristics of the conventional trickle bed reactor cannot be transferred one to one on those of the moving reactor configurations.
Keywords: Two-phase flow, moving packed bed, hydrodynamics, WMS, gamma tomography
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 22879 - Permalink

High field superconducting properties of Ba(Fe1−xCox)2As2 thin films
Hänisch, J.; Iida, K.; Kurth, F.; Reich, E.; Tarantini, C.; Jaroszynski, J.; Förster, T.; Fuchs, G.; Hühne, R.; Grinenko, V.; Schultz, L.; Holzapfel, B.;
In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the ‘122’ family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.

Publ.-Id: 22878 - Permalink

CFD for Two-Phase Flows: Status, Recent Trends and Future Needs
Lucas, D.; Laurien, E.;
This presentation discusses the status and the future developments of CFD-methods for multiphase flows.
Keywords: multiphase, CFD, bubbly flow, segregated flow
  • Invited lecture (Conferences)
    46th Annual Meeting on Nuclear Technology, 05.-07.05.2015, Berlin, Deutscland

Publ.-Id: 22877 - Permalink

Dispersed Flow Modelling - Multiple-Size Group Modelling - MUSIG
Krepper, E.;
The lesson 7 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of two phase flow. For low gas fractions the Euler/Euler approach with continuous liquid and dispersed gas can be applied. A populatioon balance model approach is described. Model validations and model applications are presented.
Keywords: CFD, Two fluid model, Bubbly flow, population balance, MUSIG
  • Lecture (Conference)
    13th Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 24.-26.11.2015, Dresden, Germany
  • Lecture (Conference)
    14th Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 08.-10.11.2016, Dresden, Germany

Publ.-Id: 22876 - Permalink

Interfacial heat and mass tansfer models
Krepper, E.; Scheuerer, G.;
The lesson 5 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.
Keywords: CFD, Two fluid model, heat transfer, mass transfer, boiling, cavitation
  • Lecture (Conference)
    13th Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 24.-26.11.2015, Dresden, Germany

Publ.-Id: 22875 - Permalink

User facilities for Positron Annihilation Spectroscopy (PAS) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Anwand, W.; Butterling, M.; Wagner, A.;
Three user dedicated facilities of PAS are built at the Institute of Radiation Physics of HZDR. The first equipment, a mono-energetic slow positron beam with 22Na as positron source, is mainly used for depth dependent Doppler broadening spectroscopy of defects in solids. The other two facilities are driven in connection with a superconducting electron linear accelerator ELBE (Electron Linac for beams with high Brilliance and low Emittance), where the positrons are created by bremsstrahlung and pair production: the Gamma-induced positron annihilation spectroscopy (GiPS) and the pulsed mono-energetic positron beam (MePS).
After an explanation of the fundamentals of PAS, the talk will present an introduction in the set-up and functionality of these three facilities. On the basis of concrete examples the usefulness of the facilities for the investigation of open-volume defects of small size and low concentration in solids will be demonstrated.
At the end of the presentation, a short outline of the procedure for application of PAS beam time will be given.
Keywords: user facilities, positron annihilation spectroscopy
  • Lecture (others)
    Seminar-Vortrag, 30.11.2015, Prague, Czech Republic

Publ.-Id: 22874 - Permalink

CFD Simulations on TOPFLOW-PTS Tests
Apanasevich, P.; Lucas, D.; Merigoux, N.; Badillo, A.; Roy, J.;
This talk presents the main results obtained during the European project NURESAFE on CFD-modelling of a two-phase Pressurized Thermal Shock szenario. The focus is on simulations on steam-water TOPFLOW-PTS experiments.
Keywords: PTS, TOPFLOW, CFD, two-phase flow
  • Lecture (Conference)
    2nd NURESAFE Open Seminar, 03.-04.11.2015, Brussels, Belgium

Publ.-Id: 22873 - Permalink

Gittersensorbasierte Visualisierung von Verweilzeit- und Geschwindigkeitsverteilungen auf einem Siebboden
Schubert, M.; Piechotta, M.; Beyer, M.; Hampel, U.;
In vielen Trennkolonnen werden Siebböden eingesetzt, bei der der Stoffaustausch zwischen Dampf- und Flüssigphase in der Sprudelschicht erfolgt. Eine ungleich-mäßige Überströmung des Bodens, z.B. aufgrund von Wölbungen oder Neigungen des Bodens sowie durch ungleichmäßige Überströmung der Wehre, kann dabei die Trennwirkung deutlich verschlechtern. Nach Bell und Solari [AIChE J., 20, 4, 688-695, 1974] kann anstatt aufwendiger Stoffanalysen anhand des Strömungsfelds der Flüssigphase auf die Trennleistung geschlossen werden.
In diesem Beitrag wird eine neue Messmethode zur Ermittlung dieses Strömungsfeldes vorgestellt. Diese basiert auf der hochaufgelösten Analyse der Wehr-zu-Wehr-Überströmung des Bodens mit einem Flüssigkeitstracer anhand eines Leitfähigkeitsgittersensors.
Aus den Tracer-Versuchen lassen sich charakteristische Strömungsparameter, wie die lokale Flüssigkeitsverweilzeit und die Wehr-zu-Wehr-Strömungsgeschwindigkeit extrahieren.
Im Rahmen der Studie wurden unterschiedliche hydraulische Belastungen und Wehranordnungen untersucht und die Überströmung visualisiert und charakterisiert.
Keywords: Siebboden, Destillation, Gittersenor, Verweilzeit
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Fluidverfahrenstechnik und Membrantechnik, 26.-27.03.2015, Bremen, Deutschland

Publ.-Id: 22872 - Permalink

Gas-Liquid Mass Transfer in a Tubular Reactor with Solid Foam Packing
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
Chemical reactors with a fixed-bed of catalyst particles are widely applied for continuous multi-phase processes in the petrochemical, chemical, and biochemical industry. However, the performance of these reactors often suffers from some drawbacks, such as high energy consumption due to high pressure drop as well as mass and heat transfer limitations. One solution is to replace particle catalysts such as tablets, spheres and cylinders with structured catalysts based on open-cell solid foams. This new structure provides large specific surface area of up to 2000 m2/m3 at high open bed porosities between 75 - 97%. As result, the pressure drop of the gas-liquid two-phase flow is comparatively low (Mohammed et al. 2013).
For the design of tubular reactors with foam packings knowledge about gas-liquid mass transfer is important. The goal of this study was to examine the volumetric gas-liquid mass transfer in dependence on operating conditions and foam pore density expressed in the unit pores per inch. The results will be compared to data from the literature for both foam packings and particle packings. The experiments were based on physical desorption and the volumetric mass transfer rates are calculated according the two-film theory by Whitman (1932). The entrance effects were eliminated by performing hydrodynamically identical tests with two different test section lengths, and using the shorter test section results for ‘subtraction’ of entrance effects from the longer test section.
The results show that the volumetric gas-liquid mass transfer coefficient rises with increasing liquid superficial velocity for all foam pore densities studied, while minor effects of the gas velocity were observed. A new correlation to predict the volumetric mass transfer coefficient is derived from the experiments. The gas-liquid mass transfer in foam packings was higher than in trickle beds and beds of rasching rings.
Keywords: solid foam, mass transfer, oxygen desorption, multiphase reactors
  • Lecture (Conference)
    ESCRE 2015 - European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeld, Deutschland

Publ.-Id: 22871 - Permalink

Correlating gas-liquid distribution and effective liquid-solid mass transfer coefficient in tubular reactors with solid foam packings
Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.;
The performance of multiphase tubular reactors with co-current downward gas-liquid two-phase flow through catalyst packings is strongly affected by the quality of the gas-liquid distribution in the packing. Non-uniform liquid phase distributions in radial and axial direction cause partial catalyst surface wetting, lead to lower catalyst utilization in reduce the effective liquid-solid mass transfer to the catalyst surface [1].
In the recent years, solid foam catalyst packings were studied as promising replacements of randomly arranged catalyst particles [2]. In principle, the open-cell structure of the solid foams allows the liquid radial flow from one cell. However, the ability of solid foams to counterbalance liquid maldistribution and the liquid spreading behavior was not yet studies. The aim of this work is to investigate the cross-sectional liquid saturation distribution in a tubular column packed with solid foams and its effects on the liquid-solid mass transfer coefficient.
The axial evolution of the gas-liquid distribution patterns in solid foam packings of different pore densities has been experimentally studied using wire-mesh sensors installed at different axial heights. Both time-averaged cross-sectional liquid saturation patterns and liquid maldistribution factors were determined for different pre-wetting modes and distributor designs. In addition, effective liquid-solid mass transfer coefficients were determined based on a modified electrochemical limiting diffusion current method and correlated with the maldistribution.
The results indicate that a uniform initial distribution above the foam packing is the most important factor for a good wetting of the solid foam surface. Accordingly, a proper selection of an appropriate liquid distributor is essential for a successful application of catalytic active solid foams. To improve the homogeneity of the cross-sectional liquid saturation, the application of the Kan-Liquid pre-wetting procedure outperforms the Levec pre-wetting procedure most probably due to the transition from rivulet to film flow texture.
The electrochemical experiments revealed that low maldistribution favor the liquid-solid mass transfer. Furthermore, the results indicated decreasing effective liquid–solid mass transfer coefficients from upper to lower part of the tubular reactor, which can be related to the worsening liquid distribution.
The extended results on the liquid distribution and liquid-solid mass transfer will be shown at with the whole paper.
Keywords: Catalysis, Chemical reactor, Foam, Hydrodynamics, Mass transfer
  • Lecture (Conference)
    10th European Congress of Chemical Engineering, 27.09.-01.10.2015, Nice, France

Publ.-Id: 22870 - Permalink

Investigations on upward, downward and counter-current two-phase pipe flows using ultrafast electron beam X-ray computer tomography
Lucas, D.; Banowski, M.; Beyer, M.;
The ultra-fast electron beam X-ray computed tomography was developed during last years at HZDR and turned out to be a suitable measuring technique to get detailed information on the structure of gas-liquid interfaces. Air-water as well as steam-water experiments were done at a vertical pipe with an inner diameter of 54 mm and a test section length of about 4 m. They include co-current upward and downward flows under a wide variety of flow conditions and also some measurements for counter-current flows. In the latter case the bubble rise velocity was larger than the downward liquid velocity leading to an upward flow of bubbles and downward flow of water. Beside the tomographic reconstruction further data processing is required to obtain reliable quantitative data. A new algorithm for binarisation of the reconstructed data was developed.
The measurements were done with high frequency (between 1000 and 5000 frames per second depending on the flow conditions). In the result the instantaneous gas-liquid distributions in two horizontal planes with a distance of about 10 mm are obtained. Basing on that quantitative data like gas volume fraction distributions, average radial gas velocity profiles (basing on a cross-correlation between the two planes), bubbles size distributions and radial gas volume fraction profiles in dependence on the bubble size are obtained.
Since (in contrast to previously presented wire-mesh sensor measurements) the flow is not influenced by the measurement a bubble registered in the upstream plane can be assigned to the corresponding bubble in the downstream plane. This allows the determination of the velocity vector for each bubble. Special attention is paid to the dependency of lateral bubble velocities in dependence on the bubble sizes and the local flow conditions. Different effects are observed in upward and downward flows and will be discussed in detail.
Keywords: multiphase flow, tomography. experiment
  • Lecture (Conference)
    7th European-Japanese Two-Phase Flow Group Meeting, 11.-15.10.2015, Zermatt, Switzerland

Publ.-Id: 22869 - Permalink

Qualification of CFD-models for multiphase flows
Lucas, D.;
While Computational Fluid Dynamics (CFD) is already an accepted industrial tool for single phase flows it is not yet mature for two-phase flows. For this reason the qualification of CFD for reactor safety relevant applications which involve multiphase flows is a present topic of research. At the CFD division of Helmholtz-Zentrum Dresden – Rossendorf (HZDR) hereby beside an application-oriented model development and validation also more generic investigations are done. Thus, the baseline model strategy aims on the consolidation of the CFD-modelling for multiphase to enable reliable predictions for well-defined flow pattern in future. In addition the recently developed GENTOP-concept broadens the range of applicability of CFD. Different flow morphologies including transitions between them can be considered in frame of this concept.
Keywords: CFD, multiphase flow

Publ.-Id: 22868 - Permalink

Ultrafast dynamics in the charge-density-wave material CeTe3 across the pressure-induced phase transition
Tauch, J.; Schäfer, H.; Obergfell, M.; Demsar, J.; Giraldo, P.; Fisher, I. R.; Pashkin, A.;
Time-resolved optical spectroscopy is a powerful tool for studying ultrafast dynamics of quasiparticles and phonons in strongly correlated electronic systems. In particular, this technique has been efficiently utilized for investigation of charge-density-wave (CDW) compounds.1-3 In all these studies the system has been tuned across the boundary of the CDW phase by temperature variation. However, application of external (or chemical) pressure can also lead to a suppression of a CDW state caused by an impairment of the Fermi surface nesting.4
Here, we combine femtosecond time-resolved optical spectroscopy and a diamond anvil cell technology to study the electron and lattice dynamics in tri-telluride compound CeTe3. The optical pump-probe measurements (400 nm pump and 800 nm probe wavelength, respectively) are performed on single crystals mounted inside the pressure cell. CsI has been used as a pressure transmitting medium in order to ensure a contact between the sample and the diamond anvil.
Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure. In addition, we observe an anomalous softening of a CDW amplitude mode. Our observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure of about 4 GPa.

[1] J. Demsar et al., Phys. Rev. Lett. 83, 800 (1999).
[2] J. Demsar et al., Phys. Rev. B 66, 041101 (2002).
[3] R.V. Yusupov et al., Phys. Rev. Lett. 101, 246402 (2008).
[4] A. Sacchetti et al., Phys. Rev. Lett. 98, 026401 (2007).
Keywords: charge-density wave, ultrafast spectroscopy, high pressure, phase transition
  • Lecture (Conference)
    Joint AIRAPT-25th & EHPRG-53rd International Conference on High Pressure Science and Technology, 30.08.-04.09.2015, Madrid, Spain

Publ.-Id: 22867 - Permalink

Ultrafast dynamics in CeTe3 near the pressure-induced charge-density-wave transition
Tauch, J.; Schäfer, H.; Obergfell, M.; Demsar, J.; Giraldo, P.; Fisher, I. R.; Pashkin, A.;
Femtosecond pump-probe spectroscopy is an efficient tool for studying ultrafast dynamics in strongly correlated electronic systems, in particular, compounds with a charge-density-wave (CDW) order. Application of external pressure often leads to a suppression of a CDW state due to an impairment of the Fermi surface nesting.
We combine time-resolved optical spectroscopy and diamond anvil cell technology to study electron and lattice dynamics in tri-telluride compound CeTe3. Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure. These observations clearly indicate a transition into the metallic state of CeTe3 induced by the external pressure.
Keywords: Correlated Electrons, Nonequilibrium Quantum Many-Body Systems
  • Lecture (Conference)
    DPG Spring Meeting 2015 (Berlin), 16.-20.03.2015, Berlin, Germany

Publ.-Id: 22866 - Permalink

Scalar fields in a non-commutative space
Bietenholz, W.; Hofheinz, F.; Mejía-Díaz, H.; Panero, M.;
We discuss the lambda phi(4) model in 2- and 3-dimensional non-commutative spaces. The mapping onto a Hermitian matrix model enables its non-perturbative investigation by Monte Carlo simulations. The numerical results reveal a phase where stripe patterns dominate. In d = 3 we show that in this phase the dispersion relation is deformed in the IR regime, in agreement with the property of UV/IR mixing. This "striped phase" also occurs in d = 2. For both dimensions we provide evidence that it persists in the simultaneous limit to the continuum and to infinite volume ("Double Scaling Limit"). This implies the spontaneous breaking of translation symmetry.
  • Open Access LogoContribution to proceedings
    XIV Mexican Workshop on Particles and Fields, 24.-29.11.2013, Oaxaca, Mexico
    Journal of Physics Conference Series, Vol. 651, UNSP 01200
    DOI: 10.1088/1742-6596/651/1/012003

Publ.-Id: 22865 - Permalink

Identification of the Main Transition Velocities in a Bubble Column Based On a Modified Shannon Entropy
Nedeltchev, S.; Schubert, M.;
The gas holdup fluctuations in a bubble column (0.15 m in ID) have been recorded by means of a conductivity wire-mesh sensor in order to extract information about the main transition velocities. These parameters are very important for bubble column design, operation and scale-up. For this purpose, the classical definition of the Shannon entropy was modified and used to identify both the onset (at Ug=0.034 m/s) of the transition flow regime and the beginning (at Ug=0.089 m/s) of the churn-turbulent flow regime. The results were compared with the Kolmogorov entropy (KE) results. A slight discrepancy was found, namely the transition velocities identified by means of the KE were shifted to somewhat higher (0.045 and 0.101 m/s) superficial gas velocities Ug.
Keywords: Bubble column, Gas holdup fluctuations, Modified Shannon entropy, Kolmogorov entropy
  • Lecture (Conference)
    18th International Conference on Chemical, Biochemical and Biomolecular Engineering (ICCBBE 2016), 25.-26.02.2016, London, United Kingdom
  • Open Access LogoInternational Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering 10(2016)2, 214-217


Publ.-Id: 22864 - Permalink

Numerical simulation of liquid metal batteries
Weber, N.; Galindo, V.; Kasprzyk, C.; Stefani, F.; Weier, T.;
Considering the increasing deployment of renewable energies, large-scale stationary energy storage will be a key-technology for the future. One potentially ideal grid-scale energy storage system is the liquid metal battery (LMB), consisting of a totally liquid interior. The long life time and abundant raw materials of LMBs offer a very cheap way of building batteries.

Building LMBs cheap means to make them large. Strong currents in the order of kA will drive a fluid flow, which may increase the battery's performance, or lead to a short circuit in the worst case.

A numerial model for describing the MHD fluid flow is presented and used to describe the Tayler instability, electro-vortex flow and interface instabilities in LMBs.
Keywords: simulation OpenFOAM liquid metal battery
  • Lecture (Conference)
    10th PAMIR International Conference: Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italien

Publ.-Id: 22863 - Permalink

Dynamic bias error correction in gamma-ray computed tomography
Wagner, M.; Bieberle, A.; Bieberle, M.; Hampel, U.;
The dynamic bias error is a well-known effect in transmission radiometry. It appears when an object distribution, e.g. a multiphase flow, changes its constitution during the scanning process and reconstructed data, e.g. a cross-sectional image, is assumed to represent a time-average of the object distribution. In gamma-ray tomography long sampling intervals are necessary in order to obtain sufficient photon count statistics. Therefore, the measured photon count projection data is inherently time-averaged. The attenuation law gives a non-linear relation between attenuation and photon counts. Therefore, the calculation of the time-averaged attenuation from the time-averaged projection data may lead to non-negligible and systematic errors, commonly an underestimation of the real attenuation, which e.g. means an overestimation of the gas holdup in tomography images of two-phase flows.
In this work the application of a recently presented dynamic bias error correction method on time-averaged gamma-ray tomography is demonstrated. As an exemplary object we scanned a mock-up of a centrifugal pump. The suitability of this method was investigated for a generic highly turbulent two-phase flow scenario with both a virtual tomography data set as well as real measured data.
Keywords: gamma-ray tomography, dynamic bias error, correct averaging

Publ.-Id: 22862 - Permalink

Hydrodynamic investigations of bubbly flow in periodic open cellular structures by ultrafast X-ray tomography
Wagner, M.; Zalucky, J.; Bieberle, M.; Hampel, U.;
Packed bubble columns are common multiphase flow reactor types in chemical engineering. Regarding process efficiency, high mass transfer rates are desirable. Especially, periodic open cell structures (POCS) are supposed to increase the interfacial density and hence the mass transfer in multiphase reactions. At the Helmholz-Zentrum Dresden – Rossendorf an ultrafast X-ray imaging technique is used to analyze a wide range of multiphase flow scenarios. A rotating electron beam induces X-ray generation on two targets which enables to produce up to 8000 cross-sectional images per second from two measurement planes with a spatial resolution of about 1 mm. We applied this tomography system in an experimental setup including POCS. In the threedimensional tomography data sets, bubbles were identified and characterized. For different gas flow rates, we determined the axial velocities of the gas-phase, bubble size distributions, bubble aspect ratios and timeaveraged gas hold-ups. We compared these results with measurements in an unpacked-bubble column. The results show that the POCS have a significant influence on the hydrodynamics, especially regarding the interfacial area density.
Keywords: ultrafast X-ray CT, two-phase flow, packed bubble column
  • Contribution to proceedings
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia
  • Poster
    10th Pacific Symposium on Flow Visualization and Image Processing, 15.-18.06.2015, Napoli, Italia

Publ.-Id: 22861 - Permalink

Requirements for a Compton camera for in-vivo range verification of proton therapy
Rohling, H.; Priegnitz, M.; Schöne, S.; Schumann, A.; Enghardt, W.; Hueso-Gonzalez, F.; Pausch, G.; Fiedler, F.;
To ensure the optimal outcome of proton therapy, in-vivo range verification is highly desired. Prompt gamma-ray imaging (PGI) is a possible approach for in-vivo range monitoring. For PGI dedicated detection systems, e.g. Compton cameras, are currently under investigation. The presented paper deals with substantial requirements regarding hardware and software that a Compton camera used in clinical routine has to meet. By means of GEANT4 simulations, we investigate the load on the detectors and the percentage of background expected in a realistic irradiation and we simulate gamma-ray detections, i.e. input data for the reconstruction. By reconstructing events from simulated sources of well-defined geometry, we show that large-area detectors are favourable. We determine the minimum number of valid events allowing for a statistically significant range assessment. Finally, an end-to-end test for a realistic patient scenario is presented: starting with a treatment plan, the gamma-ray emissions are calculated, the detector response is modelled, and the image reconstruction is performed. We conclude that, with respect to the achievable precision, the expected complexity, and high costs of an adequate detection system, in-vivo dosimetry with Compton cameras will hardly be realised.
Keywords: Prompt gamma-ray imaging, Compton camera, proton therapy, range verification, Monte Carlo simulation, end-to-end test, GEANT4

Publ.-Id: 22860 - Permalink

The effect of pulsed electrical currents on the formation of macrosegregation in solidifying Al - Si hypoeutectic phases
Zhang, Y.; Räbiger, D.; Willers, B.; Eckert, S.;
Within this study we conducted experimental investigations focusing on the formation of macrosegregation in Al-7wt-%Si alloys exposed to electric current pulses (ECP) during solidification. The distribution of eutectic phase was measured on various sections of the solidified samples. The results do not show the formation of reproducible segregation pattern. This finding can be attributed to the specific pattern and the turbulent character of the flow generated by the ECP treatment, the equiaxed growth of free-moving crystals and a non-symmetric distribution of the electromagnetic force due to an uneven wetting of the electrodes. An increasing input of energy by ECP intensifies the melt flow and increases the variations of phase distribution over a longitudinal section.
Keywords: Al - Si alloys; solidification; electric current pulse; macrosegregation; melt convection.


Publ.-Id: 22859 - Permalink

Entropy Analysis in a Bubble Column Based On Ultrafast X-Ray Tomography Data
Nedeltchev, S.; Schubert, M.;
New ultrafast X-ray tomography data has been obtained in a bubble column (0.1 m in ID) operated with an air-deionized water system at ambient conditions. Raw reconstructed images were treated by both the information entropy (IE) and the reconstruction entropy (RE) algorithms in order to identify the main transition velocities in a bubble column. The IE values exhibited two well-pronounced minima at Ug=0.025 m/s and Ug=0.085 m/s identifying the boundaries of the homogeneous, transition and heterogeneous regimes. The reconstruction entropy extracted from the central region of the column’s cross-section exhibited only one characteristic peak at Ug=0.03 m/s, which was attributed to the transition from the homogeneous to the heterogeneous regime. This result implies that the transition regime is non-existent in the core of the column.
Keywords: Bubble column, Ultrafast X-ray tomography, Information entropy, Reconstruction entropy
  • Lecture (Conference)
    18th International Conference on Chemical, Biochemical and Biomolecular Engineering, 25.-26.02.2016, London, UK
  • Open Access LogoInternational Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering 10(2016)2, 256-259


Publ.-Id: 22858 - Permalink

Prediction of Gas Holdups in Small and Large Bubble Columns Obtained from Advanced Imaging Techniques
Nedeltchev, S.; Schubert, M.; Hampel, U.;
The gas holdup is one of the most important parameters in the bubble column operation. Its successful prediction is important for the estimation of both the interfacial areas and the volumetric liquid-phase mass transfer coefficients. In the past several years, new imaging techniques for gas holdup measurements, such as the conductivity wire-mesh sensor as well as tomographic modalities have been used successfully for gas holdup measurements. Nedeltchev et al. (2014) have also shown that this data can be used for flow regime identification.

In this work, the gas holdup values were recorded in a small (0.15 m in ID) and a large (0.4 m in ID) bubble column equipped with perforated plate spargers (open area=1 %). A new model has been established, which predicts successfully the gas holdups in an air-deionized water system. It is based on both the theoretical and empirical evaluations of the gas-liquid interfacial areas. The correlation of Akita and Yoshida (1974) was assumed to be identical with the theoretical definition of the interfacial area. The Sauter-mean bubble diameters ds were estimated from the correlation of Wilkinson et al. (1994).

The theoretical gas holdups were corrected since the classical definition of the interfacial area is strictly valid for rigid spherical bubbles. All of our experimental conditions correspond to bubble diameters larger than 4.4×10-3 m, which means that the formed bubbles have an oblate ellipsoidal shape (Fan and Tsuchiya, 1990). It has been found that the common correction factor fc depends on both the bubble diameter (Eötvös number Eo) and the column diameter Dc (Bond number Bd). The effect of the column diameter (and Bond number) on the gas holdup should be carefully checked. As the superficial gas velocity Ug increased, the correction factors fc in the small column increased from 0.13 up to 0.25, whereas in the large column they increased from 1.33 to 2.55.

The approach is very useful since it predicts the gas holdups in the range 0.02 ≤ Ug ≤ 0.15 m/s irrespective of the prevailing flow regime. In the large column, the gas holdups were predicted with an average relative error (ARE) of 3.5 %, whereas in the small column ARE was 2.5 % (twelve gas holdup values in each column).
Keywords: Bubble Columns, Wire-Mesh Sensors, Gas Holdups, Prediction Model
  • Poster
    Tenth European Congress of Chemical Engineering, 27.09.-01.10.2015, Nice, France

Publ.-Id: 22857 - Permalink

Different Identification Methods for Studying the Radial Distribution of the Transition Velocities in a Bubble Column
Nedeltchev, S.; Schubert, M.; Hampel, U.;
The identification of the boundaries of the main transition velocities in a bubble column is a very important research topic since it is related to the bubble column design and scale-up. The degrees of mixing, heat and mass transfer depend on the prevailing flow regime. In the literature hitherto, very different results (even for air-water system) about the main transition velocities Utrans have been reported. A good explanation for that is the fact that different signals (differential or absolute pressure fluctuations, bubble frequency, radioactive particle trajectories, photon counts, etc.) have been recorded and further analyzed by different methods (statistical analysis, fractal analysis, chaos analysis, etc.). The main objective of this work was to perform a comparison among the transition velocities (at different radial positions) identified by different entropies (information entropy, Kolmogorov entropy, Shannon entropy, etc.). The latter were extracted from gas holdup fluctuations recorded by a conductivity wire-mesh sensor. Recently, Nedeltchev et al. (2014) have shown that this data can be used for flow regime identification.

The data were recorded in a small (0.15 m in ID) bubble column equipped with a perforated plate gas distributor (14 holes, hole diameter: ø 4×10-3 m, open area=1 %). The local gas holdup fluctuations were measured at five different dimensionless radial positions (r/R): 0.88, 0.63, 0.39, 0.14 and 0.00. It was found that there were differences between the transition velocities identified by the information entropy (IE) and the Kolmogorov entropy (KE). The KE profile at r/R=0.88 was capable of identifying (based on a well-pronounced local minima) two Utrans values at 0.045 and 0.101 m/s. The IE profiles at the same radial position distinguished almost the same Utrans values: 0.045 and 0.112 m/s. The two transition velocities discriminate the boundaries of the three main flow regimes. Nedeltchev et al. (2014) visualized the flow patterns and documented the existence of strong gas maldistribution.

The KE profiles at r/R=0.63 revealed the existence of three Utrans values: 0.034, 0.067 and 0.124 m/s. In comparison with the wall region, at this radial position the transition regime was split into two sub-regimes. They were observed by Olmos et al. (2003). The IE profile at r/R=0.63 was difficult for interpretation due to the observed multiple local minima. However, taking into account the KE results the following three Utrans values were identified: 0.034, 0.067 and 0.112 m/s. So, only the last Utrans value was somewhat lower. Our results show that the transition is only a deviation (a sharp decrease) of a single point in the entropy profiles.

Such a detailed comparison between the IE and KE values was also performed at the other three radial positions. The IE values were derived from different initial information and compared with the Shannon entropies. Such a comparison has not been performed in the literature hitherto. We have found an effect of the radial position on the Utrans values.
Keywords: Bubble column, Wire-Mesh Sensor, Transition Velocities, Kolmogorov Entropy, Information Entropy
  • Lecture (Conference)
    Tenth European Congress of Chemical Engineering, 27.09.-01.10.2015, Nice, France

Publ.-Id: 22856 - Permalink

Nanostructure, thermoelectric properties, and transport theory of V2VI3 and V2VI3 / IV-VI based superlattices and nanomaterials
Dankwort, T.; Hansen, A.-L.; Winkler, M.; Schürmann, U.; König, J. D.; Johnson, D. C.; Hinsche, N. F.; Zahn, P.; Mertig, I.; Bensch, W.; Kienle, L.;
The scope of this work is to review the thermoelectric properties, the microstructures, and their correlation with theoretical calculations and predictions for recent chalcogenide based materials. The main focus is put on thin multilayered Bi2Te3, Sb2Te3 films and bulk V2VI3/IV-VI mixed systems. For all films a systematic characterization of the thermoelectric properties as well as the micro- and nanostructure was performed. The degree of crystallinity of the multilayered films varied from epitaxial systems to polycrystalline films. Other multilayered thin films revealed promising thermoelectric properties. (SnSe)1.2TiSe2 thin films with rotational disorder yielded the highest Seebeck coefficient published to date for analogous materials. For bulk V2VI3/IV-VI mixed systems insides are given into a complete `material to module` process resulting in a high performance thermoelectric generator using (1-x)(GeTe) x(Bi2Se0.2Te2.8) (x = 0.038). Cyclic heating of this system with x = 0.063 resulted in a drastic change of the micro- and nanostructure observed by ex situ and in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM). Consequently, a degradation of ZT at 450 °C from ~2.0 to ~1.0 was observed, while the less doped sample showed a stable ZT of 1.5.
Keywords: Bi2Te3/Sb2Te3 superlattice, thermoelectrics, Germanium Telluride, thin films, nanoalloying, electron microscopy

Publ.-Id: 22855 - Permalink

From prompt gamma distribution to dose: A novel approach combining an evolutionary algorithm and filtering based on gaussian-powerlaw convolutions
Schumann, A.; Priegnitz, M.; Schoene, S.; Enghardt, W.; Rohling, H.; Fiedler, F.;
Range verification and dose monitoring in proton therapy is considered as highly desirable. Different methods have been developed worldwide, like particle therapy positron emission tomography (PT-PET) and prompt gamma imaging (PGI). In general, these methods allow for a verification of the proton range. However, quantification of the dose from these measurements remains challenging. For the first time, we present an approach for estimating the dose from prompt gamma ray emission profiles. It combines a filtering procedure based on gaussian-powerlaw convolution with an evolutionary algorithm. By means of convolving depth dose profiles with an appropriate filter kernel, prompt gamma ray depth profiles are obtained. In order to reverse this step, the evolutionary algorithm is applied. The feasibility of this approach is demonstrated for a spread-out Bragg-peak in a water target.
Keywords: proton therapy, prompt gamma imaging, dose estimation, gaussian-powerlaw convolution, evolutionary algorithm, filter kernel

Publ.-Id: 22854 - Permalink

Spatiotemporal image analysis of water flow in porous media for numerical transport modelling
Lippmann-Pipke, J.; Eichelbaum, S.; Kulenkampff, J.;
For more than a decade a spatiotemporal visualization tool for transport process observations in dense material by means of PET (positron emission tomography) was developed [1-5]. Such quantitative GeoPET images are exceptionally sensitive to displacements of pico molar tracer quantities detected within 1 mm grids on laboratory/drill core scale.
Now we reached a strategic milestone: A custom made image analysis algorithm is capable of quantitatively extracting velocity and porosity fields from such GeoPET image time series, even if the 4D image information includes discontinuous flow patterns (due to bottle neck effect related detection limits) and localized image artifacts. We present our approach with a concrete example: From an observed flow field in a dense core material the effective porosity and velocity field is extracted and this data is used in a finite element based transport simulation.
[1] Richter, M., et al. (2000) Z.angew.Geol. 46(2): 101-109.
[2] Gründig, M., et al. (2007) App.Geochem. 22: 2334-2343.
[3] Zakhnini, A., et al. (2013) Comp.Geosci. 57 183-196.
[4] Kulenkampff, J., et al. (2008) Phys.Chem.Earth 33: 937-942.
[5] Kulenkampff, J., et al. (2015) Clay Min. accepted 2015.
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 22853 - Permalink

Optical waveguides in Yb:SBN crystals fabricated by swift C ion irradiation
Liu, G.; Dong, N.; Wang, J.; Akhmadaliev, S.; Zhou, S.; Chen, F.;
We report on the fabrication of optical planar waveguides supporting both the TE and TM confinements in Yb:SBN crystal by swift C ions irradiation. A combination of the micro-photoluminescence and micro-Raman investigations have evidenced the presence of lattice distortion, damage and disordering of the SBN network along the ion irradiation path, with these effects being at the basis of the refractive index modification. The enhanced micro-photoluminescence and micro-Raman intensity in the waveguide volumes show the potential application of the obtained waveguides as active laser gain media.
Keywords: Optical waveguides; Yb:SBN crystal; Ion implantation; Confocal photoluminescence

Publ.-Id: 22852 - Permalink

Optical ridge waveguides in Er3+/Yb3+ co-doped phosphate glass produced by ion irradiation combined with femtosecond laser ablation for guided-wave green and red upconversion emissions
Chen, C.; He, R.; Tan, Y.; Wang, B.; Akhmadaliev, S.; Zhou, S.; de Aldana, J. R. V.; Hu, L.; Chen, F.;
This work reports on the fabrication of ridge waveguides in Er3+/Yb3+ co-doped phosphate glass by the combination of femtosecond laser ablation and following swift carbon ion irradiation. The guiding properties of waveguides have been investigated at 633 and 1064 nm through end face coupling arrangement. The refractive index profile on the cross section of the waveguide has been constructed. The propagation losses can be reduced considerably after annealing treatment. Under the optical pump laser at 980 nm, the upconversion emission of both green and red fluorescence has been realized through the ridge waveguide structures.
Keywords: Ridge optical waveguides; Er3+/Yb3+ co-doped phosphate glass waveguides; Upconversion; Laser ablation; Ion irradiation

Publ.-Id: 22851 - Permalink

Advances in radiotherapy special feature.
Krause, M.; Supiot, S.;
there is no abstract

Publ.-Id: 22849 - Permalink

Comparison of [18F]-FMISO, [18F]-FAZA and [18F]-HX4 for PET imaging of hypoxia - a simulation study.
Wack, L. J.; Mönnich, D.; van Elmpt, W.; Zegers, C. M.; Troost, E. G.; Zips, D.; Thorwarth, D.;

To investigate the effect of hypoxia tracer properties on positron emission tomography (PET) image quality for three tracers [18F]-fluoromisonidazole (FMISO), [18F]-fluoroazomycinarabinoside (FAZA) and [18F]-flortanidazole (HX4), using mathematical simulations based on microscopic tumor tissue sections.

Oxygen distribution and tracer binding was mathematically simulated on immunohistochemically stained cross-sections of tumor xenografts. Tracer diffusion properties were determined based on available literature. Blood activity and clearance over a four-hour period post-injection (p.i.) were derived from clinical dynamic PET scans of patients suffering from head and neck or bronchial cancer. Simulations were performed both for average patient blood activities and for individual patients, and image contrast between normoxic and hypoxic tissue areas was determined over this four-hour period p.i.

On average, HX4 showed a six-fold higher clearance than FMISO and an almost three-fold higher clearance than FAZA based on the clinical PET data. The absolute variation in clearance was significantly higher for HX4 than for FMISO (standard deviations of 5.75 *10-5 s-1 vs. 1.55 *10-5 s-1). The absolute tracer activity in these scans at four hours p.i. was highest for FMISO and lowest for HX4. Simulated contrast at four hours p.i. was highest for HX4 (2.39), while FMISO and FAZA were comparable (1.67 and 1.75, respectively). Variations in contrast of 7-11% were observed for each tracer depending on the vascularization patterns of the chosen tissue. Higher variations in clearance for HX4 resulted in an increased inter-patient variance in simulated contrast at four hours p.i.

In line with recent experimental and clinical data, the results suggest that HX4 is a promising new tracer that provides high image contrast four hours p.i., though inter-patient variance can be very high. Nevertheless, the widely used tracer FMISO provides a robust and reproducible signal four hours p.i., but with a lower contrast. The simulations revealed tracer clearance to be the key factor in determining image contrast.

Publ.-Id: 22848 - Permalink

Valproic acid modulates radiation-enhanced matrix metalloproteinase activity and invasion of breast cancer cells.
Artacho-Cordón, F.; Ríos-Arrabal, S.; Olivares-Urbano, M. A.; Storch, K.; Dickreuter, E.; Muñoz-Gámez, J. A.; León, J.; Calvente, I.; Torné, P.; Salinas, M. D.; Cordes, N.; Núñez, M. I.;

To evaluate matrix metalloproteinase (MMP) activity and invasion after ionizing radiation (IR) exposure and to determine whether MMP could be epigenetically modulated by histone deacetylase (HDAC) inhibition.

Two human breast cancer cell lines (MDA-MB-231 and MCF-7) were cultured in monolayer (2D) and in laminin-rich extracellular matrix (3D). Invasion capability, collagenolytic and gelatinolytic activity, MMP and TIMP protein and mRNA expression and clonogenic survival were analyzed after IR exposure, with and without a HDAC inhibition treatment [1.5 mM valproic acid (VA) or 1 μM trichostatin-A (TSA)].

IR exposure resulted in cell line-dependent stimulation of invasion capacity. In contrast to MCF-7 cells, irradiated MDA-MB-231 showed significantly enhanced mRNA expression of mmp-1, mmp-3 and mmp-13 and of their regulators timp-1 and timp-2 relative to unirradiated controls. This translated into increased collagenolytic and gelatinolytic activity and could be reduced after valproic acid (VA) treatment. Additionally, VA also mitigated IR-enhanced mmp and timp mRNA expression as well as IR-increased invasion capability. Finally, our data confirm the radiosensitizing effect of VA.

These results suggest that IR cell line-dependently induces upregulation of MMP mRNA expression, which appears to be mechanistically linked to a higher invasion capability that is modifiable by HDAC inhibition.
Keywords: Matrix metalloproteinases; breast cancer; epigenetic regulation; histone deacetylases; invasion; ionizing radiation; tumour microenvironment

Publ.-Id: 22847 - Permalink

ILKAP, ILK and PINCH1 control cell survival of p53-wildtype glioblastoma cells after irradiation.
Hausmann, C.; Temme, A.; Cordes, N.; Eke, I.;
The prognosis is generally poor for patients suffering from glioblastoma multiforme (GBM) due to radiation and drug resistance. Prosurvival signaling originating from focal adhesion hubs essentially contributes to therapy resistance and tumor aggressiveness. As the underlying molecular mechanisms remain largely elusive, we addressed whether targeting of the focal adhesion proteins particularly interesting new cysteine-histidine-rich 1 (PINCH1), integrin-linked kinase (ILK) and ILK associated phosphatase (ILKAP) modulates GBM cell radioresistance. Intriguingly, PINCH1, ILK and ILKAP depletion sensitized p53-wildtype, but not p53-mutant, GBM cells to radiotherapy. Concomitantly, these cells showed inactivated Glycogen synthase kinase-3β (GSK3β) and reduced proliferation. For PINCH1 and ILKAP knockdown, elevated levels of radiation-induced γH2AX/53BP1-positive foci, as a marker for DNA double strand breaks, were observed. Mechanistically, we identified radiation-induced phosphorylation of DNA protein kinase (DNAPK), an important DNA repair protein, to be dependent on ILKAP. This interaction was fundamental to radiation survival of p53-wildtype GBM cells. Conclusively, our data suggest an essential role of PINCH1, ILK and ILKAP for the radioresistance of p53-wildtype GBM cells and provide evidence for DNAPK functioning as a central mediator of ILKAP signaling. Strategies for targeting focal adhesion proteins in combination with radiotherapy might be a promising approach for patients with GBM.
Keywords: DNA repair; ILK; ILKAP; PINCH1; radioresistance

Publ.-Id: 22846 - Permalink

Abschätzung des Sekundärneutronenfeldes bei der Protonentherapie mit passiv geformten Feldern
Lutz, B.; Enghardt, W.; Swanson, R.; Fiedler, F.;
Die Strahlentherapie mit Protonen erlaubt, im Vergleich zur Bestrahlung mit Photonen, eine stärkere Lokalisierung der durch die primäre Strahlung verabreichten Dosis im Tumor. Die damit verbundene Schonung gesunden Gewebes ist der größte Vorteil dieser Form der Strahlentherapie.

Die verbleibende Belastung des gesunden Gewebes wird hauptsächlich durch sekundäre Neutronen verursacht. Der Fluss und das Spektrum der sekundären Neutronen hängen dabei stark von der gewählten Konfiguration der Therapieanlage ab.

Um das Sekundärneutronenfeld an der Protonentherapieanlage des Universitätsklinikum Carl Gustav Carus in Dresden abschätzen zu können, wird eine detaillierte Simulation der Strahlformung mit Hilfe der Software TOPAS entwickelt. Der Vortrag beschreibt die Implementation der Anlage und die erwarteten Neutronenspektren. Der Einfluß verschiedener Maschinenparameter auf das Neutronenfeld wird diskutiert. Abschließend wird die Vorhersage mit ersten Messungen der Ortsdosis am Therapieplatz verglichen.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Materie und Kosmos (SMuK), 29.02.-04.03.2016, Hamburg, Deutschland

Publ.-Id: 22845 - Permalink

On the use of HERFD-XANES at the U L3 and M4-edges to determine the uranium valence state on [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3]
Bès, R.; Rivenet, M.; Solari, P. L.; Kvashnina, K. O.; Scheinost, A. C.; Martin, P. M.;
We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using High Energy Resolution Fluorescence Detection - X-ray Absorption Near Edge Structure spectroscopy (HERFD-XANES). The spectra at both uranium L3- and M4-edges confirm that all the five non-equivalent uranium atoms are solely in the hexavalent form in this compound, as previously suggested by Bond Valence Sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the pre-edge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD-XANES appears to be the most straightforward and reliable way to assess uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or mixture of compounds.
Keywords: XANES XES HERFD uranium oxidation state

Publ.-Id: 22844 - Permalink

Pulsed-Magnet Developments at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.;
  • Lecture (Conference)
    MT24 - International Conference on Magnet Technology 24, 18.-23.10.2015, Seoul, Korea

Publ.-Id: 22843 - Permalink

Magneto-Acoustic Studies of Frustrated Quantum Magnets
Pham, T.-C.;
  • Invited lecture (Conferences)
    International Symposium on Frontiers in Materials Science 2015, 19.-21.11.2015, Tokyo, Japan

Publ.-Id: 22842 - Permalink

The gas chromatographic analysis of the reaction products of the partial isobutane oxidation as a two phase process.
Willms, T.; Kryk, H.; Hampel, U.;
The partial oxidation of isobutane to t-butyl hydroperoxide (TBHP) has been studied analytically for the first time as a two-phase process in a capillary micro reactor. In order to obtain detailed information on products, yields, selectivity and reaction pathways, the products have been investigated by GC/MS. An Rxi-5ms column and a PTV-injector have been used to analyze the liquid products. TBHP, di-t-butyl peroxide (DTBP), t-butanol (TBA), and propanone as main products as well as further by-products e.g. methanal, isopropanol, isobutanol and isobutanal in minor quantities have been identified by MS. The liquid products have been obtained by quenching the reaction and vaporizing the isobutane afterwards by pressure reduction using a mass flow controller allowing a constant mass flow. For all liquid reaction products calibrations, a validation of the method including limits of quantification and detection as well as calculation of uncertainties has been performed. The results have been applied successfully for the investigation of the selectivities of the main products (TBHP, DTBP, TBA, propanone) of the isobutane oxidation. In the frame of the analytical investigation of this reaction a correlation coefficient of r2 > 0.999 for TBHP and DTBP, which is necessary to perform a validation, has been obtained for the first time. The gaseous phase has been analyzed using a GASPRO Column, a DEANS switch, a mole sieve column and a TCD detector. Apart from the gaseous reactants, isobutene has been found.
Keywords: Isobutane oxidation, t-butyl hydroperoxide, di-t-butyl-peroxide, GC/MS, multiphase process.


Publ.-Id: 22840 - Permalink

Flüssig-Flüssig-Extraktion von Seltenen Erden mit Hilfe von Calix[4]arenen
Mansel, A.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    1. Verbundtreffen zum BMBF/PtJ-Projekt "SE-FLECX" an der Universität Leipzig, Institut für Anorganische Chemie, 26.11.2015, Leipzig, Deutschland

Publ.-Id: 22839 - Permalink

How Details of the Geometallurgical Optimisation Influence Overall Value
van den Boogaart, K. G.; Tolosana Delgado, R.; Müller, U.; Matos Camacho, S.;
The precise formulation of a geometallurgical optimisation problem is by necessity a simplification of reality. It includes implicit choices such as data availability or mining block geometry. Additional data can be ore body data, production data or market data. Often these choices are predetermined by the software, the workflow or corporate culture and as such are not even queried. There are several aspects that might play a role in the optimization. They include not only the spatial model on which the selection of mining blocks and the potential mining sequence are based, but also the complexity of the processing model, the way in which uncertainty is treated, the scope of responsibility and the complexity of the model. In addition the timing of the optimization and the availability (or lack thereof) of information influence the outcome of any optimization.

We show that different modelling choices and different model formulations for the same mine can lead to very different processing choices, substantially different NPV’s , opposite investment decisions and so to overall different values for the entire operation. The selection of adequate simplifications and corresponding formulations for the optimisation problem is thus an important task in itself.

For this purpose we introduce a method quantifying the impact of certain simplifications prior to the optimization itself. E.g. for the effect of mining block choices the effect depends mainly on the spatial structure and the structure of the processing gain function. Both can be quantified beforehand. Likewise the effect of additional data depend on the increase of information. Again this can be quantified from a spatial model.

Based on the outcome appropriate simplifications can be selected for the geometallurgical optimization.
Keywords: geometallurgy, model choice, adaptive processing
  • Contribution to proceedings
    GeoMet 2016, The third AusIMM International Geometallurgy Conference, 15.-17.06.2016, Perth, Australia
    Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, Melbourn: The Australasian Institute of Mining and Metallurg, 303-312
  • Lecture (Conference)
    GeoMet 2016, The third AusIMM International Geometallurgy Conference, 15.-17.06.2016, Perth, Australia

Publ.-Id: 22838 - Permalink

Time-Resolved Two Million Year Old Supernova Activity Discovered in the Earth’s Microfossil Record
Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Deneva, B.; Faestermann, T.; Famulok, N.; Fimiani, L.; Gómez-Guzmán, J.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.;
Massive (>10M_⊙) stars, which terminate their evolution as core collapse supernovae (CCSN), are theoretically predicted 1 to eject >10-5M_⊙ of the radioactive isotope 60Fe (half-life t1/2=(2.61±0.04) Ma; weighted average of Ref. 2 and 3). If such an event occurs sufficiently close to our solar system, one expects that traces of the supernova (SN) debris could be deposited on Earth. Since 60Fe has no or little expected anthropogenic or cosmogenic production mechanisms, its detection in terrestrial reservoirs would be an immediate proxy for a past Earth-SN interaction within the past few million years. Herein, we report for the first time a time-resolved 60Fe signal residing, at least partially, in a biogenic reservoir. Using the experimental technique of accelerator mass spectrometry (AMS), this signal was found through the direct detection of live 60Fe atoms contained within secondary Fe-oxides, among which are magnetofossils 4; the fossilized chains of magnetite crystals produced by magnetotactic bacteria 5, 6. Magnetofossil preservation precludes post-depositional Fe mobilization events, ensuring that the 60Fe record is correctly preserved. The magnetofossils were chemically extracted from two Pacific Ocean sediment drill cores. Our results show that the 60Fe signal onset occurs around 2.7 Ma, near the lower Pleistocene boundary, terminates between 1.4 Ma and 1.8 Ma, and peaks at about 2.2 Ma.
Keywords: accelerator mass spectrometry, AMS, supernova, cosmogenic nuclide
  • Open Access LogoProceedings of the National Academy of Sciences of the United States of America 113(2016)33, 9232-9237
    DOI: 10.1073/pnas.1601040113

Publ.-Id: 22837 - Permalink

On the Lorentz-force driven flow around an insulating sphere
Massing, J.; Baczyzmalski, D.; Weier, T.; Landgraf, S.; Cierpka, C.;
The Lorentz-force driven flow around an insulating sphere in a parallel electric and magnetic field was investigated experimentally and numerically. From the results, the lift force acting on the bubble due to the pressure reduction caused by the Lorentz-force driven flow was estimated, which was discussed in the literature as the primary cause for a faster bubble detachment in a parallel magnetic field. It could be shown, that the pressure force is several orders of magnitudes smaller than the buoyancy force and therefore has no significant effect on the bubble detachment. This finding is supported by the measurement results of the 3D3C velocity field around an elevated, axially magnetized sphere in an electric field. In the final paper the 3D3C flow around the bubble will be analyzed in greater detail and hydrodynamic mechanisms to explain the faster detachment will be further discussed.
Keywords: Lorentz force, electrolysis, Astigmatism Particle Tracking Velocimetry
  • Lecture (Conference)
    18th Lisbon International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, 04.-07.07.2016, Lissabon, Portugal
  • Open Access LogoContribution to proceedings
    18th Lisbon International Symposium on Applications of Laser and Imaging Techniques to Fluid Mechanics, 04.-07.07.2016, Lissabon, Portugal, 978-989-98777-8-8

Publ.-Id: 22836 - Permalink

Sodium-bismuth-lead low temperature liquid metal battery
Lalau, C.-C.; Ispas, A.; Weier, T.; Bund, A.;
The development of a low temperature liquid metal battery based on ionic liquids namely, sodium-bis(trifluoromethylsulfonyl) imide (Na[TFSI]) in tetraethylammonium-bis(trifluoromethylsulfonyl) imide ([TEA][TFSI]) will be discussed. Such a battery should be easily accessible for fluid flow measurements which is still a challenge with the conventional high temperature systems. Cells comprising a Na negative electrode, 20 mole % Na[TFSI] in [TEA][TFSI] ionic liquid electrolyte and a Pb-Bi eutectic positive electrode were constructed and operated at 160 °C. Galvanostatic cycling experiments were conducted at low C rates (C/26) for 13 h corresponding to 50 % depth of discharge. A discharge capacity of 565 mAh/g was found. Furthermore electrochemical impedance spectroscopy was used to characterize the aging of the cells.
Keywords: Liquid metal batteries, Ionic liquids, Sodium, Electrochemical impedance spectroscopy, Storage

Publ.-Id: 22835 - Permalink

Strange meson production in Al+Al collisions at 1.9 A GeV
Gasik, P.; Piasecki, K.; Herrmann, N.; Leifels, Y.; Matulewicz, T.; Andronic, A.; Averbeck, R.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Caplar, R.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dzelalija, M.; Fabbietti, L.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kis, M.; Koczon, P.; Kotte, R.; Lebedev, A.; Le Fevre, A.; Liu, J. L.; Lopez, X.; Manko, V.; Marton, J.; Münzer, R.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wisniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.;
The production of K+, K- and φ(1020) mesons are studied in Al+Al collisions at beam energy of 1.9A GeV which is close or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K± mesons are obtained. A comparison of the ratio of kinetic energy distributions of K- and K+ mesons to transport model calculations (IQMD and HSD) suggests that the inclusion of in-medium modifications of kaon properties is necessary to reproduce the ratio. The inverse slope and total yield of φ mesons are deduced. The contribution to K- production from φ meson decays is found to be 17 ± 3%. The results are in line with previous K± and φ data obtained for different colliding systems at similar incident beam energies.


Publ.-Id: 22834 - Permalink

Abschirmungs- und Aktivierungsberechnungen für den MYRRHA-Forschungsreaktor in Mol
Ferrari, A.; Konheiser, J.; Mueller, S. E.;
No abstract provided
  • Lecture (Conference)
    15. AAA Workshop, 07.12.2015, Garching, Germany

Publ.-Id: 22833 - Permalink

AER Working Group D on VVER Safety Analysis – Report of the 2015 Meeting
Kliem, S.;
The AER Working Group D on VVER reactor safety analysis held its 24th meeting in Madrid, Spain, during the period 18-19 May, 2015. The meeting was hosted by UPM Madrid and was held in conjunction with the ninth workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modelling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 19 participants attended the meeting of the working group D, 17 from AER member organizations and 2 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting. The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
• Thermal hydraulic analyses of fuel assemblies
• Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.
  • Contribution to proceedings
    25th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Hungary
    Proceedings of the 25th Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA EK, 9789637351259, 247-253
  • Lecture (Conference)
    25th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-16.10.2015, Balatongyörök, Hungary

Publ.-Id: 22832 - Permalink

Band-gap narrowing in Mn-doped GaAs probed by room-temperature photoluminescence
Prucnal, S.; Gao, K.; Skorupa, I.; Rebohle, L.; Vines, L.; Schmidt, H.; Khalid, M.; Wang, Y.; Weschke, E.; Skorupa, W.; Grenzer, J.; Hübner, R.; Helm, M.; Zhou, S.;
The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here, we present room-temperature photoluminescence and ellipsometry measurements of Ga100%−xMnxAs alloy. The upshift of the valence band is proven by the redshift of the room temperature near band-gap emission from the Ga100%−xMnxAs alloy with increasingMn content. It is shown that even a doping by 0.02% of Mn affects the valence-band edge, and it merges with the impurity band for a Mn concentration as low as 0.6%. Both x-ray diffraction pattern and high-resolution cross-sectional transmission electron microscopy images confirmed full recrystallization of the implanted layer and GaMnAs alloy formation.
Keywords: diluted magnetic semiconductors, (Ga,Mn)As , ion implantation, flash lamp annealing

Publ.-Id: 22831 - Permalink

YMnO3- based MIS structure with a selective, capacitive photo-detecting properties
Bogusz, A.; Choudhary, O. S.; Skorupa, I.; Bürger, D.; Lawerenz, A.; Schmidt, O. G.; Schmidt, H.;
This work investigates the YMnO3/Si3N4 /p-Si structures in terms of novel, capacitance-based photo-detecting properties. Photocapacitance-voltage (C-V) characteristics of the YMnO3/Si3N4 /p-Si structures have been determined at room temperature for a wide spectral range (300-980 nm). C-V characteristics indicate a charge trapping process which is used as the basis for novel approach to photodetectors. Our model discusses the immobilization of otherwise mobile charges in Si3N4 when the negative polarization charge of the multiferroic YMnO3 is at the YMnO3/Si3N4 interface. The observed capacitance minima are well-defined by the direction of bias ramp. Voltages corresponding to these minima were further used as a reference point for a read out of capacitance in retention and optical selectivity tests. Results indicate that investigated structures exhibit a good photo-sensitivity of red light and the retention properties are non-volatile for one capacitance branch.
  • Lecture (Conference)
    DPG Spring Meeting 2015, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 22830 - Permalink

Resistive switching of polycrystalline, multiferroic YMnO3 thin films
Bogusz, A.; Prucnal, S.; Blaschke, D.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.;
Resistive switching (RS) phenomena have been widely investigated in the field of materials science, physics, and electrical engineering in the past decade. Recently, multiferroics have been considered as promising candidates for memristive switches. Specific properties of multiferroics might bring additional and/or new functionalities into the memristive switches. This work investigates the RS properties of multiferroic YMnO3 thin films reported as a unipolar resistive switches. YMnO3 was grown at 400°C on Pt/Ti/SiO2/Si substrates by pulsed laser deposition (PLD) and crystallized by flash lamp annealing (FLA). Film thickness and the concentration of point defects were controlled during the PLD process. Transport and Rs properties of Au/YMnO3/Pt/Ti/SiO2 structures were determined by two-point probe measurements in a top-bottom configuration. Results imply that the filamentary, unipolar RS in YMnO3 originates from the electro-redox reactions induced by the Joule heating.
  • Lecture (Conference)
    DPG Spring Meeting, 15.-20.03.2015, Berlin, Germany

Publ.-Id: 22829 - Permalink

Interaction of europium and curium with alpha-amylase
Barkleit, A.; Heller, A.; Ikeda-Ohno, A.; Bernhard, G.;
The complexation of Eu(III) and Cm(III) with the protein α-amylase (Amy), a major enzyme in saliva and pancreatic juice, was investigated over wide ranges of pH and concentration at both ambient and physiological temperatures. Macroscopic sorption experiments demonstrated a strong and fast binding of Eu(III) to Amy between pH 5 and 8. The protein provides three independent, non-cooperative binding sites for Eu(III). The overall association constant of these three binding sites on the protein was calculated to be log K = 6.4 ± 0.1 at ambient temperature. With potentiometric titration the averaged deprotonation constant of the carboxyl groups (the aspartic and glutamic acid residues) of Amy was determined to be pKa = 5.23 ± 0.14 at 25 °C and 5.11 ± 0.24 at 37 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) revealed two different species for both Eu(III) and Cm(III) with Amy. In the case of the Eu(III) species, the stability constants were determined to be log β11 = 4.7 ± 0.2 and log β13 = 12.0 ± 0.4 for Eu:Amy = 1:1 and 1:3 complexes, respectively, while the values for the respective Cm(III) species were log β11 = 4.8 ± 0.1 and log β13 = 12.1 ± 0.1. Furthermore, the obtained stability constants were extrapolated to infinite dilution to make our data compatible with the existing thermodynamic database.

Publ.-Id: 22828 - Permalink

First tests of the prompt gamma ray timing method at a clinical proton accelerator
Hueso-González, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Janssens, G.; Kormoll, T.; Petzoldt, J.; Prieels, D.; Priegnitz, M.; Römer, K. E.; Smeets, J.; Sobiella, M.; Vander Stappen, F.; Wagner, A.; Weinberger, D.; Pausch, G.;
The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine.
Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment, the prompt gamma ray timing method has been recently proposed and tested at a research accelerator. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile.
In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies.
From the resulting distributions, particle range differences of around 5 millimetres in heterogeneous phantoms were observed by simple qualitative inspection. In conclusion, our preliminary analysis points out that the prompt gamma ray timing method for range verification is feasible in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.
Keywords: prompt gamma-ray timing, proton therapy, range verification, in vivo dosimetry
  • Open Access LogoContribution to proceedings
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Germany

Publ.-Id: 22827 - Permalink

Correct temporal averaging in gamma-ray tomography
Wagner, M.; Bieberle, A.; Bieberle, M.; Hampel, U.;
The dynamic bias error is a well-known effect in transmission radiometry. It appears when scanned processes offering a high dense variability such as phase distribution in turbulent multi-phase flows. If phases vary strongly during the data acquisition, the projection data is inherent time-averaged. Because of the non-linear relation between attenuation and measured stochastic intensity, the calculation of the classic time-averaged attenuation from the time-averaged projection data by the attenuation law produces a non-negligible phase fraction deviation. In general, this leads to an underestimation of the real attenuation which equals an overestimation of the gas phase in tomography images of two-phase flows for instance.
There are several approaches for the correction of this so called dynamic bias error. Recently, a method for correct averaging in transmission radiometry was developed. The method does not take any a priori knowledge about the flow into account but considers the Poisson distributed emission process of the radiation source. By deconvolving the Poisson distribution from the measured intensity distribution, the distribution of the attenuation is obtained. This demands the solution of an ill-conditioned equation system.
In this contribution the application of the correct averaging method (CAM) on time-averaged gamma-ray tomography is demonstrated using a mock-up of a centrifugal pump. A highly turbulent two-phase flow scenario is simulated based on both a virtual tomography data set as well as real measured data. By applying CAM, an elimination of the systematic dynamic bias error could be achieved even for very small numbers of gamma photons.
Keywords: gamma-ray tomography, dynamic bias error, correct averaging
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography
  • Lecture (Conference)
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 22826 - Permalink

Synthesis, dynamic NMR characterization and XRD studies of novel N,N’-substituted piperazines for bioorthogonal labeling
Mamat, C.; Pretze, M.; Gott, M.; Köckerling, M.;
Novel, functionalized piperazine derivatives were successfully synthesized and fully characterized by 1H/13C/19F NMR, MS, elemental analysis and lipophilicity. All piperazine compounds occur as conformers resulting from the partial amide double bond. Furthermore, a second conformational shape was observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a, monoclinic, space group C2/c, a = 24.587(2), b = 7.0726(6), c = 14.171(1) Å, β = 119.257(8)°, V = 2149.9(4) Å3, Z = 4, Dobs = 1.454 g/cm3) and the alkyne derivative 4-(but-3-yn-1-yl)-1-(4-fluorobenzoyl)piperazine (4b, monoclinic, space group P21/n, a = 10.5982(2), b = 8.4705(1), c = 14.8929(3) Å, β = 97.430(1)°, V = 1325.74(4) Å3, Z = 4, Dobs = 1.304 g/cm3) were obtained from a saturated ethyl acetate solution. The rotational conformation of these compounds was also verified by XRD. As proof of concept for future labeling purposes, both nitropiperazines were reacted with [18F]F–. To test the applicability of these compounds as possible 18F-building blocks, two biomolecules were modified and chosen for conjugation either using the Huisgen-click reaction or the traceless Staudinger ligation.
Keywords: building blocks; coalescence; dynamic NMR; labeling; Staudinger ligation

Publ.-Id: 22825 - Permalink

P1404 - Strukturierungsverfahren
Facsko, S.; Ou, X.;
Die Erfindung betrifft ein Strukturierungsverfahren zum Herstellen eines nanostrukturierten Bauelements mit periodisch angeordneten Strukturelementen, aufweisend die Schritte: Bereitstellen eines Substrats mit einer Schicht aus einem einkristallinen Schichtmaterial aus mindestens zwei chemischen Elementen; Heizen des Substrats mit der Schicht; und Bestrahlen einer Oberfläche der Schicht mit einem Ionenstrahl unter Erzeugung von Leerstellen in der Schicht.
  • Patent
    DE102014107458 - Offenlegung 03.12.2015, Nachanmeldung: 3x CN

Publ.-Id: 22824 - Permalink

The Radiochemical and radiopharmaceutical applications of radium
Gott, M.; Steinbach, J.; Mamat, C.;
This review focuses on the chemistry and application of radium isotopes to environmental monitoring, analytical, and medicinal uses. In recent years, radium has been used primarily as a tracer to study the migration of radioactive substances in environmental systems. Tracing the naturally occurring radium isotopes in mineral and water sources allows for the determination of source location, residence time, and concentrations. An understanding of the concentration of radionuclides in our food and water sources is essential to everyone’s health as alpha particle decay is highly damaging in vivo. Due to this high radiobiological effectiveness, there is increased interest in using alpha-emitting radionuclides to prepare new, therapeutic radiopharmaceutical drugs. Selected studies from the recent literature are provided as examples of these modern applications of radium isotopes.
Keywords: Alpha emitters, Radium, Radiochronology, Radiotracers, Radiotherapy

Publ.-Id: 22823 - Permalink

Design und Synthese von neuartigen Fluor-18-Radiotracern für PET-Imaging von Eph-Rezeptoren
Mamat, C.;
kein Abtract verfügbar
  • Lecture (others)
    GDCh-Kolloquium TU Dresden, 22.10.2015, Dresden, Deutschland
  • Lecture (others)
    GDCh-Kolloquium Universität Rostock, 10.12.2015, Rostock, Deutschland

Publ.-Id: 22822 - Permalink

Laser-Driven Proton Acceleration: Experimental Observation of Spatially Modulated Proton Beams & Diagnostics of the Plasma Formation Dynamics
Metzkes, J.; Kluge, T.; Zeil, K.; Bussmann, M.; Kraft, S. D.; Rehwald, M.; Cowan, T. E.; Schramm, U.;
Large effort is currently put into translating laser-driven particle sources from the status of experimental machines to accelerators ready for applications. The program at HZDR thereby focuses on laser-ion accelerators for medical applications [1]. Besides qualifying laser-accelerators for stable and reliable acceleration, the main challenge is the achievement of sufficient (~ 200 MeV for protons) particle energies. Fs-PW laser systems, going into operation in different laboratories worldwide now, might provide the necessary laser powers [2]. Hence, careful testing of the laser power scaling of the established acceleration mechanisms (e.g. TNSA) is needed, considering not only the achievable particle energies but properties as the spatial/angular distribution of particles (beam profile) as well.
In that context, we report on the experimental observation of spatially modulated proton beams emitted from micrometer thick targets which were irradiated with ultrashort (30 fs) laser pulses of a peak intensity of 5•1020W/cm2. The net-like proton beam modulations were recorded using radiochromic film and the investigation of different target systems for a laser energy range of 0.9 to 2.9 J revealed a clear dependence on laser energy and target thickness for the onset and strength of the modulations. Numerical simulations performed suggest filamentary instabilities, such as the parametric two plasmon decay and a Weibel-like instability, which occur in the laser-produced target front side plasma, as the source of the observed proton beam modulations [3].
The study is supported by pump-probe experiments of the plasma dynamics at the target front and rear surface. The method allows to connect the typical third-order autocorrelation traces [4] of the temporal pulse intensity contrast with the on-targets plasma conditions at pulse peak arrival. In that way, numerical simulations, necessary to investigate phenomena as plasma instabilities, can be matched to the real target plasma conditions more precisely.
We propose that the presented results on laser energy dependent plasma instabilities may have implications for the scaling of present acceleration mechanisms, such as target normal sheath acceleration, to higher proton energies and hence higher laser powers.
  • Lecture (Conference)
    Laser Plasma Acceleration Workshop, 10.-15.05.2015, Fort Royal, Guadeloupe


Publ.-Id: 22821 - Permalink

Towards Laser-Driven Ion Sources For Radiotherapy
Metzkes, J.;
The talk gives an overview over the multi-disciplinary research program in Dresden, which aims at the development of laser-driven ion sources for radiotherapy, including the translation of the technology into clinical application. The progress of the program will be discussed by presenting experimental results from the last years and discussing the laser facility at the Helmholtz-Zentrum Dresden – Rossendorf.
  • Invited lecture (Conferences)
    V International Symposium Topical Problems of Biophotonics – 2015 Novel Laser Applications in Biomedicine, 20.-24.07.2015, Nizhny Novgorod, Kazan, Elabuga, Russland

Publ.-Id: 22820 - Permalink

Cyclam Derivatives with a Bis(phosphinate) or a Phosphinato−Phosphonate Pendant Arm: Ligands for Fast and Efficient Copper(II) Complexation for Nuclear Medical Applications
David, T.; Kubićek, V.; Gutten, O.; Lubal, P.; Kotek, J.; Pietzsch, H.-J.; Rulíśek, L.; Hermann, P.;
Cyclam derivatives bearing one geminal bis-(phosphinic acid), −CH2PO2HCH2PO2H2 (H2L1), or phosphinic−phosphonic acid, −CH2PO2HCH2PO3H2 (H3L2), pendant arm were synthesized and studied as potential copper(II) chelators for nuclear medical applications. The ligands showed good selectivity for copper(II) over zinc(II) and nickel(II) ions (log KCuL = 25.8 and 27.7 for H2L1 and H3L2, respectively). Kinetic study revealed an unusual threestep complex formation mechanism. The initial equilibrium step leads to out-of-cage complexes with Cu2+ bound by the phosphorus-containing pendant arm. These species quickly rearrange to an in-cage complex with cyclam conformation II, which isomerizes to another in-cage complex with cyclam conformation I. The first in-cage complex is quantitatively formed in seconds (pH ≈5, 25 °C, Cu:L = 1:1, cM ≈ 1 mM). At pH >12, I isomers undergo nitrogen atom inversion, leading to III isomers; the structure of the III-[Cu(HL2)] complex in the solid state was confirmed by X-ray diffraction analysis. In an alkaline solution, interconversion of the I and III isomers is mutual, leading to the same equilibrium isomeric mixture; such behavior has been observed here for the first time for copper(II) complexes of cyclam derivatives. Quantum-chemical calculations showed small energetic differences between the isomeric complexes of H3L2 compared with analogous data for isomeric complexes of cyclam derivatives with one or two methylphosphonic acid pendant arm(s). Acid-assisted dissociation proved the kinetic inertness of the complexes. Preliminary radiolabeling of H2L1 and H3L2 with 64Cu was fast and efficient, even at room temperature, giving specific activities of around 70 GBq of 64Cu per 1 μmol of the ligand (pH 6.2, 10 min, ca. 90 equiv of the ligand). These specific activities were much higher than those of H3nota and H4dota complexes prepared under identical conditions. The rare combination of simple ligand synthesis, very fast copper(II) complex formation, high thermodynamic stability, kinetic inertness, efficient radiolabeling, and expected low bone tissue affinity makes such ligands suitably predisposed to serve as chelators of copper radioisotopes in nuclear medicine.

Publ.-Id: 22819 - Permalink

Gamma-ray computed tomography for multiphase flow analysis
Bieberle, A.;
Übersichtsvortrag zu aktuellen Ergebnissen der Gamma-CT des HZDR mit Fokussierung auf Verfahrenstechnik
Keywords: Gamma-ray-CT, chemical engineering
  • Lecture (others)
    Strategiegespräch mit Linde (Pullach), 03.12.2015, Höllriegelskreuth, Deutschland

Publ.-Id: 22818 - Permalink

Gamma-ray computed tomography for non-destructive testing and multiphase flow analysis
Bieberle, A.;
Vortrag zu aktuellen Ergebnissen des Gamma-ray-CT-Messsystems für industrielle Anwendungen.
Keywords: Gamma-ray CT, two phase flow, multi phase flow
  • Lecture (Conference)
    Innovation Days 2015, 08.-09.12.2015, Berlin, Deutschland

Publ.-Id: 22817 - Permalink

Developments for the application of the Wire-Mesh Sensor in industries
Kipping, R.; Brito, R.; Schleicher, E.; Hampel, U.;
Wire-Mesh Sensors (WMS) are applied in many research applications to determine the distribution of the phase fraction and to visualize the flow behavior within a pipe. However their application in industries is restricted due to the procedure of data acquisition. Here a new design of Wire-Mesh Sensor for monitoring void fraction and flow pattern behavior is presented. As result of online data evaluation cross-sectional void fraction information is provided in almost real-time. Additionally, the present flow pattern is determined by statistical analysis of recorded data of a time period of 10 s. This is the first time a Wire-Mesh Sensor was used for this purpose. With the help of fuzzy methodology a distinction of the four main flow patterns of vertical upward gas-liquid flow is possible. Furthermore transition regions can be identified. The algorithm is based on the evaluation of statistical void fraction distribution as result of Wire-Mesh Sensor data. Validation experiments of the new adopted algorithms are carried out in a 50 mm-ID two-phase air-water flow-loop at Tulsa University Horizontal Well and Artificial Lift Projects (TUHWALP).
Keywords: Wire-Mesh Sensor, gas-liquid flow, flow pattern identification

Publ.-Id: 22816 - Permalink

Research with HIBEF, the Helmholtz International Beamline for Extreme Fields at the European XFEL
Schramm, U.;
  • Invited lecture (Conferences)
    Applications of Laser-driven Particle Acceleration (ALPA 2015), 19.-21.11.2015, Venedig, Italien
  • Lecture (others)
    MLL Kolloquium Garching, 28.01.2016, Garching, Deutschland

Publ.-Id: 22815 - Permalink

Surfen auf der Plasmawelle - Teilchenbeschleunigung mit Laserlicht
Schramm, U.;
Mit modernen Hochleistungslasern können fuer die Dauer weniger Schwingungszyklen des Lichts elektrische Feldstärken erzielt werden, die Elektronen in nur einer Halbwelle auf relativistische Energien beschleunigen. In dem Vortrag soll anschaulich vorgestellt werden, wie diese transversalen Felder in sogenannten "relativistischen" Laserplasmen gleichgerichtet werden können, um eine effiziente Beschleunigung von Elektronen und Ionen auf nur wenigen Millimetern zu ermöglichen und für welche Anwendungsbereiche diese junge Technologie Vorteile bietet. Der Schwerpunkt wird dabei auf die Ionenstrahltherapie von Krebserkrankungen gelegt und mit etablierten Ansätzen verglichen.
Keywords: Laser Ionenbeschleunigung, Krebstherapie
  • Invited lecture (Conferences)
    Physikalisches Kolloquium Uni Halle, 03.12.2015, Halle, Deutschland

Publ.-Id: 22814 - Permalink

Influence of background electrolyte on Th(IV) sorption behavior
Hellebrandt, S.; Schmidt, M.; Knope, K. E.; Lee, S. S.; Stubbs, J. E.; Eng, P. J.; Soderholm, L.; Fenter, P.;
Studying and understanding the behavior of radionuclides at the water-mineral interface on a molecular level is of high importance for making reliable statements for the safety assessment of nuclear waste disposals. Clay minerals are relevant for nuclear waste disposal sites, due to their retardation properties. Muscovite, a phyllosilicate material, is structurally similar to clay minerals but forms large single crystals with high quality surfaces, necessary for surface X ray diffraction.
In a series of experiments we demonstrate that the background electrolyte has a significant influence on the sorption behavior of actinides, specifically thorium(IV). We study the sorption of Th(IV) (cTH = 10-4 mol/L), the softest of the tetravalent actinides, at the muscovite basal plane with several background electrolytes (NaClO4, KClO4, LiClO4). Previous investigations, with sodium chloride (10 1 mol/L) as background electrolyte, act as reference for these experiments. We find that the sorption behavior of thorium is substantially affected by both, changes in the electrolyte cation (Li+, K+) and anion (Cl-, ClO4-).
Briefly, compared to NaCl as background electrolyte, we observed increased sorption with LiClO4 in the system. On the other hand NaClO4 almost completely supressed sorption at high ionic strength, while a lower ionic strength of NaClO4, as well as KClO4, decreases sorption.
Keywords: Muscovite, Thorium, Background electrolyte, Sorption
  • Poster
    Goldschmidt (2015), 16.-21.08.2015, Praha, Česká republika
  • Poster
    MIGRATION 2015, 13.-18.09.2015, Santa Fe, USA
  • Lecture (Conference)
    GDCh-Wissenschaftsforum, 30.08.-02.09.2015, Dresden, Deutschland
  • Poster
    Doktorandenseminar des Kompetenzverbundes für Kerntechnik Ost (KOMPOST), 08.12.2015, Rossendorf, Deutschland

Publ.-Id: 22813 - Permalink

First-principles calculation of defect free energies: General aspects illustrated in the case of bcc-Fe
Posselt, M.; Murali, D.;
Modeling of nanostructure evolution in solids requires comprehensive data on the properties of intrinsic point defects, foreign atoms and defect clusters. Since most processes occur at elevated temperatures not only the energetics of these species in the ground state but also their temperature-dependent free energies must be known. These data can be used to obtain improved, temperature-dependent input parameters for atomistic or object kinetic Monte Carlo simulations and rate theory.
The first-principles calculation of contributions of phonon and electron excitations to free formation, binding, and migration energies is illustrated in the case of bcc-Fe. First of all, the ground state properties of the defects are determined under constant volume (CV) as well as zero pressure (ZP) conditions, and relations between the results of both kinds of calculations are discussed. Second, vibrational and electronic contributions to defect free energies are calculated using the equilibrium atomic positions determined in the ground state for the CV and the ZP case. Additionally, the quasi-harmonic approach is applied to ZP-based data in order to obtain results closest to the experimental conditions at elevated temperatures. However, in most cases considered this leads only to minor modifications. In contrast to ground state energetics the CV- and ZP-based defect free energies do not become equal with increasing supercell size. A simple transformation is found between the CV- and ZP-based frequencies and between the corresponding free energies. Finally, self-diffusion via the vacancy mechanism is investigated. The ratio of the respective CV- and ZP-based results for the vacancy diffusivity is nearly equal to the reciprocal of that for the equilibrium concentration. This behavior leads to almost identical CV- and ZP-based values for the self-diffusion coefficient. Obviously, this agreement is accidental and cannot be generalized to other cases.The consideration of the temperature dependence of the magnetization yields self-diffusion data in very good agreement with experiments
Keywords: defect free energy, first-principles calculation, bcc-Fe
  • Invited lecture (Conferences)
    MRS 2015 Fall Meeting, Symposium YY: Advanced Atomistic Algorithms in Materials Science, 29.11.-04.12.2015, Boston, USA

Publ.-Id: 22812 - Permalink

Unwilling U–U bonding in U2@C80: cage-driven metal–metal bonds in di-uranium fullerenes
Foroutan-Nejad, C.; Vıcha, J.; Marek, R.; Patzschke, M.; Straka, M.;
Endohedral actinide fullerenes are rare and a little is known about their molecular properties. Here we characterize the U2@C80 system, which was recently detected experimentally by means of mass spectrometry (Akiyama et al., JACS, 2001, 123, 181). Theoretical calculations predict a stable endohedral system, 7U2@C80, derived from the C80:7 IPR fullerene cage, with six unpaired electrons. Bonding analysis reveals a double ferromagnetic (one-electron-two-center) U–U bond at an rU–U distance of 3.9 Å. This bonding is realized mainly via U(5f) orbitals. The U–U interaction inside the cage is estimated to be about −18 kcal mol−1. U–U bonding is further studied along the U2@Cn (n = 60, 70, 80, 84, 90) series and the U–U bonds are also identified in U2@C70 and U2@C84 systems at rU–U ∼ 4 Å. It is found that the character of U–U bonding depends on the U–U distance, which is dictated by the cage type. A concept of unwilling metal–metal bonding is suggested: uranium atoms are strongly bound to the cage and carry a positive charge. Pushing the U(5f) electron density into the U–U bonding region reduces electrostatic repulsion between enclosed atoms, thus forcing U–U bonds.
Keywords: computational chemistry, AIM, DFT, Actinide chemistry

Publ.-Id: 22811 - Permalink

Partikelentstehung und –transport im Kern von Druckwasserreaktoren - Phase 2; Physikochemische Mechanismen (Abschlussbericht zum BMWi-Vorhaben 150 1467)
Kryk, H.; Hoffmann, W.;
Im Rahmen der deutschen Reaktorsicherheitsforschung wurden die generischen experimentellen Untersuchungen zur Aufklärung physikochemischer Mechanismen der Korrosionsproduktbildung und -ablagerung unter den wasserchemischen Bedingungen des Sumpfumwälzbetriebes in der Spätphase von Kühlmittelverluststörfällen in Druckwasserreaktoren weitergeführt. Das Vorhaben baute auf den Ergebnissen des Projektes 150 1430 auf und wurde in Kooperation mit der Hochschule Zittau/Görlitz (Vorhaben 150 1468) realisiert. Inhalt waren Laboruntersuchungen zu Entwicklung und Test von Maßnahmen zur Verhinderung der Bildung von Zinkborat-Ablagerungen an heißen Oberflächen.
Der Kontakt des borsäurehaltigen Kühlmittels mit feuerverzinkten Containment-Einbauten bewirkt eine Korrosion der Verzinkung, wodurch Zink im Kühlmittel gelöst wird. Aufgrund des im Vorhaben 150 1430 gefundenen Löslichkeitsverhaltens der entstehenden Zinkborate ist die Bildung und Ablagerung fester Korrosionsprodukte nicht auszuschließen, wenn zinkhaltiges Kühlmittel in heiße Regionen innerhalb des Kühlkreislaufes gelangt. Experimente in einer Labor-Korrosionsversuchsanlage zeigten, dass eine Zugabe von Alkalisierungsmitteln zu einer Reduzierung der Abscheideprozesse führt. Sowohl die Korrosionsrate von Zink als auch die Abscheiderate von Zinkborat verringern sich mit steigendem pH-Wert. Eine wesentliche Verringerung der Abscheiderate ist jedoch erst ab einem pH-Wert von ca. 7,5 feststellbar, wofür erhebliche Mengen Alkalisierungsmittel erforderlich sind. Eine vollständige Verhinderung der Korrosionsproduktbildung und –abscheidung war im untersuchten pH-Wert-Bereich nicht möglich. Des Weiteren hat die Differenz zwischen Sumpf- und Kerntemperatur Einfluss auf die Bildungsrate von Zinkborat. Signifikante Zinkborat-Mengen werden allerdings schon bei geringen Temperaturdifferenzen von ca. 10 K gebildet.
Untersuchungen zur Kinetik der Bildung von gelöstem Zink durch Korrosion von verzinkten Einbauten im Sicherheitsbehälter waren nicht Projektgegenstand, weshalb eine direkte quantitative Übertragbarkeit der Ergebnisse auf postulierte KMV in DWR-Anlagen derzeit noch nicht gegeben ist.
Keywords: Druckwasserreaktor, Kühlmittelverluststörfall, Korrosion, Zink, Zinkborat, Experiment
  • Other report
    Karlsruhe: FIZ Karlsruhe, 2015
    57 Seiten

Publ.-Id: 22810 - Permalink

Liquid metal batteries for large-scale stationary storage
Weier, T.; Galindo, V.; Landgraf, S.; Seilmayer, M.; Stefani, F.; Weber, N.;
Liquid metal batteries (LMBs) are high temperature systems consisting of liquid metal electrodes and a molten salt ionic conductor. The densities are chosen in such a way that a stable density stratification of the inmiscible layers results. LMBs were considered mainly as part of energy conversion systems in the 1960s and have only recently received renewed interest for economic large-scale storage. Typically, LMBs allow for high current densities due to the fast kinetics at liquid/liquid interfaces and the rapid mass transport in fluids.

Our work concentrates on the fluid dynamic aspects of this cell type with a special focus on the effects and properties of the Tayler instability (TI) and on electro-vortex flows. Both phenomena are driven by electromagnetic forces and should be considered for large cells. Due to the completely liquid interior of LMBs, fluid flow is an important aspect of their operation. It can be beneficial, when enhancing mass transfer in the cathode, or it might have harmful consequences, if the integrity of the electrolyte layer is disrupted. The latter case can result from the action of the current-driven TI or electrically driven vortex flows. We therefore studied the characteristics of the TI as well as some exemplary cases of electro-vortex flows using an integro-differential approach implemented in the open source library OpenFOAM. The TI occurs if a critical value of a dimensionless parameter Ha, the Hartmann number describing the ratio of electromagnetic to viscous forces, is exceeded. The critical Ha is lowest for an infinitely high vessel and corresponds to a total current of approx. 1 kA in the case of Na. Decreasing the aspect ratio increases the critical Ha and thereby the critical current since the wavelength selection for the TI becomes more and more restricted.

As mentioned above, current densities in LMBs are typically very high. A current density of 10 kA/m2 is a characteristic value for a Na|NaI-NaCl-NaF|Bi-system and results in an approximately 10 mm thick sodium layer transferred per hour from the anodic to the cathodic compartment. Depending on the design capacity and cell area, aspect ratios of the anodic compartment up to one seem imaginable. While flat enough cells will not suffer from TI induced short circuits, for taller ones stabilization measures can be applied to prevent negative consequences.

Using thin feeding lines to contact relatively large current collectors will most certainly result in inhomogeneous current density distributions in the fluid. They will generate electro-vortex flows that may again compromise the integrity of the electrolyte layer. A careful distribution of the charging current by several wires should solve the problem. Properly designed electro-vortex flows might even be used to gently stir the cathode thereby increasing mass transfer and improving cell performance.
Keywords: liquid metal batteries, Tayler instability, electro-vortex flows
  • Lecture (Conference)
    3rd Dresden Conference "Energy in Future", 10.-11.11.2015, Dresden, Deutschland

Publ.-Id: 22809 - Permalink

Towards a life-time-limited 8-octave-infrared photoconductive germanium detector
Pavlov, S. G.; Deßmann, N.; Pohl, A.; Abrosimov, N. V.; Mittendorff, M.; Winnerl, S.; Zhukavin, R. K.; Tsyplenkov, V. V.; Shengurov, D. V.; Shastin, V. N.; Hübers, H.-W.;
Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times.
Keywords: fast detection, germanium, photoconductive THz detector
  • Open Access LogoJournal of Physics: Conference Series 647(2015), 012070
    DOI: 10.1088/1742-6596/647/1/012070
  • Poster
    19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 19), 29.06.-02.07.2015, Salamanca, Spain

Publ.-Id: 22808 - Permalink

Direct numerical simulation of a particle attachment to an immersed bubble
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.;
The selective attachment of hydrophobic particles by gas bubbles immersed in water is at the heart of the flotation process. The valuable hydrophobic particles, such as for instance fine-grained particles of ore mineral, adhere to the fluidic interface of rising bubbles while the valueless hydrophilic material settles down the bottom of the flotation cell to eventually be discharged. The attachment process, i.e. the capture of a single hydrophobic particle by a bubble, can be divided into a sequence of three microprocesses: the particle approach, the collision process and the sliding down the bubble surface. The absence of explicit boundary between two consecutive events along with the multiphase nature of the system renders the development of predictive computer model difficult. A numerical model is here suggested for the direct numerical simulation of the particle attachment on a stationary bubble. The two fluid-particle boundaries and the fluidic boundary are replaced with diffuse interfaces. The attachment of a single particle on a stationary bubble is presently tested. Particle trajectories and velocities in the near bubble region are captured and compare qualitatively well with available experimental data.

Publ.-Id: 22805 - Permalink

Batch sorption and spectroscopic speciation studies of neptunium uptake by montmorillonite and corundum
Elo, O.; Müller, K.; Ikeda-Ohno, A.; Bok, F.; Scheinost, A.; Hölttä, P.; Huittinen, N.;
Detailed information on neptunium(V) speciation on montmorillonite and corundum surfaces was obtained by batch sorption and desorption studies combined with surface complexation modelling using the Diffuse Double-Layer (DDL) model and in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and X-ray Absorption (XAS) spectroscopies. The pH-dependent batch sorption studies and the spectroscopic investigations were conducted under carbonate-free conditions in 10 mM NaClO4 or 10 mM NaCl. Solid concentrations of 0.5 g/l and 5 g/l were used depending on the experiment. The reversibility of the neptunium(V) uptake reaction by the two minerals was investigated in desorption experiments using the replenishment technique. Neptunium(V) sorption was found to be highly reversible, however, the degree of reversibility was dependent on the solution pH. The reversibility of the sorption reaction was confirmed in the ATR FT-IR spectroscopic studies at pH 10, where all of the identified inner-sphere complexed neptunium(V), characterized by a vibrational band at 790 cm-1, was desorbed from both mineral surfaces upon flushing the mineral films with a blank electrolyte solution. In XAS investigations of neptunium(V) uptake by corundum, the obtained structural parameters confirm the formation of an inner-sphere sorbed complex adsorbed on the surface in a bidentate fashion. As the inner-sphere complexes found in the IR-studies are characterized by identical sorption bands on both corundum and montmorillonite, we tentatively assign the neptunium(V) inner-sphere complex on montmorillonite to the same bidentate complex found on corundum in the XAS investigations. Finally, surface complexation modelling using obtained batch sorption and spectroscopic results were performed to explain the neptunium(V) speciation on montmorillonite over the entire investigated pH range. The modelling results show that cation exchange in the interlayer space as well as both outer-sphere and inner-sphere complexation are required to fully explain the neptunium(V) speciation on the montmorillonite surface

Publ.-Id: 22804 - Permalink

Interaction of highly charged ions with carbon nano membranes
Gruber, E.; Wilhelm, R. A.; Smejkal, V.; Heller, R.; Facsko, S.; Aumayr, F.;
Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

Publ.-Id: 22803 - Permalink

Incorporation of Cm3+ and Eu3+ in LnPO4 ceramics – a site-selective TRLFS study
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Stumpf, T.;
The chemical durability and structural flexibility of lanthanide phosphates make these ceramics attractive as host phases for the conditioning of long-lived radionuclides produced during the nuclear fuel cycle. In the present work we have studied the structural incorporation of Cm3+ and Eu3+ in various LnPO4 monazite and xenotime phases with site-selective time-resolved laser fluorescence spectroscopy (TRLFS). The europium results indicate a full structural incorporation in the LnPO4 ceramics crystallizing in the nine-fold coordinated monazite structure (LaPO4-GdPO4) independent of the host cation radius. A local disordering can, however, be seen in mixed monazite solid solutions when going from the pure endmembers (LaPO4 and GdPO4) toward the La0.5Gd0.5PO4 composition. The smaller lanthanides crystallizing in the eight-fold coordinated xenotime structure (TbPO4-LuPO4) show only a partial uptake of Eu3+ within the host cation sites. The remainder of the dopant appears to be present as an ill-defined, partially hydrated europium species on or within the xenotime solid. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The results of the Cm-TRLFS measurements will be compared to the Eu3+-data and presented at the symposium.
  • Lecture (Conference)
    Scientific Basis for Nuclear Waste Management XXXIX, 02.-06.11.2015, Montpellier, France

Publ.-Id: 22802 - Permalink

Curium(III) and europium(III) incorporation in lanthanide phosphate ceramics for conditioning of radioactive wastes
Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Schmidt, M.; Neumeier, S.; Stumpf, T.;
The high-level radioactive waste (HLW) from spent nuclear fuel reprocessing facilities is currently immobilized in borosilicate glass. The vitrification process is well established and the flexible glass matrix is able to incorporate a very large range of elements present in the waste solution [1]. With the development of partitioning strategies, enabling the extraction of long-lived fission products and minor actinides (MA) from the PUREX raffinate, specific waste streams will be created that may require durable host matrices for their safe disposal. Especially for MA immobilization, some ceramic materials have been envisioned as host materials due to their thermal stability, high radiation tolerance, and chemical durability [2].
Lanthanide phosphate ceramics (LnPO4) are able to incorporate radionuclides in well-defined atomic positions within the crystal lattice [3] up to high (27 %) loadings [2]. The existence of very old natural analogues containing high concentrations of uranium and thorium shows that the crystalline phosphate structure is very tolerant towards self-irradiation damages as well as chemical weathering [4]. The dehydrated, high-temperature LnPO4 phases are known to crystallize in two distinct structures, depending on the ionic radius of the lanthanide cation: the larger lanthanides from La3+ to Gd3+ crystallize in the nine-fold coordinated monazite structure with a low symmetry, while the smaller lanthanides Tb3+ to Lu3+ form tetragonal, eight-fold coordinated xenotime structures.
In the present study we have used site-selective time-resolved laser fluorescence spectroscopy (TRLFS) to investigate the influence of the host cation radius as well as the crystal structure of the ceramic (monazite vs. xenotime) on the incorporation of the trivalent metal ions Eu3+ and Cm3+. We have synthesized pure monazites and xenotimes doped with 500 ppm Eu3+ or 50 ppm Cm3+ by precipitation of LnPO4 from a 0.3-0.5 M lanthanide nitrate solution with phosphoric acid followed by sintering of the precipitate at 1450°C to obtain the crystalline ceramic. The laser spectroscopy was performed either with a pulsed Nd:YAG-pumped tunable optical parametric oscillator or dye laser setup at cryogenic temperatures (~ 10 K). Excitation and emission spectra as well as luminescence lifetimes were collected for all measured samples.
Results on Eu3+-doped monazites show very narrow excitation spectra (Figure 1, left) for all investigated phases (LaPO4, SmPO4, GdPO4), indicating a complete incorporation of the dopant within the monazite crystal structure independent of the host cation radius. The emission spectra show a maximum splitting of the 7F1 and 7F2 bands (Figure 1, right), confirming the incorporation of Eu3+ on the low symmetry cation sites in the monazites.
The xenotime structure is not able to fully incorporate the europium ion within the crystal lattice. The excitation spectrum of Eu3+-doped LuPO4 in Figure 2 shows two regions of europium intensity that, upon excitation, decay with very different lifetimes. The broad signal in the wavelength region 575-580 nm corresponds to an ill-defined, partially hydrated europium species with a lifetime of approximately 580 µs (1.2 H2O). The species at 583.00 nm has a lifetime of 2700 µs indicating a full loss of the europium hydration sphere upon incorporation. The emission spectrum at this excitation wavelength shows a 2 and 4-fold splitting of the 7F1 and 7F2 bands, respectively, which is expected for an ion within the tetragonal cation site in the xenotime structure.
Our Eu3+ results demonstrate the importance of spectroscopic methods to probe the local environment of a guest cation within a solid matrix. According to our results, monazites can be considered as suitable host matrices for the immobilization of trivalent dopants. The xenotime structure on the other hand is not an ideal host for the larger lanthanide or actinide dopants due to the structure mismatch that does not allow for a complete guest ion substitution within the ceramic structure. Actinide (Cm3+)-doped LnPO4 samples have been synthesized similarly to the Eu3+ solids. The samples will be measured with TRLFS in the near future and results will be analyzed and compared to the existing Eu3+-data in order to confirm the incorporation behavior of trivalent dopants in the investigated solids. The results obtained for both dopants will be presented at the conference.
  • Lecture (Conference)
    15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Publ.-Id: 22801 - Permalink

Mass transfer measurement in a square milli-channel and comparison with results from a circular channel
Haghnegahdar, M.; Boden, S.; Hampel, U.;
In this work, we report on an experimental investigation of mass transfer from stagnant Taylor bubbles in a small square channel via measurement of the dissolution rate of an individual elongated bubble of carbon dioxide into water. As a measurement technique we used high resolution X-ray radiography and tomography. The changes in the size of the bubble at constant pressure obtained from the high-resolution X-ray images were used to calculate the liquid side mass transfer coefficient. The bubbles were continuously monitored by hydrodynamic fixation of the bubble in a down flow of the liquid. The results are compared with the available recently published data for circular channels.
The results show that the bubble dissolution curves in square channels are relatively even while the dissolution curves for bubbles in circular channels show some noticeable change in the slope. Furthermore, it is shown that the calculated liquid side mass transfer coefficient based on the measured data show good agreement with the data predicted by the penetration theory when the contact time between two phases is defined as the ratio of bubble length to the relative velocity. In addition, the comparison of the results with the data for circular channels showed that despite the fact that the rise velocity of bubbles in square channel is about three times faster than in circular channel, the liquid side mass transfer coefficients are approximately the same.
Keywords: mass transfer, Taylor bubble, carbon dioxide, square channels, X-ray imaging

Publ.-Id: 22800 - Permalink

High-energy resolution XAS/XES reveals insight into unique selectivity of La-based nanoparticles for CO2
Hirsch, O.; Kvashnina, K. O.; Luo, L.; Suess, M.; Glatzel, P.; Koziej, D.;
The lanthanum-based materials, due to their layered structure and f-electron configuration, are relevant for electrochemical application. Particularly, La2O2CO3 shows a prominent chemoresistive response to CO2. However, surprisingly less is known about its atomic and electronic structure and electrochemically significant sites and therefore, its structure–functions relationships have yet to be established. Here we determine the position of the different constituents within the unit cell of monoclinic La2O2CO3 and use this information to interpret in situ high-energy resolution fluores cence-detected (HERFD) X-ray adsorption near-edge structure (XAS) and valence-to-core X-ray emission spectroscopy (vtc XES). Compared with La(OH)3 or previously known hexagonal La2O2CO3 structures, La in the monoclinic unit cell has a much lower number of neighboring oxygen atoms, which is manifested in the whiteline broadening in XAS spectra. Such a superior sensitivity to subtle changes is given by HERFD method, which is essential for in situ studying of the interaction with CO2. Here, we study La2O2CO3-based sensors in real operando conditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied La d states and occupied O p- and La d states changes during CO2 chemoresistive sensing of La2O2CO3. The correlation between these spectroscopic findings with electrical resistance measurements leads to a more comprehensive understanding of the selective adsorption at La site and may enable the design of new materials for CO2 electrochemical applications.
Keywords: lanthanum oxycarbonate, HERFD XAS, valence-to-core XES, structure, CO2 sensing
  • Proceedings of the National Academy of Sciences of the United States of America 112(2015)52, 15803-15808
    DOI: 10.1073/pnas.1516192113

Publ.-Id: 22799 - Permalink

Neptunium characterization in uranium dioxide fuel: Combining a XAFS and a thermodynamic approach
Chollet, M.; Martin, P.; Degueldre, C.; Poonoosamy, J.; Belin, R. C.; Hennig, C.;
The effect of Np incorporation in a UO2 matrix on redox state of U and Np cations has been investigated by X-ray absorption spectroscopy (XAS) on three samples: (U0.9Np0.1)O2, (U0.9Np0.1)O2+x and pure NpO2 as a reference for Np(IV) oxidation state. XANES and EXAFS analysis show that only Uranium is oxidized in higher (V) and (VI) oxidation states in the hyperstoichiometric (U0.9Np0.1)O2+x sample in comparison to the stoichiometric (U0.9Np0.1)O2 where U appears at the (IV) oxidation state. Neptunium cation always remains at the (IV) oxidation state whatever the oxygen stoichiometry. Thermodynamic calculations performed to complete the experimental study, lead to the same conclusion. Separate UO2-NpO2 phases and homogeneous solid solution were considered. The latter case shows that the energy of mixing is insignificant in this system. These combined experimental and theoretical approaches demonstrate that any excess of oxygen in the system is carried by Uranium.
Keywords: neptunium oxide, uranium oxide, solid solution, stoichiometry, oxidation state

Publ.-Id: 22798 - Permalink

Magnetic structure of the antiferromagnetic half-Heusler compound NdBiPt
Müller, R. A.; Desilets-Benoit, A.; Gauthier, N.; Lapointe, L.; Bianchi, A. D.; Maris, T.; Zahn, R.; Beyer, R.; Green, E.; Wosnitza, J.; Yamani, Z.; Kenzelmann, M.;
We present results of single-crystal neutron-diffraction experiments on the rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits an AFM phase transition at TN = 2.18 K with an ordered moment of 1.78(9) μB per Nd atom. The magnetic moments are aligned along the [001] direction, arranged in a type-I AFM structure with ferromagnetic planes, alternating antiferromagnetically along a propagation vector τ of (100). The RBiPt (R = Ce–Lu) family of materials has been proposed as candidates for a new family of antiferromagnetic topological insulators (AFTIs) with a magnetic space group that corresponds to a type-II AFM structure where ferromagnetic sheets are stacked along the space diagonal. The resolved structure makes it unlikely that NdBiPt qualifies as an AFTI.

Publ.-Id: 22797 - Permalink

Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI
Park, J.; Jin, K. H.; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; Rhyee, J.-S.; Jhi, S.-H.; Kim, J. S.;
We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum Phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion.

Publ.-Id: 22796 - Permalink

Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin films
Molatta, S.; Haindl, S.; Trommler, S.; Schulze, M.; Wurmehl, S.; Hühne, S.;
Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is still a delicate issue in terms of simultaneous control of stoichiometry, texture, substrate/film interface properties, and superconducting properties. The high volatility of the constituents sharply limits optimal deposition temperatures to a narrow window and mainly challenges reproducibility for vacuum based methods. In this work we demonstrate the beneficial introduction of a semiconducting FeSe1−xTex seed layer for subsequent homoepitaxial growth of superconducting FeSe1−xTex thin film on MgO substrates. MgO is one of the most favorable substrates used in superconducting thin film applications, but the controlled growth of iron chalcogenide thin films on MgO has not yet been optimized and is the least understood. The large mismatch between the lattice constants of MgO and FeSe1−xTex of about 11% results in thin films with a mixed texture, that prevents further accurate investigations of a correlation between structural and electrical properties of FeSe1−xTex. Here we present an effective way to significantly improve epitaxial growth of superconducting FeSe1−xTex thin films with reproducible high critical temperatures (≥17 K) at reduced deposition temperatures (200 °C–320 °C) on MgO using PLD. This offers a broad scope of various applications.

Publ.-Id: 22795 - Permalink

Severe accident management research at HZDR
Tusheva, P.; Schäfer, F.; Altstadt, E.; Kliem, S.;
Presentation at the 1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology.
Keywords: severe accidents, accident management measures
  • Invited lecture (Conferences)
    1st Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology, 09.-12.03.2015, Shanghai, China

Publ.-Id: 22794 - Permalink

EDUKEM project - first spectroscopic insights into the U(IV)/U(VI) speciation in concentrated NaCl solution
Lehmann, S.; Steudtner, R.; Brendler, V.;
This work is embedded into the EDUKEM project, a collaboration with GRS Braunschweig and KIT-INE. Its major purpose is the provision of quality assured thermodynamic data for both tetra- and hexavalent uranium. This shall enable a better assessment of speciation and solubility limits in diluted to highly saline solutions as expected near nuclear waste repositories.
Respective experiments are based on parallel developments in electrochemical and spectroscopic tools being complementary to each other. In such a way difficult to access, systems and conditions should be explored to obtain an integral overview about aqueous uranium chemistry. This especially holds for reducing conditions. This will not only promote the characterization of complex system, e.g., encountered in nuclear waste management, but also allow a fingerprinting of unknown substances and mixtures.
We started to investigate the spectroscopic characteristics of 0.01M U(IV) and U(VI) in different background media (ClO4-, Cl-, SO42-, PO43-, CO32-) using UV/vis and fluorometry. The U(VI) was reduced by potentiostatic electrolysis using Ag/AgCl reference electrode. The reduction was monitored by UV/vis spectroscopy. The residual content of U(VI) was less than 1 %. We observed no formation of precipitations under the experimental conditions with exception of the PO43- system. There, we changed the uranium/ligand ratio from 1:100 to 1:5000 to suppress uranium phosphate precipitation. In general, the UV/vis spectra show variations in intensities and peak shifts to higher wavelengths in dependence of complexation strength in following order ClO4– < Cl– < SO42– < PO43– < CO32–.
In contrast to U(VI), which is often quenched by ions in the solution such as chloride, we obtained a luminescence spectrum of U4+ in 0.1 M HCl excited by λexc = 245 nm at a temperature of 1°C. The obtained luminescence spectrum is similar to the luminescence spectra of the free U4+ ion in acidic published by Kirishima et al. [1]. Under the experimental conditions, hydrolysis species as well as a complex formation between U(IV) and chloride should occur. The UV/vis spectra show spectral modifications which could be induced by the hydrolysis species. However, the luminescence spectra do not show spectral modifications.
In case of U(VI), first TRLFS results show the capabilities of fluorescence spectroscopy even in high chloride concentrated solutions to study U(VI) speciation. Despite the high concentration of 3 M chloride, a luminescence spectrum could be recorded in presence of carbonate in the alkaline pH region. Comparing the position of these bands with literature, we suggest a U(VI) complexation by carbonate [2].
The preliminary results of this study and of Bader et al. [3] shown that chloride quench mechanism for U(IV) and U(VI) luminescence is not fully understood yet in literature. Therefore, further studies will be performed on the spectroscopic behavior and chemistry of U(IV) as well as for U(VI) in highly concentrated chloride solutions.

1. A. Kirishima et al., “Luminescence properties of tetravalent uranium in aqueous solution” Radiochim. Acta, 92, 705-710 (2004).
2. Z. Wang et al., “Cryogenic laser induced fluorescence characterization of U(VI) in Hanford vadose zone pore waters“, Environ. Sci. Technol., 38, 5591-5597 (2004).
3. M. Bader et al., “Biosorption of uranium on the cells of the halophilic archaea Halobacterium noricense DSM 15987 under highly saline conditions”, Abstract – ABC-Salt IV Workshop 2015 – Heidelberg, Germany.
Keywords: Uranium, high salinity, fluorescence, UV/vis, speciation
  • Poster
    ABC-Salt IV Workshop 2015, 14.-15.04.2015, Heidelberg, Deutschland
  • Poster
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Deutschland

Publ.-Id: 22793 - Permalink

Effect of anisotropic microstructure of a 12Cr ODS steel on the fracture behaviour in the small punch test
Altstadt, E.; Serrano, M.; Houska, M.; Garcia-Junceda, A.;
Oxide dispersed strengthened steels can exhibit a strongly anisotropic microstructure with elongated pancake-like grains in the rolling plane. This gives rise to intergranular fracture and subsequent delamination along large-area grain boundaries. We investigated an oxide dispersed strengthened alloy with 12 mass percent Cr, manufactured by mechanical alloying, hot extrusion and cold rolling by means small punch tests and subsequent fractographic analysis. The fracture behaviour was analysed in dependence of the specimen orientation. The results from small punch tests were contrasted with those from impact tests with sub-sized samples. In both tests, the ductile to brittle transition temperatures as well as the upper shelf energies depend significantly on the orientation of the specimens. However, the delamination affects the fracture of impact and small punch test samples in different ways. Thus, it depends on the load situation whether delamination has a beneficial or a detrimental effect on the fracture behaviour.
Keywords: ODS-steel, small punch test, anisotropy, delamination

Publ.-Id: 22792 - Permalink

Disclosing the hydrodynamics of 3D foam networks for application in advanced catalytic multiphase reactors
Zalucky, J.;
In the course of the 10th PhD seminar, the so-far achieved results of the PhD are presented in a short presentation. Starting with the economical and scientific background, the topic of multiphase hydrodynamics in solid foam trickle bed reactors is presented. The results cover the highlights of the regime transition measurements as well as studies carried out using ultrafast X-ray computed tomography.
Keywords: SiSiC solid foam packed trickle-bed reactors; co-current downflow hydrodynamics; ultrafast X-ray computed tomography
  • Lecture (Conference)
    10th HZDR PhD seminar, 02.-04.11.2015, Altenberg, Deutschland

Publ.-Id: 22791 - Permalink

Disclosing the hydrodynamics of 3D cellular networks for application in multiphase reactors
Zalucky, J.; Wagner, M.; Bieberle, M.; Schubert, M.; Hampel, U.;
On behalf of the closing symposium of the Helmholtz Energy Alliance 'Energy Efficient Chemical Multiphase Processes' the scientific highlights of working packages 3.1 and 5.3 are presented. In the first part, the results concering the regime transition measurements for SiSiC solid foam packed trickle-bed reactors are presented. In the second part, the investigations concering the liquid and gas distribution studied by using ultrafast X-ray computed tomography are discussed. In the third part, the hydrodynamics in bubble columns packed with periodic open-cellular structures (POCS) are presented.
Keywords: SiSiC solid foam packed trickle-bed reactor; regime transition; phase distribution; bubble column; periodic open-cellular structures; ultrafast X-ray computed tomography
  • Lecture (Conference)
    Abschlusssymposium der Helmholtz-Energie-Allianz Energieeffiziente Chemische Mehrphasenprozesse, 30.11.-01.12.2015, Dresden, Deutschland

Publ.-Id: 22790 - Permalink

Qualitative and quantitative analysis of liquid flow distribution in SiSiC foams using X-ray tomography
Zalucky, J.; Claußnitzer, T.; Schubert, M.; Hampel, U.;
In the recent years, solid foams have attracted engineer’s interest as novel functional internals for different chemical process applications. Beside their potential usage as static mixers, distillation packings and heat transfer equipment, solid foams have been envisaged as single and multiphase catalytic support as well. The present contribution focusses on the investigation of the liquid flow distribution inside SiSiC solid foams operated in co-current downward flow. Time-averaged and dynamic flow behaviour has been studied over wide ranges of gas and liquid su-perficial velocities using the non-invasive ultrafast X-ray tomography system.
Keywords: SiSiC solid foam hydrodynamics; co-current downflow; ultrafast X-ray computed tomography; liquid saturation; pulse flow parameters
  • Poster
    European Symposium on Chemical Reaction Engineering, 27.-30.10.2015, Fürstenfeldbruck, Deutschland

Publ.-Id: 22789 - Permalink

Hydrodynamics and transport processes in structured reactor devices: Project status report april 2015
Zalucky, J.; Schubert, M.; Hampel, U.;
On the occasion of half-annual project status report, work package progress is presented. The first part covers the regime transition measurement and modelling for the co-current downflow in SiSiC solid foam packed trickle-bed reactor. The second part summarizes the results found by investigating the time-dependent liquid gas distribution using ultrafast X-ray computed tomography in the same reactor system.
Keywords: regime transition measurement; regime transition modelling; SiSiC solid foam hydrodynamcs; ultrafast X-ray computed tomography
  • Lecture (others)
    Helmholtz-Energie-Allianz EECMP: Half-annular project meeting, 13.-14.04.2015, Fürth, Deutschland

Publ.-Id: 22788 - Permalink

Co-current downward flow regime transition in solid SiSiC foams: Flow regime prediction and measurement
Zalucky, J.; Möller, F.; Schubert, M.; Hampel, U.;
In recent years, solid foams have gained rising interest as multiphase reactor internals for highly exo- or endothermic processes due to relatively low pressure drop, high specific surface areas and elevated radial transport properties. Beside the geometric bed properties, the over-all reactor performance is significantly affected by the prevailing flow regime. In the present contribution, the flow regime transition of co-current downward flows in open-cell SiSiC solid foams has been investigated by optical and acoustical observations as well as fast pressure transducer. Measurements were performed with a water-air system in different bed geometries of varied pore densities and packing diameters of 20, 30, and 45 ppi and DN50 and DN100, respectively. Additionally, aqueous systems with reduced surface tension and increased viscosity have been tested. In order to predict the regime transition from trickle to pulse flow in multiphase systems, the two predictive models of Grosser et al. (1988) and Attou & Ferschneider (2000) have been adapted from trickle bed reactors to structured solid foam fixed bed reactors and validated by the experimental transition data. Determining the onset of flow instabilities at different liquid and gas velocities based on different force balances, both models allow the prediction of regime transition by means of known single phase pressure drop, static liquid holdup and characteristic geometric parameters of the solid foam.
Keywords: Stability based regime transition predictive modelling, SiSiC solid foam
  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Mehrphasenströmung, 19.-20.03.2015, Lüneburg, Deutschland

Publ.-Id: 22787 - Permalink

INTRA r³+ Vernetzung der r³ Projekte und Transfer der Ergebnisse
Dürkoop, A.;
In diesem Vortrag werden die Ergebnisse der Begleitforschung zu r³ vorgestellt. Dabei werden Methoden zur Bewertung von innovativen Technologien und Verfahren präsentiert, erfolgte Vernetzung der r³ Projekte erläutert und der Transfer der r³ Ergebnisse in die Anwendung gezeigt.
Keywords: Ressourceneffizienz, Strategische Metalle und Mineralien
  • Invited lecture (Conferences)
    Berliner Recycling- und Rohstoffkonferenz 2016, 07.-08.03.2016, Berlin, Deutschland

Publ.-Id: 22786 - Permalink

INTRA r³+ Integration und Transfer der r³ Fördermaßnahme - Ergebnisse der Begleitforschung
Dürkoop, A.; Brandstetter, P.; Erdmann, M.; Gräbe, G.; Höck, M.; Kleeberg, K.; Moller, B.; Ostertag, K.; Schneider, K.; Tercero, L.; Wilken, H.; Pfaff, M.; Büttner, P.;
Die r³ Fördermaßnahme wurde in einem Zeitraum von gut vier Jahren zwischen Ende 2011 bis Anfang 2016 durch das Bundesministerium für Bildung und Forschung mit 30 Mio. € gefördert. In 28 r³ Verbundprojekten forschten bundesweit mehr als 100 Unternehmen, Forschungseinrichtungen und Behörden daran, wie nicht-energetische mineralische Rohstoffe zukünftig effizienter genutzt werden können (Abb. 1). Der Fokus lag auf den wirtschaftsstrategisch wichtigen Metallen wie Indium, Germanium, Gallium und seltene Erden, aber auch Industrieminerale wie beispielsweise Flussspat, die zukünftig effizienter gewonnen, recycelt und in Produkten verwendet werden sollen (BMBF 2010). Strategische Metalle und Mineralien werden vor allem für die Herstellung von Hightech-Produkten (Abb. 2) und Energiesparlampen, aber auch für Dauermagnete benötigt. Zwar werden diese Ressourcen nicht in großen Mengen verwendet, sind aber wirtschaftsstrategisch von großer Bedeutung. Da die Rohstoffe zunehmend schlechter verfügbar sind, steigen die Produktionskosten für solche Hightech-Produkte. Die Versorgungslage für diese strategischen Rohstoffe ist in Deutschland unsicher, was zu Versorgungsengpässen im Rohstoffimportland Deutschland führen könnte. Die Ergebnisse der r³ Verbundprojekte zeigen, dass die Versorgungslage für einige dieser Rohstoffe für Deutschland verbessert werden könnte.
Die Bewertung der Ergebnisse aus r³ erfolgte im Rahmen des Projekts INTRA r³+ (Abb. 3) unter der Leitung des Helmholtz-Instituts Freiberg für Ressourcentechnologie (HIF). Zur Bewertung der Nachhaltigkeit der r³ Ergebnisse wurden zum einen ökonomisch-ökologisch-soziale Aspekte analysiert und zum anderen gesamtwirtschaftliche Betrachtungen durchgeführt. Zudem wurde die Vernetzung der r³ Verbundprojekte untereinander aber auch mit externen Initiativen und Projekten mit diversen Maßnahmen angeregt. Darüber hinaus wurde mit Öffentlichkeitsarbeit-Maßnahmen durchgeführt und der Technologietransfer in die Wirtschaft vorbereitet. Partner von INTRA r3+ sind neben dem HIF die Technische Universität Bergakademie Freiberg (TUBAF), der Lehrstuhl für Ganzheitlich Bilanzierung an der Universität Stuttgart (LBP), das Fraunhofer Institut für System- und Innovationsforschung (ISI), das Fraunhofer-Institut für Chemische Technologie (ICT) und die Deutsche Rohstoffagentur (BGR/DERA).
Keywords: Ressourceneffizienz, strategische Metalle, Versorgungssicherheit, Nachhaltigkeitsbewertung
  • Open Access LogoContribution to proceedings
    Berliner Recycling- und Rohstoffkonferenz, 07.-08.03.2016, Berlin, Deutschland
    Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 978-3-944310-27-5, 253-272
  • Book chapter
    Karl J. Thomé-Kozmiensky; Daniel Goldmann: Recycling und Rohstoffe Band 9, Neuruppin: TK Verlag, 2016, 978-3-944310-27-5

Publ.-Id: 22785 - Permalink

Experimental investigation of cocurrent water/air down flow in SiSiC solid foam packed reactors
Claußnitzer, T.;
Trickle bed reactors (TBR) are widely used in the chemical industry, especially for oxidation, hydrogenation and hydrodesulfurization processes. Since overall performance of TBR is essentially affected by the hydrodynamic properties of the package, lot of work has been done to improve characteristics of the reactor interior. Decreasing the particle size of conventional packings like spheres and cylinders increases the specific surface area but also the pressure drop.
Compared to commonly used packings, solid foams are promised to provide less pressure drop but higher surface area at once. To investigate to hydrodynamics in these packings, solid foams of three different pore densities (20 ppi, 30 ppi, 45 ppi) have been studied in an air/water cocurrently downflow system using ultrafast X-ray tomography to determine their hydrodynamic properties as well as their suitability as reactor packing.
Experiments were carried out at a broad range of gas and liquid superficial velocities of 0.2 ms-1 to 1.0 ms-1 and 0.01 ms-1 to 0.04 ms-1, respectively, covering different flow regimes, namely trickle flow, pulsing flow as well as the transition region.
With spatially-resolved measurements the liquid distribution behavior of solid foams has been investigated. It was shown, that the initial liquid distribution primarily depends on liquid distributor and the pore density of the applied foam, but is not as good as expected.
Following, temporally-resolved measurements at fixed measurement height were carried out. There, for each measurement setup the liquid saturation has been determined and a correlation has been proposed to describe the liquid saturation as a function of pore size as well as gas and liquid flow rate.
In the pulsing regime, investigations were accomplished regarding pulse properties like frequency and velocity. A strong influence of the pore density of the applied foams was found.
Keywords: trickle bed reactor; SiSiC solid foams; ultrafast X-ray tomography; hydrodynamics; co-current downflow
  • Diploma thesis
    TU Dresden, 2015
    Mentor: Zalucky, J., Hampel, U.
    160 Seiten

Publ.-Id: 22784 - Permalink

Zum Verständnis der Flotierbarkeit - Untersuchungen zu spezifischen Oberflächenenergieverteilungen und hydrophoben Wechselwirkungen
Rudolph, M.;
Spätestens seit dem Patent der Gebrüder Bessel aus Dresden von 1877 nutzt man die Anhaftung hydrophober Partikel an Gasblasen in der Flotation, einer Heterokoagulationstrennung, technologisch aus, um Partikelgemische auf Basis ihrer chemisch veränderlichen Benetzungseigenschaften voneinander zu trennen. Ein wesentlicher Mikroprozess ist hierbei der Anlagerungsvorgang, bestimmt durch das Wechselwirkungspotential zwischen einem Partikel und einer Gasblase. Die klassische DLVO Wechselwirkungstheorie beinhaltet für diese Partner nur repulsive Terme, d.h. abstoßende Doppelschichtwechselwirkung und abstoßende van der Waals Wechselwirkung durch eine negative Hamaker-Konstante. Über die Physik der zwingend notwendigen, weil prozessbestimmenden, weit reichenden, anziehenden Wechselwirkungskomponente ist man sich in der Literatur noch nicht einig. Viele Wissenschaftler sehen feinste Gasdomänen auf hydrophoben Oberflächen, oft als Nanobubbles oder Micropancakes bezeichnet, als Vermittler von weit reichenden kapillaren Anziehungskräften. Andere sehen eine weit reichende Wasserstrukturstörung an hydrophoben Oberflächen als Ursache für eine somit entropisch begründete Anziehung.
Am Helmholtz-Institut Freiberg für Ressourcentechnologie werden in Grundlagenuntersuchungen zur Flotation atomare Gesamtwechselwirkungen zwischen unterschiedlich benetzenden Oberflächen (z.B. Mineralen) und hydrophoben Modellpartikeln in Lösung mit Hilfe der Partikelsonden Rasterkraftmikroskopie analysiert. Zudem wird mit der Methode der inversen Gas Chromatographie die Änderung der spezifischen Oberflächenenergieverteilung als fundamentaler Benetzungsparameter untersucht und mit der Flotierbarkeit in der Mikroflotation in Verbindung gebracht. Der Vortrag fasst den aktuellen Stand der grundlegenden Untersuchungen zusammen. Im Zusammenhang mit den rasterkraftmikroskopischen Untersuchungen werden hydrophobe Wechselwirkungen diskutiert. Auf Basis der Analyse von Oberflächenenergieverteilungen im Zusammenhang mit der Mikroflotation wird ein neues Flotierbarkeitskriterium, die freie Wechselwirkungsenthalpie zwischen einem Partikel und einer Gasblase im Wasser eingeführt und kritisch diskutiert.
Keywords: Flotation, iGC, AFM, Hydrophobicity, Minerals, Collectors
  • Lecture (Conference)
    Aufbereitung und Recycling Jahrestagung 2015, 11.-12.11.2015, Freiberg, Deutschland

Publ.-Id: 22783 - Permalink

The energy of interactions between bubbles and particles – specific surface free energy distributions and microflotation
Rudolph, M.; Chelgani, S.; Meier, K.; Hartmann, R.;
In fundamental flotation studies typically the contact angle is used to describe wettability and correlated with floatability. However, a more fundamental parameter is the specific surface free energy, related to the contact angle via Young’s equation. Inverse gas chromatography (iGC) is a suitable method to determine specific surface free energy components and their distributions on particulate surfaces. In this study the pure minerals quartzite (SiO2), fluoro-apatite (Ca5[F,(PO4)3]) and magnetite (Fe3O4) are examined for microflotation floatability and surface energy considering different methods of sample treatment and the effect of the collectors sodium oleate and dodecyl ammonium acetate. The parameter of specific net free energy of interaction between bubbles and particles immersed in water ΔGpwb derived from the complex surface energy analysis is introduced and used to evaluate the hydrophobicity of the mineral surface correlated with microflotation floatability. Results lead to the provocative hypothesis that only small fractions of the surface and their change by flotation reagent adsorption will inherently define floatability of minerals.
Keywords: Flotation, iGC, Apatite, Quartz, Surface Free Energy, Heterogeneity, Interfaces, Collectors
  • Lecture (Conference)
    Flotation '15, 16.-19.11.2015, Cape Town, South Africa

Publ.-Id: 22782 - Permalink

Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets
Huebl, A.; Kluge, T.; Widera, R.; Hilz, P.; Schreiber, J.; Schramm, U.; Bussmann, M.;
We present simulation results regarding the acceleration of ions from mass limited solid density targets with short-pulse high power lasers. Taking advantage of large scale 3D3V PIC simulations (8000 GPUs each, INCITE award 2015) allows to give a detailed insight into the dynamics and unique features of truly isolated targets that were used in recent experiments.
We discuss the pre-plasma evolution, its dependence on laser contrast and its crucial influence on the dominant acceleration mechnanism and on the directionality of the laser-accelerated ion beams. Extensive 2D3V parameter scans are presented for comparison with commonly used flat, wire or mounted target designs.
Keywords: Laser Ion Acceleration, Mass Limited Target, Simulation, PIC, HPC, GPU, PIConGPU
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22781 - Permalink

Charge Exchange and Energy Loss of Slow Highly Charged Ions in Graphene
Wilhelm, R. A.; Gruber, E.; Kozubek, R.; Smejkal, V.; Schleberger, M.; Facsko, S.; Aumayr, F.;
Slow highly charged ion (HCI) interaction with surfaces 100 was studied extensively in recent years and revealed many 7+ interesting aspects of the underlying processes [1]. Nanostructure formation by single HCI impact was successfully 10 linked to defect mediated desorption or even surface melting due to HCI induced local electronic excitations. The neutralization dynamics of a slow (v ≪ v0 = αc, α: fine structure constant, c: speed of light) HCI in front of a solid surface is well described by the classical-over-barrier model. However, not much is known about the neutralization below the surface, i.e. in the material. Below surface neutralization becomes important for normal incidence, because here the interaction time above the surface is not sufficient for neutralization and relaxation of the HCI. We present results on charge exchange and energy loss measurements of slow highly charged Xe ions with charge states of 10 < Q < 35 transmitted through freestanding single Xe16+ layer graphene as the thinnest and lightest solid target material there is. We find that the charge exchange is not bimodal as in case of transmission through 1 nm thick carbon 1 nanomembranes [2], but only very large charge exchange is observed. We attribute this to (1) the availability of solely smallimpactparameters (p<1.5Å ̊) in graphene as well as (2) very high mobilities of charge carriers and subsequently transfer of (at least) 20-30 electrons within less than 10 fs. Especially the second fact is surprising, because here the charge transfer is hardly conceivable as a sequential, but rather as a collective electron transfer process. For incident charge states Q > 25 we observe a saturation of charge exchange, i.e. the exit charge state distribution has a mean value Qmean ≈ Qin − 20 (see fig. 1). The contributions of above surface charge transfer and charge transfer during collision as well as energy loss and its dependence on the charge state and charge exchange will be discussed.
  • Invited lecture (Conferences)
    International Workshop on Inelastic Ion-Surface Collisions (IISC), 18.-23.10.2015, San Sebastian, Spanien

Publ.-Id: 22780 - Permalink

Co2Mn0.6Fe0.4Si: A Heusler compound opening new perspectives in magnon spintronics
Sebastian, T.; Hillebrands, B.;
This chapter addresses magnon propagation in the Heusler compound Co2Mn0.6Fe0.4Si and the corresponding perspectives for the emerging field of magnon spintronics. The concept of magnon spintronics requires the utilization of advanced materials providing, in particular, a low magnetic Gilbert damping and compatibility with industrial standards concerning the fabrication ofmicro-and nanostructures. We present how this challenge can be addressed by the use of low-damping Co2Mn0.6Fe0.4Si films on the basis of recent studies using micro-focus Brillouin light scattering spectroscopy. The low damping in this Heusler compound not only allows for the realization of increased propagation distances. The pronounced occurrence of nonlinear phenomena might even lead the way towards novel concepts and functionalities in magnonic devices.
  • Book chapter
    Claudia Felser, Atsufumi Hirohata: Häusler Alloys - Properties, Growth, Applications, Switzerland: Springer, 2015
    DOI: 10.1007/978-3-319-21449-8_13

Publ.-Id: 22779 - Permalink

Slow highly charged ion transmission through carbon nanomembranes and graphene
Wilhelm, R. A.; Gruber, E.; Heller, R.; Facsko, S.; Aumayr, F.;
Slow highly charged ions (HCI) showed in many studies their efficiency in formation of surface nanostructures especially on insulating surfaces [1]. Here we report on transmission of HCI through carbon foils with a thickness of only 1nm and below (graphene). At these thicknesses the neutralization of the slow HCI is not completed in the solid and thus effects of pre-charge-equilibrium stopping of slow ions can be addressed experimentally.
We find that transmitted highly charged Xe ions with charge states between Q=10 and Q=30 show a bimodal charge state distribution, i.e. one part of the ions is transmitted in low exit charge states combined with a large charge exchange enhanced kinetic stopping. The other part of the ions, however, shows only a very small charge exchange with almost no kinetic energy loss [2]. Both charge exchange regimes are attributed to different impact parameter regimes, i.e. close collision lead to extremely large charge exchanges and distant collisions are connected with weak ion-target interactions. Thus, our measurements reveal that sub-surface neutralization of HCI proceeds in a step-like fashion, i.e. either the ion approaches a target atom closely and correspondingly neutralizes almost completely (∆Q > 20 for Q = 30) or it passes through the material almost unchanged (∆Q < 5) until it hits a target atom at some larger depth. A bimodal charge state distribution could therefore not be observed for larger target thicknesses [3], except for the inverse case of a swift heavy ion charging up during transmission through a silicon single crystal under random vs. channeling direction [4]. Gas phase experiments on the other hand cannot lead to slow HCI neutralization in one single scattering event using light target atoms (e.g. carbon), because here only atomically bound electrons can contribute to the neutralization process (6 electrons in case of carbon) rather than de-localized electrons in a solid target.
  • Poster
    International Summer School on Vacuum, Electron and Ion Technologies, 21.-25.09.2015, Sozopol, Bulgarien

Publ.-Id: 22778 - Permalink

Electron emission from solid surfaces due to slow highly charged ion impact
Wilhelm, R. A.; Heller, R.; Meissl, W.; Aumayr, F.; Facsko, S.;
Slow highly charged ions (HCI) and their interaction with surfaces reveal many interesting phenomena, e.g. nanostructure formation, non-equilibrium ion stopping and charge exchange as well as extremely large electron emission yields [1,2].
The emission of electrons is tightly connected to the neu- tralization process of the HCI above and below the sur- face. When the ion approaches the surface it starts to capture electrons near the Fermi edge into high Rydberg states in the ion and subsequently emits Auger electrons upon de-excitation. The process is well described by the classical-over-barrier model [3]. However, for normal incidence the time for neutralization of the ion above the surface is not sufficient. Hence, the neutralization pro- ceeds below the surface with accompanied sub-surface electron emission.
We present here recent experimental data on the second- ary electron emission yield from highly charged Xe im- pinging on Au, KBr, LiF and CaF2 surfaces (see fig. 1). The data shows that so called potential emission, i.e. secondary electron emission by neutralization (potential energy conversion) becomes significant for low ion ve- locities (v < 105 m/s) [4].
The large amount of HCI induced electrons emitted from the surface opens the possibility of correlative studies of nanostructuring by HCI and subsequent electron spec- tromicroscopy.
Our planned Low Energy Ion Nano-Engineering Facility (LEINEF) at the Ion Beam Center of the Helmholtz- Zentrum Dresden-Rossendorf will comprise several HCI sources, a medium and low energy ion scattering set-up, a focused ion beam set-up, Auger and x-ray photoelec- tron spectroscopy as well as a low energy electron mi- croscope (LEEM). The latter one may be equipped with an ion gun or a HCI source to perform correlative nanostructuring and electron spectromicroscopy with electrons from the LEEM source as well as ion induced secondary electrons.
  • Poster
    Low Energy Electrons: Dynamics and Correlation near Surfaces and Nanostructures (LEE2015), 07.-11.09.2015, Hernstein, Österreich

Publ.-Id: 22777 - Permalink

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