Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Gouy phase shift of a tightly focused, radially polarized beam

Kaltenecker, K. J.; König-Otto, J. C.; Mittendorff, M.; Winnerl, S.; Schneider, H.; Helm, M.; Helm, H.; Walther, M.; Fischer, B. M.

Radially polarized beams represent an important member of the family of vector beams, in particular due to the possibility of using them to create strong and tightly focused longitudinal fields, a fundamental property that has been exploited by applications ranging from microscopy to particle acceleration. Since the properties of such a focused beam are intimately related to the Gouy phase shift, proper knowledge of its behavior is crucial. Terahertz microscopic imaging is used to extract the Gouy phase shift of the transverse and longitudinal field components of a tightly focused, radially polarized beam. Since the applied terahertz time-domain approach is capable of mapping the amplitude and phase of an electromagnetic wave in space, we are able to directly trace the evolution of the geometric phase as the wave propagates through the focus. We observe a Gouy phase shift of 2π for the transverse and of π for the longitudinal component. Our experimental procedure is universal and may be applied to determine the geometric phase of other vector beams, such as optical vortices, or even arbitrarily shaped and polarized propagating waves.

Keywords: Gouy phase; EOS; THz

Publ.-Id: 22905

Metallurgical infrastructure: a key enabler of a circular economy

Reuter, M. A.

Base metals such as copper, lead, nickel, cobalt, zinc etc. form the basic crucial carrier metals for a sustainable society – the Web of Metals. This paper discusses the special and crucial role these metals have in acting as enablers in any recycling efforts as they carry and release important and vital minor elements at the heart of high-tech applications and products. Through examination of the rising needs for such carriers, this paper examines the approach and technologies which need to be considered by any producer of base metals. Attention is paid to the limits and extent of this carrier role in the typical processing of materials.
Examples of specialised technology and flowsheet needs are presented with consideration given to a “whole of chain” or Systems-Integrated Metal Production (SIMP) approach as a cornerstone of a circular economy. Also outlined are the challenges facing not only producers, but legislators who need to consider the balance between providing our societal needs with baseline technology infrastructure requirements for valuable metals extraction. In summary, the message of this paper states simply that not only is the criticality of metals important but the criticality of the infrastructure (Infrastructure Criticality) that can recover metals from complex designed “mineral” mixtures. Base metals are at the heart of a Circular Economy, therefore key enablers of the Internet-of-Metallurgical-Things.

Keywords: Resource efficiency base metals; Recycling; System integration; Design for Recycling (DfR)

  • Invited lecture (Conferences)
    On metal by-products recovery, 12.-13.11.2015, Brüssel, Belgien
  • Invited lecture (Conferences)
    Cleantech Innovations in Mineral Production, 10.09.2015, Helsinki, Finland

Publ.-Id: 22904

Kreislaufwirtschaft 4.0

Reuter, M. A.

Kreislaufwirtschaft 4.0

  • Invited lecture (Conferences)
    UBA-Workshop „Rückgewinnung von Edel- und Sondermetallen“, 02.11.2015, Berlin, Deutschland

Publ.-Id: 22903

Application of CFD towards the thermal-hydraulic analysis of Spent Fuel Pool accidents

Oertel, R.; Krepper, E.; Lucas, D.

After a spent fuel assembly is removed from the reactor core, its decay heat production is still too large for pure conductive cooling. It is placed in a Spent Fuel Pool, where the decay heat is removed from the assembly by means of natural convection, while the pool cooling system keeps the water temperature at about 40-50°C. The fuel assemblies are typically arranged in high density racks which consist of borated steel in order to prevent criticality accidents. The rack cells are closed to the sides and force the coolant flow along the axial direction. In the event of a failure of the cooling system followed by boil-off, the water level might decrease below the top of the assemblies. Then the natural circulation path in the water phase is blocked and the dominant cooling mechanisms for the uncovered section of the fuel assemblies are the forced convection due to steam production and the solid heat conduction into the remaining water, as well as towards the upper end. The latter mechanism depends on the boundary conditions at the fuel assembly head, which are determined by the temperature and velocity field in the pool and reactor building atmosphere. Additionally, if the decay heat load of the neighboring fuel assemblies differs significantly, some heat will be exchanged in the radial direction. In the nuclear community, system codes are widely used for safety studies. They deliver fast and reliable results for the flow and heat transfer inside the fuel assemblies. But since three-dimensional convective phenomena can only be taken into account in the form of simplified assumptions, they do not entirely qualify for studies related to Spent Fuel Pools. In this work, CFD is used to study the flow field above and around the exposed storage racks in order to identify large scale convective phenomena. It is expected that the large scale flow field is dictated by the temperature field in the pool, which in turn influences the cooling of the individual fuel assemblies. These interdependencies need to be quantified as a function of the storage rack arrangement and the overall distribution of the fuel assemblies with respect to their decay heat. A porous body approach is employed for the modeling of the fuel assemblies. Best Practice Guidelines are applied as far as possible, since there is no experimental data available that allows a straightforward validation of the simulation results. In this work, the Spent Fuel Pool design of Fukushima's Unit 4 serves as a test case. A loss of coolant by boil-off is postulated, leading to partially uncovered fuel assemblies. Several pool loading strategies for a constant total decay heat load will be presented and conclusions will be drawn as to which configuration is the most favorable from a thermohydraulic standpoint.

Keywords: Spent Fuel Pool safety; loading strategies; CFD; convective heat transfer

  • Lecture (others)
    10. Doktorandenseminar des Kompetenzverbundes für Kerntechnik Ost, 08.12.2015, Dresden, Deutschland

Publ.-Id: 22902

Investigations on the anisotropy of charge carrier excitation in graphene with low energetic photons

Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.; Winnerl, S.

Recently we have demonstrated anisotropic excitation and relaxation of charge carriers in graphene [1]. A near-infrared pump probe experiment with varied angle between pump and probe polarization revealed anisotropic carrier populations on a 100 fs timescale as predicted by microscopic theory. An isotropic distribution is then reached by scattering via optical phonons.
Now we perform an experiment where scattering of electrons with optical phonons is strongly suppressed. To this end a photon energy of 88 meV, i.e. far below the optical phonon energy, is applied and the sample is kept at 20 K. The experiments, where the free-electron laser FELBE was used as a source, revealed an anisotropic charge carrier distribution on timescales of up to 10 ps (cf. Fig. 1). In particular we investigate the dependence of the pump-probe signals on pump fluence. We find that the anisotropy is most pronounced for low fluences and vanishes for fluences in the µJ/cm2 range. These results, complemented by microscopic theory, give clear insights in the role of Coulomb scattering on the carrier dynamics. Due to the predominantly collinear nature of Coulomb scattering, the anisotropy at low fluences is preserved on timescales larger than the ~30 fs timescale of the thermalization due to Coulomb scattering. At high fluences, however, Coulomb scattering efficiently redistributes carriers towards an isotropic distribution.

[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl, Nano Lett., 14, 1504-1507, (2014)

Keywords: graphene; ultrafast dynamics

  • Poster
    Graphene Week 2015, 22.-26.06.2015, Manchester, UK

Publ.-Id: 22901

Anisotropic carrier distribution in optically excited graphene: The role of Coulomb scattering

Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.; Winnerl, S.

Anisotropic carrier distribution in optically excited graphene: The role of Coulomb scattering

Keywords: graphene; ultrafast dynamics

  • Poster
    3. SPP Workshop, 17.-20.05.2015, Kremmen, Deutschland

Publ.-Id: 22900

Large Scale CFD Simulations of Spent Fuel Pool Accident Scenarios Using a Porous Body Approach

Oertel, R.; Krepper, E.; Lucas, D.

After the accident at the Fukushima Daiichi nuclear power plant, the safety of Spent Fuel Pools moved into the focus of nuclear safety research. For the thermo-hydraulic analysis, system- or severe accident codes are used predomenantly, although simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. The present work uses CFD in order to investigate the large scale convective phenomena involved and to examine their influence on the cooling of the individual fuel assemblies. All relevant thermophysical phenomena are discussed together with the corresponding modeling. The Spent Fuel Pool of Fukushima’s Unit 4 with the loading at the time of the accident serves as a test case. The paper gives a first qualitative impression on the emerging flow paths for the scenario of partially as well as fully uncovered fuel assemblies. Finally an outlook is given, how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.

Keywords: Spent Fuel Pool safety; CFD; partially uncovered fuel assemblies; convective heat transfer

  • Contribution to proceedings
    46th Annual Meeting on Nuclear Technology (AMNT 2015), 05.-07.05.2015, Berlin, Deutschland
  • Lecture (Conference)
    46th Annual Meeting on Nuclear Technology (AMNT 2015), 05.-07.05.2015, Berlin, Deutschland

Publ.-Id: 22899

Long-lived anisotropic carrier populations in graphene excited by THz pulses

Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.; Winnerl, S.

Calculations of non-equilibrium charge carrier distributions excited by polarized light indicate anisotropic occupations in momentum space. For most materials experimental insight in this anisotropy is obscured due to complex valence band structures [1]. Recently we have experimentally verified anisotropic carrier distributions and investigated their relaxation in graphene [2]. A near-infrared pump probe experiment with varying angle between pump and probe polarizations revealed anisotropic carrier populations on a 100 fs timescale as predicted by microscopic theory. An isotropic distribution is then reached by scattering via optical phonons. In graphene the Coulomb scattering, in first approximation, is restricted to collinear scattering along a line of the cone-like band structure and therefore preserves the angular orientation of the distribution.
By shifting the photon energies into the THz range (88 meV) and cooling the sample down to 20K we were now able to observe anisotropic charge carrier distributions with a lifetime as long as several picoseconds. Under these conditions scattering via optical phonons, with energies of about 200meV, is strongly suppressed. Note that the observed distribution has a very unusual character: It is completely thermalized for each k-direction pointing radially away from the Dirac point, but at the same time it is strongly anisotropic. The anisotropy is most pronounced for low pump fluences. Increasing the pump fluence from several nJ/cm² to µJ/cm² results in a transition from anisotropic to isotropic distributions. We suggest that this is associated with optical phonon scattering that is enabled at high electron temperatures. The experimental results are compared with microscopic theory that takes into account combined effects of Coulomb and carrier-phonon scattering.

[1] J. Rioux, J.E. Sipe, Physica E 45, 1-15 (2012)
[2] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl, Nano Lett. 14, 1504-1507 (2014)

Keywords: graphene; ultrafast dynamics

  • Poster
    German THz Conference 2015, 08.-10.06.2015, Dresden, Deutschland

Publ.-Id: 22898

Pressure-induced shift of energy levels and structural phase transition in CdSe/ZnS quantum dots

Tauch, J.; Braun, J. M.; Keller, J.; Hinz, C.; Haase, J.; Seletskiy, D. V.; Leitenstorfer, A.; Pashkin, A.

Electronic band structure of CdSe/ZnS quantum dots under high pressures is studied using fluorescence spectroscopy. We observe a strong blue shift of about 40 meV/GPa for the emission line at 655 nm. At moderate pressures (below 3GPa) this shift is linear and it is dominated by increase of the fundamental band gap of CdSe under pressure [1,2]. In contrast to bulk CdSe where the fluorescence is quenched above 3GPa as a result of the phase transition into the rock-salt structure [3,4], the CdSe/ZnS quantum dots remain structurally stable up to 6.5GPa. This structural robustness together with the high fluorescence yield and the large pressure-induced line shift, exceeding that of bulk ruby crystals by a factor of 40, make CdSe quantum dots a promising candidate for precise pressure calibration at moderate pressures.
[1] W. Shan et al., Appl. Phys. Lett. 84, 67 (2004).
[2] B. S. Kim et al., J. Appl. Phys. 89, 8127 (2001).
[3] S. H. Tolbert and A. P. Alivisatos, J. Chem. Phys. 102, 4642 (1995).
[4] S. H. Tolbert and A. P. Alivisatos, Science 265, 373 (1994).

Keywords: quantum dots; high pressure; CdSe/ZnS

  • Poster
    DPG-Frühjahrstagung 2015, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 22897

Investigations on the polarization dependent carrier excitation in graphene with low energetic photons

Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.; Winnerl, S.

We demonstrate that in graphene a nonequelibrium charge carrier distribution retains its anisotropic nature on a 10 ps timescale if the photon energy is below the optical phonon energy. Recently evidence for an anisotropic carrier distribution has been found in near-infrared pump-probe experiments with varied angle between the orientation of pump and probe polarization [1]. This anisotropy vanishes after 150 fs due to electron optical-phonon scattering. Extending this study to the mid-infrared range (E_Photon = 74 meV), i.e. to energies below the optical phonon energy, allows to strongly suppress this scattering mechanism. In accord with microscopic theory, traces of an anisotropic distribution on a 10 ps timescale are found. Note that carrier-carrier scattering, acting on a 10 fs timescale, is mainly colinear and therefor preserves the anisotropic distribution on rather long timsecales.
[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm and S. Winnerl Nano Lett. 2014, 14, 1504-1507

Keywords: graphene; ultrafast dynamics

  • Lecture (Conference)
    DPG-Frühjahrstagung, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 22896

Application of CFD towards the thermo-hydraulic analysis of Spent Fuel Pool accidents

Oertel, R.; Krepper, E.; Lucas, D.

The thermo-hydraulic analysis of Spent Fuel Pool accident scenarios is predominantly carried out using one-dimensional codes. This implies that simplified assumptions have to be made for the flow paths around the storage racks and inside the reactor building. Here, CFD is employed to investigate the convective phenomena involved and to examine their relevance for the cooling of the individual fuel assemblies, which themselves are modeled as porous bodies. The paper includes a discussion of relevant thermohydraulic aspects and the modeling on the fuel assembly scale as well as the reactor building scale. First preliminary large scale simulations are presented, using the design of Fukushima’s Unit 4 with the corresponding Spent Fuel Pool loading as a test case. A loss of coolant due to the outage of the cooling system and subsequent boil-off is assumed, leading to partially or fully uncovered fuel assemblies. The emerging flow paths are described qualitatively. This ongoing work gives an outlook how CFD can help to study the safety of Spent Fuel Pools as a standalone tool or by delivering input to one-dimensional codes.

Keywords: Spent Fuel Pool Safety; Boil-Off/Drainage Scenarios; CFD; Porous-Body-Approach

  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics(NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Lecture (Conference)
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 22895

Industrial challenges in ion beam processing and metrology in the 3D era

England, J.; Möller, W.

Ion beam mechanisms present in plasma doping have been investigated by comparing SIMS measurements of Ge implants into deposited layers of As on Si wafers to planar dynamic ion beam models of the implants and SIMS analyses. Industrial devices are overcoming the limitations of lateral scaling by using the vertical direction. The same modelling approach would be valuable for interpreting 1.5D SIMS analyses of plasma doping of 3D-NAND test structures but 3D dynamic codes do not yet have all the capabilities to allow this. The required features are being developed within a static 3D code, TRI3DSTP, which has been used to qualitatively explain the good uniformity of a P plasma doping process and indicate where more quantitative explanations will be possible once the full dynamic capabilities are available.

Keywords: 3D NAND; Ion beam modelling; Ion-implantation; Plasma doping

Publ.-Id: 22894

P1505 - Komplementärer Widerstandsschalter

Bürger, D.; Du, N.; Schmidt, H.; Skorupa, I.; You, T.

Die Erfindung betrifft eine schaltbare Widerstandsstruktur (3) mit einem ersten elektrisch leitfähigen Kontakt (T1), einem zweiten elektrisch leitfähigen Kontakt (T2), einer ersten piezoelektrischen oder ferroelektrischen Schicht (11a) und einer zweiten piezoelektrischen oder ferroelektrischen Schicht (11b), wobei die beiden piezoelektrischen oder ferroelektrischen Schichten miteinander in körperlichem Kontakt stehen und zwischen den beiden Kontakten angeordnet sind, wobei mindestens einer der Kontakte mit der betreffenden piezoelektrischen oder ferroelektrischen Schicht einen Schottky-Kontakt bildet und wobei die zweite piezoelektrische oder ferroelektrische Schicht (11b) mit mindestens einem zusätzlichen Metall und/oder einem zusätzlichen Halbmetall als Dotand dotiert ist.

  • Patent
    EP2940749 - Offenlegung 04.11.2015

Publ.-Id: 22893

Experimental investigation of electromagnetic stirring affecting the mould flow in a liquid metal model

Willers, B.; Eckert, S.; Barna, M.; Reiter, J.

In this work an experimental study using a 1:3 scale acrylic glass model of the round bloom caster from voestalpine Stahl Donawitz GmbH is presented. The model experiment uses the eutectic alloy GaInSn at room temperature. An electromagnetic stirrer was installed at the mould producing a rotating magnetic field (RMF). The flow field inside the mould was measured using the ultrasound Doppler velocimetry (UDV). Up to 10 ultrasonic transducers were employed simultaneously in order to obtain a two-dimensional reconstruction of the flow structure. The experiment provides an extensive and valuable data base for validation of numerical methods. The application of electromagnetic fields for flow and solidification control in continuous casting will be a crucial point of our future work

Keywords: Continuous casting; electromagnetic stirring; rotating magnetic field; physical modelling; flow measurements; Ultrasound Doppler velocimetry

  • Contribution to proceedings
    Experimental investigation of electromagnetic stirring affecting the mould flow in a liquid metal model, 15.-19.06.2015, Düsseldorf, Deutschland
    European Steel Technology and Application Days, 978-3-00-049542-7 (CD)

Publ.-Id: 22892

Fluorinated PET tracers for molecular imaging of σ1 receptors in the central nervous system.

Weber, F.; Brust, P.; Laurini, E.; Pricl, S.; Wünsch, B.

At first the role of σ1 receptors in various neurological, psychiatric and neurodegenerative disorders is discussed. In the second part, the principle of positron emission tomography (PET) is described and the known fluorinated PET tracers for labeling of σ1 receptors are presented. The third part focuses on fluoroalkyl substituted spirocyclic PET tracers, which represent the most promising class of fluorinated PET tracers reported so far. The homologous fluoroalkyl derivatives 12-15 show high σ2 subtype (408 – 1331-fold). The enantiomers of the fluoroethyl derivative fluspidine 13 were prepared and pharmacologically characterized. Whereas the (S)-configured enantiomer (S)-13 (Ki = 2.3 nM) is 4-fold less active than the (R)-enantiomer (R)-13 (Ki = 0.57 nM), (S)-13 is metabolically more stable. The interactions of (S)-13 and (R)-13 with the σ1 receptor were analyzed on molecular level using the 3D homology model. In an automated radiosynthesis [18F](S)-13 and [18F](R)-13 were prepared by nucleophilic substitution of the tosylates (S)-17 and (R)-17 with K[18F]F in high radiochemical yield, high radiochemical purity and short reaction time. Application of both enantiomers [18F](S)-13 and [18F](R)-13 to mice and piglets led to fast uptake into the brain, but [18F](R)-13 did not show washout from the brain indicating a quasi-irreversible binding. Both radiotracers [18F](S)-13 and [18F](R)-13 were able to label regions in the mouse and piglet brain with high σ1 receptor density. The specific binding of the enantiomeric tracers [18F](S)-13 and [18F](R)-13 could be replaced by the selective σ1 ligand SA4503.

  • Book chapter
    Smith, S. B.; Su, T.-P.: Sigma Receptors: Their Role in Disease and as Therapeutic Targets, Berlin, Heidelberg: Springer, 2017, 978-3-319-50172-7, 31-48
    DOI: 10.1007/978-3-319-50174-1_4

Publ.-Id: 22891

Accretion rate of IDPs onto the Earth by means of 53Mn and 41Ca AMS measurement in Antarctic snow

Gomez Guzman, J. M.; Bishop, S.; Faestermann, T.; Feige, J.; Fimiani, L.; Hain, K.; Kipfstuhl, S.; Korschinek, G.; Ludwig, P.; Merchel, S.; Rodrigues, D.; Sterba, J.; Welch, J.; Weller, R.

Interplanetary Dust Particles (IDPs) are small grains, a few hundred micrometers in size and mainly originated in the Asteroid Belt. During their flight to the Earth they are irradiated by GCR and SCR and 41Ca (T1/2 = 1.03 × 105) and 53Mn (T1/2 = 3.68 × 106 yr) are formed.
Since there are no significant terrestrial sources for those radionuclides they can be used as a key tracer to determine the accretion rate of IDPs onto the Earth. For this project, 550 kg of snow have been collected at the Antarctic German station Kohnen to be processed to extract 41Ca and 53Mn. Also the filter used will be processed to check the existence of IDPs surviving evaporation during their entry in the atmosphere. The AMS measurements will be made at the MLL in Garching, a facility with sensitivity down to 10−16 for 41Ca and 10-14 for 53Mn.

Keywords: accelerator mass spectrometry; IDP; AMS

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22890

Supernova-produced 60Fe in Earth’s microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Deneva, B.; Faestermann, T.; Fimiani, L.; Gómez-Guzmán, J. M.; Hain, K.; Korschinek, G.; Hanzlik, M.; Merchel, S.; Rugel, G.

It is possible for a nearby supernova (SN) explosion to deposit a fraction of its ejecta on Earth. Due to the lack of significant anthropogenic and cosmogenic background, 60Fe (T1/2 = 2.6 Ma) is perfectly suited to serve as a radioactive tracer of recent SN events. The ratio of 60Fe/Fe was measured in over 100 samples extracted from two sediment cores from the Eastern Equatorial Pacific. The AMS samples were produced using a carefully tuned chemical leaching technique that specifically targets fine-grained iron-oxides, such as magnetofossils.
Magnetofossils are the remains of magnetosome chains, built up by magnetotactic bacteria, which are abundantly present in our sediment, as shown by magnetic analysis and electron microscopy.
The AMS samples were measured at the GAMS setup at the Maier-Leibnitz-Laboratory in Garching, where the use of a gas-filled magnet for isobaric suppression provides a sensitivity of 60Fe/Fe ≈ 5 x 10-17.
Our results reveal a 60Fe signature over a time-range of about 1.7-2.7 Ma, which is attributed to the deposition of SN debris.

Keywords: accelerator mass spectrometry; supernova

  • Poster
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 22889

Analysis of activated sludge aerated by membrane and monolithic spargers with ultrafast X-ray tomography

Sommer, A.-E.; Wagner, M.; Reinecke, S.; Bieberle, M.; Barthel, F.; Hampel, U.

Up to 80 % of the total energy budget of wastewater treatment plants is consumed by the activated sludge process. Current optimizations are mostly based on limited instrumentation for single points of measurement which cannot express the complex hydrodynamic and biochemical processes. Therefore, the ultrafast electron beam X-ray tomography system ROFEX of HZDR is used as a new measurement technique to capture the temporal evolution of the multiphase flow in the opaque active sludge. A detailed study has been carried out in a vertical column of 3.5 m height at HZDR to obtain an improved understanding of the hydrodynamics of aerated sludge and an evaluation of different aerators. The target parameters are bubble size distribution, equivalent Sauter mean diameter of the bubbles, bubble rise velocity and local gas hold-up under the variation of sparger type (rubber, monolithic material), gas flow rate, rheology of the fluid (deionized water, salty water, sludge) and height in the liquid column. Therefore, in-house developed advanced image analysis algorithms were applied to the reconstructed tomographic images, which are also presented in the paper. The experiments showed that with ROFEX reliable measurement data of opaque multiphase flows is produced and is expected to be used in further investigations for the validation of computational fluid dynamics (CFD) models. The different sparger types showed comparable hydrodynamic performance.

Keywords: Ultrafast X-ray tomography; activated sludge; aeration

Publ.-Id: 22888

Calculation of Debye-Scherrer diffraction from polycrystalline samples under an arbitrary stress field

Macdonald, M. J.; Vorberger, J.; Drake, R. P.; Glenzer, S. H.; Fletcher, L. B.

Calculating Debye-Scherrer diffraction patterns from polycrystalline materials under dynamic compression has been done in the Voigt (iso-strain) limit or in the Reuss (iso-stress) limit for small deviatoric stresses. These methods are appropriate for materials with low yield strength, where only small deviations from the hydrostat can be supported by the crystal structure or materials with low elastic anisotropy where the Voigt limit is valid. Here we present a method to calculate Debye-Scherrer diffraction patterns from polycrystalline samples under an arbitrary stress field. This method can calculate the strain tensor for each crystallite and can account for arbitrary sample texture and probe x-ray sources.

Keywords: x-ray; crystallography; stress; strain

Publ.-Id: 22887

Secondary Neutron Field at the Dresden Proton Therapy

Lutz, B.; Enghardt, W.; Swanson, R.; Fiedler, F.

Particle therapy is a strongly growing field in cancer therapy. Almost 60 treatment centres are currently operating worldwide and the total number will reach more than 90 by 2017~\cite{PTCOG}. The majority of the centres uses protons to treat patients.

With the increasing importance of particle therapy, the development of application-specific monitoring systems has received a significant boost. On the one side, there are the radio-protection questions like the secondary dose to patients or to radio-sensitive equipment. On the other side, there are the methods that intend to verify the correct application of the treatment dose, during or short after the treatment, like prompt-gamma-imaging or -timing, or PET. For both groups of measurements, a good understanding of the secondary radiation field is crucial.

The greatest challenge in determining the secondary radiation field comes from neutrons. The spectra of the neutrons, generated by protons of therapeutic energies, extend far beyond the specification of most commercially available dosimeters. Additionally, the generated neutron fields are spatially nonuniform and in case of passive field formation strongly dependent on the operational setting. Combined with the very limited spatial and spectral resolution of the available neutron detectors, many details of the field cannot be experimentally resolved. Therefore, a dependable measurement of the neutron field requires a detailed simulation of the neutron generation in the treatment system.

The OncoRay treatment centre at the University Hospital Carl Gustav Carus operates an IBA universal nozzle that is capable of providing both scattered and scanned proton beams. This nozzle has been modelled in detail by means of the TOPAS software~\cite{TOPAS}. TOPAS provides a text-file based interface to Geant4~\cite{Geant4} Simulation Toolkit with focus on proton therapy applications.

The talk gives an overview of the specific implementation of the IBA nozzle. It presents the predicted secondary neutron fields and discusses how these depend on the operational parameters of the nozzle. Finally the results are compared to experimental measurements.

  • Lecture (Conference)
    1st Workshop Helmholtz Cross Program Activity - Querschnittsthema Strahlenforschung “Sekundäre Neutronen in Medizin und Strahlenschutz”, 24.-26.11.2015, München, Deutschland

Publ.-Id: 22886

Metals: Key enablers of a Circular Economy

Reuter, M. A.

Base metals such as copper, lead, nickel, cobalt, zinc etc. form the basic crucial carrier metals for a sustainable society – the Web of Metals. This paper discusses the special and crucial role these metals have in acting as enablers in any recycling efforts as they carry and release important and vital minor elements at the heart of high-tech applications and products. Through examination of the rising needs for such carriers, this paper examines the approach and technologies which need to be considered by any producer of base metals. Attention is paid to the limits and extent of this carrier role in the typical processing of materials. Examples of specialised technology and flowsheet needs are presented with consideration given to a “whole of chain” or Systems-Integrated Metal Production (SIMP) approach as a cornerstone of a circular economy. Also outlined are the challenges facing not only producers, but legislators who need to consider the balance between providing our societal needs with baseline technology infrastructure requirements for valuable metals extraction. In summary, the message of this paper states simply that not only is the criticality of metals important but the criticality of the infrastructure (Infrastructure Criticality) that can recover metals from complex designed “mineral” mixtures. Base metals are at the heart of a Circular Economy, therefore key enablers of the Internet-of-Metallurgical-Things.

Keywords: Resource efficiency base metals; Recycling; System integration; Design for Recycling (DfR)

  • Invited lecture (Conferences)
    Cleantech Innovations in Minerals Production, 08.-10.09.2015, Helsinki, Finnland

Publ.-Id: 22885

Ultrafast Insulator-Metal Transition in VO2 Driven by High-field THz Excitation

Pashkin, A.; Mayer, B.; Schmidt, C.; Grupp, A.; Oelmann, J.; Marvel, R. E.; Haglund Jr., R. F.; Oka, T.; Leitenstorfer, A.

Vanadium dioxide (VO2) is a prime example of a transition metal oxide with a sharp insulator-metal transition (IMT) at 340 K accompanied by a change of the lattice symmetry. A possibility to induce the metallic state in VO2 by electric field has attracted a lot of attention due to its potential applications in optics and high-speed electronics. However, numerous efforts to control the electronic state by applied electric bias have demonstrated that the switching mechanism is governed by resistive heating, dramatically limiting the operation speed. Recent developments in generation of high-field broadband THz transients offer an attractive way to apply extremely high electric fields on ultrashort timescales.
Here, we demonstrate an IMT in VO2 thin films driven by high-field multi-THz transients on a sub-100 fs timescale. Our broadband and phase-stable THz transients with extremely high peak electric fields of up to 17 MV/cm are generated via difference frequency mixing in a GaSe crystal. A typical excitation transient and the induced relative transmission change T/T traced by 8-fs-short near-infrared pulses are shown in Fig. 1(a). An ultrafast decrease of the transmission indicates the THz-driven switching into the metallic state, succeeded by a relatively slow relaxation on longer timescales. Besides that, the lattice dy-namics related to the coherent wave packet motion of the vanadium dimers manifests itself as an oscillation at a frequency of 5.9 THz [Fig. 1(a)]. Our experiments show that the observed non-thermal switching into a metastable metallic state is governed solely by the amplitude of the applied THz field. In contrast to resonant near-infrared excitation below the threshold fluence, no signatures of excitonic self-trapping are observed down to the lowest fluences of the THz excitation.
Our results can be understood as the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The total density of the delo-calized carriers proportional to the increase in optical conductivity Δσ1 at THz frequencies depicted in Fig. 1(b) shows a highly nonlinear dependence on the peak excitation field expected for a many-body tunneling process. We find good agreement with theoretical equation describing pair production in a Mott insulator and determine an electronic correlation length of 2.1 Å.

Keywords: terahertz; insulator-to-metal transition; non-thermal transition; field-induced tunneling

  • Lecture (Conference)
    German THz conference, 08.-10.06.2015, Dresden, Germany

Publ.-Id: 22884

Fully intensity and timing jitter compensated ultra-fast experiments at accelerator-driven photonsources at high repetition rates

Kovalev, S.; Green, B.; Golz, T.; Stojanovic, N.; Fisher, A. S.; Kampfrath, T.; Gensch, M.

Timing jitter and power instabilities are crucial parameters which greatly reduce the applicability of accelerator driven light sources for time-resolved experiments. In this contribution we present a technique that allows achieving few 10 fs time-resolution in experiments operating at cw repetition rates of up to 100 kHz by employing high repetition rate data acquisition. The method employs a fs-level arrival time monitor based on electro-optic sampling of residual pulses from a coherent diffraction radiator and a fast THz detector allowing for pulse to pulse detection of arrival time and pump intensity. The monitor can operate at high repetition rates cw (presently up to a few 100 kHz) and low electron bunch charges (sub pC). The prototype device has been tested at the quasi CW SRF accelerator (ELBE) by performing an ultra-fast THz driven magnetization dynamics experiment. Our method has high potential to provide few fs level timing on next generation large scale X-ray photon sources based on high repetition rate electron accelerators such as LCLSII. A demonstrator aiming at operation up to 4.7 MHz is under development for the European X-FEL.

Keywords: Timing Jitter; ultrafast experiments; super radiance

  • Lecture (Conference)
    International beam instrumentation conference 2015, IBIC2015., 13.09.2015, Melbourne, Australia

Publ.-Id: 22883

Ermittlung der Referenztemperatur T0 nach dem Master-Curve-Konzept mit Miniatur-C(T)-Proben

Viehrig, H.-W.; Houska, M.

Mini 0,16T-C(T)-Proben wurden aus halben ISO-V-Proben von zwei RDB-Stählen und einem RDB-Schweißgut hergestellt und nach ASTM E1921 geprüft. Die mit diesen Proben ermittelten und auf eine Dicke von 1T (25,4 mm) umgerechneten Bruchzähigkeiten, KJc(1T), folgen dem Verlauf der Master Kurven. Mit 1T-, 0,5T-, 0,25T und 0,16T-C(T)-Proben aus RDB-Stahl 22 NiMoCr 3-7 wurden vergleichbare Referenztemperaturen T0 bestimmt. Die geringe Messkapazität, KJc(limit), der 0,16T-C(T)-Proben begrenzt das Messfenster auf einen Temperaturbereich von T0 minus 15 K bis 50 K. Die Seitkerbung der 0,16T-C(T)-Proben bewirkt eine gleichmäßigere Spannung und Verteilung der Rissinitiierungsorte über die Nettoprobendicke (Ermüdungsrissfront).

Miniature 0.16T-C(T) specimens were machined from halves of already tested ISO-V specimens of two RPV steels and one RPV multilayer weld metal. The specimens were tested according to ASTM E1921. The progression of the 1T (25.4 mm) size adjusted fracture toughness, KJc(1T) values follow the Master Curve. The T0 values determined with 1T , 0.5T-, 0.25T- and 0.16T-C(T) specimens of 22 NiMoCr 3-7 RPV steel are comparable. The small measuring capacity of the 0.16T-C(T) specimen limits the test temperature window to T0 minus 15 K to 50 K. Side grooving results in a more uniform stress and distribution of cleavage initiation sites along the net thickness (fatigue crack front).

Keywords: Spaltbruch; Bruchzähigkeit; Master Curve Konzept; C(T)-Proben; Seitkerbung; cleavage fracture; fracture toughness; Master Curve approach; C(T) specimen; side-grooving

  • Contribution to proceedings
    48. Tagung des DVM-Arbeitskreises Bruchvorgänge und Bauteilsicherheit, 16.-17.02.2016, Freiburg, Deutschland
    Bruchmechanische Werkstoff- und Bauteilbewertung: Beanspruchungsanalyse, Prüfmethoden und Anwendungen, DVM-Bericht 247:, Berlin: DVM, 1616-4687, 229-239

Publ.-Id: 22882

Ion Implantation Induced Damage in Oxide Dispersion Strengthened Steels and FeCr Alloys Investigated by DB and cDB

Anwand, W.; Heintze, C.; Leguey, T.

FeCr alloys and oxide dispersion strengthened (ODS) FeCr steels are candidates for structural materials for Generation IV and fusion reactors, owing their advantageous physical and chemical properties for such applications as, e.g., resistance against oxidation, creep and radiation.
For an optimal steel composition, depending on the application, it is important to understand how alloying components and oxide additives affect the materials behaviour to irradiation. For this purpose, Fe-Cr alloys have been employed as model materials in irradiation experiments and subsequent characterization of irradiation damage. Ion implantation was demonstrated an efficient tool for simulation of radiation damage similar to that in fission/fusion power plant materials, but without any induced activation.
FeCrNiSiP samples with two Cr contents of 5 wt.% and 9 wt.% were implanted with 5 MeV Fe ions at different temperatures with a damage of 0.1 displacements per atom (dpa) and 0.5 dpa, respectively. The influence of the alloying elements on the evaluation of the damage after ion implantation was investigated for the complete FeCrNiSiP alloy and separately for each FeCr added with the single alloying elements.
Furthermore model Fe14wt.%Cr alloys and two ODS Fe14Cr steels with 0.3wt.%Y2O3 and with and without Ti and W additions were implanted at low temperature with 1 MeV Fe ions up to a high damage of 15 dpa.
A slow positron beam has been used in order to investigate the depth dependence of the ion implantation induced vacancy-type defect in the materials by single Doppler broadening (DB) measurements with positron energies from 30eV to 35keV, corresponding to a depth from 1 nm down to 3 µm. Furthermore, coincidence DB measurements at selected positron energies were applied for a more precise examination of a possible defect decoration of the open volume by alloying elements.
Slow positron beam techniques turned out to be an effective tool for the characterization of open-volume defects after ion implantation. It could be shown that a Ni addition to FeCr led to an increase of the open-volume defects after ion implantation, whereas Si or P reduced them. A minimal damage could be detected for the complete alloy FeCrNiSiP.
A lower Cr content of 5wt.% is advantageous against 9wt.% for a defect annealing during implantation at temperatures below 450 °C. At 450 °C all defects annealed out already during implantation.
The influence of Y2O3 nanoparticles on the stabilization of defects in FeCr steels could be demonstrated by DB and cDB measurements and will be discussed in detail.

Keywords: FeCr alloys; Oxide Dispersion Strengthened Steels; ion implantation induced damaged; positron annihilation spectroscopy

  • Lecture (Conference)
    17th International Conference on Positron Annihilation, 20.-25.09.2015, Wuhan, PR China

Publ.-Id: 22881

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 Logo Contribution 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

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 Logo International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering 10(2016)2, 214-217


Publ.-Id: 22864

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

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

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

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

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

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 Logo International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering 10(2016)2, 256-259


Publ.-Id: 22858

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

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

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

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

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

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

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

Advances in radiotherapy special feature.

Krause, M.; Supiot, S.

there is no abstract

Publ.-Id: 22849

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

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

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

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

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

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

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

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

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

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

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 Logo Proceedings of the National Academy of Sciences of the United States of America 113(2016)33, 9232-9237
    Online First (2016) DOI: 10.1073/pnas.1601040113

Publ.-Id: 22837

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 Logo Contribution 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

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

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

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

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

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

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

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

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

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 Logo Contribution to proceedings
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Germany

Publ.-Id: 22827

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  • Open Access Logo Physical Chemistry Chemical Physics 17(2015), 24182-24192
    Online First (2015) DOI: 10.1039/C5CP04280A

Publ.-Id: 22811

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

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

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 Logo Journal 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

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

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

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

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

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