Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35809 Publications

H2Ti6O13, a new protonated titanate prepared by Li+/H+ ion exchange: synthesis, crystal structure and electrochemical Li insertion properties

Perez-Flores, J. C.; Baehtz, C.; Hoelzel, M.; Kuhn, A.; Garcia-Alvarado, F.

The hexatitanate H2Ti6O13 is obtained by a simple successive Na+/Li+/H+ ion exchange of Na2Ti6O13. The crystal structure of H2Ti6O13 was solved from both synchrotron and neutron powder diffraction. H2Ti6O13 crystallizes in the monoclinic space group C2/m, with a = 14.6702(3) angstrom; b = 3.7447(1) angstrom; c = 9.2594(2) angstrom; beta = 96.941(2)degrees. The monoclinic symmetry of the [Ti6O13](2-) framework is preserved during the exchange reaction. When compared to the positions of Na and Li in Na2Ti6O13 and Li2Ti6O13, the position of the proton is shifted towards the O3 atomic position, where it forms a covalent O-H bond. The vicinity of the proton to the O5 atom across the tunnel allows for the formation of a classical (asymmetric) hydrogen bond. H2Ti6O13 has been tested as a Li insertion material to assess its use as an electrode in lithium rechargeable batteries. It reacted irreversibly with ca. 6 Li ions per formula unit at an average voltage of 1.5 V vs. Li+/Li, with a specific discharge capacity of 315 mA h g(-1). However, after first discharge, a reversible specific capacity of 170 mA h g(-1) was developed. H2Ti6O13 then yielded a higher reversible specific capacity than Na2Ti6O13 and comparable to Li2Ti6O13. Besides structural details, IR spectroscopy has been used to further assess possible reaction mechanisms pointing to the transformation of H2Ti6O13 to Li2Ti6O13 when reacting with the very first two lithium ions.

Keywords: RECHARGEABLE LITHIUM BATTERIES; NEUTRON POWDER-DIFFRACTION; LAYERED STRUCTURE; INTERCALATION; LI2TI6O13; ELECTRODE; BEHAVIOR; NA2TI3O7; LIMNO2; TIO2

Permalink: https://www.hzdr.de/publications/Publ-17621
Publ.-Id: 17621


In situ investigations of a Li-rich Mn–Ni layered oxide for Li-ion batteries

Simonin, L.; Colin, J.-F.; Ranieri, V.; Canévet, E.; Martin, J.-F.; Bourbon, C.; Baehtz, C.; Strobel, P.; Daniel, L.; Patoux, S.

A Li-rich layered oxide with the formula Li[Li0.2Mn0.61Ni0.18Mg0.01]O2 was successfully synthesised and characterised using several in situ characterisation techniques. The electronic state and structural evolution of the material upon cycling were investigated using in situ XRD, EXAFS and XANES measurements. XANES and SQUID magnetic measurements showed that the initial material contains a certain amount of Mn3+ in a low spin configuration (average Mn oxidation state: +3.75). In situ measurements showed that the first part of the charge (up to 4.4 V vs. Li+/Li) corresponds to oxidation of the Mn3+ fraction, and that the oxidation of nickel occurs only later, on the main charge plateau at 4.5 V. Electrochemical and structural results tend to show that the main first-charge plateau is a twophase process where a new phase is created. This new phase is structurally very close to the starting one, and could be an oxygen-deficient spinel with a ¼ 8.25 A. This process is non-reversible, and further cycling occurs in the new phase formed in situ.

Keywords: lithium ion battery; x-ray diffraction; EXAFS

Permalink: https://www.hzdr.de/publications/Publ-17620
Publ.-Id: 17620


Full structural and electrochemical characterization of Li2Ti6O13 as anode for Li-ion batteries

Pérez-Flores, J. C.; Baehtz, C.; Hoelzel, M.; Kuhn, A.; García-Alvarado, F.

A detailed structural and electrochemical study of the ion exchanged Li2Ti6O13 titanate as a new anode for Li-ion batteries is presented. Subtle structural differences between the parent Na2Ti6O13, where Na is in an eightfold coordinated site, and the Li-derivative, where Li is fourfold coordinated, determine important differences in the electrochemical behaviour. While the Li insertion in Na2Ti6O13 proceeds reversibly the reaction of lithium with Li2Ti6O13 is accompanied by an irreversible phase transformation after the first discharge. Interestingly, this new phase undergoes reversible Li insertion reaction developing a capacity of 170 mAh/g at an average voltage of 1.7 V vs. Li+/Li. Compared with other titanates this result is promising to develop a new anode material for lithium ion rechargeable batteries. Neutron powder diffraction revealed that Na in Na2Ti6O13 and Li in Li2Ti6O13 obtained by Na/Li ion exchange at 325 1C occupy different tunnel sites within the basically same (Ti6O13)2- framework. On the other hand, electrochemical performance of Li2Ti6O13 itself and the phase released after the first full discharge is strongly affected by the synthesis temperature. For example, heating Li2Ti6O13 at 350 1C produces a drastic decrease of the reversible capacity of the phase obtained after full discharge, from 170 mAh/g to ca. 90 mAh/g. This latter value has been reported for Li2Ti6O13 prepared by ion exchange at higher temperature.

Keywords: lithiumtitanate; lithium ion batterie; x-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-17619
Publ.-Id: 17619


On the Mechanisms of Ni-Catalysed Graphene Chemical Vapour Deposition

Weatherup, R. S.; Bayer, B. C.; Blume, R.; Baehtz, C.; Kidambi, P. R.; Fouquet, M.; Wirth, C. T.; Schlögl, R.; Hofmann, S.

How does your graphene grow? In situ X-ray photoelectron spectroscopy and X-ray diffraction measurements during chemical vapor deposition on Ni catalyst films show that graphene forms both isothermally and by precipitation on cooling (see picture). A coherent graphene growth model is devised and sub-surface dissolved carbon is shown to play an important role.

Keywords: chemical vapor deposition; graphene; nickel; photoelectron spectroscopy; X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-17618
Publ.-Id: 17618


Water and n-heptane volume fractions in a rotor-stator spinning disc reactor

Visscher, F.; Bieberle, A.; Schubert, M.; van der Schaaf, J.; de Croon, M.; Hampel, U.; Schouten, J.

This paper presents the volume fractions of n-heptane and water measured in a rotor-stator spinning disc reactor. The volume fractions were measured using γ-ray tomography and photographic image analysis. The volume fractions were determined as a function of rotational disc speed, flow ratio, position in the reactor, and rotor material. In addition, the effect of the density difference between water and n-heptane was determined by dissolving potassium iodide in the water phase. Below a rotational disc speed of 75 RPM the volume fraction measured by tomography and photographic image analysis are within 10% deviation. For low rotational disc speeds, the n-heptane volume fraction decreases slightly with increasing rotational disc speed: the centrifugal force accelerates the larger n-heptane droplets to the center. At higher rotational disc speeds the droplets become smaller accordingly, the friction between the phases determines the flow and the n-heptane volume fraction becomes equal to the n-heptane to total flow ratio. An increase in density difference from 0.31 to 0.79 kg/dm³ did not influence the volume fractions.

Keywords: Rotor-stator spinning disc reactor; liquid-liquid flow; hydrodynamics; γ-ray tomography; multiphase reactor

  • Industrial & Engineering Chemistry Research 51(2012)51, 16670-16676
    DOI: 10.1021/ie301439s

Permalink: https://www.hzdr.de/publications/Publ-17617
Publ.-Id: 17617


Investigation of gas-liquid two-phase flow in multiphase contactor using low-intrusive measuring methods

Zheng, G.; Schlusemann, L.; Schubert, M.; Hampel, U.; Gruenewald, M.

Multiphase contactors are the most important apparatuses for reaction and separation in chemical engineering. Limited by the measuring methods, the analysis of their hydrodynamic behavior is usually done using superficial liquid and gas flow velocities. Several new measuring techniques for the investigation of multiphase flows in vessel cross sections have been developed in the last decades. Especially the use of tomographic visualization techniques is of great interest since these are noninvasive and thus non-intrusive methods, and enable the visualization of phase distributions.
However, currently developed nonintrusive methods have considerable drawbacks. The computer tomography methods can obtain high spatial resolution. In comparison, the temporal resolution is relative low. For the application of topographic measurement techniques in multiphase flows, especially with fast changing flow patterns, a high temporal resolution is essential. Electrical tomography has a high temporal resolution. However, reconstruction algorithm is complex and the electrical field lines are not linear, therefore spatial resolution rate is relative low. Therefore, no exact mass balance could be established and the resulting phase fractions cannot be applied for model developments.

  • Lecture (Conference)
    AIChE Annual Meeting, 28.10.-02.11.2012, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-17616
Publ.-Id: 17616


Hydrodynamic investigation of a flow reactor with foam packings

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.

The effects of superficial liquid and superficial gas velocities, cell density of the foam and liquid properties on liquid holdup, residence time distribution, axial dispersion and pressure drop were investigated. Hydrodynamic multiplicity was found in flow reactor with different solid foam packings depending on the pre-wetting conditions. Furthermore, liquid distribution, and regime transition as well as stability of flow conditions were studied. The study was based on novel wire mesh sensors aligned along the vertical axis of the reactor.

Keywords: solid foam; hydrodynamics; multiplicity; pressure drop; wire-mesh sensor

  • Lecture (Conference)
    International Symposium on Chemical Reaction Engineering, ISCRE22, 02.-05.09.2012, Maastricht, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-17615
Publ.-Id: 17615


Hydrodynamics and mass transfer in the horizontal rotating foam stirrer reactor

Leon, M. A.; Maas, R. J.; Bieberle, A.; Schubert, M.; Nijhuis, T. A.; van der Schaaf, J.; Hampel, U.; Schouten, J. C.

The rotating foam stirrer reactor is a novel type of multi-phase reactor where highly open-celled materials, solid foams, are used both as a catalyst support and as a stirrer. One of the advantages of rotating foam stirrer reactors compared to e.g. slurry reactors is the absence of a catalyst separation step. Moreover, in the standard foam stirrer configuration, i.e., the foam structures (blades or donut-shaped foam blocks) are mounted on a vertical shaft, the formation of finely dispersed bubbles and the fast refreshment of the catalyst surface lead to better mass transfer rates.
In this work, a new foam stirrer design is presented. A donut-shaped foam block is mounted on a horizontal shaft. Using gamma-ray tomography, the hydrodynamics of the system is described. When the reactor is partially filled with liquid, a "spray regime" is observed which leads to the formation of fine liquid droplets and fine gas bubbles enhancing the gas-liquid mass transfer rate. Furthermore, due to the centrifugal forces at high rotational speeds, the gas is separated from the catalyst only by a very thin liquid film. This enhances the liquid-solid mass transfer of the gas reactant, which is often the limiting component in hydrogenation or oxidation reactions. Mass transfer measurements will be discussed for different operation conditions.

Keywords: multiphase reactors; solid foams; hydrodynamics; mass transfer; computed tomography

  • Lecture (Conference)
    AIChE Annual Meeting, 28.10.-02.11.2012, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-17614
Publ.-Id: 17614


Investigating annular flows and the effect of functional spacers in an adiabatic double-subchannel model of a BWR fuel bundle by ultra-fast X-ray tomography

Zboray, R.; Guetg, M.; Kickhofel, J.; Barthel, F.; Sprewitz, U.; Hampel, U.; Prasser, H.-M.

Dryout of the coolant liquid film at the upper part of the fuel assemblies of a boiling water reactor (BWR), where annular flow prevails, represents a safety concern and an economical constraint. To be able to deal with this issue, annular flows must be well understood. Therefore we have investigated such flows in a double-subchannel model of a BWR fuel bundle using X-ray imaging at the Rossendorf Ultrafast Electron Beam X-ray Tomograph (ROFEX) facility. Adiabatic experiments slightly above atmospheric conditions using air-water annular flows have been carried out. In annular flows a significant portion of the liquid is present as droplets in the gas flowing in the middle of the conduit. Using functional spacer grids is the common method in nuclear technology to influence the annular flow such to enhance the deposition of droplets into the liquid film on the fuel pins thereby increasing dryout margins. The tests include, besides investigating the liquid film thickness in the plain channel, the investigation of the effect of a functional spacer on the liquid film. Using NaI as contrast agent in water enhances the image quality. The high time-resolution of the tomography enables to follow the wavy structure of the annular film flow. The paper aims at extracting quantitative information on the liquid film thickness distributions from the reconstructed tomographic images.

Keywords: boiling water reactor; dry-out; ultrafast X-ray tomography; fuel rods

  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada
    Proceedings

Permalink: https://www.hzdr.de/publications/Publ-17613
Publ.-Id: 17613


Measurement of liquid distributions in separation columns

Schubert, M.; Hampel, U.; Kenig, E. Y.; Grünewald, M.

Design and optimization of separation units, e.g. distillation and absorption columns, both reactive and non-reactive, require detailed knowledge about the underlying phenomena and their impact on the process behaviour. Although the separation efficiency is pre-determined by complex hydrodynamic conditions in the columns, current studies are mainly based on conventional techniques with strongly limited insights, e.g. on using compartment-type liquid collectors below packings. Except for the Chemical Engineering group at the University of Liège (e.g., Aferka et al., 2010) tomographic imaging technique so far has not found a proper place in investigations of separation columns with structured internals.
Compared to catalytic packings that contain active elements for heterogeneous reaction, column internals are mainly designed to provide sufficient mass transfer area and to generate local turbulence for high mass transfer rates. To meet this goal, both structured packings (e.g., corrugated sheet Sulzer KatapakTM and MellapakTM) and random packings (e.g., Pall rings, Raschig rings, Bearl saddles) have been designed. The strong challenge in flow visualization in such packings is attributed to the flow patterns that incorporate thin liquid films on the surface of the structures, and to their dynamics. Thus, high temporal and spatial resolution is required. In this regard, the application of up-to-date measurement techniques and new visualization concepts would make a step forward in evaluating such processes and in re-designing the apparatuses and internals. In the present work, a detailed study was performed focusing on important hydrodynamic aspects in packings, namely:

  • liquid distribution in the cross-section in and below the packing
  • resolution of the packing structure
  • visualization of liquid film structures, dynamics and their detection limit
  • classification of by-passing wall flow and utilizable core flow
  • disturbance of the disperse liquid flow using new wire-based sensors
  • dynamics of the transition from the loading to the flooding point
Ultra-fast X-ray tomography, high resolution gamma-ray tomography and wire-mesh sensor techniques were applied. In our contribution, the potential of the new measurement techniques for separation columns is discussed and new insights on the hydrodynamic behaviour are provided.

Keywords: Separation columns; hydrodynamics; tomography

  • Lecture (Conference)
    10th Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering, 26.-29.06.2011, Braga, Portugal

Permalink: https://www.hzdr.de/publications/Publ-17612
Publ.-Id: 17612


Wire-mesh based hydrodynamic and thermal studies in packed beds

Schubert, M.; Schäfer, T.; Kryk, H.; Hampel, U.

Gas/liquid operated packed bed reactors are the workhorses in the wide field of chemical and petrochemical industry. Intense research effort has been undertaken to explore all sub-processes of hydrodynamics, mass and heat transfer, to predict process behaviour, to define reliable scale-up and design rules etc. However, still many details are unsolved and require deeper insights at multiple scales. Particularly in co-current downflow trickling bed reactors (TBR), the interactions between fluid phases and packings and in turn, hydrodynamics and transfer steps are very complex and not yet fully understood.
Catalyst utilization and reactor efficiency suffers clearly from maldistribution of liquid in the cross-section of packings, channelling effects and bypassing liquids. Accompanied by maldistribution, local hot spots may form in packed bed reactors. If not detected early, they can have a detrimental impact on the yield of the desired products and, in addition, they may pose safety hazards, i.e. reaction runaway due to phase transition and accelerated reaction rate which are main reason for major chemical plant accidents.
To take corrective action, indicators of conditions, such as non-irrigated zones and emerging elevated temperature zones must be detected. In the past two decades, considerable effort has been made to visualize and characterize multiphase flows in packings. Since local sensors inserted at selected locations in the bed fail to provide information about spatial distributed phenomena, powerful tomographic methods well known from medical imaging were successfully transferred into chemical engineering applications. However, tomographic techniques are expensive, low speed and don’t yield any information about fluid velocities. Considering industrially suitable temperature monitoring systems, no spatial-resolved array-type system is available.
Prasser et al. (1998) developed an electrode-mesh tomograph for gas-liquid flows in bubble columns which is advantageous considering costs, simplicity and safety. Based on this principle, our contribution presents results of spatially resolved hydrodynamic studies in a pilot-scale TBR using new capacitance wire-mesh sensors for determination of liquid saturation and axial liquid velocities simultaneously for all sensing points of the whole cross-section depending on gas and liquid flow. Furthermore, a new temperature-monitoring sensor was developed installing Pt2000 elements at the cross-points of a wire-mesh based array system.

  • Lecture (Conference)
    19th International Congress of Chemical and Process Engineering CHISA 2010 and the 7th European Congress of Chemical Engineering (ECCE-7), 28.08.-01.09.2010, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17611
Publ.-Id: 17611


Anwendung von Optical Flow Verfahren für die Atembewegungskorrektur in der Positronen-Emissions-Tomographie

Langer, B.

kein Abstract verfügbar

  • Diploma thesis
    TU Dresden, 2011
    68 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17610
Publ.-Id: 17610


Multiphase flow investigations with ultrafast electron beam X-ray tomography

Hampel, U.; Barthel, F.; Bieberle, M.; Schubert, M.; Schleicher, E.

We introduce ultrafast electron beam X-ray tomography as an imaging modality for multiphase flow studies. A dedicated electron beam tomography scanner (ROFEX) has been developed which allows cross-sectional X-ray tomography with 1 mm spatial resolution and up to 7000 cross-sectional images per second recording speed. It is applicable to flow problems in vessels with up to 120 mm diameter and moderate X-ray attenuation. The tomography system has been applied in various flow studies, including gas-liquid two-phase flow in vertical pipes and channel structures.

Keywords: electron beam tomography; multiphase flow measurement

  • Lecture (Conference)
    The 7th International Symposium on Measurement Techniques for Multiphase Flows ISMTMF-2011, 17.-19.09.2011, Tianjin, China

Permalink: https://www.hzdr.de/publications/Publ-17609
Publ.-Id: 17609


Study of multiphase flow in bubble - and packed columns using low-intrusive measuring methods

Zheng, G.; Schubert, M.; Hampel, U.; Grünewald, M.

Multiphase contactors are the most important apparatuses for reaction and separation in chemical engineering. Limited by the measuring methods, the analysis of their hydrodynamic behavior is usually done using superficial liquid and gas flow velocities. Several new measuring techniques for the investigation of multiphase flows in vessel cross sections have been developed in the last decades. Especially the use of tomographic visualization techniques is of great interest since these are noninvasive and thus non-intrusive methods, and enable the visualization of phase distributions.
However, currently developed nonintrusive methods have considerable drawbacks. The computer tomography methods can obtain high spatial resolution. In comparison, the temporal resolution is relative low. For the application of topographic measurement techniques in multiphase flows, especially with fast changing flow patterns, a high temporal resolution is essential. Electrical tomography has a high temporal resolution. However, reconstruction algorithm is very complex and the electrical field lines are not linear, therefore spatial resolution rate is relative low. Therefore, no exact mass balance could be established and the resulting phase fractions cannot be applied for model developments.
In this research, Wire-Mesh Sensor (WMS) is used for the study of phase distribution in multiphase contactors. The WMS comprises two planes, in each plane there are sensing wires. Wires from different planes are orthogonally arranged. Since water and air have different electrical permittivity values and thus, produce different capacitances in the sensing points of the WMS, images of phase distributions can be generated from the measurements of the local capacitance.
Phase distribution in multiphase contactor, e.g. bubble column and packed column, were studied with a WMS. It was shown that the flow regime in bubble column at various gas superficial velocity ((a) uG=8.4 cm/s; (b) uG=16.8 cm/s). Gas-liquid phase distribution in packed column measured with WMS and that measured with gamma-tomography can be characterized.
Measurements of phase distribution with WMS could supply more accurate information of spatial phase distribution to update the theoretical models used in multiphase flow.

  • Lecture (Conference)
    Jahrestreffen der Fachgruppe "Mehrphasenströmungen", 15.-21.03.2012, Weimar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17608
Publ.-Id: 17608


New insights into gas/liquid textures in rotating solid foams

Bieberle, A.; Schubert, M.; Hampel, U.; Tschentscher, R.; Njihuis, T. A.; van der Schaaf, J.; Schouten, J. C.

For flexible production of fine chemicals and pharmaceuticals still slurry catalysts in batch reactors are used. However, production efficiency suffers from necessary filtration after reaction is finished and abrasion effects make re-usage of catalyst often not possible. Additionally, the mass transfer rates are limited due to low relative velocities between particles and the gas/liquid phases.
Alternatively, a new three-phase reactor design based on rotating solid foams were developed by the Chemical Reactor Engineering group at Eindhoven University of Technology (Tschentscher et al., 2010). The solid foam is applied both as catalyst support and stirrer in order to mix the gas and liquid phases and to create fine bubbles.
Measurements of the gas-liquid mass transfer revealed clearly improved reactor performance compared to Rushton stirrers. The visual observation suggested that the rotation of the foam block leads to a structuring of the reactor volume into sections with considerable different gas holdup, flow behaviour and bubble size distribution. However, access to the patterns in the solid foam was so far not possible.
In our contribution, results of a comprehensive non-invasive tomographic study will be presented. A high-resolution gamma-ray setup was applied to visualize the gas/liquid textures in the reactor, especially in the solid foam block. Therefore, an acrylic reactor system was built that ensure minimal attenuation. Two different reactor heights, stirrer speed from 150 to 300 rpm and two solid foams with different geometric properties were applied. To study the effect of the liquid viscosity, glycerol-water mixtures as well as pure liquids were used. Additionally, flow patterns of non-Newtonian liquids (carboxy methyl cellulose, CMC), foaming liquids (cetyltrimethyl ammonium bromide, STAB) and non-Newtonian foaming liquids (CMC+STAB) were compared with the air-water system.
The observed flow patterns can be related to the mass transfer characteristics and conclusions on an optimized reactor/foam design can be drawn.

Keywords: Multiphase reactor; solid foam; tomography; flow texture

  • Lecture (Conference)
    10th Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering, 26.-30.06.2011, Braga, Portugal

Permalink: https://www.hzdr.de/publications/Publ-17607
Publ.-Id: 17607


Untersuchungen zu Flüssigkeitsholdup und -verteilung in strukturierten Packungen mittels schneller Elektronenstrahl-Röntgen-Tomographie. Jahrestreffen der Fachgruppen CFD und Fluidverfahrenstechnik

Schubert, M.; Janzen, A.; Barthel, F.; Kenig, E. Y.; Hampel, U.

Strukturierte Packungen werden vielfältig als trennwirksame Einbauten in Destillations- und Absorptionskolonnen eingesetzt. In Gegenstromfahrweise stellt der Flutpunkt den oberen Punkt des Betriebsfensters dar, bei dem in den Packungskanälen Flüssigkeit akkumuliert und die Gasphase dispergiert wird. Durch die Modifikation der Packungsgeometrie kann der Flutpunkt zu höheren Durchsätzen verschoben und damit die Kapazität von Kolonnen erhöht werden. Zur Optimierung der Packungsstruktur sowie zur Prozessmodellierung ist eine genaue Kenntnis der Strömung in der Packung notwendig.
Zur Untersuchung der Phasenverteilung in Gas-Flüssig-Kontaktapparaten wurde eine neue Messtechnik eingesetzt. Im Gegensatz zu klassischen strahlungsbasierten Tomographieverfahren benötigt die schnelle Elektronenstrahl-Röntgen-Tomographie keine Rotation von Objekt oder Messsystem. Stattdessen erzeugt ein ablenkbarer Elektronenstrahl auf einem ringförmigen Target um das Objekt einen bewegten Röntgenfleck. Die Schwächung der Röntgenstrahlung in Abhängigkeit der vorliegenden Phasenverteilung wird durch den kreisförmig angeordneten Detektor gemessen. Damit kann die Phasen-Verteilung in der Packung mit einer sehr schnellen Bildrate von 2000 Hz und höher visualisiert werden.
Die Verteilung der Flüssigphase wurde in einer 80 mm Kolonne bei unterschiedlichen Gas- und Flüssigkeits-Beladungen (Stoffsystem Wasser/Luft) gemessen. Zwei Packungen unterschiedlicher spezifischer Oberfläche (Montz B1-350MN, B1-500MN) wurden eingesetzt, um den Einfluss der Packungsgeometrie zu untersuchen. Die rekonstruierten Bilder der tomographischen Messungen wurden aufbereitet und die Verteilung der Flüssigphase analysiert. Der sich einstellende Holdup wurde vor und am Flutpunkt berechnet und mit konventionell gemessenen Werten verglichen. Die schnelle Röntgentomographie erlaubt ganz neue Einblicke in die Dynamik der Flüssigkeitsströmung innerhalb der strukturierten Packung.

  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics und Fluidverfahrenstechnik, 12.-14.03.2012, Weimar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17606
Publ.-Id: 17606


Tomographic imaging for multiphase flows

Schubert, M.; Reinecke, S.

Multiphase flows are a common phenomenon in many processes and systems in the chemical and mineral oil industry. Those flows occur in many different forms such as disperse gas-liquid flows in bubble column reactors, gas-solid flows in fluidized-beds or bubble-, splash- and film flows in distillation systems. Due to their nature, they are difficult to record by means of standard measurement techniques, challenging to characterize theoretically and complex to model numerically. In order to monitor and characterize those flows in industrial systems as well as in research facilities it is necessary to apply methods with the ability to measure the phase distribution, phase interface density, turbulence- and velocity parameters in continuum phases and also the thermal-, material- and impulse transports between the different phases with high spatial and temporal resolution. Because in many cases multiphase flows are opaque, the application of common optical measurement principles is limited. In addition, industrial processes run at high pressure and temperature in vessels with thick metal walls. This limits the means of instrumentation and demands for robust measurement equipment.
In the recent past, the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has undertaken great efforts in the development of tomographic imaging principles that allow the understanding of multiphase flows with high spatial and temporal resolution. Some results of these developments, like the wire-mesh-sensors, the gamma ray computed tomography and the ultrafast X-ray computed tomography will be presented in the talk. With the wire mesh sensor, it was possible to analyze transient gas liquid flows with frame rates up to 10,000 pictures per seconds and a spatial resolution of 2 mm for the first time. The gamma ray computed tomography allows the investigation on high-pressure instruments and facilities with a spatial resolution of 2 mm. Finally, the Ultrafast X-ray computed tomography combines various positive features, such as contactless measurement with high spatial (~ 1 mm) and temporal (~ 10,000 frames per second) resolution as well as the visualization of opaque and solids-bearing flows. The talk introduces the described measurement technologies regarding their physical and technological principle and provides an insight into potential applications and methods for image data analysis.

  • Lecture (others)
    ACHEMA 2012, 18.-22.06.2012, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17605
Publ.-Id: 17605


Investigation of liquid hold-up in structured packings under flooding conditions using ultra-fast electron beam X-ray tomography

Janzen, A.; Barthel, F.; Schubert, M.; Hampel, U.; Kenig, E. Y.

Structured packings are column internals widely used in countercurrent separation processes, such as distillation or absorption. Due to the countercurrent flow, flooding of the packed column represents the upper operation limit. At this point, the high shear stresses between the phases cause a liquid-phase accumulation accompanied by the dispersion of the gas phase. Shifting the flooding point towards higher loads by modifying the packing geometry would result in a capacity increase of the column. Therefore, understanding of the fluid flow character inside the packing is necessary both for process modelling and for packing optimisation.
In this work, a new measurement technique, ultra-fast electron beam X-ray tomography, is applied to investigate dynamic phase distribution in gas-liquid contact devices. Contrary to classical tomographic systems, electron beam X-ray tomography does not require a rotating object or a source-detector setup. Instead, an electron beam is very rapidly swept across a target producing a moving X-ray spot. Thus, a high temporal resolution with frame rates of 2000 images per second and higher can be achieved.
The liquid-phase distribution in an experimental setup containing a DN80 column was measured for the system water/air at different gas and liquid loads. Two packing types with different specific surface area (Montz B1-350MN and B1-500MN) were used to investigate the influence of the packing geometry. The reconstructed image series were post-processed and analysed with respect to the spatial distribution of the liquid and its hold-up before and at the flooding point. Furthermore, the liquid hold-up measurement results were compared with those obtained from a conventional draining method. The new fast measurement technique is capable of providing new insights on the liquid flow dynamics.

  • Lecture (others)
    ACHEMA 2012, 18.-22.06.2012, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17604
Publ.-Id: 17604


Geschüttelt oder gerührt oder …? - Mehrphasenströmungen in der chemischen Industrie.

Schubert, M.

Viele Produkte des täglichen Lebens werden in Industrieapparaten hergestellt, in denen Gase und Flüssigkeiten gemeinsam strömen. Der Vortrag gibt einzigartige Einblicke in die komplexe Welt der Mehrphasenströmungen und zeigt Forschungsansätze für eine effiziente und ressourcenschonende Produktion.

  • Lecture (others)
    Lange Nacht der Wissenschaften, TU Dresden, 06.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17603
Publ.-Id: 17603


Charakterisierung von Mehrphasenströmungen in der Verfahrenstechnik

Schubert, M.

Der Vortrag zeigt exemplarisch den Einsatz neuer bildgebender Messverfahren für die Untersuchung von Mehrphasenströmungen in der Verfahrenstechnik.

  • Lecture (others)
    Prozessverfahrenstechnisches Seminar, TU Dresden, 05.07.2011, 05.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17602
Publ.-Id: 17602


Visualisation of gas-liquid two-phase flow in opaque systems

Hampel, U.; Schubert, M.; Barthel, F.; Szalinski, L.; Bieberle, M.

Measurement and visualisation of two-phase flow is of high scientific and engineering relevance, for instance in mineral oil processing, chemical reaction engineering, and energy systems engineering. However, it is also a great challenge, because traditional visualisation tools, such as high-speed camera imaging and ultrasound measurements fail in multiphase systems. Tomographic methods are being considered as the key technology for multiphase flow visualisation, however, to date only few methods are suited because of stringent requirements for high spatial and temporal resolution. In particular, methods are sought, which can visualize two-phase flow in complex geometries. Examples are reactor vessels with internals, rod bundles of heat exchangers or nuclear fuel rod assemblies, but also porous media of fixed bed reactors or rock samples.
The presentation introduces two novel imaging modalities, namely wire mesh sensors and ultrafast X-ray tomography and their use in two-phase flow measurement in complex flow domain geometries. It will be shown, how gas-liquid flows can be visualized in fixed bed packings and flow channels intransparent walls.

Keywords: two-phase flow measurement; wire mesh sensor; electron beam tomography

  • Invited lecture (Conferences)
    4th International Workshop on Process Tomography, 21.-23.09.2011, Chengdu, China
  • Contribution to proceedings
    4th International Workshop on Process Tomography, 21.-23.09.2011, Chengdu, China
    Proceedings

Permalink: https://www.hzdr.de/publications/Publ-17601
Publ.-Id: 17601


Multiphase flow investigations with ultrafast electron beam X-ray tomography

Hampel, U.; Barthel, F.; Bieberle, M.; Schubert, M.; Schleicher, E.

We introduce ultrafast electron beam X-ray tomography as an imaging modality for multiphase flow studies. A dedicated electron beam tomography scanner (ROFEX) has been developed which allows cross-sectional X-ray tomography with 1 mm spatial resolution and up to 7000 cross-sectional images per second recording speed. It is applicable to flow problems in vessels with up to 120 mm diameter and moderate X-ray attenuation. The tomography system has been applied in various flow studies, including gas-liquid two-phase flow in vertical pipes and channel structures.

Keywords: electron beam tomography; multiphase flow measurement

  • Contribution to proceedings
    The 7th International symposium on measurement techniques for multiphase flows ISMTMF-2011, 17.-19.09.2011, Tianjin, China
    AIP Conf. Proc.: American Institute of Physics 1428, 978-0-7354-1011-4, 167-174
  • AIP Conference Proceedings 1428(2012), 167-174
    DOI: 10.1063/1.3694703

Permalink: https://www.hzdr.de/publications/Publ-17600
Publ.-Id: 17600


Ultrafast tomography for multiphase flow measurement in process applications

Hampel, U.; Fischer, F.; Bieberle, M.; Schubert, M.

The study of multiphase flows in process engineering requires sufficiently fast observation tools. Studies of hydrodynamics in bubble columns, fluidized beds, or mixing drums for instance, would enormously profit form cross-sectional or even volume imaging with at least 1000 frames per second speed. Unfortunately, optical techniques, such as high speed cameras and PIV, which are widely used to study transparent single phase flows, fail in multiphase flows due to their opaqueness. In the past electrical imaging techniques, such as electrical impedance tomography and wire mesh sensors, were frequently used for multiphase flow studies. But these techniques have some severe drawbacks. Thus electrical tomography has a very low spatial resolution. Wire mesh sensors are intrusive and cannot be used for particulate systems. Recently our group has introduced ultrafast electron beam X-ray tomography for multiphase flow studies. We developed the ROFEX scanner which is able to visualise different types of multiphase flows, such as gas-liquid or gas-particle systems, with scan rates up to 7000 frames per second, one millimetre spatial resolution and for cross-sections up to 120 mm diameter. The scanner utilizes electron beam technology. An electron beam of up to 150 keV energy is produced by an electron gun, focussed onto a semicircular X-ray production target and swept rapidly across the target by means of an electromagnetic deflection system. This way X-rays are generated from a fast moving focal spot. A fast detector inside the scanner head records the X-ray projection data which is subsequently reconstructed to cross-sectional images of the density distribution of the object of interest.
In an overview presentation we will discuss the applicability of this new imaging technology to different multiphase processes which are to be found in chemical and mechanical process engineering. The repertory includes hydrodynamics in pipes, bubble columns, stirred tanks, powder mixing drums, monoliths, foams, fixed beds, fluidized beds, and corrugated sheets of destillation packings. The presentation will address measuring accuracy with respect to disperse and separated flows, limits of the methods and implications for process optimization and CFD code development.

Keywords: Electron beam tomography; X-ray tomography; flow measurement; two-phase flow

  • Lecture (Conference)
    10th Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering, 26.-30.06.2011, Braga, Portugal

Permalink: https://www.hzdr.de/publications/Publ-17599
Publ.-Id: 17599


General overview of the TOPFLOW-PTS experimental program

Péturaud, P.; Hampel, U.; Barbier, A.; Dreier, J.; Dubois, F.; Hervieu, E.; Martin, A.; Prasser, H.-M.

During a hypothetical loss-of-coolant accident, cold emergency core cooling water may be injected in a partially uncovered cold leg, and related two-phase CFD simulations are required to demonstrate the reactor pressure vessel integrity further to the resulting pressurized thermal shock. To complement the physical validation of the two-phase CFD codes in this configuration, a dedicated integral-type experimental program – TOPFLOW-PTS – has been setup; this paper (i) supports the validation data needs, (ii) presents the related experimental setup, and (iii) provides the general guidelines of the test matrix definition and test procedure.

Keywords: pressurized thermal shock; TOPFLOW

  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada
    Proceedings
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-17598
Publ.-Id: 17598


Investigating annular flows and the effect of functional spacers in an adiabatic double-subchannel model of a BWR fuel bundle by ultra-fast X-ray tomography

Zboray, R.; Guetg, M.; Kickhofel, J.; Barthel, F.; Sprewitz, U.; Hampel, U.; Prasser, H.-M.

Dryout of the coolant liquid film at the upper part of the fuel assemblies of a boiling water reactor (BWR), where annular flow prevails, represents a safety concern and an economical constraint. To be able to deal with this issue, annular flows must be well understood. Therefore we have investigated such flows in a double-subchannel model of a BWR fuel bundle using X-ray imaging at the Rossendorf Ultrafast Electron Beam X-ray Tomograph (ROFEX) facility. Adiabatic experiments slightly above atmospheric conditions using air-water annular flows have been carried out. In annular flows a significant portion of the liquid is present as droplets in the gas flowing in the middle of the conduit. Using functional spacer grids is the common method in nuclear technology to influence the annular flow such to enhance the deposition of droplets into the liquid film on the fuel pins thereby increasing dryout margins. The tests include, besides investigating the liquid film thickness in the plain channel, the investigation of the effect of a functional spacer on the liquid film. Using NaI as contrast agent in water enhances the image quality. The high time-resolution of the tomography enables to follow the wavy structure of the annular film flow. The paper aims at extracting quantitative information on the liquid film thickness distributions from the reconstructed tomographic images.

Keywords: boiling water reactor; dry-out; ultrafast X-ray tomography; fuel rods

  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-17597
Publ.-Id: 17597


Time-dependent Hamiltonians with 100% evolution speed efficiency

Uzdin, R.; Günther, U.; Rahav, S.; Moiseyev, N.

The evolution speed in projective Hilbert space is considered for Hermitian Hamiltonians and for non-Hermitian (NH) ones. Based on the Hilbert-Schmidt norm and the spectral norm of a Hamiltonian, resource-related upper bounds on the evolution speed are constructed. These bounds are valid also for NH Hamiltonians and they are illustrated for an optical NH Hamiltonian and for a non-Hermitian PT-symmetric matrix Hamiltonian. Furthermore, the concept of quantum speed efficiency is introduced as measure of the system resources directly spent on the motion in the projective Hilbert space. A recipe for the construction of time-dependent Hamiltonians which ensure 100% speed efficiency is given. Generally, these efficient Hamiltonians are NH, but there is a Hermitian efficient Hamiltonian as well. Finally, the extremal case of a non-Hermitian non-diagonalizable Hamiltonian with vanishing energy difference is shown to produce a 100% efficient evolution with minimal resources consumption.

Keywords: non-Hermitian Hamiltonian; projective Hilbert space; resource efficiency; PT-symmetric Hamiltonian; exceptional point; evolution speed; Hilbert-Schmidt norm; spectral norm

Permalink: https://www.hzdr.de/publications/Publ-17596
Publ.-Id: 17596


Hydrodynamik und Transportprozesse in Strukturapparaten

Schubert, M.; Hampel, U.

Durch den Einsatz neuer bildgebender Messverfahren werden strukturierter Mehrphasenreaktoren hydrodynamisch charakterisiert und Strömungsdaten aus sonst optisch unzugänglichen Strukturen, wie keramischen Monolithen und Schäumen sowie metallischen zellularen Packungen vor allem unter prozessnahen Betriebsbedingungen gewonnen.

  • Lecture (others)
    Dresden-internes Auftakttreffen HGF-Energie-Allianz, 13.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17595
Publ.-Id: 17595


Energieeffiziente Chemische Mehrphasenprozesse (Vorstellung der Helmholtz‐Energie‐Allianz)

Schubert, M.; Hampel, U.

Visionäres Ziel der Forschung ist es, neue Reaktorkonzepte für energie- und ressourceneffiziente chemische Prozesse auf Basis prozess- und reaktionsangepasster strukturierter Mehrphasenapparate zu entwickeln. Im Rahmen der HGF-Energie-Allianz werden dazu umfassende Grundlagenarbeiten im Bereich der Reaktionsaufklärung, zur Herstellung neuer funktionalisierter Strukturelemente, auf den Gebieten Mehrphasenströmungsmechanik und Mehrphasenthermodynamik, sowie in der numerischen Simulation und der Prozessmesstechnik durchgeführt.

  • Lecture (others)
    Dresden-internes Auftakttreffen HGF-Energie-Allianz, 13.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17594
Publ.-Id: 17594


Propagation of Spectral Functions and Dilepton Production at SIS Energies

Wolf, G.; Kämpfer, B.; Zetenyi, M.

The time evolution of vector meson spectral functions is studied within a BUU-type transport model. Applications focus on ρ and ω mesons being important pieces for the interpretation of the dielectron invariant mass spectrum. Since the evolution of the spectral functions is driven by the local density, the inmedium modifications turn out to compete, in this approach, with the known vacuum contributions.

Permalink: https://www.hzdr.de/publications/Publ-17592
Publ.-Id: 17592


Spectroscopic Studies of Complexation Behaviour of Uranium(VI) by Schiff Bases

Lindner, K.; Günther, A.; Bernhard, G.

Uranium can be released into the natural environment especially from mining areas by weathering, erosion and anthropogenic activities as well as by nuclear incidents and thus represents a hazard potential for humans. New supramolecular complexing agents with N, O, S donor function are developed for the use in nuclear field and environmental protection to separate the metals of the d- and f-block and thus to clean contaminated areas. An essential basic component of these new organic ligands are Schiff bases.
In this study the complexation of uranium(VI) with Schiff bases N-benzylideneaniline (NBA), 2-(2-hydroxybenzylidenamino)phenol (HBAP) and alpha-(4-hydroxyphenylimino)-p-cresol (HPIC) was investigated in alcoholic solution using the UV-vis spectroscopy and time-resolved laser fluorescence spectroscopy with ultrashort laser pulses (fs-TRLFS). Through the change of the absorption or emission properties of organic ligands can be observed the complexation with uranium(VI).
The complexation of uranium(VI) with NBA was observed by a hypsochromic shift in the NBA band to 237 nm with the UV-vis spectroscopy. Investigations with the ligand HBAP show a bathochromic shift to 281 nm. The UV-vis absorption spectra of HPIC with uranium(VI) show no spectral shift, but a decrease in intensity of the double band at 283nm and 332 nm in comparison to the free ligand. All three ligands form complexes MLx with more ligand molecules (x=2,3).
The fs-TRLFS as a sensitive speciation technique was used to determine the luminescence properties of formed complexes in the uranium(VI)-NBA, uranium(VI)-HBAP and uranium(VI)-HPIC systems. The emission signals had a hypsochromic, bathochromic and hypsochromic shift in comparison to the emission maxima of the uncomplexed ligand. This fs-TRLFS investigation opens up the possibilities for the determination of very short-lived complex species via the fluorescence of the organic compounds by delocalized -electron systems. The calculation of corresponding complex formation constants is shown and discussed.

Keywords: Uranium(VI); Schiff Bases; fs-TRLFS; UV-vis

  • Open Access Logo Contribution to proceedings
    EuCheMS International Conference on Nuclear and Radiochchemistry (NRC-8), 16.-21.09.2012, Como, Italien
  • Poster
    EuCheMS International Conference on Nuclear and Radiochchemistry (NRC-8), 16.-21.09.2012, Como, Italien

Permalink: https://www.hzdr.de/publications/Publ-17591
Publ.-Id: 17591


Release of helium from vacancy defects in yttria-stabilized zirconia under irradiation

Ou, X.; Kögler, R.; Zhou, H.; Anwand, W.; Grenzer, J.; Hübner, R.; Voelskow, M.; Butterling, M.; Zhou, S.; Skorupa, W.

Fission gas retention or release has a critical impact on the function of advanced nuclear materials. Helium trapping in, and release from, radiation defects induced by neutrons and by α decay in YSZ (yttria-stabilized zirconia) is experimentally simulated using synchronized Zr+ and He+ dual ion beam irradiation. The measured damage profiles consist of two peaks which agree well with the calculated profiles of implantation induced excess point defects. This special implantation related effect has to be carefully considered in the evaluation of experimental investigations which simulate isotropic irradiation effects such as α decay. First-principles calculations show that helium is energetically favorable to be trapped by Zr vacancies in YSZ. Implanted helium alone in YSZ is accumulated in undesirable helium bubbles and results in local surface swelling and lift-off. However, under dual beam irradiation helium is released from vacancy defects and is out-diffused at room temperature. Helium is mobilized by a vacancy-assisted trapping/detrapping mechanism induced by the simultaneous Zr+ ion implantation. This behavior avoids the deleterious helium bubble formation and contributes to the suitable application characteristics of YSZ which result in its excellent radiation hardness.

Keywords: yttria-stabilized zirconia; dual beam irradiation; He release; “½Rp” effect

Permalink: https://www.hzdr.de/publications/Publ-17590
Publ.-Id: 17590


Nonlinear PT−symmetric plaquettes

Li, K.; Kevrekidis, P.; Malomed, B.; Günther, U.

Four basic two-dimensional (2D) plaquette configurations are introduced with onsite cubic nonlinearities, which may be used as building blocks for 2D PT-symmetric lattices. For each configuration, a dynamical model is developed and its PT symmetry is examined. The corresponding nonlinear modes are analyzed starting from the Hamiltonian limit, with zero value of the gain-loss coefficient. Once the relevant waveforms have been identified (chiefly, in an analytical form), their stability is examined by means of linearization in the vicinity of stationary points. This reveals diverse and, occasionally, fairly complex bifurcations. The evolution of unstable modes is explored by means of direct simulations. In particular, stable localized modes are found in these systems, although the majority of identified solutions is unstable.

Keywords: PT quantum mechanics; PT oligomers; 2D plaquettes; 2D PT-symmetric lattices; nonlinear dynamics; bifurcations; stationary solutions; stability analysis; exceptional points

Permalink: https://www.hzdr.de/publications/Publ-17589
Publ.-Id: 17589


Call for papers: Special issue on quantum physics with non-Hermitian operators

Bender, C.; Fring, A.; Günther, U.; Jones, H.; (Editors)

This is a call for contributions to a special issue of Journal of Physics A: Mathematical and Theoretical dedicated to quantum physics with non-Hermitian operators. The main motivation behind this special issue is to gather together recent results, developments and open problems in this rapidly evolving field of research in a single comprehensive volume. We expect that such a special issue will become a valuable reference for the broad scientific community working in mathematical and theoretical physics. The issue will be open to all contributions containing new results on non-Hermitian theories which are explicitly PTsymmetric and/or pseudo-Hermitian or quasi-Hermitian. The main novelties in the past years in this area have been many experimental observations, realizations, and applications of PT symmetric Hamiltonians in optics and microwave cavities. We especially invite contributions on the theoretical interpretations of these recent PT-symmetric experiments and on theoretical proposals for new experiments.

Keywords: PT symmetry; PT quantum mechanics; pseudo-Hermitian operators

Permalink: https://www.hzdr.de/publications/Publ-17588
Publ.-Id: 17588


Bypassing the bandwidth theorem with PT symmetry

Ramezani, H.; Schindler, J.; Ellis, F.; Günther, U.; Kottos, T.

The beat time associated with the energy transfer between two coupled oscillators is dictated by the bandwidth theorem which sets a lower bound. We show, both experimentally and theoretically, that two coupled active LRC electrical oscillators with parity-time (PT) symmetry bypass the lower bound imposed by the bandwidth theorem, reducing the beat time to zero while retaining a real valued spectrum and fixed eigenfrequency difference. Our results foster design strategies which lead to (stable) pseudo-unitary wave evolution, and may allow for ultrafast computation, telecommunication, and signal processing.

Keywords: PT symmetry; PT quantum mechanics; LRC circuits; bandwidth theorem; PT-brachistochrone; tachistochrone; evolution time contraction; evolution time dilation; beat time reduction

Permalink: https://www.hzdr.de/publications/Publ-17587
Publ.-Id: 17587


Two PT symmetry topics

Günther, U.

New results are reported on two PT-symmetry topics. In the first part of the talk, an entanglement related quantum state discrimination scheme is described which is based on the fine-tuned Naimark-dilation of a PT-symmetric subsystem in 2D Hilbert space. (Work together with Carl M. Bender, Dorje C. Brody and Boris F. Samsonov). In the second part of the talk, the stability properties of nonlinear PT-symmetric 2D
plaquettes are discussed. Specific emphasis is laid on the role of the nonlinear terms in shifting the PT-threshold of associated linear systems. This part of the talk is based on common work with Panayotis Kevrekidis, Kai Li and Boris Malomed (arXiv:1204.5530[quant-ph]) as well as on newer results going beyond the findings in this e-print.

Keywords: PT quantum mechanics; quantum state discrimination; Naimark dilation; POVM; Helstrom bound; PT oligomers; 2D plaquettes; 2D PT-symmetric lattices; nonlinear dynamics; bifurcations; stationary solutions; stability analysis; exceptional points

  • Lecture (Conference)
    PHHQP XI: Non-Hermitian Operators in Quantum Physics, 27.-31.08.2012, Paris, France

Permalink: https://www.hzdr.de/publications/Publ-17586
Publ.-Id: 17586


Nonlinear PT−symmetric plaquettes

Günther, U.; Li, K.; Kevrekidis, P.; Malomed, B.

Four basic two-dimensional (2D) plaquette configurations are introduced with onsite cubic nonlinearities, which may be used as building blocks for 2D PT-symmetric lattices. For each configuration, a dynamical model is developed and its PT symmetry is examined. The corresponding nonlinear modes are analyzed starting from the Hamiltonian limit, with zero value of the gain-loss coefficient. Once the relevant waveforms have been identified (chiefly, in an analytical form), their stability is examined by means of linearization in the vicinity of stationary points. This reveals diverse and, occasionally, fairly complex bifurcations. The evolution of unstable modes is explored by means of direct simulations. In particular, stable localized modes are found in these systems, although the majority of identified solutions is unstable. Based on arXiv:1204.5530.

Keywords: PT quantum mechanics; PT oligomers; 2D plaquettes; 2D PT-symmetric lattices; nonlinear dynamics; bifurcations; stationary solutions; stability analysis; exceptional points

  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics X, 04.-07.06.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17585
Publ.-Id: 17585


2 topics in PTQM: I. Tachistochrones in PT−symmetric LRC circuits; II. PT−symmetric Jaynes-Cummings models via gauged Hamiltonians

Günther, U.

The presentation consists of two parts. In the first part, recent results on PT-symmetric LRC circuits are reported, including the hidden special representations of the linear parity involution P and the antilinear time reversal operation T. Analytical formulae for the evolution time contraction (so called tachistochrone solutions) and dilation are presented. The simple underlying phase-shift-versus-amplitude-enhancement mechanism is explained. (Partially based on common work with Hamid Ramezani, Joseph Schindler, Fred Ellis, and Tsampikos Kottos published in Phys. Rev. A 85, (2012), 062122.)

In the second part of the talk, it is shown that the mathematical investigation of the symmetry structures hidden in gauged PT-symmetric systems indicates on possible realizations of such setups as Jaynes-Cummings type models. The latter ones are used e.g. to describe multilevel artificial atoms in cavity QED. A question that naturally arises is whether PT-symmetric extensions of cavity QED might become feasible experimentally and how to possibly realize them. (Partially based on common work with Sergii Kuzhel published in J. Phys. A 43, (2010), 392002.)

Keywords: PT quantum mechanics; PT brachistochrone; tachistochrone; ultra-fast evolution; time contraction; time dilation; LRC circuit; Jaynes-Cummings model; cavity QED; multilevel artificial atoms; gauged PT-symmetry; Lie triple systems; Cartan decomposition of Lie algebras

  • Invited lecture (Conferences)
    Non-Hermitian degeneracies: new directions of research and applications., 21.-24.04.2012, Haifa, Israel

Permalink: https://www.hzdr.de/publications/Publ-17584
Publ.-Id: 17584


Krein spaces and PT Quantum Mechanics

Günther, U.

In 1998, 1999 it was shown by Bender and collaborators that there are certain classes of Hamiltonians which at a first glance seem not selfadjoint in Hilbert spaces, but which nevertheless are having real spectra. Examples are Hamiltonians of the type H=p2+x2(ix)μ. For parameters μ ∈ [0,1] these Hamiltonians have positive real eigenvalues with square integrable eigenfunctions defined over the real line. It was found that the reality of the eigenvalues was connected with an underlying PT-symmetry of the Hamiltonians and their eigenfunctions, i.e. the systems are in a sector of unbroken PT-symmetry. There exist other sectors like μ ∈ (-1,0) where this PT-symmetry is spontaneously broken: although the Hamiltonian remains PT-symmetric, part of its eigenfunctions loose PT-symmetry and the corresponding eigenvalues are coming in complex conjugate pairs. A PT phase transition occurs at μ=-0.
It turns out that the PT-symmetry of the Hamiltonian H induces a natural indefinite metric structure in Hilbert space and that H, instead of being selfadjoint in a usual Hilbert space (with positive definite metric), is selfadjoint in a generalized Hilbert space with an indefinite metric --- a so called Krein space. Similar to time-like, space-like and light-like vectors in Minkowski space a Krein space has elements of positive and negative type as well as neutral (isotropic) elements. Moreover in analogy to passing via Wick-rotation from Minkowski space to Euclidian space, in the sector of exact PT-symmetry there exists an operator which allows to pass from a Krein space description of the system to a description in a Hilbert space with a highly nontrivial metric operator. At the PT phase transition point this operator becomes singular and the corresponding mapping breaks down.
In the talk, on an introductory level, some of the basic structures of PT-symmetric quantum mechanics and their relation to corresponding Krein-space setups are sketched. For gaining some rough intuition, the facts are illustrated by simple matrix models. The richness of the systems is demonstrated on the simple example of a PT-symmetric two-mode Bose-Hubbard model, PT-symmetric brachistochrone setups and gain-loss-balanced PT-symmetric optical waveguide systems.

Keywords: PT quantum mechanics; PT-symmetry; non-Hermitian operators; Krein space; indefinite metric; phase transition; quantum brachistochrone; Bose-Hubbard model; PT-symmetric optical waveguides; gain-loss balanced systems

  • Lecture (others)
    Extended special seminar of the Nonlinear Dynamics & Complex Scattering group, 16.11.2011, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-17583
Publ.-Id: 17583


PT brachistochrone and state discrimination

Günther, U.

In recent work by Bender, Brody, Caldeira and Meister it was shown that the brachistochrone solution of PT Quantum Mechanics (PTQM) can be used to orthogonalize a set of two originally non-orthogonal quantum states. The still remaining draw-back of the proposed technique is in its use of a non-Hermitian PT-symmetric Hamiltonian to achieve the PTQM brachistochrone evolution --- a Hamiltonian which up to now for quantum systems is beyond experimental reach.

We demonstrate that the Bender-Brody-Caldeira-Meister approach can be naturally extended into a higher-dimensional Hilbert space. This allows to interpret the PTQM setup as a very special subsystem of a larger Hermitian system. Moreover we show that this extension can be connected with the standard text-book scheme of unambiguous quantum state discrimination. Technical details of the extension procedure are discussed and ways toward a time-optimal unambiguous state discrimination scheme are indicated.

Keywords: PT quantum mechanics; unambiguous state discrimination; time-optimal state discrimination; PT brachistochrone; extension scheme

  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics IX, 12.-15.12.2011, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17582
Publ.-Id: 17582


In situ identification of the U(VI) surface speciation on iron oxide phases by ATR FT-IR spectroscopy

Foerstendorf, H.; Heim, K.; Jordan, N.

The identification of the molecular interactions occurring at solid-liquid interfaces is of great signifi-cance to the assessment of the migration behavior of heavy metal ions in the environment. In particu-lar, the dissemination of radioactive metals, such as uranium (U), in soils and aquifers is determined by sorption and desorption processes at mineral surfaces.
Information of the molecular structures of the sorption complexes can be obtained by vibrational spec-troscopy. The application of the Attenuated Total Reflection (ATR) technique in combination with a flow cell experiment potentially provides insights into the dynamic processes occurring during com-plex formation at the solid-liquid interface [1]. This technique allows an on line monitoring of the sorption processes with a time resolution in the sub minute range and under selective conditions ap-proaching near environmental relevant conditions [2,3]. In particular, the variation of selective ex-perimental parameter, e.g. pH, c(UO22+) or pCO2, and the selection of modified solid phases are ex-pected to generate selective spectral changes which potentially facilitate the identification of molecular features.
In this work, we provide vibrational spectroscopic data from binary and ternary U(VI) surface species on iron oxide mineral phases in the absence and presence of atmospherically derived CO2¸ respec-tively. In a comparative study of two iron oxide phases, namely ferrihydrite and maghemite, the dif-ferent character of sorption complexes can be spectroscopically identified. From the frequency of the ν3(UO2) mode, the formation of different types of surface species, that is inner- and outer-sphere com-plexes, can be derived. This is corroborated by time-resolved spectra of the sorption step and of the subsequently induced desorption process. From the time courses of these reactions, a first assignment to the different types of surface species predominantly formed at the different mineral surfaces can be given.
Results from the ternary sorption systems (U(VI)/atm. CO2/iron oxide phase) demonstrate signifi-cantly different affinities of the carbonate ions to the different mineral phases. While atm. CO2 forms binary and ternary sorption species on ferrihydrite in the absence and presence of U(VI), respectively, only ternary uranyl carbonato species were observed at the maghemite-water interface.

[1] Voegelin, A. et al. (2003) Environ. Sci. Technol. 37, 972-978.
[2] Müller, K. et al. (2012) Geochim. Cosmochim. Acta 76, 191-205.
[3] Foerstendorf, H. et al. (2012) Journal of Colloid and Interface Science 377, 299-306.

  • Lecture (Conference)
    International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 05.-07.11.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17581
Publ.-Id: 17581


Scanning near-field infrared nano-spectroscopy on buried InAs quantum dots

Jacob, R.; Fehrenbacher, M.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Helm, M.; von Ribbeck, H.-G.; Eng, L. M.; Atkinson, P.; Schmidt, A. R. O. G.

Since providing optical resolution on the nanometer length scale, scanning near-field optical microscopy (SNOM) has turned out to be a powerful technique to investigate the optical properties of perovskites and nanostructured semiconductors, e.g. having a buried doping profile. Using a scattering-type-SNOM (s-SNOM) combined with a tunable free-electron laser (FEL) light source operating in the mid- and far-infrared regime we investigated the electronic structure of single InAs quantum dots (Q-dots) that were capped with a 70 nm thick GaAs layer. Spectroscopic near-field scans on individual Q-dots clearly identified two inter-sublevel transitions at 85 meV and 120 meV, providing optical contrast to the surrounding GaAs substrate. As a consequence the room temperature linewidth of these transitions measure 5 - 8 meV only, hence being significantly smaller as compared to the inhomogeneously broadened peaks resulting from integral spectroscopic analysis. Moreover, spatially scanning the s-SNOM tip at fixed excitation energies allowed mapping the spatial distribution of such buried quantum dots.

Keywords: Spectroscopy on single quantum dots; self-assembled quantum dots; near-field microscopy; intersublevel transitions

  • Poster
    WE-Heraeus-Seminar on Free-Electron Lasers: from Fundamentals to Applications, 10.-13.04.2012, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17580
Publ.-Id: 17580


Scanning near-field infrared micro-spectroscopy on buried InAs quantum dots

Jacob, R.; Fehrenbacher, M.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Helm, M.; von Ribbeck, H.-G.; Eng, L. M.; Atkinson, P.; Rastelli, A.; Schmidt, O. G.

Providing an optical resolution on the nanometer length scale, scanning near-field optical microscopy (SNOM) turned out to be a capable technique to investigate the optical properties of perovskites, buried semiconductors and single quantum dots. Thereby, the line-width of the observed resonances (5 - 8 meV) is significantly smaller than the inhomogeneously broadened line-width of other spectroscopic measurements.
Using a scattering-type-SNOM (s-SNOM) combined with a tunable free-electron laser (FEL) light source we investigated the electronic structure of single InAs quantum dots, capped under a 70 nm thick GaAs layer. Spectroscopic near-field scans clearly identified two inter-sublevel transitions within the quantum dots at 85 meV and 120 meV, contrasting from the surrounding medium. Moreover, spatially scanning the s-SNOM tip at fixed excitation energies allowed mapping the 3D distribution of such buried quantum dots.

Keywords: Spectroscopy on single quantum dots; self-assembled quantum dots; near-field microscopy; intersublevel transitions

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17579
Publ.-Id: 17579


Hochskalierende Partikelsimulationen auf GPGPU-Clustern

Burau, H.; Bussmann, M.; Hübl, A.; Juckeland, G.; Schmitt, F.; Widera, R.

PIConGPU ist ein Particle-in-Cell (PIC) Code fur Grakprozessoren (GPUs). Der Particle-in-Cell Algorithmus ist ein zentraler Algorithmus in der Plasmaphysik. Er erlaubt die Dynamik eines Plasmas, die Bewegung der Elektronen und Ionen, auf Basis der Maxwell-Gleichungen voll relativistisch zu beschreiben.
Das PIConGPU Projekt integriert die 3D-Physiksimulation, eine Online-Visualisierung zur interaktiven Auswertung sowie eine einfache Parametrisierung der Simulationsläufe. Die Umsetzung erfolgte so generisch, dass PIConGPU auch als Grundlage fur weitere GPU-Simulationen dienen kann. Um komplexe physikalische Probleme simulieren zu können ist die Skalierbarkeit auf massiv-parallele GPU-Cluster ausgelegt.

Keywords: particle-in-cell; PIConGPU; CUDA; GPGPU; HPC; laser-plasma; numerics

  • Poster
    OUTPUT.DD 2012, 10.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17578
Publ.-Id: 17578


Physics verification tests on a 3 dimensional GPU-driven PIC-code (PIConGPU 3D)

Hübl, A.; Steiniger, K.; Pausch, R.; Widera, R.; Debus, A.; Burau, H.; Köhler, A.; Irman, A.; Bussmann, M.

We present the validation of the key physics features of PIConGPU according to known physical scenarios. For this, we evaluate the evolution of position and energy errors for analytically known particle trajectories and the numerical dispersion of a Gaussian wavepacket over time.
Furthermore, we present a new approximation within the particle push step.
This allows for a comparison of the established CPU/FORTRAN code ILLUMINATION with the GPU/C++ code PIConGPU for selected physical test cases in laser-electron acceleration.

Keywords: particle-in-cell; PIConGPU; CUDA; GPGPU; laser-electron acceleration; laser-plasma interaction; underdense plasma; numerics; HPC; cluster

  • Poster
    International Workshop on Laser-Plasma Interaction at Ultra-High Intensity 2nd Dresden Exchange on Laser-Plasma Interaction Theory ENLITE, 16.-20.04.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17577
Publ.-Id: 17577


Comparison of a new simple system for high depth resolution RBS with the magnetic spectrometer

Munnik, F.; Hanf, D.; Wilhelm, R. A.; von Borany, J.; Lange, H.

With decreasing layer thicknesses e.g. in semi-conductor devices, there is a strong need for increasing depth resolution in analytical methods used for the determination of elemental depth profiles. Standard RBS using Si detectors has a depth resolution of about 5 – 15 nm mainly depending on incidence angle and energy resolution. The traditional and high-tech solution is to use a magnetic spectrometer or a time-of-flight system to improve the energy resolution of the detector and thus the depth resolution.
At HZDR, a Browne-Buechner type magnetic spectrometer is available for high depth resolution measu¬rements with sub-nm depth resolution in a near-surface region  5 nm. However, such a system is expensive and requires complicated operation. In addi¬tion, the small energy window of the magnetic spectrometer limits the measurement to one element and about 10 nm depth range. Currently we are implementing a low-tech detection system that uses improvements in amplifiers and cooling to improve the energy resolution of standard semiconductor detectors to sub-10 keV values. The capabilities of such a system are described and compared to the magnetic spectrometer.

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 10.-11.07.2012, Augsburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17576
Publ.-Id: 17576


Nanostructures created in SiO2 surface: A comparison between the impingement by slow highly charged ions and by swift heavy ions

El-Said, A. S.

Swift heavy ions (SHI) of MeV–GeV energy lead to the creation of nanometric surface structures as well as modifications in the bulk along the ion penetration depth. Recently, similar surface modifications have been observed for the impact of individual slow highly charged ions (HCI). Non-amorphizable ionic-halide single crystals, like KBr, CaF2 and BaF2, are considered as the most intensively studied materials after irradiation with HCI.
In this contribution we study the creation of surface nanostructures in an amorphizable material, namely SiO2 quartz after irradiation with slow highly charged Xe ions from the Electron Beam Ion Trap at Helmholtz Zentrum Dresden-Rossendorf and swift xenon ions from Universal Linear Accelerator at GSI in Darmstadt. After irradiation at room temperature, the crystals were investigated by scanning force microscopy. For both SHI and HCI, the created nanostructures exhibit the shape of hillocks. Moreover UV–VIS spectroscopy was performed to identify the defects created by ion irradiation at high fluence. The results are discussed in terms of the creation mechanisms driven by the dependence on both potential and kinetic energies of the ions.

Keywords: SiO2; Surface nanostructures; Highly charged ions; Swift heavy ions

Permalink: https://www.hzdr.de/publications/Publ-17575
Publ.-Id: 17575


Remarks on Scientific Poetry

Brauer, G.

Some personal remarks on scientific poetry in general are presented together with a little poetry collection, in particular about the positron and its fate.

Keywords: poetry; positron; positron annihilation; Higgs boson

  • Book chapter
    B.N. Ganguly, G. Brauer: Near Surface Depth Profiling by Mono-energetic Positrons, Switzerland: Trans Tech Publishers, 2012, 978-3-03785-524-9, 3-6
    DOI: 10.4028/www.scientific.net/DDF.331.3

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-17574
Publ.-Id: 17574


Status and new trends in FIB processing

Bischoff, L.

In the last decade focused ion beams (FIB) became an irrecoverable instrument in research and industry. Sample preparation, local ion implantation and ion analysis are the main application topics. Most of the systems are equipped with a gallium liquid metal ion source (LMIS). But, modern trends in nanotechnology require more extended properties like variable ion species, non-contaminating milling at higher rates or higher lateral resolution in the field of ion microscopy.
In this contribution the status and application of new source concepts including prototypes will be reviewed in particular high current gas sources (ECR, ICP) for effective high rate milling, ion trap sources providing highly charged ions or used for SIMS applications as well as gas field ion sources for high resolution ion microscopy in the sub-nm range. Furthermore the use of alloy liquid metal ion sources and its characterization for mass separated FIB systems and ToF-SIMS applications will be presented.
New trends and prospective developments in FIB instrumentation will be discussed.

Keywords: Focused Ion Beam; Liquid Metal (Alloy) Ion Source; FIB SIMS

  • Lecture (Conference)
    Workshop Ionenstrahlphysik 2012, 10.-11.07.2012, Augsburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17573
Publ.-Id: 17573


Messung von Geschwindigkeitsfeldern in Flüssigmetallen mit der Ultraschall-Doppler Methode

Eckert, S.; Gerbeth, G.

Der Mangel an kommerziell verfügbarer Messtechnik zum Einsatz in heißen, nichtransparenten Fluiden erschwert Strömungsmessungen in einer Reihe von technologischen Prozessen, in denen Flüssigmetalle oder Halbleiterschmelzen eine wichtige Rolle spielen. Ultraschall-methoden erscheinen für derartige Anwendungen äußerst attraktiv, da sie in der Lage sind, quantitative Messdaten aus opaken Schmelzen zu liefern. Dieser Artikel gibt einen Überblick über internationale Forschungsaktivitäten der letzten 3 Jahrzehnte, die auf eine Nutzung dieser Methode für Strömungsmessungen in Metallschmelzen abzielen.

Keywords: flow measurements; ultrasound Doppler method; liquid metals; magnetohydrodynamics

Permalink: https://www.hzdr.de/publications/Publ-17572
Publ.-Id: 17572


Inspired by nature: Novel biosensors based on an assembly of self-assembling S-layer proteins, aptamers and fluorescence dyes

Weinert, U.; Pollmann, K.; Strehlitz, B.; Raff, J.

The detection of pharmaceuticals in drinking water and food becomes of increasing relevance. Currently there are only few methods available allowing their reliable detection. These methods are mostly highly complicated and time consuming. Therefore, new techniques are required which enable a fast and easy detection of traces of pharmaceuticals. Biosensors based on natural self-organising biomolecules may provide new approaches for a highly specific detection of pharmaceuticals.

Aim of the presented project is the development of such a sensory layer. Our sensory device consists of S layer proteins, aptamers and fluorescence dyes. The S layer proteins serve as binding matrix, aptamers are used as receptors and fluorescence dyes represent our transducer system.
S layer proteins are structural proteins found in numerous bacteria and almost all archaea. They are able to self-assemble in aqueous solutions and on surfaces forming highly ordered crystalline structure with different symmetries. The proteins expose many COOH and NH2-groups that can be modified and functionalized. Aptamers are short DNA or RNA oligonucleotides which are able to reversibly bind specific analytes due to their 3D-structure. For the optical signal of our sensory layer we use two fluorescence dyes which are able to perform a fluorescence resonance energy transfer (FRET).
This effect is very sensitive and is affected by its environment. In our assembly, fluorescence dyes and aptamers are very close to each other. It is expected that a binding of an analyte to the aptamer will also affect FRET.

Our experiments prove a FRET between two fluorescence dyes linked to S layer proteins in solution and on a surface. In addition, the Anti-Thrombin-aptamer, used as model aptamer, was successfully coupled to S-layer proteins without losing its function. These results provide the basis for the intended sensor concept.

Keywords: FRET; S-layer proteins; sensory layer; aptamers

  • Poster
    bio-inspired Materials, 20.-23.03.2012, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17571
Publ.-Id: 17571


Selective liquid-liquid extraction of Sr-85 with modified calixarenes

Poetsch, M.; Mansel, A.; Schnorr, R.; Haupt, S.; Kersting, B.

Sr-90 is a long-lived radionuclide (T(1/2) = 28.6 a), produced as a by-product in nuclear power plants. Due to its chemically similarity to calcium, it follows the food chain from environment (e.g. aquatic systems and soil) to fauna and human in case of release in the biosphere. Strontium can be, as well as calcium, incorporated in bones. Stable isotopes of strontium might not be harmful, but radioactive strontium can lead to bone disorders and diseases, including leukaemia[1].
Calixarenes and their functionalised derivatives are research subjects in the development of extracting agents, transporters, stationary phases[2] or biosensors. We used modified calixarenes, including derivatives having carbonyl binding sites, for the extraction of strontium[3] by means of a liquid-liquid extraction in a chloroform / water system. As a simulated contamination solution with Sr-90, the aqueous strontium phase was traced using the short-lived radionuclide Sr-85 (T(1/2) = 64.9 d), which was produced and purified at the in-house 18 MeV-cyclotron[4].
Under alkaline conditions, strontium extraction yields of >(90±4)% were obtained. Furthermore, the impact of inorganic and organic impurities, competing ions like sodium, calcium, acetate or tartaric acid, to the extraction performance was studied. The used carboxy-modified calixarenes are highly potent and selective extracting agents towards strontium, under conditions near to nature (e.g. synthetic groundwater).

The authors gratefully thank the German Federal Ministry of Education and Research (BMBF) for financial support of this study (project no. 02NUK014).

[1] Wallova, G., N. Kandler, and G. Wallner, Monitoring of radionuclides in soil and bone samples from Austria. Journal of Environmental Radioactivity, 2012. 107(0): p. 44-50.
[2] Wendel, V., Neuartige Wirt-Gast-Komplexe basierend auf Cycloheptatrienbausteinen, Mathematisch-Naturwissenschaftliche Fakultät I 1998, Humboldt-Universität zu Berlin: Berlin.
[3] Casnati, A., et al., New Efficient Calixarene Amide Ionophores for the Selective Removal of Strontium Ion from Nuclear Waste: Synthesis, Complexation, and Extraction Properties. J. Am. Chem. Soc., 2001. 123: p. 12182-12190.
[4] Mansel, A., et al., Production of Sr-85 at a 18 MeV-cyclotron and purification for geochemical investigations, 2012. (submitted)

Keywords: calixarene; radio strontium; liquid-liquid extraction

  • Poster
    EuCheMS International Conference on Nuclear and Radiochemistry (NRC-8), 16.-21.09.2012, Como, Italia

Permalink: https://www.hzdr.de/publications/Publ-17570
Publ.-Id: 17570


Developing sensory layers as combination of S-layer proteins, aptamers and fluorescence dyes

Weinert, U.; Strehlitz, B.; Pollmann, K.; Raff, J.

In recent years detection of pharmaceuticals in drinking water and food becomes increasing relevance. Nevertheless, most recently used methods are complex and time consuming. Thus, new solutions are required allowing a fast and their reliable detection of pharmaceuticals.

Therefore we are developing sensory layers which are able to specifically detect small amounts of pharmaceuticals. This sensory device will consist of surface(S)-layer proteins, aptamers and fluorescence dyes.
S-layer proteins are structural proteins found in numerous bacteria and archaea. They have the ability to self assembly in aqueous solutions and on surfaces building highly ordered paracrystalline structures. On the surface of such a layer different functional groups are available which can be modified without the loss of its paracrystalline structure. Hence S-layer proteins are useful binding blocks for the defined arrangement of aptamers and fluorescence on an area of a few nanometers. Thereby aptamers serve as receptor for specific analytes and two fluorescence dyes allowing a FRET a signal transducer system.

In first experiments we coupled the model aptamer, Anti-thrombin-aptamer, on S-layer proteins and proved its functionality after being linked to the protein. Furthermore we modified S-layer proteins with a FRET pair containing a green and red fluorescence dye and succeed to detect a FRET between those S-layer linked fluorescence dyes.

In subsequent work we will assemble the components, aptamers and fluorescence dyes, on the S layer proteins. The aptamer will bind the specific analyte. It is supposed that the binding will affect the fluorescence dyes and disturb FRET due to their close proximity to each other. As a result a sensory layer is created which uses the high specifity of aptamers in combination with the sensitivity of fluorescence dyes, thus enabling the easy and reliable detection of analytes by an optical signal.

Keywords: S-layer proteins; FRET; aptamers; sensory layer

  • Poster
    Nanofair 2012, 12.-13.06.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17569
Publ.-Id: 17569


Ion-beam mixing in crystalline and amorphous germanium isotope multilayers

Radek, M.; Bracht, H.; Posselt, M.; Schmidt, B.

Self-atom mixing induced by Gallium (Ga) implantation in crystalline and amorphous germanium (Ge) is investigated using an isotopic multilayer structure of alternating 73Ge and natGe layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and ion-beam induced depth-dependent mixing was determined by means of the secondary ion mass spectroscopy (SIMS). The position and form of the implanted Ga peak is very similar in the amorphous and crystalline Ge and can be reproduced accurately by computer simulations based on binary collision approximation (BCA), whereas the ion-beam induced self-atom mixing strongly depends on the state of the Ge structure. The data from SIMS-measurements reveal a stronger mixing in the crystalline than in the amorphous Ge. Atomistic simulation based on BCA can reproduce the experimental data only if unphysically low displacement energies are assumed. The low displacement energies deduced within the BCA approach are confirmed by experiments with mixing induced by silicon implantation. The disparity observed in the ion-beam mixing efficiency of crystalline and amophous Ge indicates different dominant mixing mechanisms. We propose that self-atom mixing in crystalline Ge is mainly controlled by radiation enhanced diffusion during the early stage of mixing before the crystalline structure turns into an amorpous state, whereas in an already amoprhous state self-atom mixing is mediated by cooperative diffusion events.

Keywords: ion-beam mixing; Si; Ge; isotope multilayers

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 25.-30.03.2012, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17568
Publ.-Id: 17568


Ion-beam mixing in crystalline and amorphous Si und Ge

Radek, M.; Bracht, H.; Posselt, M.; Schmidt, B.; Bougeard, D.; Haller, E. E.; Itoh, K.

Molecular dynamics simulations using Stillinger-Weber-type interatomic potentials were performed in order to investigate ion-beam mixing by 400 eV self-ion implantation at different fluences and temperatures. In general the magnitude of mixing in an amorphous structure was found to be higher than in its crystalline counterpart. This supports the results of earlier calculations (K. Nordlund et al., J. Appl. Phys. 83 (1998) 1238). The trends observed in our simulations are compared to our experimental results on ion beam mixing in crystalline and amorphous isotopically modulated Si and Ge multilayer structures.

Keywords: ion-beam mixing; Si; Ge; molecular dynamics

  • Poster
    11th International Conference on Computer Simulation of Radiation Effects in Solids, 24.-29.06.2012, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-17567
Publ.-Id: 17567


Experimental investigations of slurry bubble column using ultra-fast electron beam x-ray tomography

Rabha, S.; Schubert, M.; Wagner, M.; Lucas, D.; Hampel, U.

The hydrodynamic flow behaviour of the gas phase in a slurry bubble column was investigated using ultra-fast electron beam X-ray tomography, which provides images at temporal resolution of 7000fps and spatial resolution of 1 mm. Bubble coalesces and breakup regime was observed with the addition of wettable solids particles. The effect of solid volumetric concentration (0 ≤ Cs ≤ 0.36) on the radial distribution of gas holdup in a slurry bubble column was established at different scanning heights (30, 60, 95 cm) and at different superficial gas velocity (0.02 ≤ UG ≤ 0.05 m/s).

Keywords: Slurry bubble column; gas hold-up; solid concentration; X-ray tomography

  • Invited lecture (Conferences)
    International Symposium on Chemical Reaction Engineering, 02.-05.09.2012, Masstricht, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-17566
Publ.-Id: 17566


Configurational contributions to the free energy of embedded nanoclusters

Posselt, M.; Al-Motasem, A. T.

Nanostructure evolution is a common phenomenon occurring during ion and neutron irradiation as well as during thermal treatment. It is characterized by diffusion and reaction processes that can cause the formation of embedded nanoclusters which often leads to a modification of the materials properties. Multiscale modeling can substantially contribute to a better understanding of nanostructure evolution. Atomic-scale molecular dynamics and kinetic Monte Carlo simulations are applicable on relatively small length and time scales whereas coarse-grained methods such as object kinetic Monte Carlo simulations and rate theory can be used on scales more easily accessible by experiments. The latter methods need a number of input parameters. One of the most important is the free binding energy of a monomer to a cluster which can be hardly obtained by experimental investigations but can be provided by atomistic simulations. The fundamental quantity that must be determined is the free formation energy of the clusters which consists not only of the formation energy but also of vibrational and configurational contributions. The focus of the present work is on the evaluation of the configurational part of the free formation energy. The simple example of coherent Cu nanoclusters in bcc-Fe is considered. First, at T=0 the most stable cluster configurations are determined by Metropolis Monte Carlo simulations and their formation and binding energies are calculated. Second, a modified Wang-Landau Monte Carlo method is employed in order to determine the contribution of all possible geometrical configurations of nanoclusters to the free formation energy. Finally, the total and monomer free binding energies are calculated. It is shown that even at moderate temperatures such as 600 K the configurational contributions to the free formation energy cannot be neglected. The calculation scheme applied in this work can be extended to other types of embedded nanoclusters in solids. The presented method should be especially important for nanoclusters with relatively low formation energies. Further investigations are required in order to estimate the vibrational contribution to the free formation energy and to perform a comparison with the configurational part.

Keywords: nanoclusters; free energy; configurational contributions

  • Poster
    11th International Conference on Computer Simulation of Radiation Effects in Solids, 24.-29.06.2012, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-17565
Publ.-Id: 17565


Chemical Processes of Galvanized Steel Corrosion in the Post-LOCA Phase of a PWR and the Prevention of Sump Screen Clogging

Hoffmann, W.; Kryk, H.

The Emergency Core Coolant System has to remove the decay heat in case of a Loss of Coolant Accident (LOCA). Sump strainers are mounted at the pump inlets to retain particles and fibrous insulation material during recirculation. However, fiber fragments, debris or corrosion products could initiate a critical head loss on strainers. Problems of insulation materials NUKON® (fiberglas) or CalSil and aluminum may appear if containment spray systems using alkaline additives are installed. In such cases, dissolution / precipitation reactions resulting from insulation materials were observed, which increase the risk of sump screen blockage. In German NPPs, there are no containments spray systems, and insulation consists of more resistant materials like mineral wool (rock wool) and stainless steel. However, large scale experiments from AREVA have shown that sump screen clogging may be initiated by boric acid containing leakage jets directed towards galvanized containment internals.
The down-scaled test facility KorrVA was designed for generic corrosion investigations of galvanized steel under post-LOCA conditions. About 90 experiments were carried out with galvanized steel gratings and galvanized steel coupons in boric acid media in order to determine corrosion mechanisms depending on different experimental conditions like temperature, water chemistry and hydrodynamic conditions (flow impact, simulated by different nozzles). Changes of the chemical composition of the circulating media were determined by chemical analysis and general parameters such as conductivity and pH were measured. Galvanized samples and fiber beds were examined after each experiment by means of photographic methods, light-microscopy and different kinds of chemical analysis.
The chemical analyses of the deposits on fiber beds showed that the clogging is predominantly caused by the corrosion products of iron and lower amounts of zinc compounds. Thus, the corrosion of galvanized steel in boric acid is explained by a mechanism starting at the surface with fast Zn dissolution but without formation of solid corrosion products. The Zn corrosion is mainly influenced by pH and concentration of zinc ions in the coolant. Since boric acid/borate acts as a buffer system, the pH value increases faster at the beginning and reaches up to 6.8 in case of sufficient solved Zn, generated by corrosion. A local (flow induced) corrosion occurs if a fast liquid flow strikes the top face of a horizontal galvanized coupon. Precondition for this process is a sufficiently low pH of solution in connection with a high hydrodynamic impact of the liquid flow on the corroding surface.
For a limited period, the risk of strainer clogging due to formation of corrosion products of galvanized steel may be reduced by an additional amount of submerged Zn or changing the coolant chemistry by alkaline additions. These two possibilities were investigated by test series using galvanized steel coupons. The addition of borax seems to be the most effective method to reduce the corrosion rate and the risk of sump screen clogging.
The results were validated with galvanized gratings in a further test series since the flow conditions of a liquid jet on flat coupons significantly differ from those on gratings. Three different regions of corrosion attack were noticed on these real samples contributing to the increase of solved Zn. But the Zn dissolution should be limited since it may lead to undesired secondary effects by deposition of sparingly soluble borate salts depending on coolant temperature.

Keywords: LOCA; zinc; corrosion; sump screen clogging; PWR

  • Poster
    NPC2012, Nuclear Plant Chemistry Conference, 24.-27.09.2012, Paris, Frankreich
  • Contribution to proceedings
    NPC2012, Nuclear Plant Chemistry Conference, 24.-27.09.2012, Paris, Frankreich
    CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-17564
Publ.-Id: 17564


Reaktionsaufklärung der Partialoxidation von Isobutan zu tert.-Butylhydroperoxid (TBHP)

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

Die Aufgaben des Arbeitspaketes 2.5 des Projektes „Energieeffiziente chemische Mehrphasenprozesse“ werden kurz vorgestellt. Das Potential der Energieeffizienzverbesserung der Oxidation von Iso-butan mit Sauerstoff zu tert.-Butylhydroperoxid wird angesichts der Technologie mikrostrukturierter Reaktoren evaluiert. Ein vereinfachter Mechanismus der Reaktion wird angegeben. Darauf aufbauend wird das weitere Vorgehen zur Reaktionsaufklärung im Rahmen des Projekts skizziert, sowie die Verknüpfungen des Arbeitspaketes 2.5 mit anderen Arbeitspaketen aufgezeigt.

  • Lecture (others)
    Universitätsinternes Kick-off-Meeting zur Helmholtz-Energie-Allianz "Energieeffiziente chemische Mehrphasenprozesse", 13.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17563
Publ.-Id: 17563


CFD modeling of graphite dust transport, deposition and resuspension with OpenFOAM

Lecrivain, G.; Hampel, U.

In a high temperature pebble-bed reactor, carbonaceous dust is conveyed by the cooling carrier phase and eventually deposits in the primary circuit of the reactor. The numerical dispersion and deposition of Lagrangian aerosol particles in a turbulent flow is here investigated. The flow field is simulated using a Reynolds-averaged Navier-Stokes method. A Langevin equation is implemented to reproduce the turbulent dispersion of particles. Results of the deposition experiments in a vertical and horizontal square duct flow show good agreement with recently published experimental data.

Keywords: Turbulent square duct flow; aerosol particles; particle dispersion; particle deposition; numerical experiment; CFD

  • Lecture (Conference)
    THINS Workshop Thermal-Hydraulics of Innovative Nuclear Systems, 06.-08.02.2012, Ljubljana, Slovenia

Permalink: https://www.hzdr.de/publications/Publ-17561
Publ.-Id: 17561


Defect characterization of ion-implanted Fe-Cr alloys using Positron Doppler Broadening Spectroscopy

Butterling, M.; Anwand, W.; Bergner, F.; Cowan, T. E.; Heinze, C.; Ulbricht, A.; Wagner, A.; Krause-Rehberg, R.

Depth resolved positron Doppler broadening spectroscopy was used to investigate the effect of neutron irradiation (simulated by self-implantation with Fe ions) on the defect structure of Fe-Cr alloys with different Cr content (2.5at% - 12at%). Different defect situations depending on the Cr content were found for the alloys.

Keywords: Fe-Cr alloys; Positron Annihilation Spectroscopy; ion implantation induced damage

  • Lecture (Conference)
    Workshop Ionenstrahlphysik 2012, 09.-11.07.2012, Augsburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17560
Publ.-Id: 17560


Experiments on the deposition and resuspension of nuclear aerosol particles

Barth, T.

In this presentation the state of the ongoing gas/graphite transport experiments is presented. In the frame of the EU projects THINS and ARCHER two small-scale test facilities were designed to study the particle transport in complex geometries. Background motivation is the carbonaceous dust issue in the primary circuit of the High Temperature Reactor. It is a safety issue to explore the deposition and resuspension behaviour of such graphite particles to assess the transport behaviour during loss of coolant accidents. The first facility is called Gas Particle Loop and it is used to study the particle deposition and resuspension behaviour in a turbulent square duct flow field. The turbulent flow field was recorded using a Particle Image Velocimetry system. Furthermore, single particle as well as multilayer particle deposition and resuspension experiments were conducted to generate a data basis for the understanding of the particle transport behaviour. The second facility is called Pebble Bed Loop was specially design to generate a particle laden turbulent flow through a pebble bed. The test section is designed to fit into a Positron Emission Tomography (PET) scanner situated at the Reactive Transport Division in Leipzig. The time and space resolved formation of the particles was recorded by means of this PET scanner. The data presented can be used for CFD code development.

Keywords: High Temperature Reactor; aerosol particle; deposition; resuspension; Particle Image Velocimetry; Positron Emission Tomography

  • Lecture (Conference)
    Doktorandenseminar KOMPOST, 08.12.2011, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17559
Publ.-Id: 17559


Measurement techniques and experimental investigations for multiphase flows

Hampel, U.

The presentation is a short-course lecture that introduced the current state of the art in multiphase flow measurement techniques. Sensors and measurement techniques, which are intoduced are: electrical and optical needle probes, wire-mesh sensors and tomography techniques. Beside the physical measuring and sensor construction principles the presentation addresses the topic of data processing for multiphase flow measurements.

Keywords: multiphase flow measurment; multiphase flow sensors

  • Invited lecture (Conferences)
    10th Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 12.-14.06.2012, Dresden, Germany
  • Invited lecture (Conferences)
    11th Multiphase Flow Conference and Short Course, 26.-28.11.2013, Dresden, Germany
  • Invited lecture (Conferences)
    12th Multiphase Flow Conference and Short Course, 25.-27.11.2014, Dresden, Germany
  • Invited lecture (Conferences)
    13th Multiphase Flow Conference and Short Course, 24.-26.11.2015, Dresden, Germany
  • Invited lecture (Conferences)
    14th Multiphase Flow Conference and Short Course, 07.-09.11.2016, Dresden, Germany
  • Invited lecture (Conferences)
    15th Multiphase Flow Workshop - Short Course and Conference, 14.-17.11.2017, Dresden, Deutschland
  • Invited lecture (Conferences)
    16th Multiphase Flow Workshop - Short Course and Conference, 13.-16.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17558
Publ.-Id: 17558


Structural characterization of ZnO thin films grown on various substrates by pulsed laser deposition

Novotny, M.; Cizek, J.; Kuzel, R.; Bulir, J.; Lancok, J.; Connolly, J.; Mccarthy, E.; Krishnamurthy, S.; Mosnier, J.-P.; Anwand, W.; Brauer, G.

ZnO thin films were grown by pulsed laser deposition on three different substrates: sapphire (0 0 0 1), MgO (1 0 0) and fused silica (FS). The structure and morphology of the films were characterized by x-ray diffraction and scanning electron microscopy and defect studies were carried out using slow positron implantation spectroscopy (SPIS). Films deposited on all substrates studied in this work exhibit the wurtzite ZnO structure and are characterized by an average crystallite size of 20-100 nm. However, strong differences in the microstructure of films deposited on various substrates were found. The ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. Domains with different orientation relationships with the substrate were found in both films. On the other hand, the film deposited on the FS substrate exhibits fibre texture with random lateral orientation of crystallites. Extremely high compressive in-plane stress of sigma similar to 14 GPa was determined in the film deposited on the MgO substrate, while the film deposited on sapphire is virtually stress-free, and the film deposited on the FS substrate exhibits a tensile in-plane stress of sigma similar to 0.9 GPa. SPIS investigations revealed that the concentration of open-volume defects in the ZnO films is substantially higher than that in a bulk ZnO single crystal. Moreover, the ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit a significantly higher density of defects than the film deposited on the amorphous FS substrate.

Permalink: https://www.hzdr.de/publications/Publ-17557
Publ.-Id: 17557


WP4.1.3 Gas/graphite transport experiments

Barth, T.; Lehmann, A.; Preuß, J.; Reiche, M.

In this presentation the state of the ongoing gas/graphite transport experiments is presented. In the frame of the EU THINS project a small-scale test facility was designed to study the particle transport in turbulent duct flows. Background motivation is the carbonaceous dust issue in the primary circuit of the High Temperature Reactor. It is a safety issue to explore the deposition and resuspension behaviour of such graphite particles to assess the transport behaviour during loss of coolant accidents. The turbulent flow field was recorded using a Particle IImage Velocimetry system. Furthermore, single particle as well as multilayer particle deposition and resuspension experiments were conducted to generate a data basis for the understanding of the particle transport behaviour. This data basis can be used for CFD code development.

Keywords: High Temperature Reactor; carbonaceous dust; turbulent flow; deposition; resuspension

  • Lecture (Conference)
    THINS – Cluster workshop, 06.-09.02.2012, Ljubljana, Slowenien

Permalink: https://www.hzdr.de/publications/Publ-17556
Publ.-Id: 17556


Bubble size and radial gas hold-up distributions in a slurry bubble column using ultrafast electron beam X-ray tomography

Rabha, S.; Schubert, M.; Wagner, M.; Lucas, D.; Hampel, U.

Gas hold-up and bubble size distribution in a slurry bubble column (SBC) were measured using the advanced non-invasive ultrafast electron beam X-ray tomography technique. Experiments have been performed in a cylindrical column (DT = 0.07 m) with air and water as the gas and liquid phase and spherical glass particles (dP = 100 µm) as solids. The effects of solids concentration (0 ≤ Cs ≤ 0.36) and superficial gas velocity (0.02 ≤ UG ≤ 0.05 m/s) on the flow structure, radial gas hold-up profile and approximate bubble size distribution at different column heights in a SBC were studied. Bubble coalescence regime was observed with addition of solid particles, however, at higher solids concentrations, larger bubble slugs were found to break-up. The approximate bubble size distribution and radial gas hold-up was found to be dependent on UG and Cs. The average bubble diameter calculated from the approximate bubble size distribution was increasing with increase of UG. The average gas hold-up was calculated as a function of UG and agrees satisfactorily with previously published findings. The average gas hold-up was also predicted as a function of Cs and agrees well for low Cs and disagrees for high Cs with findings of previous literature.

Keywords: Slurry bubble column; gas hold-up; bubble size distribution; ultrafast electron beam X-ray tomography

Permalink: https://www.hzdr.de/publications/Publ-17555
Publ.-Id: 17555


Helmholtz-Energie-Allianz Energieeffiziente Chemische Mehrphasenprozesse

Hampel, U.

Der Vortrag stellt die neue Helmholtz-Energie-Allianz Energieeffiziente Chemische Mehrphasenprozesse vor.

  • Lecture (others)
    HZDR Klausurtagung, 28.07.2012, Bad Schandau, Germany

Permalink: https://www.hzdr.de/publications/Publ-17554
Publ.-Id: 17554


Experimentelle Studien und CFD-Simulation der Thermofluiddynamik bei kaltstrangseitiger Notkühleinspeisung (TOPFLOW-PTS)

Hampel, U.; Apanasevich, P.; Beyer, M.; Lucas, D.

Bei Kühlmittelverluststörfällen in Kernreaktoren wird die Kernkühlung unter anderem durch Notkühleinspeisung (emergency core cooling, ECC) in den kalten oder heißen Strang des Primärkreislaufs unterstützt. Hierbei wird zusätzliches Kühlmittel aus Notkühlreservoirs in die mit dem Reaktordruckbehälter (RDB) verbundenen Hauptkühlmittelleitungen eingespeist. Ein sicherheitsrelevantes Problem dieser Maßnahme sind thermomechanische Belastungen der Reaktordruckbehälterwand durch plötzliche Abkühlung. Das stark unterkühlte Notkühlwasser vermischt sich in der Hauptkühlmittelleitung mit dem dort stehenden Sattwasser, dessen Höhe in der Leitung durch den aktuellen RDB-Füllstand und dessen Sättigungstemperatur durch den aktuellen Systemdruck gegeben sind. Das in den Ringraum des RDB einströmende Wasser kann bei unzureichender Vermischung eine plötzliche Abkühlung der Reaktordruckbehälterwand (Thermoschock) unterhalb des Leitungsstutzens mit dem Risiko einer Rissbildung bewirken. Das Risiko eines Behälterversages hängt damit einerseits vom aktuellen strukturmechanischen Zustand der Behälterwand ab, andererseits von den die Vermischung bestimmen thermohydraulischen Phänomenen in der Hauptkühlmittelleitung. Letztere umfassen die durch die Strömungsdynamik bestimmte thermische Vermischung (Jet-Form, Turbulenz, Dampfblasenmitriss) sowie den Wärmetransport durch Kondensation am ECC-Strahl und an der Wasseroberfläche und hängen von einer Vielzahl von Parametern, wie dem ECC-Massenstrom, der ECC-Unterkühlung, dem aktuellen Systemdruck (Sättigungstemperatur) und der Höhe der Wasservorlage in der Hauptkühlmittelleitung ab.
Im Rahmen eines seit 2006 laufenden Konsortialprojektes der Partner HZDR, EDF France, AREVA NP France, IRSN, CEA, PSI Switzerland und ETH Zürich werden an der TOPFLOW-Anlage parametrische experimentelle Untersuchungen zu dem oben beschriebenen Thema durchgeführt. Ziel ist die Bereitstellung hochaufgelöster Experimentaldaten für die Ertüchtigung von CFD-Codes, die unter anderem in den europäischen Projekten NURESIM, NURISP und NURESAFE entwickelt werden. Der Vortrag gibt einen Überblick über das Projekt und seine Zielsetzungen, über den Versuchsstand und seine Instrumentierung sowie über das bisherige Experimentalprogramm, ausgewählte experimentelle Ergebnisse sowie CFD-Simulationsrechnungen.

Keywords: pressurized thermal shock

  • Lecture (others)
    Institutsseminar, 21.06.2012, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-17553
Publ.-Id: 17553


Dust deposition and remobilisation in a pebble bed - description of the test facility

Barth, T.; Hampel, U.

The presentation gives an overview over the ongoing project activities of HZDR in the ARCHER EU project. An air-particle test loop GPLoop has been setup in the HDZR laboratory and was equipped with various measurement systems. The purpose is the study of graphite dust deposition and remobilization in a pebble bed heap. Studies will be done with positron emission tomography.

Keywords: high temperature gas cooled reactor; graphite dust; particle transport; positron emission tomography

  • Lecture (Conference)
    ARCHER Project Meeting, 6.3.2012, Jülich, Germany

Permalink: https://www.hzdr.de/publications/Publ-17552
Publ.-Id: 17552


The TOPFLOW PTS project status report

Hampel, U.; Beyer, M.

The presentation describes the actual status of the TOPFLOW-PTS consortial project on thermal hydraulics of pressurized thermal shock.

  • Lecture (others)
    The TOPFLOW PTS Steering Committee Meeting, 16.02.2012, Paris, France
  • Lecture (others)
    The TOPFLOW PTS Steering Committee Meeting, 17.07.2012, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-17551
Publ.-Id: 17551


Condensation in Horizontal Heat Exchanger Tubes

Leyer, S.; Zacharias, T.; Maisberger, F.; Lamm, M.; Vallee, C.; Beyer, M.; Hampel, U.

Many innovative reactor concepts for Generation III nuclear power plants use passive safety equipment for residual heat removal. These systems use two phase natural circulation. Heat transfer to the coolant results in a density difference providing the driving head for the required mass flow. By balancing the pressure drop the system finds its operational mode. Therefore the systems depend on a strong link between heat transfer and pressure drop determining the mass flow through the system. In order to be able to analyze these kind of systems with the help of state of the art computer codes the implemented numerical models for heat transfer, pressure drop or two phase flow structure must be able to predict the system performance in a wide parameter range. Goal of the program is to optimize the numerical models and therefore the performance of computer codes analyzing passive systems. Within the project the heat transfer capacity of a heat exchanger tube will be investigated. Therefore the tube will be equipped with detectors, both temperature and pressure, in several directions perpendicular to the tube axis to be able to resolve the angular heat transfer. In parallel the flow structure of a two phase flow inside and along the tube will be detected with the help of x-ray tomography. The water cooling outside of the tube will be realized by forced convection. It will be possible to combine the flow structure measurement with an angular resolved heat transfer for a wide parameter range. The test rig is set up at the TOPLFOW facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), so that it will be possible to vary the pressure between 5 and 70 bar. The steam mass content will be varied between 0 and 100 percent. The results will be compared to the large scaled Emergency Condenser Tests performed at the INKA test facility in Karlstein (Germany). The paper will explain the test setup and the status of the project will be presented.

Keywords: emergency condenser; passive safety systems; steam condensation

  • Lecture (Conference)
    2012 International Congress on the Advances in Nuclear Power Plants, 24.-28.06.2012, Chicago, USA
  • Contribution to proceedings
    2012 International Congress on the Advances of Nuclear Power Plants, 24.-28.06.2012, Chicago, USA
    Conference Proceedings, Paper No. 12334

Permalink: https://www.hzdr.de/publications/Publ-17550
Publ.-Id: 17550


Experiments at TOPFLOW and ROCOM

Hampel, U.; Kliem, S.; Lucas, D.; Beyer, M.

The presentation introduces to activities at HZDR, which are related to thermal hydraulics safety concerns of Gen II and GEN-III nuclear reactors. We show examples of thermal hydraulic studies conducted at the TOPFLOW facility, which comprises two-phase pipe flow experiments, condensation experiments, pressurized thermal shock experiments, counter-current flow experiments, and boiling experiments. The ROCOM facility was created to study mixing and boron dilution in a 1:5 scaled-down PWR model. Both facilities, though serving different purposes and working in different parameter ranges, are equipped with most sophisticated measurement techniques and contribute to the answers on many thermal hydraulic phenomena occurring in today’s light water reactor systems.

Keywords: experimental fluid dynamics; nuclear thermal hydraulics

  • Invited lecture (Conferences)
    SILENCE Foundation Meeting, 05.-06.07.2012, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-17549
Publ.-Id: 17549


Radiation based tomography for multiphase flow

Hampel, U.

Multiphase flows are widely found in many fields of science, engineering, and industry. Examples are mineral oil processing, chemical reaction engineering, and nuclear thermal hydraulics. Measurement and visualisation of multiphase flows is therefore of high scientific and engineering relevance. In particular the development and validation of multiphase CFD models requires measurement data from flow scenarios with high spatial and temporal resolution.
Since multiphase flows are complex in space and time, high-resolution imaging modalities are needed as measurement tools. Unfortunately, multiphase flow research made only partial benefit from the recent tremendous progress in optical, laser and ultrasound based measurement techniques, because of the opaqueness of such flows for light and sound. Especially radiation based tomographic methods are therefore being considered as the key technology for multiphase flow visualisation. However, to date only few methods are suited because of the stringent requirements for high spatial and temporal resolution. In particular, methods are sought, which can visualize multiphase flow in complex geometries, within vessels with opaque walls and inserts, such as chemical reactors, heat exchangers or fuel rod assemblies, but also porous media of fixed bed reactors or rock samples. The presentation now will give an introduction to the recent progress in radiation based tomographic imaging techniques for multiphase flow measurement and discuss their particular role with respect to CFD code development.

Keywords: multiphase flow measurement techniques; tomography

  • Invited lecture (Conferences)
    7th OpenFOAM® Workshop, 25.-28.06.2012, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-17548
Publ.-Id: 17548


Ultrafast tomography for multiphase flow

Hampel, U.

The presentation gives an overview over state-of-the art ultrafast and high resolution tomographic imaging methods for multiphase flows. In particular the presentation elucidates recent developments in wire mesh sensor imaging, high resolution gamma ray tomography for process vessels and ultrafast X-ray tomography for real time flow studies. Sensor and hardware issues will be addressed along with problems and solutions for massive 3D image data processing and flow parameter extraction.

Keywords: multi phase flow; flow measurement; process tomography

  • Invited lecture (Conferences)
    6th International Symposium on Process Tomography, 26.-28.03.2012, Capetown, South Africa

Permalink: https://www.hzdr.de/publications/Publ-17547
Publ.-Id: 17547


Advanced imaging techniques for multiphase flows

Hampel, U.

Multiphase flows are widely found in different fields of science, engineering, and industry. Examples are mineral oil processing, chemical reaction engineering, and nuclear thermal hydraulics. Measurement and visualisation of multiphase flows is therefore of high scientific and engineering relevance. In particular the development of multiphase CFD codes requires measurement data from flow scenarios with high spatial and temporal resolution, in order to develop and validate physics based models for momentum, heat and mass transfer. If information about phase distributions, interfacial area structure, velocity and species concentration fields in flows are required, high-resolution imaging modalities are needed as measurement tools. However, yet there is no universal measurement or imaging modality for multiphase flow. Traditional visualisation tools, such as high-speed camera imaging and ultrasound measurements fail in multiphase systems due to the nonlinear propagation and attenuation of the signal carriers, e.g. light and sound waves. Especially radiation based tomographic methods are therefore being considered as the key technology for multiphase flow visualisation. However, to date only few methods are suited because of the stringent requirements for high spatial and temporal resolution. In particular, methods are sought, which can visualize multiphase flow in complex geometries, often with opaque walls and inserts, such as chemical reactor vessels, heat exchangers or nuclear fuel rod assemblies, but also porous media of fixed bed reactors or rock samples. The presentation introduces two novel imaging modalities, namely wire mesh sensors and ultrafast X-ray tomography and their use in two-phase flow measurement in complex flow domain geometries. It will be shown how gas-liquid and gas-solid flows can be visualized in in pipes, columns, fixed bed packings and flow channels with inserts. The presentation shows results of dedicated flow studies and introduces data analysis methods for extraction of quantitative flow parameters.

Keywords: multiphase flow; flow measurement

  • Invited lecture (Conferences)
    ITUN Seminar, 31.5.12, Freiberg, Germany
  • Invited lecture (Conferences)
    36th Tulsa University Separation Technology Projects Advisory Board Meeting, 15.5.2012, Tulsa, USA
  • Invited lecture (Conferences)
    Brazilian Multiphase Flow Week 2012 (EBECEM), 07.-11.05.2012, Curitiba, Brazil
  • Invited lecture (Conferences)
    Petrobras Multiphase Flow Meeting, 11.05.2012, Rio de Janeiro, Brazil
  • Invited lecture (Conferences)
    Multiphase Flow & Flow Assurance Program Meeting, 14.05.2012, San Antonio, USA
  • Invited lecture (Conferences)
    Chevron Multiphase Flow Meeting, 17.05.2012, Houston, USA

Permalink: https://www.hzdr.de/publications/Publ-17546
Publ.-Id: 17546


Strong paramagnetism of Gold nanoparticles deposited on a Sulfolobus acidocaldarius S-layer

Bartolome, J.; Bartolome, F.; Garcia, L. M.; Figueroa, A. I.; Repolles, A.; Martinez, M. J.; Luis, F.; Magen, C.; Selenska-Pobell, S.; Pobell, F.; Reitz, T.; Schönemann, T.; Herrmannsdörfer, T.; Merroun, M.; Geissler, A.; Wilhelm, F.; Rogalev, A.

Magnetic properties of Au nanoparticles deposited on an archaeal S-layer are reported. XMCD and SQUID magnetometries demonstrate that the particles are strongly paramagnetic, without any indication of magnetic blocking down to 16 mK. The average magnetic moment per particle is 2.36(7) mkB. This contribution originates at the particles Au 5d band, in which an increased number of holes with respect to the bulk value is observed. The magnetic moment per Au atom is 25 times larger than any measured in other Au nanoparticles or any other configurations up to date.

Keywords: Au nanoparticles; archaeal S-layer; XMCD; SQUID; paramagnetism

Permalink: https://www.hzdr.de/publications/Publ-17545
Publ.-Id: 17545


Feasibility study for MeV electron beam tomography

Hampel, U.; Bärtling, Y.; Hoppe, D.; Kuksanov, N.; Fadeev, S.; Salimov, R.

Electron beam tomography is a promising imaging modality for the study of fast technical processes. But for many technical objects of interest X-rays of several hundreds of keV energy are required to achieve sufficient material penetration. In this article we report on a feasibility study for fast electron beam computed tomography with a 1 MeV electron beam. The experimental setup comprises an electrostatic accelerator with beam optics, transmission target, and a single X-ray detector. We employed an inverse fan-beam tomography approach with radiographic projections being generated from the linearly moving X-ray source. Angular projections were obtained by rotating the object.

Keywords: electron beam tomography; ultrafast tomography

Permalink: https://www.hzdr.de/publications/Publ-17544
Publ.-Id: 17544


Capacitance wire-mesh sensor applied for the visualization of three-phase gas-liquid-liquid flows

Da Silva, M. J.; Hampel, U.

This short communication describes the application of a capacitance wire-mesh sensor for the investigation of a simulated gas-liquid-liquid three-phase flow in a laboratory setup. Experiments with air, silicone oil and water are performed first in static and second in dynamic conditions. The capacitance mesh sensor is capable of generatinge images of the cross-sectional distribution of relative permittivity values, which in turn is an indication to the phases present in the multiphase mixture. Initial tests show that the sensor is a valuable tool to investigate such three-phase flows, which are very common in the oil industry.

Keywords: wire mesh sensor; three phase flow; multiphase flow; flow measurement

Permalink: https://www.hzdr.de/publications/Publ-17543
Publ.-Id: 17543


Development of high-rate MRPCs for high resolution time-of-flight systems

Wang, J.; Wang, Y.; Gonzalez-Diaz, D.; Chen, H.; Fan, X.; Li, Y.; Cheng, J.; Kaspar, M.; Kotte, R.; Laso Garcia, A.; Naumann, L.; Stach, D.; Wendisch, C.; Wüstenfeld, J.

We show how the high charged-particle fluxes (1-20 kHz/cm²) expected over the 150 m² large time-of-flight wall of the future Compressed Baryonic Matter experiment (CBM) at FAIR can be realistically handled with Multi-gap Resistive Plate Chambers (MRPCs). This crucial 100-fold increase of the chamber rate capability, as compared to that of standard MRPCs presently employed in experiments resorting to sub-100 ps timing, has been achieved thanks to the development of a new type of low-resistive doped glass. Following the encouraging results previously obtained with small counters, two types of modules (active area: ~150 cm²) have been built at Tsinghua University with the new material. The measurements conveyed in this work, obtained with a quasi-minimum ionizing electron beam, prove their suitability as the building blocks of the present hadron-identification concept of the CBM experiment. Namely, they provide a time resolution better than 80 ps and an efficiency above 90% at particle fluxes of 50 kHz/cm², being at the core of a modular concept that is easily scalable. Recent measurements of the electrical and mechanical properties of this new material, together with its long-term behavior, are shortly summarized.

Permalink: https://www.hzdr.de/publications/Publ-17542
Publ.-Id: 17542


Production and purification of 56Co at the Leipzig cyclotron

Mansel, A.; Franke, K.

60Co (T1/2 = 5.27 a) is one of the most used radionuclide for sterilization of medical equipment, as a radiation source for medical radiotherapy, industrial radiography and food irradiation due to the high gamma-energy of 1.33 MeV. In case of release in the geosphere, e.g. soil and aquatic systems, the migration behaviour of cobalt is not well understood. For geochemical investigations, e.g. migration and adsorption studies in soil and rock formations, the short-lived isotope 56Co (T1/2 = 77 d) can be used.
We produced 56Co at a recently installed 18 MeV-cyclotron by using the nuclear reaction 56Fe(p,n)56Co.[1] The target was prepared by pressing metallic iron powder into an aluminium plate and cover it with an aluminium foil. After the irradiation with 11 MeV protons for 1 h at a current of 25 µA, the iron was dissolved with a mixture of concentrated HCl and concentrated H2O2.[2] The separation of 56Co from the target material was done by liquid-liquid extraction with methyl-tert-butylether (MTBE) from 5.2 M HCl.[3] Alternatively, an anionic exchange with DOWEX 1x8 as a column material can be used.[4] Due to the shorter separation time the liquid-liquid extraction is preferred. The radiochemical yield was 82% ± 6%. The activity concentration in the 56Co stock solution was ~4.5 MBq / ml.

[1] Jenkins, I. L., Wain, A. G., (1970) J. Inorg. Nucl. Chem. 32(5) 1419-1425.
[2] Lagunas-Solar, M. C., Jungerman, J. A., (1979) Int. J. Appl. Radiat. Isot. 30(1) 25-32.
[3] V. Wiskamp, S. Zenker, (1997), Eisenextraktion mit tertiärem Butylmethylether. CLB 48 (Beilage Memory) 22.
[4] Kraus, K. A., Moore, G. E., (1953) J. Am. Chem. Soc. 75(6) 1460-1462.

  • Lecture (Conference)
    NRC 8 - International Conference on Nuclear and Radiochemistry, 16.-21.09.2012, Como, Italy

Permalink: https://www.hzdr.de/publications/Publ-17541
Publ.-Id: 17541


Dose-Controlled Radiobiological Experiments with Laser Accelerated Proton Pulses as a Prerequisite for Radiation Therapy

Schramm, U.

  • Invited lecture (Conferences)
    EPS / ICPP - 39th European Physical Society Conference on Plasma Physics / 16th International Congress on Plasma Physics, 02.-06.07.2012, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-17540
Publ.-Id: 17540


Synthesis, Characterization and Evaluation of Radiometal-Containing Peptide Nucleic Acids

Stephan, H.; Förster, C.; Gasser, G.

As described in Chapter, peptide nucleic acids (PNAs) have very attractive properties, which include, among them, high selectivity towards DNA/RNA recognition. It is therefore not surprising that their potential in nuclear medicine and biology to explore in vitro and in vivo processes has also been investigated. The high thermal and radiolytic stability as well as resistance toward nuclease/protease degradation of these bioconjugates offers new opportunities in this field of research, which could, potentially, lead to a transformation of the whole scope of diagnostically and therapeutically relevant radionuclides. Importantly, as demonstrated in Chapter with metal complexes, PNAs can be synthetically modified allowing their intrinsic physico-chemical properties to be significantly modulated. For example, the attachment of appropriate spacer elements and specific building blocks, such as targeting units, to both the C- and N-terminus of PNAs allows a broad variation of the pharmacologic properties of PNA bioconjugates, hence enabling the development of application-orientated probes for imaging of gene expression. Furthermore, the high metabolic resistance of these non-natural oligonucleotides makes them interesting for therapeutic applications. In this book chapter, we report on the current developments towards the preparation of radiometal-containing PNA constructs and summarize the protocols for labeling these oligonucleotides with 99mTc, 111In, 64Cu, 90Y and 177Lu.

Keywords: Peptide Nucleic Acid (PNA); Radiometal Complexes; Bifunctional Chelating Agents; Molecular Imaging; Endoradionuclide Therapy

  • Book chapter
    P. E. Nielsen, D. H. Appella: Peptide Nucleic Acids: Methods and Protocols, 2nd ed., Series: Methods in Molecular Biology, Vol. 1050, New York: Springer, Humana Press, 2014, 978-1627035521, 37-54

Permalink: https://www.hzdr.de/publications/Publ-17539
Publ.-Id: 17539


Polyoxometalates as versatile enzyme inhibitors

Stephan, H.; Müller, C. E.

Polynuclear metal compounds may have considerable potential as metallic drugs. The most prominent representatives are polyoxometalates (POMs) which have been investigated since the last third of the 19th century. In addition to applications in catalysis, separation, analysis, and as electron-dense imaging agents, some of these substances have been shown to exhibit biological activity in vitro as well as in vivo ranging from anti-cancer, antibiotic, and antiviral to anti-diabetic effects.
Polyoxometalates represent a diverse ensemble of nanostructures with an almost infinite variability of chemical, physical and biological properties. The size of typical covalent bridged cluster compounds is in the range from 1 to 3 nm. The attachment of special surface groups on the periphery of cluster compounds may result in self-assembled non-covalent organized structures larger than 5 nm which are characteristic for bio-molecules, such as enzymes. Cells of mammalian organisms are typically 10 to 30 µm. However, sub-cellular organelle dimensions are smaller and range in sub-µm sizes. This comparison of size dimension illustrates that polymetalates are small enough to allow the cell membrane to be penetrated without too much interference. Evidently, some types of polyoxometalates are able to be transported into cells, particularly into mitochondria. However, many of such polyanions are only slightly taken up by cells, obviously caused by negatively charged membranes.
On the way to explore the biological activity of polynuclear cluster compounds, we recently recognised POMs as a new class of potent enzyme inhibitors. Certain polyanionic complexes are able to inhibit extracellular E-NTPDases (ecto-nucleoside triphosphate diphosphohydrolases) that are surface-located nucleotide-hydrolyzing enzymes involved in the regulation of signaling cascades by activating P2 (nucleotide) receptors.
We want to present a brief overview about the potential of POMs as E-NTPDase inhibitors and P2 receptor antagonists.

  • Lecture (Conference)
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17538
Publ.-Id: 17538


Look-Locker Acquisition for Estimation of partial volume fractions in ASL Data

Petr, J.; Schramm, G.; Hofheinz, F.; Langner, J.; Steinbach, J.; van den Hoff, J.

Due to the relatively low spatial resolution, arterial spin labeling (ASL) images are strongly affected by partial volume effects (PVE). This can make the qualitative analysis of ASL images difficult and it also significantly decreases the accuracy of cerebral blood flow (CBF) quantification. The PVE can be corrected for by using gray matter (GM) and white matter (WM) tissue segmentation of high-resolution T1-weighted images as proposed by Asllani et al1. The main drawback of this method is the need for precise knowledge of the partial volume ratios. However, the segmentation of T1-weighted images is very difficult at the border of GM and WM. Moreover, ASL images contain susceptibility induced deformations typical for EPI images and thus a correct registration with T1-weighted images is not always possible. Hence, the PVE correction using segmented T1-weighted images can introduce artifacts. In this study, we analyze an alternative method to obtain the partial volume ratios through the longitudinal magnetization relaxation times obtained from a Look-Locker sampling acquired in a multiple inversion time (TI) ASL sequence.

  • Contribution to proceedings
    ISMRM 20th Annual Meeting, 05.-11.05.2012, Melbourne, Australia
    2012 Annual Meeting Proceedings, 2001
  • Poster
    ISMRM 20th Annual Meeting, 05.-11.05.2012, Melbourne, Australia

Permalink: https://www.hzdr.de/publications/Publ-17537
Publ.-Id: 17537


Validierung eines Gammatomographen zur Bestimmung der Phasenanteilsverteilung in einem geneigt rotierenden Festbettreaktor

Arlit, M.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) beschäftigt sich unter anderem mit der Untersuchung mehrphasiger verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate und -reaktoren.
Ein solches neuartiges Konzept stellt der geneigt rotierende Festbettreaktor dar. Im Gegensatz zum zeitlich-periodischen Reaktorbetrieb erfolgt die Prozessintensivierung hier durch Aufprägung einer örtlichen Periodizität unter ansonsten stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich durch die Wahl von Reaktorneigung und Reaktordrehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der Diplomarbeit ist ein tomographisches Messsystem für die Ermittlung von Phasenanteilen zu validieren. Weiterhin ist der Einfluss von Reaktorneigung und –drehzahl auf die Verteilung der Phasenanteile und den Druckverlust bei ausgewählten Gas- und Flüssigkeitsdurchsätzen zu untersuchen und mit dem etablierten Rieselbettreaktor zu vergleichen.

Keywords: Fixed bed reactor; Liquid Holdup; Phase Distribution; Inclination; Rotation; Gamma-ray Tomography

  • Diploma thesis
    TU Dresden, 2012
    130 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17536
Publ.-Id: 17536


High specific activity 61Cu via 64Zn(p,α)61Cu reaction at low proton energies

Thieme, S.; Walther, M.; Preusche, S.; Rajander, J.; Pietzsch, H.-J.; Solin, O.; Steinbach, J.

The PET radionuclide 61Cu is accessible through several nuclear reactions. Besides the common production route via 61Ni(p,n)61Cu the 64Zn(p,α)61Cu reaction offers some advantages. Especially the comparatively cheap enriched 64Zn makes this process economical. For fast product purification and recycling of target material an ion exchanger cascade was developed. In addition a separation technique with a copper selective resin was tested. 61Cu with specific activities up to 1000 GBq/µmol was produced with these methods.

Permalink: https://www.hzdr.de/publications/Publ-17535
Publ.-Id: 17535


Absorption saturation in optically pumped graphene

Winzer, T.; Knorr, A.; Mittendorff, M.; Winnerl, S.; Sun, D.; Norris, T. B.; Helm, M.; Malic, E.

We investigate the saturation of the optical absorption in graphene induced by ultrafast optical pulses. Within a microscopic theory, we study the momentum-, angle-, and time-resolved interplay of anisotropic excitation, carrier-carrier and carrier-phonon scattering and its influence on the saturation of absorption and transmission as a function of the input intensity. In agreement with recent experiments, we observe a linear regime for the intensity-dependence of the transmission at low pump fluences and a nonlinear saturation in the high excitation regime. Applying 10 fs-pulses we obtain a saturation fluence of approximately 6.5mJ/cm2. We demonstrate how the interplay of Pauli-blocking and intensity-dependent relaxation determines the saturation behavior.

Permalink: https://www.hzdr.de/publications/Publ-17534
Publ.-Id: 17534


1550 nm ErAs:In(Al)GaAs Large Area Photoconductive Emitters

Preu, S.; Mittendorff, M.; Lu, H.; Weber, H. B.; Winnerl, S.; Gossard, A. C.

We report on high power Terahertz emission from ErAs-enhanced InAlAs-InGaAs superlattices for operation at 1550 nm. ErAs clusters act as ecient recombination centers. The optical power is distributed among a large, microstructured area in order to reduce the local optical intensity. A THz field strength of 0.7 V/cm (1 V/cm peak-to-peak) at 100 mW average optical power has been obtained, with emission up to about 4 THz in air, limited by the detection crystal used in the system.

Permalink: https://www.hzdr.de/publications/Publ-17533
Publ.-Id: 17533


Relaxation dynamics in epitaxial graphene investigated in the whole infrared spectral range

Winnerl, S.; Göttfert, F.; Mittendorff, M.; Schneider, H.; Helm, M.; Orlita, M.; Potemski, M.; Winzer, T.; Knorr, A.; Malic, E.; Sprinkle, M.; Berger, C.; de Heer, W. A.

As a gapless material with linear dispersion graphene is of great interest for the infrared spectral range. In this study we investigate the carrier relaxation dynamics of graphene in a wide spectral range from the near to the far-infrared, covering more than two orders of magnitude in photon energy.
The samples for this study are epitaxially grown graphene layers on the carbon-terminated face of SiC, which behave essentially like a stack of electronically uncoupled layers. In the near infrared (NIR) spectral range (photon energy 0.41 eV – 1.5 eV) degenerate and two-color experiments were performed. In the mid (MIR) and far infrared (FIR) range (photon energy 10 meV – 250 meV) degenerate pump-experiments were carried out employing the free-electron laser FELBE as a source.
In the NIR range pump-induced transmission was observed in two-color experiments with both red and blue shifted probe radiation. The signals in case of the blue shifted probe are evidence for a hot carrier distribution. The thermalization process is beyond the temporal resolution of our experiment (~ 100 fs in the near infrared). The observed decay times are in the range of 2 – 4 ps. In the MIR range we observe a significant increase of the relaxation time as the photon energy is decreased to values below the optical phonon energy (~200 meV). These experiments are complemented by microscopic theory based on the density matrix formalism [1]. The theory reflects the trends seen in the experiment well. It reveals the contribution of Coulomb scattering as well as the role of both optical and acoustic phonons in the observed dynamics.
In the FIR range an unexpected change from enhanced transmission to enhanced absorption is found (cf. Fig. 1). It is caused by an interplay of interband and intraband processes. For photon energies above twice the value of the Fermi energy, bleaching of interband transitions results in pump-induced transmission. For smaller photon energies, however, interband transitions are not possible. Here intraband transitions cause a heating of the carrier distribution, which is responsible for the intraband absorption.

  • Poster
    International Conference on Superlattices, Nanostructures and Nanodevices, 22.-27.07.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17532
Publ.-Id: 17532


Graphene excited with short infrared pulses: fundamental aspects and application perspectives

Winnerl, S.

Detailed knowledge of the ultrafast carrier dynamics is of crucial importance for the development of novel electronic and optoelectronic devices. Graphene, a gapless semiconductor, is very attractive for broadband photonic and optoelectronic applications. We performed pump-probe experiments on graphene samples in a wide spectral range from the near-infrared to the terahertz region (wavelength 0.8 µm – 120 µm). We show results on the relaxation dynamics and identify the main relaxation channels, namely optical phonons, intraband carrier-carrier scattering, and Auger-type processes [1]. Furthermore the saturation behaviour of the signals is investigated. This is important with respect to graphene-based saturable absorbers. Here we find that the intensity required for full beaching of graphene decreases by three orders of magnitude, when the pump wavelength is increased from 5 µm to 40 µm. Finally we present a fast graphene-based terahertz detector, which can be operated at room temperature.
This work was carried out in collaboration with M. Mittendorff, F. Göttfert, H. Schneider, and M. Helm from the Helmholtz-Zentrum Dresden Rossendorf, M. Orlita and M. Potemski from LNCMI-CNRS Grenoble. Modelling based on microscopic theory was performed by T. Winzer, E. Malic, and A. Knorr at the TU Berlin, sample growth by M. Sprinkle, C. Berger, and W.A. de Heer from the Georgia Institute of Technology, Atlanta. We acknowledge support by the German Science Foundation (DFG) in the framework of the priority program “Graphene”.
[1] S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. Malic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider, and M. Helm, Phys. Rev. Lett. 107, 237401 (2011).

  • Invited lecture (Conferences)
    7th International Conference on Surfaces, Coatings and Nanostructured Materials, 18.-21.09.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17531
Publ.-Id: 17531


Intersublevel spectroscopy on single InAs-quantum dots by terahertz near-field microscopy

Jacob, R.; Winnerl, S.; Fehrenbacher, M.; Bhattacharyya, J.; Schneider, H.; Wenzel, M. T.; von Ribbeck, H.-G.; Eng, L. M.; Atkinson, P.; Schmidt, O. G.; Helm, M.

Using scattering-type near-field infrared microscopy in combination with a free-electron laser, intersublevel transitions in buried single InAs quantum dots are investigated. The experiments are performed at room temperature on doped self-assembled quantum dots capped with a 70 nm GaAs layer. Clear near-field contrast of single dots is observed when the photon energy of the incident beam matches intersublevel transition energies, namely the p-d and s-d transition of conduction band electrons confined in the dots. The observed room-temperature linewidth of 5 – 8 meV of these resonances in the mid-infrared range is significantly below the inhomogeneously broadened spectral lines of quantum dot ensembles. The experiment highlights the strength of near-field micro-spectroscopy by demonstrating signals from bound-to-bound transitions of single electrons in a probe volume of the order of (100 nm)^3.

Permalink: https://www.hzdr.de/publications/Publ-17530
Publ.-Id: 17530


Cyclammonopropionic acid- a promising chelating system for radiocopper isotopes

Kubeil, M.; Peschel, L.; Stephan, H.; Steinbach, J.

A wide variety of radiometal-chelating bioconjugates have been studied intensively to design effective radiopharmaceuticals for diagnostic and therapeutic purposes. Azamacrocycles offer an enormous potential to achieve highly stable radiometal complexes and allow the covalent attachment of targeting and/or fluorescence units at the ligand skeleton. In this context, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA) is quite often used for the development of copper-based target-specific radiopharmaceuticals, although demetallation and transchelation occur in biological systems. In contrast, radiolabeling of propionic acid analogues has not been reported so far.
An appropriate building block to form very stable complexes with copper(II) is N-mono-(2-(carboxy)ethyl)-1,4,8,11-tetraazacyclotetradecane (Cyclammonopropionic acid, CMPA) which permits the formation of stable radiocopper complexes as well as a facile approach to obtain peptide multimers. An improved pharmaceutical targeting might be utilized due to the multimeric peptide functionalization of the chelating agent. The Epidermal-Growth-Factor-Receptor (EGFR), which is overexpressed on a multitude of tumors, has been chosen as target system to be studied.
Herein, we want to report about coupling reactions of the model dipeptide H-(L)-Leu-(L)-Ala-OH, which is a part of an EGFR-specific peptide, with the cyclammonopropionic acid skeleton. Radiolabeling of CMPA-peptide conjugates with copper-64 indicate high in vitro stability of the complexes formed. So far, this promising behavior may pave the way to develop attractive candidates for radiopharmaceutical applications.

  • Lecture (Conference)
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17529
Publ.-Id: 17529


Relaxation dynamics in graphene

Winnerl, S.

The peculiar properties of graphene, most importantly its gapless, linear band structure, give rise to exciting phenomena such as constant optical absorption over a wide range of photon energies and an unusual quantum Hall effect. Furthermore graphene is considered as an interesting material for electronic and optoelectronic applications. A good understanding of the relaxation dynamics is essential both for fundamental research and applications.
After an introduction into graphene research, I will present our results of pump-probe experiments in the mid- and far-infrared spectral range (photon energy 245 meV – 10 meV). We identify the role of optical phonons in the relaxation dynamics and discuss contributions from Auger-type processes and acoustic phonons. Furthermore an interesting change in sign of the pump-probe signal is observed at low photon energies (20 – 30 meV), which can be explained by an interplay of intraband and interband absorption processes [1]. In the second part of the talk I will focus on the relaxation dynamics in Landau-quantized graphene. Since the Landau levels (LLs) in graphene are not equidistant but scale with both the square root of the LL index and the square root of the magnetic field, optical pumping of individual LL-transitions is possible. Here we focus on the LL-1 → LL0 and LL0 → LL1 transitions, which exhibit equal transition energies but can be distinguished by applying either right-handed or left-handed circularly polarized light. Employing all four combinations of pumping and probing with right-handed and left-handed circularly polarized light, respectively, results in complex pump-probe signals: They involve fast and slow components, which exhibit either positive or negative signs. The relaxation dynamics in this regime can be understood by attributing the fast components to Auger-type processes and the slower components to phonon-mediated energy relaxation.
[1] S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. Malic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider, and M. Helm, Phys. Rev. Lett. 107, 237401 (2011).

  • Lecture (others)
    Seminar der Arbeitsgruppe Prof. Wiek, 06.07.2012, Bochum, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17528
Publ.-Id: 17528


Charakterisierung der Bindungseigenschaften rheniumhaltiger Clusterverbindungen gegenüber Dendrimeren

Kuhlmann, M.

kein Abstract verfügbar

  • Diploma thesis
    TU Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie und Lebensmittelchemie, 2009
    74 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17527
Publ.-Id: 17527


The FELBE user facility

Seidel, W.; Winnerl, S.; Bhattacharyya, J.; Teich, M.; Fehrenbacher, M.; Drachenko, O.; Schneider, H.; Helm, M.; Bauer, C.; Gensch, M.; Schurig, R.; Lehnert, U.; Michel, P.

The FELBE user facility located at the Helmholtz-Zentrum Dresden-Rossendorf operates two free-electron lasers (FELs). Here we discuss the basic parameters of the FELs and the experimental opportunities at the facility. The FELs are based on the superconducting electron linear accelerator ELBE, which provides short (picosecond) electron bunches with energies up to 35 MeV at a 13 MHz repetition rate. The two FELs of FELBE (FELBE stands for FEL@ELBE) are equipped with two undulators, one for the mid-infrared spectral range (wavelengths 4 – 22 μm) and one for the far-infrared or THz range (wavelengths 20 – 250 μm). The key feature which distinguishes FELBE from other FEL user facilities is the possibility of “quasi cw” operation (meaning a continuous train of pulses, also called micropulses), made possible by the superconducting accelerator cavities. The FEL thus provides picosecond optical pulses at a repetition rate of 13 MHz. In this mode, the average power can reach up to 30 W (depending on the wavelength) corresponding to more than 1 μJ pulse energy. Additionally FELBE can be operated in a macrobunch mode and, via pulse-picking, a 1 kHz mode. The two FELs can be synchronized to a number of tabletop femtosecond and picosecond lasers, enabling two-color experiments from the near-infrared to the THz frequency range. The main techniques at FELBE are pump-probe spectroscopy [1-3] and time-resolved photoluminescence [4]. Furthermore there is a lab devoted to near-field microscopy [5,6]. Spectroscopy with FELBE radiation is also possible in pulsed high magnetic fields up to 70 T (150 ms magnetic pulse duration) [7,8]. FELBE is operated as a user facility, i.e., scientists from other institutions are invited to submit short research proposals and apply for beamtime.
References
[1] D. Stehr et al., Appl. Phys. Lett. 92, 051104 (2008).
[2] E.A. Zibik, et al., Nature Mat. 8, 803 (2009).
[3] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[4] J. Bhattacharyya et al., Rev. Sci. Instr. 82, 103107 (2011).
[5] S.C. Kehr et al., Phys. Rev. Lett. 100, 256403 (2008).
[6] S.C. Kehr et al., Nature Comm. 2, 249 (2011).
[7] S. A. Zvyagin, et al, Rev. Sci. Instr. 80, 073102 (2009).
[8] O. Drachenko et al., Phys. Rev. B 79, 245207 (2011).

  • Poster
    503th Wilhelm and Else Heraeus Seminar Free-Electron Lasers: from Fundamentals to Applications, 10.-13.04.2012, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17526
Publ.-Id: 17526


Biofunctionalisation and 64Cu-labeling of pyridine-containing TACN ligands for specific targeting of EGF-receptor

Hesse, J.; Viehweger, K.; Stephan, H.; Steinbach, J.

The application of radiolabeled peptides in biomedicine is increasing rapidly and offers excellent prospects for the development of target-specific tumor imaging agents. In this perspective, the incorporation of the positron-emitting radionuclide 64CuII into ligand-peptide conjugates would permit the use of positron emitting tomography (PET) for tumor identification. An important requirement is that the resulting radiocopper-ligand complex is both kinetically and thermodynamically stable in vivo. We have developed a ligand scaffold based on bis(2-pyridylmethyl)triazacyclononane (DMPTACN) that forms very stable CuII complexes [1]. This structure allows for the introduction of linker groups, such as carboxylic acids, maleimide or isothiocyanate, thereby facilitating coupling of targeting molecules.
Among many characteristic targets of cancer tissue, the epidermal growth factor receptor (EGFR) is one of the most important mediators involved in the development of highly malignant tumors. This surface receptor is overexpressed in several tumor entities. The altered expression of EGFR during tumor growth, invasion, and metastasis present an interesting molecular target for tumor diagnosis and therapy.
Meanwhile, some specific peptides are identified capable of recognition EGFR-rich cancer tissue. Among these, the hexapeptide D4 (Leu-Ala-Arg-Leu-Leu-Thr) has been described [2]. We want to present the synthesis of a DMPTACN-peptide conjugate, applying thiourea coupling of the hexapeptide D4 by a DMPTACN isothiocyanate derivative. Radiochemical and radiopharmacological properties will be reported. In vitro binding characteristics of the [64Cu]CuII-labeled DMPTACN-peptide conjugate in EGFR overexpressing cancer cells ( FaDu, A431) using an immunoprecipitation protocol point to specific interactions.

[1] G. Gasser, L. Tjioe, B. Graham, M. J. Belousoff, S. Juran, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 9, 719-730.
[2] S. Song, D. Liu, J. Peng, H. Deng, Y. Guo, L. X. Xu, A. D. Miller, Y. Xu, FASEB J. 2009, 23, 1396–1404.

  • Lecture (Conference)
    4th EuCheMS Chemistry Congress, 26.-30.08.2012, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-17525
Publ.-Id: 17525


Semiconductor quantum structures in high THz fields

Winnerl, S.

Electronic resonances in semiconductor quantum structures such as quantum wells and quantum dots are often accompanied by nonlinear phenomena. The intense, spectrally narrow radiation of a free-electron laser (FEL) is ideally suited for studying these nonlinear effects. We briefly discuss effects that can be treated in a perturbative way, such as the appearance of THz-sidebands around near-infrared absorption lines of quantum wells and quantum dots. Mainly we focus on an effect, which is beyond the perturbative description, namely the Autler-Townes splitting of excitonic absorption lines. Photogenerated electrons and holes in semiconductors form excitons, which exhibit a hydrogen-like energy spectrum. Due to the presence of the crystal lattice, however, the energy is scaled to the meV range. Excitation with intense THz pulses from an FEL "dresses" the excitonic states and leads to a splitting of energy levels. This splitting can be observed by probing the samples's transmission with broadband near-infrared radiation. While the main features, such as the dependence of the peak position on the THZ intensity, can be explained by a simple two-level model, other observations such as the relative strength of the peaks require more complex modelling. The mauin results presented here were obtained by M. Wagner, D. Stehr, H. Schneider and M. Helm on a sample grown by A. M. Andrews, S. Schartner, and G. Strasser.

  • Invited lecture (Conferences)
    503th Wilhelm and Else Heraeus Seminar Free-Electron Lasers: from Fundamentals to Applications, 10.-13.04.2012, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17524
Publ.-Id: 17524


Dose controlled irradiation of cancer cells with laser accelerated proton pulses

Zeil, K.; Baumann, M.; Beyreuther, E.; Burris-Mog, T.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kraft, S. D.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Oppelt, M.; Richter, C.; Sauerbrey, R.; Schürer, M.; Schramm, U.; Pawelke, J.

Proton beams are a promising tool for the improvement of radiotherapy of cancer, and compact laserdriven proton radiation (LDPR) is discussed as an alternative to established large-scale technology acilitating wider clinical use. Yet, clinical use of LDPR requires substantial development in reliable beam generation and transport, but also in dosimetric protocols as well as validation in radiobiological studies. Here, we present the first dose-controlled direct comparison of the radiobiological effectiveness of intense proton pulses from a laser-driven accelerator with conventionally generated continuous proton beams, demonstrating a first milestone in translational research. Controlled dose delivery, precisely online and offline monitored for each out of *4,000 pulses, resulted in an unprecedented relative dose uncertainty of below 10 %, using approaches scalable to the next translational step toward radiotherapy application.

Permalink: https://www.hzdr.de/publications/Publ-17523
Publ.-Id: 17523


Synthesis and cytotoxicity of pyridine and quinoline oxorhenium(V) complexes with tridentate (NS2, S-3)/monodentate (s) coordination

Segal, I.; Zablotskaya, A.; Kniess, T.; Shestakova, I.

New oxorhenium complexes with tridentate 3-thia- and 3-methylazapentane-1,5-dithiolate and monodentate pyridine and quinoline derivatives have been synthesized. As a result of investigation of biological activity a high cytotoxicity was found for the synthesized complexes in relation to tumor cells. The specificity of the 2-pyridylthiolato[3-(N-methyl)azapentane-1,5-dithiolato]oxorhenium(V) cytotoxic action towards cells of mouse hepatoma MG-22A on a background of low acute toxicity was established.

Keywords: oxorhenium(V) complexes; pyridine; quinoline; rhenium; cytotoxicity

Permalink: https://www.hzdr.de/publications/Publ-17522
Publ.-Id: 17522


Ultrafast relaxation dynamics close to the Dirac point in graphene

Winnerl, S.; Malic, E.

The relaxation dynmics in graphene is studied in the mid- and far-infrared spectral range.

  • Poster
    International Workshop on THz dynamics in carbon based nanostructures, 05.-07.03.2012, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-17521
Publ.-Id: 17521


Modularisierung der Geometrieinformation einer C++/Qt-basierten iterativen Bildrekonstruktion in der Positronen-Emissions-Tomographie

Domula, S.

kein Abstract verfügbar

  • Diploma thesis
    Hochschule für Technik und Wirtschaft Dresden, 2012
    78 Seiten

Permalink: https://www.hzdr.de/publications/Publ-17520
Publ.-Id: 17520


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