Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Tuning the quality of nanoscale ripple patterns by sequential ion-beam sputtering

Keller, A.; Facsko, S.

It is demonstrated that the quality of nanoscale ripple patterns on silicon surfaces can be substantially improved by applying sequential ion-beam sputtering. A flat silicon surface is sputtered at an intermediate incident angle which leads to the spontaneous formation of a periodic ripple pattern with 25 nm periodicity oriented normal to the direction of the incident ion beam. After rotating the sample by an azimuthal angle of 90, the surface is sputtered parallel to the ripples under grazing incidence. At the low fluences applied in this second step, no ripple pattern oriented parallel to the ion beam forms. However, due to geometrical shadowing and preferential erosion of pattern defects, grazing incidence sputtering enhances the order and regularity of the ripple pattern. The quality of the ripple pattern is assessed by evaluating its normalized density of topological defects which is determined from atomic force microscopy images. During grazing incidence ion sputtering, the normalized defect density is found to decrease exponentially with the applied ion fluence. It is shown that in this way the defect density of the initial ripple pattern can be reduced by at least 40% while keeping its periodicity approximately constant. Numerical integrations of the Kuramoto-Sivashinsky equation are in good qualitative agreement with the experimental results and suggest that the observed reduction in the density of pattern defects during sequential ion-beam sputtering is a universal effect present in a large variety of experimental systems.


Publ.-Id: 15035

Experiments on the transport, deposition and resuspension of nuclear aerosols

Barth, T.; Banowski, M.; Hampel, U.

Nuclear aerosol deposition and the assessment of its resuspension during a design basis accident in the primary circuit are a key issue in the development and certification of advanced pebble bed High Temperature Reactors (HTRs). Nuclear aerosols, in particular graphite dust in size of d = [0.1; 50] μm, are deposited during operation in the primary circuit (Moormann (2008)). It is of general interest how much of these aerosols escape from the primary circuit into the containment during a depressurization scenario. The knowledge about the amount of resuspended dust allows the detailed estimate of the dose escaping the primary circuit Flow conditions in the primary circuit range from laminar flows in the recuperator till turbulent high Reynolds number flows in the pipes and ducts. Considering the particle size distribution published by Moormann (2008), particle Stokes numbers will range from very small Stk << 1 till moderately high Stk > 1. In order to investigate the fluid mechanic behavior between the flow and the aerosol within the set of characteristic numbers, we designed a small scale gas aerosol test facility .
We found a turbulent square duct flow most suitable because all the flow features such as streamwise and spanwise velocity gradients, as well as vortical structures are apparent. Furthermore, there will be a wide range of experimental and numerical data for comparison.
The test facility is a small scale wind tunnel in total length of 6 m with a 10 x 10 cm² square duct section. A 500 W radial fan at the outlet of the channel accelerates the flow field from 0 up to 7.5 m/s which is equivalent to a Reynolds number of about Re = 50 k.
The inlet is equipped with a HEPA filter to clean the incoming air. A nozzle contracts the flow into a square duct which is divided into a flow formation zone (15 x d) and a test section (5 x d). In the beginning of the flow formation zone the dust feeder or the aerosol generator injects the aerosol. The length of 15 x d for the flow formation zone ensures that the test section is streamed by a well developed turbulent channel flow with an evenly distributed aerosol. Both, test section and flow formation zone, are made of transparent acrylic glass to allow optical flow field measurements, such as PIV, high speed camera imaging for the analysis of the flow field and microscopic imaging techniques for the surface particle detection.
A diffusor stage decelerates the flow before it enters the electrostatic filter for air cleaning purposes. Finally, the 500 W radial fan produces the pressure drop for the desired flow speed.
Preliminary measurements of total pressure drop in the square duct section and time averaged mean center velocity profiles for different Reynolds number will be presented on the poster.

Keywords: Nuclear Aerosol Particles; Particle Image Velocimetry; VHTR; Deposition; Resuspension

  • Poster
    Doktorandenseminar 2010 im Rahmen des Kompetenzzentrums Ost für Kerntechnik, 16.12.2010, Dresden, Deutschland

Publ.-Id: 15034

Surface protection of TiAl alloys and Ti against high-temperature environmental degradation

Yankov, R. A.; Kolitsch, A.; Munnik, F.; von Borany, J.; Donchev, A.; Schütze, M.

Ti and TiAl alloys are lightweight materials that hold great promise for advanced aerospace, automotive and power generation applications. They are, however, limited in applicability by their poor oxidation resistance at elevated temperatures. We have developed viable techniques for enhancing the high-temperature environmental durability of these materials. In the case of TiAl, the process has involved a single step, i.e. plasma immersion implantation (PIII) of fluorine relying on the so-called “halogen effect”. Optimum processing conditions have been established under which the F-implanted alloys acquire a stable, adherent and highly protective alumina scale upon subsequent high-temperature oxidation in air. The extent of oxidation protection has been evaluated by testing F-implanted TiAl laboratory coupons as well as machine components (e.g. turbine blades and turbochargers) at temperatures as high as 1050°C, and for times up to 6000 h under conditions of both isothermal and thermal cyclic oxidation. Analytical methods such as elastic recoil detection, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis have been used for materials characterization. In the case of Ti, an efficient protective coating that serves as a barrier to the oxygen in-diffusion has been developed. Specifically, the coating consists of a γ-phase TiAl formed by magnetron co-sputtering of Ti and Al onto the Ti substrate, and subsequent vacuum annealing. After PIII of F, the coating has proven capable of forming a protective alumina scale upon exposure to air for extended times at temperatures up to 600°C.

  • Poster
    Dresdner Werkstoffsymposium Werkstoffe der Energietechnik, 09.-10.12.2010, Dresden, Germany

Publ.-Id: 15033

Comparison of different fluorine-treatments for improved high temperature oxidation resistance of TiAl-alloys

Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.

Intermetallic TiAl-alloys can replace the heavier Ni-based superalloys in several high temperature applications with regard to their mechanical properties but they can not be used at temperatures above 800°C in oxidizing environments for longer times because of an insufficient oxidation resistance. Despite an Al-content of about 45 at.% in technical alloys no protective alumina layer is formed because the thermodynamic stabilities of titanium oxide and aluminum oxide are in the same order of magnitude. Therefore a mixed TiO2/Al2O3-scale is formed which is fast growing so that the metal consumption rate is quite high. On the other hand the formation of a slowly growing alumina layer is promoted by a fluorine treatment. This so-called fluorine effect leads to the preferential intermediate formation of gaseous aluminum fluorides at elevated temperatures if the fluorine content at the surface is being kept within a certain concentration range. These fluorides are then converted into solid Al2O3 due to the high oxygen partial pressure of the high temperature service environment forming a protective pure Al2O3 surface scale. In this paper results of high temperature oxidations tests of several technical TiAl-alloys will be presented. Different F-treatments such as dipping or spaying which are easy to apply or, alternatively, more sophisticated ion beam and plasma-based techniques have been used for surface modification, and their results will be compared. The weight change data of the F-treated specimens are always lower than those of the untreated ones. Analytical methods such as light microscopy, scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of a thin alumina layer on the F-treated samples after optimization of the process while a thick mixed scale is found on the untreated samples. The results will be discussed in view of both the development of an optimized process, and the future use of TiAl-components in high temperature environments.

  • Lecture (Conference)
    2010 MRS Fall Meeting, 29.11.-03.12.2010, Boston, USA

Publ.-Id: 15032

Experiments on the transport, deposition and resuspension of nuclear aerosols

Barth, T.; Hampel, U.

Nuclear aerosol deposition and the assessment of its resuspension during a design basis accident in the primary circuit are a key issue in the development and certification of advanced pebble bed High Temperature Reactors (HTRs). Nuclear aerosols, in particular graphite dust in size of d = [0.1; 50] μm, are deposited during operation in the primary circuit (Moormann (2008)). It is of general interest how much of these aerosols escape from the primary circuit into the containment during a depressurization scenario. The knowledge about the amount of resuspended dust allows the detailed estimate of the dose escaping the primary circuit
Flow conditions in the primary circuit range from laminar flows in the recuperator till turbulent high Reynolds number flows in the pipes and ducts. Considering the particle size distribution published by Moormann (2008), particle Stokes numbers will range from very small Stk << 1 till moderately high Stk > 1. In order to investigate the fluid mechanic behavior between the flow and the aerosol within the set of characteristic numbers, we designed a small scale gas aerosol test facility (Figure 1).

We found a turbulent square duct flow most suitable because all the flow features such as streamwise and spanwise velocity gradients, as well as vortical structures are apparent. Furthermore, there will be a wide range of experimental and numerical data for comparison.
The test facility is a small scale wind tunnel in total length of 6 m with a 10 x 10 cm² square duct section. A 500 W radial fan at the outlet of the channel accelerates the flow field from 0 up to 7.5 m/s which is equivalent to a Reynolds number of about Re = 50 k.
The inlet is equipped with a HEPA filter to clean the incoming air. A nozzle contracts the flow into a square duct which is divided into a flow formation zone (15 x d) and a test section (5 x d). In the beginning of the flow formation zone the dust feeder or the aerosol generator injects the aerosol. The length of 15 x d for the flow formation zone ensures that the test section is streamed by a well developed turbulent channel flow with an evenly distributed aerosol. Both, test section and flow formation zone, are made of transparent acrylic glass to allow optical flow field measurements, such as PIV, high speed camera imaging for the analysis of the flow field and microscopic imaging techniques for the surface particle detection.
A diffusor stage decelerates the flow before it enters the electrostatic filter for air cleaning purposes. Finally, the 500 W radial fan produces the pressure drop for the desired flow speed.
Preliminary measurements of total pressure drop in the square duct section and time averaged mean center velocity profiles for different Reynolds number will be presented on the poster.

Keywords: Nuclear Aerosol Particles; Deposition; Resuspension; VHTR

  • Poster
    International Aerosol Conference – IAC 2010, 29.08.-03.09.2010, Helsinki, Finnland

Publ.-Id: 15031

Feasibility study of flow control by dynamic vane vortex generators based on piezoceramic actuators

Barth, T.; Scholz, P.; Wierach, P.

This investigation is an fundamental study about the perfomance of dynamic operated solid/mechanical vane vortex generators (VVGs). Fluidic vortex generators or so called vortex generator jets (VGJs) are more efficient in dynamic operation. Thus, the scope is to explore if VVGs are superior in dynamic operation, too. Besides, the influence of higher frequencies will be observed. The motion of the VVGs is generated by piezoceramic actuators or so called Marco Fiber Composites (MFC).The MFC actuators consist of bimoporh carbon fibre bars with applied piezoceramic face actuators on the top and downside. These MFC actuators generate a sinusoidal motion of the VVGs and were designed by analytical and experimental investigations. The MFC actuators are operated in resonance to gain the required displacement. Mass clamps applied on the bar tune the eigenfrequency into the operating point. Both, VVGs and MFC actuators, will bei integrated into a flat plate in a low speed wind tunnel. The VVGs penetrate through small plastic slits into a turbulent boundary layer. A stereo PIV system will record phase locked flow field pictures. The transient formation of the position and circulation of the vortex centers states that dynamic operated VVGs are supiror to static VVGs.

Keywords: vortex generator; Stereo PIV; active flow control; turbulent boundary layer

Publ.-Id: 15030

Zeitaufgelöste, Laser-induzierte Fluoreszenzspektroskopie am Beispiel von Untersuchungen zur Sekundärphasenbildung auf Geschossprojektilen aus abgereichertem Uran

Baumann, N.

Untersuchungen zur Speziationsaufklärung fluoreszierender Schwermetallionen mittels der zeitaufgelösten, Laser-induzierten Fluoreszenzspektroskopie (TRLFS) werden am Beispiel der Sekundärphasenanalyse auf Geschossprojektilen aus abgereichertem Uran erläutert, wobei die niedrigen Nachweisgrenzen der TRLFS und damit die Tauglichkeit der Methode zur Lösung von Problemen in umweltrelevanten Konzentrationsbereichen von Uran(VI) Spezies verdeutlicht werden. Zur Petrografie Bezug nehmend wird die Möglichkeit der Identifikation winzigster Uranylmineralmengen durch die TRLFS aufgezeigt.
Baumann N. et al. (2008) ES&T 42 8266-8269.
Geipel G. et al. (2000) Radiochim Acta 88 757-762.

  • Lecture (others)
    Jahrestreffen des petrographischen Studienkreises, 02.05.2010, Kulmbach, Deutschland

Publ.-Id: 15029

Characterization of Mesoporous ZnO:SiO2 Films Obtained by the Sol-gel Method

Martins, R. M. S.; Musat, V.; Mücklich, A.; Fortunato, E.

ZnO:SiO2 films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO2 films are of great interest as catalyst and gas sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films.
The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO2 films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by x-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix was investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO2 films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation.
Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO2 nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.

  • Poster
    Materials Research Society Fall Meeting (Symposium MM: Transparent Conducting Oxides and Applications), 29.11.-03.12.2010, Boston, MA, USA

Publ.-Id: 15028

In-situ X-ray Diffraction Studies During Magnetron Co-sputtering of Ni-Ti Shape Memory Alloy Films

Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J.; Braz Fernandes, F. M.

The study of Ni-Ti shape memory alloy films is of great technological interest for applications in the field of microengineering. They can work as sensors and actuators at the same time.
However, there are still important issues unresolved like formation of film texture and its control. Films exhibiting the two-way shape memory effect are also required.
A better understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in-situ techniques. A two-magnetron sputter deposition chamber mounted into the six-circle diffractometer of the Rossendorf Beamline at the European Synchrotron Radiation Facility has been used for the processing of the Ni-Ti films. The in-situ x-ray diffraction studies enabled us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters (Ti target power) during film growth.
It has been found that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films. In some cases they exhibit a pronounced depth dependence of their preferential orientations. Amorphous SiO2 and TiN buffer layers have been used to successfully control their crystallographic orientations. This is an important achievement since the texture has a strong influence on the extent of the strain recovery of the Ni-Ti films. The deposition conditions leading to films mainly containing grains with (100) or (110) planes of the B2 phase parallel to the film surface are presented.
The deposition of graded Ni-Ti films by changing deliberately the Ti:Ni ratio, thereby altering microstructure and transformation temperatures across the film thickness, has also been performed. The aim has been the optimization of the deposition parameters in order to fabricate films with a “two-way” actuation (films with a combination of superelasticity and shape memory characteristics). It will lead to the development of smaller devices due to an optimal design of microdevices regarding size and weight (i.e., no consideration has to be paid to a resetting spring).

  • Lecture (Conference)
    Materials Research Society Fall Meeting (Symposium UU: Real-Time Studies of Evolving Thin Films and Interfaces), 29.11.-03.12.2010, Boston, MA, USA

Publ.-Id: 15027

Surface Modification of Ni-Ti for Biomedical Applications by Plasma-immersion Ion Implantation

Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.

The enormous elasticity of Ni-Ti is becoming integral to the design of a variety of new medical products. The wide spectrum of application in implantology imposes special requirements on the biocompatibility of Ni-Ti. The biological response to implant materials is a property directly related to their surface conditions and an optimum surface layer is thus desired.

The plasma-immersion ion implantation (PIII) technique was used to modify and improve the surface of a Ni-Ti alloy (~ 50.2 at.% Ni, superelastic at body temperature) for biomedical applications. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material. Ion implantation of oxygen was carried out. The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer. The working plan also comprised ion implantation of nitrogen. In this case, the formation of titanium oxynitride (TiNxOy) was observed. The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with 40 keV.

The deposition of a coating by a PVD technique would have disadvantages due to the interface between the coating and the bulk (lower adhesion). PIII creates a graded interface between the modified surface and the bulk. Techniques like thermal oxidation and nitriding could also lead to an improved corrosion resistance and Ni-depleted Ni-Ti surface. However, the high temperature necessary for the experimental procedure would lead to modification of the phase transformation characteristics and loss of specific mechanical properties of the alloy. Heat treatments tests performed at temperatures above 350ºC led to a shift of the transformation temperatures of the Ni-Ti alloy used in this work. Moreover, the R-phase is then present at body temperature, which is not the case for Ni-Ti samples modified by the PIII technique. This technique only changes the properties of the Ni-Ti alloy top layer.

  • Lecture (Conference)
    Materials Research Society Fall Meeting (Symposium N: Intermetallic-Based Alloys for Structural and Functional Applications), 29.11.-03.12.2010, Boston, MA, USA

Publ.-Id: 15026

Large per-shot numbers of photons from Thomson scattering with variable energy and bandwidth

Debus, A. D.; Bussmann, M.; Siebold, M.; Jochmann, A.; Irman, A.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.

Finite bandwidth x-ray pulses generated in the interaction of a bunch of relativistic electrons with a high-intensity, ultra-short laser pulse are interesting for a variety of experiments that do not require the very small bandwidth delivered by x-ray free electron lasers.
We present a new scheme for Thomson scattering in which we use a grating setup similar to that found in a grating compressor as used in high-power short-pulse laser systems. The gratings are used to introduce a tilt of the laser pulse front and to compensate for dispersion and other unwanted effects on the laser pulse interacting with the electrons. Electron and laser beam are brought in overlap in a side scattering geometry for which the laser pulse is elongated in one spatial direction using an elliptical mirror so that the region of overlap between laser pulse and electron bunch is greatly increased compared to a simple head-on scenario for Thomson scattering..
This increase in size allows to increase the laser pulse energy while keeping the local intensity of the light seen by the electrons low, thus effectively increasing the number of scattered photons by up to three orders of magnitude.
By increasing the length of the overlap region one can decrease the bandwidth of the scattered x-ray photons for a given laser pulse energy, while changing the pulse front tilt angle allows to vary the wavelength of the x-ray photons without changing the electron beam energy.

Keywords: thomson scattering; electron; relativistic; laser; pulse; side-scattering; energy; bandwidth; traveling wave; twts

  • Poster
    470. Wilhelm and Else Heraeus Seminar on Particle Accelerator and High Intensity Lasers, 13.-17.12.2010, Bad Honnef, Deutschland

Publ.-Id: 15025

Scaling up the energy of laser-accelerated ions using novel target structures

Kluge, T.; Gaillard, S.; Flippo, K. A.; Gall, B.; Lockard, T.; Geissel, M.; Offermann, D. T.; Schollmeier, M.; Kraft, S. D.; Metzges, J.; Zeil, K.; Schramm, U.; Sentoku, Y.; Enghardt, W.; Sauerbrey, R.; Bussmann, M.; Cowan, T. E.

We present results on laser acceleration of ions using various designs for micro-structured targets. Our analysis compares recent experimental results on ion acceleration at FZD and Los Alamos to extensive realistic large-scale particle-in-cell simulations.
We focus on the electron dynamics leading to an enhancement in ion energy and show how the interplay of target structure and laser pulse parameters such as temporal contrast, peak intensity and pulse duration can be used to increase the ion energy in a robust way.
As two prominent examples we firstly discuss the role of grazing laser interaction with the walls of a conical target structure on the generation of hot electrons and secondly analyse the effect of lateral target size on repeated electron recirculation for simple mass reduced targets.
While the ion acceleration mechanism itself is based on the well-know target normal sheath acceleration mechanism and is thus robust enough for future applications such as radio therapy of tumours, the transfer of laser energy to electron energy is shown to greatly depend on laser parameters and target structure and thus needs detailed analysis using simulations.
In order to connect the electron dynamics during the short time the laser interacts with the electrons to the dynamics of the ion acceleration that evolve on a time scale that is typically three orders of magnitude longer, particle-in-cell simulations up to a few picoseconds duration, equating to some hundred thousand time steps, have been used.

Keywords: laser; ion; acceleration; cone; target; laser pressure; mass-limited; particle-in-cell; pic; simulation; maximum energy

  • Poster
    470. Wilhelm and Else Heraeus Seminar on Particle Accelerator and High Intensity Lasers, 13.-17.12.2010, Bad Honnef, Deutschland

Publ.-Id: 15024

Simulating realistic laser wakefield acceleration scenarios on the fly using GPUs

Bussmann, M.; Burau, H.; Berninger, F.; Debus, A.; Irman, A.; Jochmann, A.; Hönig, W.; Widera, R.; Schmitt, F.; Juckeland, G.; Nagel, W.; Schramm, U.; Cowan, T. E.

In order to optimise internal and external injection of electrons into laser-driven wakefields generated and the subsequent acceleration it is necessary to get fast response from simulations. This means that when considering a number of parameters such as plasma density, laser intensity, laser focal position and size or plasma density gradients, the optimum set of parameters is not easy to obtain by realistic particle-in-cell (PIC) simulations.
PIC simulations take into account the full dynamics of the particles in the interaction of the laser pulse with the plasma and thus give a detailed and realistic view of the plasma dynamics that can be used for optimisation. However, such detailed simulations usually require a lot of computing power not easily available to small-scale laboratories and universities.
We present PIConGPU, a fully relativistic, scalable implementation of the PIC algorithm on graphic cards (GPUs) that gives a speed up of orders of magnitude compared to PIC implementations on CPUs. Our code allows for an execution time below one nanoseond per macroparticle simulated (2D3V). This gives the user “real-time” feedback from the simulation, seeing on the fly the influence of the chosen parameter set on the injection and acceleration of electrons into the laser-driven wakefield. With this tool, the optimisation of injection schemes for the laser wakefield acceleration of electrons using realistic particle-in-cell simulations is in reach.

Keywords: gpu; laser wakefield acceleration; electron; parallel; computing; particle-in-cell; pic

  • Poster
    470. Wilhelm and Else Heraeus Seminar on Particle Accelerator and High Intensity Lasers, 13.-17.12.2010, Bad Honnef, Deutschland

Publ.-Id: 15023

The spatial structure of longitudinal and transversal fields in focussed terahertz beams

Winnerl, S.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.

While for many applications the terahertz (THz) frequency range is the least technologically developed region of the electromagnetic spectrum, which is often referred to as the THz gap, this region offers unique research opportunities. For example, coherent detection of single cycle and few cycle pulses has been developed in the THz range and is now extended to the full infrared range. Here we apply coherent detection via electro-optic sampling in ZnTe crystals of different orientation to study amplitude and phase of longitudinal and transversal field components in focused terahertz beams. The THz radiation is generated by two types of scalable photoconductive emitters. The electrode pattern is optimized for generation of linearly polarized beams in one case and radially polarized beams in the second case. We show that these beams can be described well as Bessel Gauss beams, which are solutions of the vector Helmholtz equation. Consistent with the theory we observe a larger amplitude and a smaller spot size for the longitudinal component of a radially polarized beam as compared to a similarly focused linearly polarized beam.

Keywords: Terahertz; radially polarized beams; longitudinal electromagnetic fields

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 15022

First experiments at the new 6 MV-Tandetron at HZDR

Akhmadaliev, S.; Heller, R.; Hanf, D.; Merchel, S.

The 6 MV tandem type accelerator replaces the old 5 MV machine in the beginning of 2011. Besides ion beam analysis (IBA) and material modification via high-energy ion implantation, the system is equipped for accelerator mass spectrometry (AMS). The first interest is in the radioisotopes 10Be, 26Al, 36Cl, 41Ca, and 129I [1]. An energy calibration of the machine and a test of ion beam energy stability have been carried out as a first experiment using the 1H(15N,alpha gamma)12C nuclear reaction with a sharp resonance at anenergy of 6385 keV. The total energy resolution for the system is about 12 keV. First tests of the Dresden AMS system (DREAMS) [2] have been performed and demonstrated background levels of 2E-16 for 10Be/9Be, 7E-16 for 26Al/27Al and 8E-15 for 41Ca/40Ca, respectively. The background of 2E-13 for 129I/127I originates from intrinsic 129I (MERCK KI), whereas the reasons for high 36Cl/35Cl background of 3E-15 are under discussion.

[1] Sh. Akhmadaliev et al., MS6.2, DPG Frühjahrstagung der Sektion AMOP, Hannover 2010.

Keywords: IBA; AMS; Tandetron

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15021

Time-resolved terahertz spectroscopy and imaging at the FELBE free-electron laser facility

Winnerl, S.; Schneider, H.; Stehr, D.; Helm, M.; Seidel, W.; Michel, P.; Zibik, E. A.; Carpenter, B. A.; Porter, N. E.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Liu, H. C.; Y. Song, C.; Bründermann, E.

Free-electron lasers are the only high-power, continuously tunable radiation sources in the terahertz range. Here we highlight some outstanding experiments performed at the FELBE free-electron laser at the Forschungszentrum Dresden-Rossendorf and discuss the influence of the beam parameters on the feasibility of these studies. FELBE is driven by a superconducting accelerator operating at a repetition rate of 13 MHz. The laser can be tuned in an extremely wide spectral range from 1.2 THz to 75 THz. The pulse duration is 1 – 25 ps, the pulse energy 10 nJ – 2 µJ, depending on the wavelength. Correspondingly, the average power can be up to several Watts. Most experiments at FELBE are studies in the field of condensed matter physics, with a special focus on semiconductor quantum structures. Here we present two time-resolved terahertz experiments, a study of two-photon currents in GaAs/AlGaAs quantum-well infrared photodetectors (QWIP) [1] and a pump-probe study of the relaxation dynamics in self-organized InGaAs quantum dots [2]. In a two-photon QWIP operated at 7.1 THz a quadratic dependence of the photocurrent on the THz intensity is observed over 3 orders of magnitude. Quadratic photocurrent signals were observed already at pulse energies of only few pJ. Fringe resolved autocorrelation traces were measured. An analysis showed that their duration is determined by the duration of the FELBE pulses rather than by intrinsic time constants. For the quantum dots a change of the relaxation time by 3 orders of magnitude was observed when the photon energy of the FELBE pulses was varied only by a factor of two (1.5 ns for 3.4 THz, 2 ps for 7 THz, respectively). All photon energies were below the longitudinal optical phonon energy in GaAs, hence the fast relaxation via those phonons was suppressed. The relaxation dynamics in these experiments is governed by polarons which decay into acoustic phonons. A theoretical description taking into account all possible acoustic phonon decay channels provides an excellent agreement with the measured relaxation times.
THz imaging in reflection geometry was demonstrated in an experiment, where an oil painting was scanned through the attenuated focused FELBE beam. The result is compared with earlier THz images, where broadband radiation from photoconductive antennas was applied. The higher spatial resolution and the improved contrast of the image can be explained by the higher frequency (3.4 THz) of FELBE compared to the spectrum of the THz antenna (below 1 THz). The wavelength was chosen in order to maximize the reflection from lead white pigments [3]. In general the spectral range from 1 – 15 THz seems more appropriate for art studies, since many pigments have spectral fingerprints in this region, while their transmission and reflection spectra are basically flat in the range below 1 THz [3].

[1] H. Schneider, H.C. Liu, S. Winnerl , C.Y. Song, M. Walther and M. Helm, Opt. Express, 17, 12279 (2009).
[2] E.A. Zibik, T. Grange, B.A. Carpenter, N.E. Porter, R. Ferreira, G. Bastard, D. Stehr, S. Winnerl, M. Helm, H.Y. Liu, M. S. Skolnick, and L. R. Wilson, Nature Mat., 8, 803 (2009).
[3] K. Fukunaga, Y. Ogawa, Sh. Hayashi, and I. Hosako, IEICE Electronics Express 4, 258 (2007).

Keywords: time resolves spectroscopy; terahertz; THz imaging; free-electron laser

  • Lecture (Conference)
    International Forum on Terahertz Spectroscopy and Imaging, 02.-03.03.2010, Kaiserslautern, Deutschland

Publ.-Id: 15020

Ion-assisted phase separation during the growth of carbon-transition metal nanocomposite thin films

Abrasonis, G.

Nanostructures determine material properties at the macroscale, and are therefore a key issue in materials science of thin films. This is of particular importance for nanoscale multiphase films due to their multifunctionality and the combination of properties which cannot be predicted from the constituents alone. Control over the morphology and spatial correlations at the nanoscale becomes one of the major challenges. In this context, the tools allowing the structure control at the nanoscale are of utmost importance. The ion-solid interactions in the hyperthermal ion energy range (~10 -100 eV) are confined in the nanometer scale, and are therefore of key relevance. In this talk I will summarize recent research activities of our group on the phase separation during the growth of carbon-transition metal thin films. These materials are relevant in the context of sensing, fusion, electrochemistry, tribology, information storage as well as spintronics. Different processes can be 'switched off/on' by external control of the experimental parameters such as temperature, substrate type, matrix/dispersed phase chemical affinity or incoming particle energy. This results in a large variety of lateral or vertical composition modulations, such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays. The latter deserve a special interest. They occur during ionized-PVD conditions if the metal amount surpasses a critical value. In addition, the ion induced atomic mobility is not isotropic, as it would be in the case of thermally excited migration, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. Such self-organization process is versatile as different carbon-transition metal systems show this effect. The observed tendencies will be discussed on the basis of the interplay of thermal and energetic ion induced phenomena. As the dominating driving force for the pattern formation is of neither thermal nor chemical origin, we believe that the presented results are applicable to other immiscible or partially miscible systems and can be used to sculpt (multi)functional nanomaterials.

  • Lecture (others)
    Talk at Département Physique et Mécanique des Matériaux, Institut P', UPR 3346 CNRS, Université de Poitiers, 07.12.2010, 86962 Futuroscope Chasseneuil Cedex, France

Publ.-Id: 15019

Environment Controlled De-wetting Kinetics of Rh-Pd Bilayer/Alloy Thin Films on Silica: A Physical Approach to Synthesize Core-Shell Nanoparticles

Abrasonis, G.; Wintz, S.; Liedke, M. O.; Aksoy, F.; Liu, Z.; Kuepper, K.; Krause, M.

The control of morphology and surface composition of nanoalloys is the key factor in order to tune or to extend the range of their optical, magnetic and chemical properties. Therefore it is one of the major tasks in nanoalloy materials science. As the chemical environment has a profound influence on the structure of supported metallic nanoparticles, it can be used as a powerful tool to tune their structure and properties. This study concerns the in-situ investigation of the oxidizing/reducing environment influence on the de-wetting dynamics and kinetics of a Rh-Pd bilayer/alloy thin film model system.
Thin films of ~3nm thickness were grown at RT by molecular beam epitaxy electron beam evaporation on thermally oxidized silicon substrates. These films were subsequently subjected to different combinations of heating and chemical environment (CO and NO) treatments. The film surface composition and the chemical state was determined in-situ by ambient pressure environmental x-ray photoelectron spectroscopy.
Independently on whether the initial state is an alloy or a bilayer with Rh on the top, the film surface shows an enrichment of Pd upon heating in vacuum. Exposure to NO or CO at ~250-300°C results in the surface enrichment with either Rh or Pd, respectively, and subsequent film rupture. The metallic islands, produced by the film de-wetting, also show a similar response to the environment changes. On the other hand, de-wetting caused by heating in NO or CO shows significant differences in the surface chemical composition evolution and, consequently, in the de-wetting onset temperature.
The results are discussed on the basis of the interplay between thermodynamic and kinetic factors, e.g. the energetics of the metallic surfaces in response to the NO/CO adsorbates, the atomic mobility of metallic and oxide surfaces, and the role of mobile Pd/Rh carbonyl or nitrosyl species. The study demonstrates the effect of the chemical environment on the morphology as well as on the composition of supported nanostructures. The nanoalloy/ bilayer approach presented here opens a new route for the fabrication of supported arrays of core-shell nanoparticles.

  • Lecture (Conference)
    2010 MRS Fall Meeting, 29.11.-03.12.2010, Boston, United States of America

Publ.-Id: 15018

Tilting of precipitation patterns in carbon-transition metal nanocomposite thin films by hyperthermal ion deposition

Abrasonis, G.; Oates, T. W. H.; Kovacs, G. J.; Tucker, M.; Grenzer, J.; Persson, P. O. A.; Heinig, K. H.; Martinavicius, A.; Jeutter, N.; Baehtz, C.; Bilek, M. M. M.; Möller, W.

The structure control, especially at the nanoscale, is of the primary importance in the field of the materials science of thin films. Here, the hyperthermal ion induced self-organization caused by phase separation during the carbon-transition metal (Ni, Cu) thin film growth is reported. The films have been grown by ionized physical vapour deposition using filtered cathodic vacuum arc. Influence of the metal type, film composition, ion energy and incidence angle is studied. The film morphology has been determined by transmission electron microscopy and grazing incidence small angle x-ray scattering.
At these growth conditions, atomic displacements are caused solely by impacting energetic ions, resulting in phase separation in an advancing surface layer. If the metal amount surpasses some critical value, this layer switches to an oscillatory mode and a nanoscale precipitation pattern emerges. The results show that for the perpendicular incoming depositing ion incidence the C:Ni film structure consists of alternating self-organized nickel carbide and carbon layer oriented parallel to the film surface. Moreover, the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion, but conserves to a large extent the initial direction of the incoming ions, resulting in a tilting of the periodic precipitation structures for the oblique ion incidences. The metal nanopatterns no longer align with the advancing surface, but with the incoming ions. While both type of films show tilted structures, for C:Cu films the ‘tilted-lying’ transition is observed when increasing Cu content.
We establish a dependence of the nanopattern morphology on the growth parameters and demonstrate a method for controlling the nanopatterning. The results are discussed on the basis of the interplay between thermodynamically driven phase separation and energetic ion induced ballistic effects. Application of this concept opens new ways for the bottom-up nanostructure control for composite materials.

  • Lecture (Conference)
    2010 MRS Fall Meeting, 29.11.-03.12.2010, Boston, United States of America

Publ.-Id: 15017

The cyclotron resonance of holes in InGaAs/GaAs heterostructures with quantum wells in quantizing magnetic fields

Spirin, K. E.; Ikonnikov, A. V.; Gavrilenko, V. I.; Kozlov, D. V.; Drachenko, O.; Schneider, H.; Helm, M.

The spectra of the cyclotron resonance of holes in the InGaAs/GaAs selectively doped heterostructures with quantum wells are studied in pulsed magnetic fields as high as 50 T at 4.2 K. The previously observed effect of the inverted (compared with the results of the single-particle calculation of the Landau levels) ratio of the spectral weight of two split components of the line of the cyclotron resonance, which is attributed to the effects of the exchange interaction of holes, is confirmed. It is found that the ratios of intensities of the components of the line of the cyclotron resonance profoundly differ on the ascending and descending branches of the magnetic field pulse, which may be associated with a long time of the spin relaxation of holes between the two lowest Landau levels, which constitute tens of milliseconds.

Keywords: Cyclotron resonance; spin; lifetime; InGaAs

Publ.-Id: 15016

Noncovalent Tripeptidyl Benzyl- and Cyclohexyl-Amine Inhibitors of the Cysteine Protease Caspase-1

Löser, R.; Abbenante, G.; Madala, P. K.; Halili, M.; Le, G. T.; Fairlie, D. P.

Potent and noncovalent inhibitors of caspase-1 were produced by incorporating a secondary amine (reduced amide) isostere in place of the conventional electrophile (e.g., aldehyde) that normally confers high potency to cysteine protease inhibitors. Benzyl- or cyclohexylamines produced potent, reversible, and competitive inhibitors that were selective for caspase-1 (e.g., Ki=47 nM) over caspases 3 and 8with minimal cytotoxicity. Unlike most cysteine protease inhibitors, these compounds do not react covalently and indiscriminately with thiols.

Publ.-Id: 15015

Antimalarial activity of azadipeptide nitriles

Löser, R.; Gut, J.; Rosenthal, P. J.; Frizler, M.; Gütschow, M.; Andrews, K. T.

Azadipeptide nitriles—novel cysteine protease inhibitors—display structure-dependent antimalarial activity against both chloroquine-sensitive and chloroquine-resistant lines of cultured Plasmodium falciparum malaria parasites. Inhibition of parasite’s hemoglobin-degrading cysteine proteases was also investigated, revealing the azadipeptide nitriles as potent inhibitors of falcipain-2 and -3. A correlation between the cysteine protease-inhibiting activity and the antimalarial potential of the compounds was observed. These first generation azadipeptide nitriles represent a promising new class of compounds for antimalarial drug development.

Publ.-Id: 15014

Synthesis and 99mTc-Labeling of a PNA Oligomer Containing a New Ligand Derivative of 2,2´-Dipicolylamine

Jäger, K.; Gasser, G.; Zenker, M.; Bergmann, R.; Steinbach, J.; Stephan, H.; Metzler-Nolte, N.

The search for chelating ligands which can be efficiently labeled with radiometals, and which also contain a functional group allowing a facile conjugation to biomolecules is currently a hot topic in radiopharmacy. The 2,2’-dipicolylamine (Dpa) has already been found to be a good candidate for labeling with 186Re, 188Re and 99mTc1 while the Cu(I)-catalyzed [2+3] azide/alkyne cycloaddition, often referred to as Click Chemistry,2 has been shown to be an effective coupling method. With this in mind, we recently developed the facile synthesis of an azido derivative of Dpa (Dpa-N3, Figure 1).3 Furthermore, as a proof of principle of the possible functionalization of our ligand to a biomolecule, Dpa-N3 was successfully coupled, on the solid phase, to a ethinyl-substituted Peptide Nucleic Acid (PNA) oligomer employing the Click Chemistry methodology to give the expected Dpa-ethyl-triazol-PNA. Both Dpa-N3 and Dpa-ethyl-triazol-PNA could be efficiently labeled with 99mTc using the precursor [99mTc(H2O)3(CO)3]+ to afford [99mTc(CO)3(Dpa-ethyl-triazol-N3)]+ and [99mTc(CO)3(Dpa-ethyl-triazol-PNA], respectively. The radionuclide 99mTc was tightly bound by the Dpa-chelator avoiding the formation of pertechnetate for at least 24h. Partitioning experiments in a 1-octanol/water system confirmed that both [99mTc(CO)3(Dpa-N3)]+ and [99mTc(CO)3(Dpa-ethyl-triazol-PNA] are rather hydrophilic. Biodistribution studies of [99mTc(CO)3(Dpa-ethyl-triazol-PNA] in Wistar rats showed a fast blood clearance and only a modest accumulation in the kidneys. Similar results were found when a mouse model (NMRI nu/nu) was used.


1. T. Storr, C. L. Fisher, Y.Mikata, S. Yano, M. J. Adam, C. Orvig, Dalton Trans., 2005, 654-655.
2. M. V. Gil, M. J. Arévalo, Ó. López Synthesis, 2007, 11, 1589-1620.
3. G. Gasser, K. Jäger, M. Zenker, R.Bergmann, J. Steinbach, H. Stephan, N. Metzler-Nolte, 2010, submitted.

  • Poster
    5th International Symposium on Bioorganometallic Chemistry, 05.-09.07.2010, Bochum, D

Publ.-Id: 15013

Radiomarkierung eines PNA-DPA (2-2´-Dipicolylamin)-Konjugates mit 99mTc

Jäger, K.; Gasser, G.; Bergmann, R.; Stephan, H.; Steinbach, J.

Ein großes Problem bei der Verwendung radiomarkierter Antikörper in der Tumorbehandlung ist deren langsame Anreicherung im Zielgewebe. Daraus ergibt sich eine erhebliche Strahlenbelastung des ganzen Körpers. Um dieses Problem zu umgehen, wurden bereits verschiedene Strategien, die auf einem Pretargeting-Konzept beruhen, untersucht. Diese basieren auf dem Prinzip, erst den Antikörper um Tumor anreichern zu lassen, und anschließend eine radiomarkierte Substanz zu applizieren, die sich schnell am Antikörper anreichert. Hierzu ist die Anwendung von komplementären Verbindungen notwendig. Insbesondere die Systeme (Strept-)Avidin/Biotin und MORF wurden bisher intensiv erforscht. Es gibt jedoch auch Ansätze, weitere metabolisch stabile Oligonukleotide zu verwenden. Unser Ziel ist es, PNA(Peptidnukleinsäure)-Derivate zu entwickeln, die sich für einen Pretargeting-Einsatz eignen.

Es wurde eine 12mer PNA mittels Festphasensynthese hergestellt, an die mittels Click-Chemie der bereits für die Komplexierung von Technetium und Rhenium gut untersuchte DPA-Chelator angebracht wurde. Für die Anbindung des Chelators wurde die so genannte Huisgen-Reaktion verwendet, bei der ein Alkin und ein Azid kupfervermittelt einen Triazolring bilden. Es wurde PNA-Alkin und DPA-Azid eingesetzt.
Die Radiomarkierung des entstandenen PNA-DPA-Konjugates wurde mit [99mTc(H2O)3]+ durchgeführt, wobei die Markierungsbedingungen mittels Radio-HPLC optimiert wurden. Zudem wurde die Bioverteilung des 99mTc-markierten Konjugates in gesunden Wistar-Ratten untersucht.

Das Konjugat konnte mit sehr guten Ausbeuten >90% mit 99mTc markiert werden. Bioverteilungsstudien zeigten, dass das Konjugat schnell über die Nieren ausgeschieden wird. Es wurde keine erhöhte Aufnahme von Aktivität im Magen und der Schilddrüse gefunden.

Unsere Untersuchungen deuten darauf hin, dass PNA-DPA-Konjugate zur stabilen Radiomarkierung mit 99mTc geeignet sind.
Mit den verwendeten 99mTc-PNA-DPA-Konjugaten wurde eine hohe in vivo Stabilität gepaart mit einer schnellen Blutclearance erreicht. Die Verweilzeit des Konjugates im Blut ist aber noch zu niedrig, um eine ausreichende Hybridisierung mit dem komplementären Strang in höherem Maße zu gewährleisten. Eine längere Zirkulation des radiomarkierten Präparates wäre wünschenswert. Die schnelle und fortdauernde Anreicherung in den Nieren stellt dennoch eine Belastung für das Nierengewebe dar. Die Modelluntersuchungen mit dem diagnostischen Radionuklid 99mTc sollen mit dem Therapienuklid 188Re fortgesetzt werden.

[1] O. C. Boerman, F. G. van Schaijk, W. J. G. Oyen, F. H. M. Corstens, J. Nucl. Med. 2003, 44, 3, 400-411
[2] G. Liu, S. Dou, J. He, D. Yin, S. Gupta, S. Zhang, Y. Wang, M. Rusckowski, D. J. Hnatowich, Appl. Radiat. Isot. 2006, 64, 9, 971-978
[3] M. Rusckowski, T. Qu, F. Chang, D. J. Hnatowich, Cancer, 1997, 80, 12, 2699-2705
[4] G. Gasser, K. Jäger, M. Zenker, R. Bergmann, H. Stephan, J. Steinbach, N. Metzler-Nolte. J. Inorg. Biochem. 2010; doi:10.1016/j.jinorgbio.2010.06.011

  • Lecture (Conference)
    18. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie der DGN, 16.-18.09.2010, Bad Boll, D

Publ.-Id: 15012

Kinetics and thermodynamics of defects, impurities, nanostructures and interfaces

Posselt, M.

Computer simulations using classical interatomic potentials are an efficient and promising tool to investigate and understand atomic-level properties and processes in advanced materials. They allow the consideration of length and time scales which are often hardly accessible by experiments. However, the accuracy of the interatomic potentials employed in such type of simulations determines decisively the quality of the obtained results. Therefore, these potentials must be continuously improved and evaluated.
In the present contribution three applications of atomistic computer simulations are illustrated. The focus is on kinetics, energetics and thermodynamics of defects, impurities, nanostructures and interfaces in materials for micro- and nanoelectronics and in structural materials for fission reactors.

The first example deals with molecular dynamics simulations on basic migration mechanisms of mono- and di-(self-)interstitials in Si. Both the atomic mobility due to the presence of the defect and the defect mobility itself were determined. The mechanism of di-interstitial migration depends on temperature, in contrast to that of the mono-interstitial.

In the second example amorphous Si and Ge as well as their solid-phase epitaxial recrystallization (SPER) are considered. Results obtained by different interatomic potentials are compared. The molecular dynamics simulations yield amorphous material with realistic structural and thermodynamic properties, but the SPER rate is strongly overestimated. It is shown that a more realistic SPER rate can be obtained using a modified interatomic potential which yields a higher melting temperature of the amorphous phase. This is explained by the fact that both melting and SPER are essentially determined by the flexibility of atomic bonds.

The subject of the third example is the formation of coherent clusters containing vacancies, Cu and Ni in bcc-Fe. Using the most recent interatomic potential for Fe-Cu-Ni alloys, the structure, energetics and thermodynamics of the clusters were determined. Many clusters up to a size of 200 monomers (vacancies, Cu and Ni atoms) were studied. In the case of vacancy-Cu clusters a core-shell structure is found where Cu atoms coat the outer surface of vacancy clusters. In a vacancy-Cu-Ni cluster Ni atoms are never first nearest neighbors of vacancies, and the Ni atoms cover the Cu-surface of inner vacancy-Cu cluster. The total and monomer binding energy as well as the nucleation free energy of the clusters were calculated. The monomer binding energy is an important input parameter of rate theory and object kinetic Monte Carlo simulations. For further application in these calculations compact and physically-based fit formulae were derived from the atomistic data.

Keywords: atomistic computer simulation; kinetics; thermodynamics; defects; interfaces; nanostructures

  • Lecture (others)
    Seminarvortrag, SRMP, Department des Materiaux pour le Nucleaire, CEA Saclay, 10.12.2010, Saclay/Paris, France

Publ.-Id: 15011

Verification and validation of numerical models of the transport of insulation debris

Cartland Glover, G. M.; Kratzsch, A.; Krepper, E.; Renger, S.; Seeliger, A.; Zacharias, F.; Alt, S.; Kästner, W.; Kryk, H.; Weiss, F.-P.

Damage to insulation materials located near to a primary circuit coolant leak may compromise the operation of the emergency core cooling system (ECCS). Insulation material in the form of mineral wool fiber agglomerates (MWFA) maybe transported to the containment sump strainers, where they may block or penetrate the strainers. Though the impact of MWFA on the pressure drop across the strainers is minimal, corrosion products formed over time may also accumulate in the fiber cakes on the strainers, which can lead to a significant increase in the strainer pressure drop and result in cavitation in the ECCS.
An experimental and theoretical study performed by the Helmholtz-Zentrum Dresden-Rossendorf and the Hochschule Zittau/Görlitz is investigating the phenomena that maybe observed in the containment vessel during a primary circuit coolant leak. The study entails the generation of fiber agglomerates, the determination of their transport properties in single and multi-effect experiments and the long-term effect that corrosion and erosion of the containment internals by the coolant has on the strainer pressure drop.
The focus of this paper is on the verification and validation of numerical models that can predict the transport of MWFA. A number of pseudo-continuous dispersed phases of spherical wetted agglomerates represent the MWFA. The size, density, the relative viscosity of the fluid-fiber agglomerate mixture and the turbulent dispersion all affect how the fiber agglomerates are transported. In the cases described here, the size is kept constant while the density is modified. This definition affects both the terminal velocity and volume fraction of the dispersed phases. Note that the relative viscosity is only significant at high concentrations.
Three single effect experiments were used to provide validation data on the transport of the fiber agglomerates under conditions of sedimentation in quiescent fluid, sedimentation in a horizontal flow and suspension in a horizontal flow. The experiments were performed in a rectangular column for the quiescent fluid and a racetrack type channel that provided a near uniform horizontal flow. The numerical models of sedimentation in the column and the racetrack channel found that the sedimentation characteristics are consistent with the experiments. For channel suspension, the heavier fibers tend to accumulate at the channel base even at high velocities, while lighter phases are more likely to be transported around the channel.

Keywords: Mineral Wool Fiber Agglomerates; Loss of Coolant Accidents; Containment Sump; Computational Fluid Dynamics; Multiphase Flow

  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 25.-29.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), CD-ROM
  • Lecture (Conference)
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 25.-29.09.2011, Toronto, Canada

Publ.-Id: 15010

Setting-up an accelerator mass spectrometry (AMS) facility: The role of chemistry

Merchel, S.; Munnik, F.; Andermann, C.; Bourlès, D.; Braucher, R.; Gloaguen, R.; Martschini, M.; Steier, P.

Medium-energy AMS facilities such as the 5 MV British SUERC and French ASTER or the two 6 MV German DREAMS at Dresden[1] and Cologne AMS have recently been installed. These machines need physicists to get them running but also scientists to establish AMS chemistry on-site. As it is not advisable to change simultaneously two ”things”, i.e. machine and chemistry, a cooperation with the teams of ASTER and VERA helped to check the new sample preparation of DREAMS. A ”good” AMS sample has two features: high stable isotope current and low isobar concentration. High chemical yields and low concentrations of other elements, from the matrix or chemical products used, are less important, but may play a role if e.g. a matrix contains Ti being introduced into BeO-targets as shown by µ-XRF [2] and recent µ-PIXE analyses of final AMS-targets at HZDR. A processing blank with low radionuclide/stable nuclide ratio is essential for projects near the detection limit. Finally, a fast, easy and cheap separation guarantees high sample throughput and reasonable costs. Ref.: [1] [2] S. Merchel et al., NIMB 266 (2008) 4921. Ackn.: Thanks to T. Schildgen, C. Yildirim (Potsdam), K. Klemm, M. Fuchs (TUBA), M. Arnold, G. Aumaître (ASTER), A. Wallner (VERA).

Keywords: accelerator mass spectrometry

  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) 2011, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15009

The Rossendorf Beamline at ESRF - A unique facility to perform X-ray absorption spectroscopy of radionuclides

Scheinost, A. C.

The Rossendorf Beamline at ESRF - A unique facility to perform X-ray absorption spectroscopy of radionuclides

Keywords: XAS; Actindies

  • Invited lecture (Conferences)
    Seminar des Instituts fuer Energie- und Klimaforschung, FZ Juelich, 25.03.2010, Juelich, Germany

Publ.-Id: 15007

Probing redox reactions at the mineral/water interface by X-ray absorption spectroscopy: Reduction of Se, Sb and Pu by Fe(II)-bearing minerals

Scheinost, A. C.

Probing redox reactions at the mineral/water interface by X-ray absorption spectroscopy: Reduction of Se, Sb and Pu by Fe(II)-bearing minerals

Keywords: EXAFS; XANES; Redox; Antimony; Plutonium; selenium; mackinawite; magnetite; siderite; clays

  • Invited lecture (Conferences)
    Graduiertenkolleg "Spurenanalytik von Elementspezies: Methodenentwicklungen und Anwendungen", 23.03.2010, Mainz, Germany

Publ.-Id: 15006

Vorschlag für ein Aktivierungsbenchmark an WWER-440 Reaktordruckbehältern

Konheiser, J.

Bei der Stilllegung von KKW spielt die Radioaktivität des Reaktordruckbehälters (RDB) eine entscheidende Rolle. Geeignete Messdaten für die Validierung von Programmen für die Fluenz- und Aktivitätsberechnungen sind schwer zu finden bzw. nicht vorhanden. Die genommene Trepans vom RDB des KKW Greifswald bietet eine einzigartige Möglichkeit Daten zu diesem Zweck zu gewinnen. In der Präsentation wird deshalb ein Aktivierungbechmark auf Basis von experimentellen Daten der Trepans vorgeschlagen.

At the decommissioning of NPP, the radioactivity of the reactor pressure vessel (RPV) is of crucial importance. Generally, suitable measurement data for the validation of codes for the calculation of fluences and aktivities are not easy to be found. Trepans taken from dismantled VVER-440 RPVs of Greifswald NPP provide a unique opportunity for this purpose. In the presentation an activation benchmark to carry out is suggested based on the experimental data of trepans.

Keywords: decommissioning; benchmark; fluence calculation; aktivity calculation

  • Lecture (others)
    10. AAA Usergroup Meeting, 06.12.2010, Garching bei München, Deutschland

Publ.-Id: 15005

Kelvin probe force microscopy in the presence of intrinsic local electric fields

Baumgart, C.; Müller, A.-D.; Müller, F.; Schmidt, H.

Kelvin probe force microscopy (KPFM) is used to investigate the electrostatic force between a conductive probe and doped semiconductors. The observed frequency dependence of the probed KPFM bias is strongly related to sample-specific intrinsic local electric fields. Equilibrium drift and diffusion of excess charge carriers at low operation frequencies influence the characteristics of the asymmetric electric dipole in the surface region of the investigated semiconductors during the KPFM measurement. The sample-specific KPFM background signal does not influence the frequency-dependent lateral variation of the electrical signal. The KPFM bias probed on doped semiconductor nanostructures with high or small enough operation frequencies allows for quantitative dopant profiling or investigation of diffusion processes in internal electric fields, respectively.

Keywords: Kelvin probe force microscopy (KPFM); Semiconductors; Dopant profiling

Publ.-Id: 15004

Strangeness measurements at the HADES experiment

Schmah, A.; Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Díaz, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gil, A.; Golubeva, M.; González-Díaz, D.; Guber, F.; Hennino, T.; Holzmann, R.; Huck, P.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kopp, A.; Korcyl, G.; Kornakov, G. K.; Kotte, R.; Kozuch, A.; Kraza, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Kählitz, P.; Ladygin, V.; Lamas-Valverde, J.; Lang, S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Müntz, C.; Naumann, L.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roskoss, J.; Rustamov, A.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

We report on high acceptance di-electron spectrometer (HADES) measurements of strange hadrons in the collision systems Ar(1.756 AGeV)+KCl and p+p at 3.5 GeV. Comparisons of K0s transverse mass and rapidity spectra to IQMD transport model calculations give a strong hint to a repulsive kaon–nucleon potential. The effect of the potential shows up strongest at very low transverse momenta, which were measured by HADES with high statistics. Statistical model fits show a fair agreement to the particle yields measured in the heavy-ion data, apart from the Ξ− yield which is off by more than an order of magnitude. Furthermore, first results from the Σ(1385)+ reconstruction in p+p reactions are presented, showing an excellent agreement with published data.

Publ.-Id: 15003

Study of elementary reactions with the HADES dielectron spectrometer

Ramstein, B.; Agakishiev, G.; Agodi, C.; Balanda, A.; Bellia, G.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Braun-Munzinger, P.; Cabanelas, P.; Castro, E.; Christ, T.; Destefanis, M.; Díaz, J.; Dohrmann, F.; Dybczak, A.; Fabbietti, L.; Fateev, O. V.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzón, J. A.; Gernhäuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; González-Díaz, D.; Grosse, E.; Guber, F.; Heilmann, M.; Hennino, T.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Kozuch, A.; Krasa, A.; Krizek, F.; Krücken, R.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Marin, J.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Morinière, E.; Mousa, J.; Müntz, C.; Naumann, L.; Novotny, R.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Sudol, M.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.; Zhou, P.; Zumbruch, P.

Results obtained with the HADES dielectron spectrometer at GSI are discussed, with emphasis on dilepton production in elementary reactions.

  • Open Access Logo Acta Physica Polonica B 41(2010), 365

Publ.-Id: 15002

Molecular Dynamics Simulations of BMP-2 Adsorption on a Hydrophobic Surface

Oliveira, A. F.; Gemming, S.; Seifert, G.

In the present work, the adsorption of BMP-2 on a hydrophobic surface model is investigated by means of molecular-dynamics simulations within the NVT ensemble. The adsorption paths of the single monomer and the homodimer of BMP-2 have been compared. The nature of the residues interacting directly with the hydrophobic monolayer at different adsorption stages is shown. Conformational changes driven by the adsorption process, as well as the influence of aqueous environment on the stabilization of the BMP-2 secondary structure are also discussed.

Keywords: bone remodeling; bone replacement; biomineralization; molecular dynamics; force field; BMP


Publ.-Id: 15001

Conformational Analysis of Aqueous BMP-2 Using Atomistic Molecular-Dynamics Simulations

Oliveira, A. F.; Gemming, S.; Seifert, G.

BMP-2 is an osteoinductive protein, involved in the differentiation and proliferation of osteoblasts, with potential application as bioactive agent in bone implants and scaffolds. Since the three-dimensional structure of a protein usually determines its bioactivity, in order to efficiently design bone implants activated with BMP-2 it is essential to identify the factors influencing the protein conformation. In the present work, atomistic molecular-dynamics simulations are employed to investigate the BMP-2 monomer and homodimer in vacuum and water. The influence of each environment on the BMP-2 structure is analyzed regarding protein structural changes and energy contributions driving the BMP-2 conformation.

Keywords: bone replacement; bone remodeling; molecular dynamics; force field; biomineralization

Publ.-Id: 15000

BioMin - Funktionalisierte Mineraloberflächen: Sorptionsmechanismen von wachstumsstimulierenden Proteinen an Oberflächen von Knochenersatzwerkstoffen auf Calciumphosphatbasis

Fischer, H.; Lindner, M.; Schickle, K.; Kirsten, A.; Seifert, G.; Oliveira, A.; Gemming, S.; Jennissen, H. P.; Zurlinden, K.; Meißner, M.; Müller-Mai, C.

The manufactured samples of amorphous and recrystallized bioactive glass 45S5 were sterilized for further investigations especially for the in vivo testing. Two common sterilization procedures for solid bodies, steam sterilization and hot air sterilization, were tested. After the steam sterilization the surface topography and the chemical content at the surface of the samples changed. This effect could not be observed after hot air sterilization. Hence, hot air sterilization procedure was chosento sterilize the samples. We developed a manufacturing process to produce porous -tricalcium phosphate specimens. NH4HCO3 was succesfully used to create pores inside the samples. The advantage of this material is that it decomposes at low temperature (60 °C) and so only can affect the samples a short temperature range from room temperature up to 60 °C. Hence, no cracks where detected at the surface and the core of the samples. Different kind of pore sizes and amount of porosity was created in the ceramic parts by using this porosifying agent. The bounding ability of the BMP-2 (Bone Morphogenic Protein) of amorphous and recrystallized bioactive glass was characterized by two different concentrations of the BMP-2 in the immersion fluid. The results show that a doubling of the concentration of the BMP-2 in the immersion fluid resulted in the two-fold amount of BMP-2 at the surface of the amorphous and the recrystallized bioactive glass. However, the release of the BMP-2 showed a difference with respect to these two materials. Both materials show an initial burst phase in the release of the bone morphogenetic protein from the surface of about two days followed by a sustained release. During the initial burst phase more BMP-2 was released from the recrystallized surface compared to amorphous surface of the bioactive glass. As experimental results on the BMP-2 activity on mineral surfaces indicate that a non-covalent attachment to an unpolar surface functionalization yields the best coverage, the relevant structural characteristics of BMP-2 under osteogenic conditions were studied by molecular dynamics simulations with a biological force field. An analysis of the local flexibility of BMP monomers and dimers in solution and on a non-polar functionalization revealed major structure changes at the N-terminus, close to the -helix, and around the disulfide bridge in the dimer. As all secondary structure elements remained intact in the bonded dimer, the results indicate that the flexible areas in-between may facilitate the docking of BMP-2 to surfaces, but are not involved in sterically driven osteogenic activity. Electronic structure calculations suggest alkylphosphonic acids and nucleotides as suitable surface func¬tio¬nalizations, which bind to the mineral surface with the polar part and expose an unpolar part to attach. The amorphous and recrystallized bioactive glass coated and not coated with BMP, respectively, were implanted in New Zealand white rabbits for four different implantation times (7, 28, 84, 168 days). 6 implants were used for one kind of material and implantation time, i. e. overall 96 cylindrical implants (3.96 mm diameter, 8.1 mm height) have been inserted. At present, the evaluations of specimens prior implantation and at 7 days were completed. Due to the implantation procedure a gap healing was observed, leading to a delay in bone formation in comparison to former studies in the same animal model with bioactive implants. Up to 7 days after implantation no bone-bonding was observed in any of the specimens. All of the materials (amorphous, crystalline each with and without BMP-coating) displayed no obvious changes in surface density and structure up to now indicating a lower surface reactivity as known from 45S5 bioactive glass. At 7 days the highest expression of an early marker, which indicates that the bone matrix is activated, was observed at the amorphous coated implants. Therefore, stimulation in bone formation around the BMP-coated implants is possible. Subsequently, we will histologically analyze the samples of longer implantation times to confirm this observation.

Keywords: bone remodeling; multi-scale modeling; density-functional; phase-field; bone replacement; bioglass

  • Lecture (Conference)
    Mineral Surfaces - From Atomic Processes to Industrial Application, 26.-27.10.2010, Mainz, Deutschland
  • Contribution to proceedings
    Mineral Surfaces - From Atomic Processes to Industrial Application, 26.-27.10.2010, Mainz, Deutschland
    Geotechnologien - Science Report 16: Mineral Surfaces - From Atomic Processes to Industrial Application, Potsdam: Koordinierungsbüro GEOTECHNOLOGIEN, ISSN: 1619-7399, 19-32

Publ.-Id: 14999

Materials Research at the FZD

Gemming, S.; Merchel, S.

General info about the FZD, AMS ice core measurements, simulation of structure formation in sea ice.

Keywords: sea ice; ice cores; brine channels; multiscale modeling; phase-field

  • Invited lecture (Conferences)
    1. Norwegian-German Sea-Ice Workshop, 06.-07.12.2010, Bremerhaven, Deutschland

Publ.-Id: 14998

Nanostrukturierte Verschleißschutzschichten für den Automobilbau - von der Konzeption zur Anwendung

Fassbender, J.; Möller, W.; Beyer, E.; Seifert, G.; Zellbeck, H.; Abrasonis, G.; Gemming, S.; Hübner, M.; Joswig, J.-O.; Krause, M.; Kunze, T.; Leson, A.; Makowski, S.; Posselt, M.; Weihnacht, V.

Optimierte, leichte, aber widerstandsfähige Werkstoffe eröffnen dem Fahrzeugbau die Möglichkeit, Energieeffizienz- und Klimaschutzziele mit einer Verbesserung der funktionalen Fähigkeiten des Fahrzeugs zu verbinden. Ziel des Projekts ist die Herstellung und Optimierung der dafür erforderlichen neuartigen, nanoskalig strukturierten, harten und selbstschmierenden Schichten für verschleißbelastete Motorenteile. Konventionelle dünne Funktionsschichten auf Kohlenstoffbasis werden in der Regel durch Niederdruck-Beschichtungsverfahren hergestellt. In den letzten Jahren sind neue Ansätze zur Weiterentwicklung dieser Materialklasse entstanden, die besonders auf nanoskalig strukturierte Systeme fokussieren, und die in Teilprojekt D1 ‘NanoCarbCoat’ für den automobilen Leichtbau erschlossen werden sollen. Dazu verbindet das betont interdisziplinär ausgerichtete Teilprojekt die Expertise von Partnern aus Natur- und Ingenieurwissenschaften zur Abscheidung und physikalischen Charakterisierung kohlenstoffbasierter Schichten, zur Modellierung der tribologischen Vorgänge an Schichten im Kontakt miteinander und mit einem Schmierstoff und zum Test der Beschichtung unter realistischen Bedingungen im Verbrennungsmotor.

Keywords: tribology; wear-resistant coatings; nanotribology; multiscale modeling; motor

  • Lecture (Conference)
    1. Internationales ECEMP-Kolloquium, 02.-03.12.2010, Dresden, Deutschland
  • Other report
    Dresden: ECEMP -Eigenverlag, 2010
    36 Seiten

Publ.-Id: 14997

Multifunctional oxides - Influence of defects on the ferroic properties

Gemming, S.; Zschornak, M.; Weißbach, T.; Stöcker, H.; Meyer, D. C.; Gemming, T.; Lubk, A.; Spaldin, N. A.

Transition metal oxides exhibit a wealth of physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. In addition, transition metal oxides are sensitive to the chemical environment via the external partial pressure of oxygen; changes induce stoichiometry deviations, which cause conductivity changes and modify the ferroic characteristics. The present study focuses on SrTiO3, YMnFeO5, and BiFeO3 and correlates local changes due to point and planar defects with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional calculations, which yield the basis for more large-scale simulations with effective Hamiltonian approaches. Under oxygen-poor conditions oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. In an Sr/O-rich environment the phases SrO(SrTiO3)n are formed, which yield a distinct change of the X-Ray reflectivity due to the regular arrangement of extrinsic SrO(001) stacking faults. YMn2O5 has a series of complex antiferromagnetic phases in coexistence with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found and ferroelectricity is absent. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the Fe-substituted and the mangenese-only compounds and relates them to crystal-field interactions. BiFeO3 is a rhombohedral multiferroic with several domain wall configurations. Among them, the 109 and 180 walls have a significant change in the component of their polarization perpendicular to the wall; the corresponding step in the
electrostatic potential is consistent with a recent report of electrical conductivity at the domain walls. Changes in the Fe-O-Fe bond angles at the walls change the canting of the Fe magnetic moments which can enhance the local magnetization.

Keywords: multifunctional; oxides; oxide electronics; density-functional; DFT; multiferroic

  • Lecture (Conference)
    MMM 2010, 04.-08.10.2010, Freiburg Brsg., Deutschland
  • Invited lecture (Conferences)
    Seminar of the Collaborative Research Centre/Transregio TRR 80, 26.05.2011, Garching, Deutschland

Publ.-Id: 14996

CFD analyses of fibre transport and fibre deposition at plunging jet conditions

Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiß, F.-P.; Alt, S.; Kratzsch, A.; Renger, S.; Kästner, W.

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behaviour of emergency core cooling systems during all types of loss of coolant accidents. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modelling efforts are concentrated at Forschungszentrum Dresden-Rossendorf. In the current paper, the basic concepts for CFD modelling are described and feasibility studies are presented. The model capabilities are demonstrated via complex flow situations, where a plunging jet agitates insulation debris.

Keywords: insulation debris; transport; sedimentation; CFD; simulation; experiments; model validation

  • Kerntechnik 76(2011)1, 30-38

Publ.-Id: 14995

Gas–liquid flows in medium and large vertical pipes

Duan, X. Y.; Cheung, S. C. P.; Yeoh, G. H.; Tu, J. Y.; Krepper, E.; Lucas, D.

Gas–liquid bubbly flows with wide range of bubble sizes are commonly encountered in many industrial gas–liquid flow systems. To assess the performances of two population balance approaches – Average Bubble Number Density (ABND) and Inhomogeneous MUlti-SIze-Group (MUSIG) models – in tracking the changes of gas volume fraction and bubble size distribution under complex flow conditions, numerical studies have been performed to validate predictions from both models against experimental data of Lucas et al. (2005) and Prasser et al. (2007) measured in the Forschungszentrum Dresden-Rossendorf FZD facility. These experiments have been strategically chosen because of flow conditions yielding opposite trend of bubble size evolution, which provided the means of carrying out a thorough examination of existing bubble coalescence and break-up kernels. In general, predictions of both models were in good agreement with experimental data. The encouraging results demonstrated the capability of both models in capturing the dynamical changes of bubbles size due to bubble interactions and the transition from ‘‘wall peak’’ to ‘‘core peak’’ gas volume fraction profiles caused by the presence of small and large bubbles. Predictions of the inhomogeneous MUSIG model appeared marginally superior to those of ABND model. Nevertheless, through the comparison of axial gas volume fraction and Sauter mean bubble diameter profiles, ABND model may be considered an alternative approach for industrial applications of gas–liquid flow systems.

Keywords: Population balance; Bubble columns; Bubble Multiphase flow; Coalescence; Break-up

Publ.-Id: 14994

Sugar-decorated dendritic nanocarriers: Encapsulation and release of the octahedral rhenium cluster complex [Re6S8(OH)6]4-

Kubeil, M.; Stephan, H.; Pietzsch, H.-J.; Geipel, G.; Appelhans, D.; Voit, B.; Hoffmann, J.; Brutschy, B.; Mironov, Y. V.; Brylev, K. A.; Fedorov, V. E.

The encapsulation of a nanometer sized octahedral anionic rhenium cluster complex with six terminal hydroxo ligands [Re6S8(OH6]4- in maltose-decorated poly (propylene amine) dendrimers (POPAM, generation 4 and 5) has been investigated. Ultrafiltration experiments showed that maximal loading capacity of the dendrimers with the cluster complex is achieved after about ten hours in aqueous solution. To study the inclusion phenomena, three different methods have been applied: UV/vis, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and laser induced liquid bead ion desorption mass spectrometry (LILBID-MS). From the results obtained, it could be concluded that: (i) the hydrolytic stability of the rhenium cluster complex is significantly enhanced in the presence of dendritic hosts; (ii) the cluster anions are preferentially bound inside the dendrimers; (iii) the number of cluster complexes encapsulated in the dendrimers increases with rising dendrimer generation. On average, 4 – 5 cluster anions can preferentially be captured in the interior of sugar-coated dendritic carriers. An asymptotical progression of the release of cluster complexes from the loaded dendrimers was observed under physiologically relevant conditions (isotonic sodium chloride solution: ~ 93% within 4 days for loaded POPAM-G4-maltose; ~ 86% within 4 days for loaded POPAM-G5-maltose). Those encapsulation and release properties of maltose-decorated nanocarriers imply the possibility for the development of the next generation of dendritic nanocarriers with specific targeting of destined tissue for therapeutic treatments.


Publ.-Id: 14993

Effect of secondary phase formation on optical properties of the Al-doped ZnO

Vinnichenko, M.; Cornelius, S.; Krause, M.; Gago, R.; Munnik, F.; Sergeev, O.; Chakanga, K.; von Maydel, K.; Kolitsch, A.; Möller, W.

The electrical properties of low-cost Al-doped ZnO (AZO) films are known to deteriorate substantially during growth by different deposition techniques at temperatures above a certain optimum value. As it has been shown recently using techniques based on synchrotron radiation, the formation of an insulating metastable homologous (ZnO)3Al2O3 phase [1] at elevated temperatures is the reason for the observed behavior of the electrical properties in case of the films grown by reactive pulsed magnetron sputtering (RPMS) [2]. Little is known about optical properties of ZnO-Al2O3 solid solutions in general and (ZnO)3Al2O3 phase in particular. The optical properties in the UV spectral range are of special importance because they provide information about the fundamental and above-band gap band-to-band electron transitions. The present work focuses on characterization of AZO and undoped ZnO films in a wide spectral range by spectroscopic ellipsometry (photon energy range 0.73-5.8 eV) and spectrophotometry (0.5-6 eV). Selected samples were studied using Raman spectroscopy. The optical investigations complement results of Hall-effect, X-ray diffraction, X-ray absorption near edge structure (XANES) measurements, and elastic recoil detection analysis [2]. Films with defined Al concentrations (cFAl=0-20 at.%) grown by RPMS at temperatures ranging from RT to 550 °C were investigated.
The comparison of undoped ZnO and AZO films with the highest crystallinity shows that an addition of ~1 at.% of Al leads to the best electrical properties, although (ZnO)3Al2O3 phase signature appears in its Al K-edge XANES spectra. The latter may be a reason for the observed substantial decrease of the refractive index in the whole spectral range and for the broadening of the parametric semiconductor model (PSEMI) oscillator around the fundamental transition energies. This is accompanied by the broadening of the allowed ZnO Raman lines and appearance of the broad band around 565 cm-1 which is characteristic of ZnO with high defect concentrations. The AZO films remain conductive with cFAl values increasing up to ~8-10 at.%, while their (ZnO)3Al2O3 phase-related peaks in Al K-edge spectra scale with cFAl. In this case, refractive index decreases and PSEMI oscillator broadens further which is in agreement with deteriorating film crystallinity. At this level of doping the allowed ZnO Raman lines are no longer detectable. On the other hand, the defect induced Raman features change their intensity distribution. Finally, increasing cFAl>10 at.% leads to formation of insulating nanocrystalline films, which show even more intense (ZnO)3Al2O3 phase-related XANES peaks. These films have the lowest refractive index, which, however, is still substantially higher than that of amorphous Al2O3. The observed increasing UV transmittance can be explained by a significantly decreasing amplitude and a blue-shift of the PSEMI oscillator of these films. The latter may be explained neither by the Burstein-Moss shift because the films are insulating nor by effective medium approximation using optical constants of ZnO and Al2O3. Instead, it may be understood in analogy to optical properties of the metastable wurtzite MgXZn1-XO alloys. This assumption requires more detailed investigations which are currently in progress.
[1] S. Yoshioka et al, J. Appl. Phys. 103, 014309 (2008).
[2] M. Vinnichenko et al, Appl. Phys. Lett. 2010 (in press).

Keywords: transparent conducting oxides; magnetron sputtering; spectroscopic ellipsometry; Raman spectroscopy; spectral photometry

  • Lecture (Conference)
    3rd International Symposium on Transparent Conductive Materials, 17.-21.10.2010, Analipsi / Hersonissos, Crete, Greece

Publ.-Id: 14992

Examination of different flow regimes in the mold of a model of continuous casting using the contactless inductive flow tomography

Wondrak, T.; Timmel, K.; Gundrum, T.; Stefani, F.; Gerbeth, G.

In the continuous casting process the flow structure in the mold plays an important role for the quality of the steel produced. Open problems are the influence of a two phase flow in the submerged entry nozzle and the influence of electromagnetic stirrers. One possible method to determine the flow structure in the mold is the contactless inductive flow tomography (CIFT) which is able to reconstruct the three-dimensional velocity field in electrically conducting melts from externally measured induced magnetic fields. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external magnetic field and to measure the induced fields at the narrow faces of the mold. The actual time resolution is about 1 Hz. We will present the results of an experiment with a two phase flow regime and the effects of an electromagnetic stirrer around the submerged entry nozzle on the flow field in the mold.

Keywords: continuous casting; velocity measurement; liquid metal; contactless inductive flow tomography

  • Lecture (Conference)
    13th MHD-days, 22.-23.11.2010, Forschungszentrum Dresden-Rossendorf, Germany

Publ.-Id: 14991

EduGATE - simple examples for educative purpose using the GATE simulation platform

Pietrzyk, U.; Zakhnini, A.; Axer, M.

The GATE (1) platform is based on the GEANT4 package developed at CERN/Geneva. It has received a wide acceptance in the field of simulating medical imaging devices including SPECT, PET, CT and also applications in radiation therapy. This is mainly due to the fact, that GATE can be configured by commands, which are, for the sake of simplicity, listed in a collection of one or more macro files. The aim of this contribution is to use all helpful features of GATE to provide insights into the physics of medical imaging by means of a collection of very basic and simple GATE macros in connection with analysis programs based of ROOT.
Simplifying or extending examples for GATE (current version: 6), which come with the basic distribution, we configured the relevant macro files for running GATE in such a way, they are easily modified with a text editor, hence, allowing the user or student to study the effect of changing the material of a phantom, switching the type of radioactive source or to select or de-select a specific type of electro-magnetic interaction. The results from the simulation are usually stored in binary files readable by the ROOT package, as projection files useful for reconstruction programs or even in ASCII format, for fast inspection. Especially the ROOT package turned out to be a very useful utility to analyze the output data from the simulation under various aspects. ROOT programs, written in c++, serve as tools to either simply visualize basic distributions or select or resort the data into formats readable by programs for image reconstruction. The detector setups are kept very simple but expose the basic principles of imaging. The EduGATE examples were tested and successfully presented during medical physics lectures to point the students to the various aspects of medical imaging related to the basic physical principles. Currently, four imaging systems have been created: simple coincidence channel, PET, Gamma camera (planar) and SPECT. The users can select from a list of various isotopes, different detector material, experience the influence of attenuating material in the form of an extra cylinder around the source, whose shape and activity can also be varied. Analysis modules to be applied within the ROOT environment are also
provided. They serve as a means for students to start exploring the data structures and learn, how to analyze and evaluate a specific detector configuration that has be simulated under various conditions.
It opens an interesting opportunity for lecturers as well as students to use powerful tools, while becoming acquainted with the world of medical imaging. EduGATE uses solely Open Source software, which is freely available and can be used on any platform, where GATE and ROOT are operating.
(1) S. Jan et al 2004 GATE: a simulation toolkit for PET and SPECT. Phys. Med. Biol. 49, 4543–4561

  • Poster
    NuklearMedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 14988

18F-Labelled Alkyl-Substituted Spirocyclic Piperidines – Potential Radiotracers For PET Imaging Of σ1 Receptors

Deuther-Conrad, W.; Maisonial, A.; Fischer, S.; Hiller, A.; Schepman, D.; Große Maestrup, E.; Funke, U.; Steinbach, J.; Wünsch, B.; Brust, P.

Objectives: Neuroprotective effects mediated by signal transduction via the transmembrane σ1 receptor localised in the endoplasmatic reticulum make this receptor a promising target for novel approaches in the therapy of neurodegenerative diseases. Furthermore, behavioural changes are assumed to be related to alterations in the expression of σ1 receptors mainly expressed in the striatum. Thus, molecular imaging of σ1 receptors of the brain may hold potential in diagnostics and drug development, and we have compared in mice radiotracer properties of a series of new 18F-labelled spirocyclic piperidine derivatives with high affinity and selectivity for σ1 receptors.

Methods: Radiosynthesis of fluoromethyl- ([18F]WMS1850), fluoroethyl- ([18F]fluspidine), fluoropropyl- ([18F]WMS1813), and fluorobutyl-([18F]WMS1847) substituted derivatives was performed by nucleophilic substitution of the corresponding tosylate precursors using K[18F]F-K222-carbonate complex. Organ distribution of radiotracers applied i.v. was determined in female CD-1 mice at 5, 30, 60, and 120 min p.i. Spatial distribution of the radiotracer binding sites was examined by ex vivo brain autoradiography at 45 min p.i. Target specificity was investigated in blocking studies with pre-application of 1 mg/kg of the σ1 receptor ligand haloperidol by assessing the organ distribution of the respective radiotracer at 60 min p.i. The metabolic stability in vivo of each radiotracer was evaluated by radio-TLC and -HPLC analyses of brain, plasma, and urine samples.

Results: The radiotracers were obtained with radiochemical yields of 35-53%, radiochemical purities >98.5%, and specific activities >150 GBq/µmol. All radiotracers readily passed the blood-brain barrier with high brain uptake values at 30 min p.i.: [18F]fluspidine = 4.71 ± 1.39 % ID/g, [18F]WMS1813 = 3.18 ± 0.68 % ID/g, [18F]WMS1850 = 2.65 ± 0.68 %ID/g, and [18F]WMS1847 = 1.78 ± 0.16 %ID/g. High initial radioactivity uptake was also observed in peripheral organs which express σ1 receptors such as spleen, thymus, kidney, and stomach. In brain as well as in these organs the uptake of radioactivity was significantly reduced in mice pre-treated with haloperidol. Distribution patterns of the radiotracer binding sites in brain were resembling for all four radiotracers with [18F]fluspidine possessing the highest target (facial nucleus)-to-nontarget (olfactory bulb) ratio (4.69 at 45 min p.i.). The metabolic stability in vivo was high for all radiotracers (75% parent radiotracer in plasma at 30 min p.i.), and none of the peripherally detected radiometabolites crossed the blood-brain barrier.

Conclusion: Fluoroalkylated spirocyclic piperidines are high affinity ligands for σ1 receptors with high brain uptake, specific binding, and good metabolic stability. Within the herein reported series of 18F-labelled derivatives, the in vivo data identify [18F]fluspidine as the most suitable radiotracer for further development in molecular imaging of σ1 receptors. [18F]fluspidine radiosynthesis is selected for transfer to an automated radiosynthesis module for further preclinical development.

  • Poster
    BRAIN 2011, 24.-28.05.2011, Barcelona, Spain

Publ.-Id: 14987

X-ray photoelectron study of Si+ ion implanted polymers

Tsvetkova, T.; Balabanov, S.; Bischoff, L.; Krastev, V.; Avramova, P.; Stefanov, I.

X-ray photoelectron spectroscopy was used to characterize different polymer materials implanted with low energy Si+ ions (E=30 keV, D= 1.1017 cm-2). Two kinds of polymers were studied – ultra-high-molecular-weight poly-ethylene (UHMWPE), and poly-methyl-methacrylate (PMMA). The non-implanted polymer materials show the expected variety of chemical bonds: carbon-carbon, carbon being three- and fourfold coordinated, and carbon-oxygen in the case of PMMA samples. The X-ray photoelectron and Raman spectra show that Si+ ion implantation leads to the introduction of additional disorder in the polymer material. The X-ray photoelectron spectra of the implanted polymers show that, in addition to already mentioned bonds, silicon creates new bonds with the host elements – Si-C and Si-O, together with additional Si dangling bonds as revealed by the valence band study of the implanted polymer materials.

Keywords: X-ray photoelectron spectroscopy; Si-implantation; PMMA

  • Lecture (Conference)
    16th ISCMP: Progress in Solid State and Molecular Electronics, Ionics and Photonics, 29.08.-03.09.2010, Varna, Bulgaria
  • Open Access Logo Journal of Physics: Conference Series 253(2010), 012070-1-012070-6
    DOI: 10.1088/1742-6596/253/1/012070

Publ.-Id: 14986

Assessment of alpha 7 nicotinic acetylcholine receptor availability in juvenile pig brain with [18F]NS10743

Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Becker, G.; Cumming, P.; Xiong, G.; Funke, U.; Sabri, O.; Peters, D.; Brust, P.

Purpose: To conduct a quantitative assessment with PET of the specific binding sites in brain of juvenile pigs for [18F]NS10743, a novel diazabicyclononane derivative targeting α7 nicotinic acetylcholine receptors (α7 nAChRs).

Methods: Dynamic PET recordings were made in isoflurane-anaesthetized juvenile pigs during 120 min after administration of [18F] S10743 in a baseline condition (n=3) and after blocking of the α7 nAChR with NS6740 (3 bolus + 1 continuous infusion; n=3). Arterial plasma samples were collected for determining the input function of the unmetabolized tracer. Kinetic analysis of regional brain time-radioactivity curves was performed, and parametric maps were calculated relative to arterial input.

Results: Plasma [18F]NS10743 passed readily into brain, with peak uptake occurring in α7 nAChRexpressing brain regions such as the colliculi, thalamus, temporal lobe, and hippocampus. The highest SUVmax was approximately 2.3, whereas the lowest uptake was in the olfactory bulb (SUVmax: 1.53 ± 0.32). Administration of NS6740 significantly decreased [18F]NS10743 binding late in the emission recording throughout the brain, except in the olfactory bulb, which was therefore chosen as reference region for calculation of BPND. The baseline BPND ranged from 0.39 ± 0.08 in cerebellum to 0.76 ± 0.07 in the temporal lobe. Pretreatment and constant infusion with NS6740 significantly reduced the BPND in regions with high [18F]NS10743 binding (temporal lobe: -29 %, p = 0.01; midbrain: -35 %, p = 0.02), without significantly altering the BPND in low binding regions (cerebellum: -16 %, p = 0.2).

Conclusion: This study confirms the potential of [18F]NS10743 as a target-specific radiotracer for the molecular imaging of central α7 nAChRs by PET.

Keywords: Nicotinic acetylcholine receptors; α7 nAChR; PET; Neurology; Metabolism; Diazabicyclononane

  • European Journal of Nuclear Medicine and Molecular Imaging 38(2011)8, 1541-1549

Publ.-Id: 14985

Preliminary investigations on high energy electron beam tomography

Bärtling, Y.; Hoppe, D.; Hampel, U.

In computed tomography (CT) cross-sectional images of the attenuation distribution within a slice are created by scanning radiographic projections of an object with a rotating X-ray source detector compound and subsequent reconstruction of the images from these projection data on a computer. CT can be made very fast by employing a scanned electron beam instead of a mechanically moving X-ray source.

Now this principle was extended towards high-energy electron beam tomography with an electrostatic accelerator. Therefore a dedicated experimental campaign was planned and carried out at the Budker Insitute of Nuclear Physics (BINP), Novosibirsk. There we investigated the capabilities of BINP’s accelerators as an electron beam generating and scanning unit of a potential high-energy electron beam tomography device. The setup based on a 1 MeV ELV-6 (BINP) electron accelerator and a single detector.

Besides tomographic measurements with different phantoms, further experiments were carried out concerning the focal spot size and repeat accuracy of the electron beam as well as the detector’s response time and signal to noise ratio.

Keywords: tomography; electron beam tomography; x-ray tomography

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-544 2010
    ISSN: 1437-322X


Publ.-Id: 14984

CFD Modellierung von Siedevorgängen in Brennelementbündeln eines Druckwasserreaktors

Krepper, E.

Der Vortrag beschreibt CFD-Modellansätze zur Modellierung unterkühlten Siedens und zeigt Anwednungsmöglichkeiten bei der Beurteilung von Abstandhaltergeometrien von DWR-Brennelementen auf.

Keywords: CFD; unterkühltes Sieden; Brennelement Druckwasserreaktor

  • Invited lecture (Conferences)
    Festakt zum 15-jährigen Bestehen des IPM, 19.11.2010, Zittau, Deutschland

Publ.-Id: 14983

Modeling of the evolution of bubble size distribution of gas-liquid flow inside a large vertical pipe : influence of bubble coalescence and breakup models

Liao, Y.; Lucas, D.

The range of gas-liquid flow applications in today’s technology is immensely wide. Important examples can be found in chemical reactors, boiling and condensation equipments as well as nuclear reactors. In gas-liquid flows, the bubble size distribution plays an important role in the phase structure and interfacial exchange behaviors. It is therefore necessary to take into account the dynamic change of the bubble size distribution to get good predictions in CFD. An efficient 1D Multi-Bubble-Size-Class Test Solver was introduced in Lucas et al. (2001) for the simulation of the development of the flow structure along a vertical pipe. The model considers a large number of bubble classes. It solves the radial profiles of liquid and gas velocities, bubble-size class resolved gas fraction profiles as well as turbulence parameters on basis of the bubble size distribution present at the given axial position. The evolution of the flow along the height is assumed to be solely caused by the progress of bubble coalescence and break-up resulting in a bubble size distribution changing in the axial direction. In this model, the bubble coalescence and breakup models are very important for reasonable predictions of the bubble size distribution. Many bubble coalescence and breakup models have been proposed in the literature. However, some obvious discrepancies exist in the models; for example, the daughter bubble size distributions are greatly different from different bubble breakup models, as reviewed in our previous publication (Liao & Lucas, 2009a; 2010). Therefore, it is necessary to compare and evaluate typical bubble coalescence and breakup models that have been commonly used in the literature.
Thus, this work is aimed to make a comparison of several typical bubble coalescence and breakup models and to discuss in detail the ability of the Test Solver to predict the evolution of bubble size distribution.

Keywords: Bubble size distribution; bubble coalescence and breakup model; vertical pipe flow

  • Open Access Logo Contribution to proceedings
    Jahrestagung Kerntechnik 2011, 17.-19.05.2011, Berlin, Germany
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2011, 17.-19.05.2011, Berlin, Germany

Publ.-Id: 14982

Annual Report 2009 - Institute of Safety Research

Weiss, F.-P.; Schäfer, F.; (Editors)

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-541 2010
    ISSN: 1437-322X


Publ.-Id: 14981

Updated analysis of the TOPFLOW CCFL experiments in a model of the hot leg of a PWR

Vallée, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Helmholtz-Zentrum Dresden Rossendorf (HZDR). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of HZDR, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, a discrepancy was first observed between the air/water and steam/water series. Further investigations show that the steam was probably wet due to heat losses and to liquid entrainment from the heater circuit. Consequently, a correction of the steam measurements was required. The amount of parasitic water was evaluated indirectly over the zero liquid penetration noticed in the CCFL diagram. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a pressurised water reactor over a wide range of pressure and temperature conditions.

Keywords: two-phase flow; counter-current flow limitation; flooding; hot leg; pressurised water reactor

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2011, 17.-19.05.2011, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2011, 17.-19.05.2011, Berlin, Deutschland, Berlin: CPO HANSER SERVICE GmbH

Publ.-Id: 14980

Doping of the Si nanowires

Ou, X.; Das Kanungo, P.; Koegler, R.

review of doping of SiNW and the electrical characterization

  • Invited lecture (Conferences)
    6th IUPAC International Symposium on Novel Materials and their Synthesis (NMS-VI), 11.-14.10.2010, Wuhan, China

Publ.-Id: 14979

Underground accelerators in Europe

Bemmerer, D.

Nuclear reaction studies have to be carried out directly at or at least near the astrophysically relevant energies, in order to limit theoretical uncertainties. This entails the measurement of very small cross sections at energies far below the Coulomb barrier, leading to countrates that are lower than the laboratory background in a detector.

This problem can be solved by placing an accelerator laboratory deep underground. The world's only underground accelerator, the LUNA 0.4 MV machine, has driven great progress in the understanding of nuclear reactions in our Sun. However, the LUNA energy range is too limited to address more massive stars. For these scenarios, helium and carbon burning reactions and the neutron sources for the astrophysical s-process need to be studied in stable-beam experiments.

Therefore, there is a call in the community for a new European underground accelerator of 2-3 MV accelerating potential to address these science cases. Related projects are under discussion in Italy (Gran Sasso), Spain (Canfranc), the UK (Boulby), and recently also Germany (Felsenkeller). An analogous effort is made in the US (DUSEL).

  • Lecture (Conference)
    First EuroGENESIS Workshop: Origins of the elements and nuclear history of the universe, 24.-26.11.2010, Dubrovnik, Croatia

Publ.-Id: 14978

Doping and electrical characterization of individual silicon nanowire

Das Kanungo, P.; Ou, X.; Koegler, R.; Nikolai, Z.; Werner, P.; Skorupa, W.; Goesele, U.

As the drive to use silicon nanowires in nano-electronic devices and circuits is getting stronger, a clear understanding of the incorporation mechanism and electrical behavior of dopants in the nanowires is becoming more important. Owing to the quasi-one-dimensional structure of the nanowires leading to their high surface to volume ratio, the surface effects are expected to play a stronger role on the dopants in a nanowire than in planar silicon devices. We doped silicon nanowires of diameter ~ 100 nm uniformly - 1) in-situ with boron during growth by molecular beam epitaxy (MBE), and 2) ex-situ separately with boron, phosphorus and arsenic by ion implantation. In addition, the in-situ boron doping was combined with phosphorus ion implantation to fabricate an intra-nanowire p-n junction. Electrical current-voltage measurements of individual nanowires with a micro-manipulator revealed that - 1) for the uniformly implanted nanowires the electrical conductivity increases in accordance with the expected dopant concentration, and 2) the p-n junction nanowires show excellent diode characteristics. In order to understand the surface effects, profiling of electrically active dopants in individual nanowires was performed by scanning spreading resistance microscopy (SSRM). It revealed a ‘higher doped core-lower doped shell’ type of structure confirming the surface segregation of dopants. This effect was most pronounced in phosphorus-doped nanowires.

  • Poster
    2010 Materials Research Society (MRS) Spring Meeting, 05.-09.04.2010, San Fransisco, USA

Publ.-Id: 14977

Doping of vertical Si nanowires and the carrier profiling

Ou, X.; Das Kanungo, P.; Koegler, R.; Werner, P.; Goesele, U.; Skorupa, W.

Due to the very promising application of the Si nanowires (SiNW) in the eletrionic, optoelectronic and photovoltaic nano device integration the doping which endows with the functionality to the NW were intensively investigated in the last decades. In this study, individual vertical MBE-grown Si-NWs doped either by ion implantation or by in-situ dopant incorporation are investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. Furthermore,The potential of the SSRM for three-dimensional (3D) carrier profiling of the NW was demonstrated. The mechanism of the dopant surface segregation and deactivation was discussed.

  • Lecture (Conference)
    The International Conference on Ion Implantation Technology (IIT), 06.-11.06.2010, Kyoto, Japan
  • Lecture (Conference)
    EMRS 2010 Spring meeting, 06.-11.06.2010, Strasbourg, France
  • Lecture (Conference)
    Workshop Ion Beam Physics, 29.-31.03.2010, Dresden, Germany

Publ.-Id: 14976

Doping of Vertical Si Nanowires and Carrier Profiling by Scanning Spreading Resistance Microscopy

Ou, X.; Das Kanungo, P.; Koegler, R.; Werner, P.; Goesele, U.; Skorupa, W.

The future application of silicon nanowires (Si NWs) in nano electronics requires their doping and the precise control of their electrical properties. However, the dopant incorporation process in Si NWs is not yet fully understood. In this study, individual vertical MBE-grown Si-NWs doped either by ion implantation or by in-situ dopant incorporation are investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. Furthermore, three-dimensional (3D) SSRM of the NW was obtained by measuring the cross sections at different depth position of the same NW in succession. Carrier profiling reveals a multi-shell structure of the carrier distribution across the NW diameter which consists of a lower doped core region, a higher doped shell region and a carrier depleted sub-surface region.

  • Lecture (Conference)
    2010 Materials Research Society (MRS) Fall Meeting, 29.11.-03.12.2010, Boston, USA

Publ.-Id: 14975

Secondary particle yields from 400 MeV/u carbon ion and 250 MeV proton beams incident on thick targets

Ferrari, A.; Ferrarini, M.; Pelliccioni, M.

The double differential particle yield produced by hadron beams striking thick targets of copper, tungsten and ICRU tissue have been determined by means of the Monte Carlo transport code FLUKA (version FLUKA 2008.3b.1). 400 MeV/u carbon ions and 250 MeV proton pencil beams have been considered. Secondary neutrons, photons and protons have been scored. In order to validate the obtained data, a few simulations have been also repeated with MCNPX 2.6.0. The calculated results are presented and compared with the experimental data reported in literature. They should be very useful to solve a number of problems related to technological aspects of hadrontherapy.

Keywords: particle yields; hadrontherapy; FLUKA; MCNPX

Publ.-Id: 14974

PEGylierung von radioaktiv markierbaren L-Oligonukleotiden zur Optimierung ihrer Pharmakokinetik

Förster, C.

keine Abstract verfügbar

  • Lecture (Conference)
    18. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie der DGN, 16.-18.09.2010, Bad Boll, D

Publ.-Id: 14973

Matching of fluid flow observations in geological material (GeoPET, mm3 resolution) with lattice Boltzmann simulations in μm resolved structures

Kulenkampff, J.; Wolf, M.; Enzmann, F.; Gründig, M.; Richter, M.; Lippmann-Pipke, J.

Scaling is a fundamental problem in groundwater hydrology. A typical challenge is the verification that hydrodynamic parameters obtained in laboratory experiments well represent a situation on the field scale. Here were propose that for reactive transport modeling, the prediction of the large scale fluid dynamics and concentration distributions should be based on the characteristics of hydromechanic and geochemical parameter sets on the millimeter and micrometer scale. While it is common sense that chemical reactions take place on the atomic scale, here we show with tomograhic process observation and modeling that also hydrodynamic processes are considerably influenced even by sub-µm scale characteristics of the geomaterial and thus determine the fate and dynamics of the system components in the fluid phase.

We applied the spatially highly resolving computer tomography (μXCT) on rock cores for determining the open pore structures. Based on these µm scaled structural information the lattice Boltzmann simulations were conducted. Column experiments were performed on the same samples while applying the process visualization method GeoPET that allows for the non-invasive, quantitative monitoring of e.g. dissolved positron-emitting radio tracers ([18F]KF, [124I]KI) added to the eluent. Visualizing and quantifying transport processes in geological material by means of GeoPET provides a high volume resolution of 1.5 μl (1.3 mm) and extreme high sensitivity for tracer concentrations (10−15 to 10−12 moles/ml). The matching of measured time resolved fluid flow patterns and simulated small scale fluid dynamics is conducted by means of geostatistic methods (variography). It allows validating the structurally related hydromechanical parameters like flow velocities derived from the simulation and offers insights to the linking between ongoing processes on the micrometer scale and its impact on the centimeter scale. The applied scale independent geostatistical tools provide scale independent parameters, like the correlation lengths. Such parameters are a suggested fundamentally important base for valid upscaling to the field scale.

We provide results from rock cores with both, relatively simple structured pathways as well as complex ones. In both types only a small part of the available pathway is passed through by the mobile fluid implying that only fractions of the inner surface were available for chemical reactions. Such findings should fertilize the concepts of reactive transport models aiming at larger scales.

Therefore we conclude: Microscale information is essential for improving reactive transport models.

  • Poster
    AGU 2010 Fall Meeting, 13.-17.12.2010, San Francisco, USA

Publ.-Id: 14972

Electroluminescence from Er and Yb co-doped silicon dioxide layers: The excitation mechanism

Prucnal, S.; Rebohle, L.; Skorupa, W.

The excitation mechanism of photo- (PL) and electroluminescence (EL) of erbium ions co-implanted with ytterbium into the SiO2 layer of light emitting MOS devices (MOSLED) was investigated. Ytterbium implanted and annealed samples exhibit the blue and near infrared electroluminescence. The blue electroluminescence at 470 nm appears due to cooperative up-conversion emission in the Yb3+-Yb3+ system, and the near infrared EL at 975 and 1025 nm corresponds to transitions from the multiple state 2F5/2 to the 2F7/2 ground state in the Yb3+ ions. The Er implanted SiO2 exhibits the luminescence in the blue-green and infrared region. The green and blue peaks correspond to radiative transitions from the 2H11/2 or 4S3/2 energy levels and from the 2H9/2 or 4F5/2 energy levels to the 4I15/2 ground state, respectively. We have found that the energy transfer from Yb3+ to Er3+ ions exists only during photoluminescence excitation. The electroluminescence investigation shows the cooperative up-conversion in the Er3+ - Yb3+ system.

Keywords: electroluminescence; rare earth; SiO2; MOSLED

Publ.-Id: 14971

Study of the processes of corium-melt retention in the reactor pressure vessel (INVECOR)

Zhdanov, V.; Baklanov, V.; Bottomley, P. D. W.; Miassoedov, A.; Tromm, W.; Journeau, C.; Altstadt, E.; Clement, B.; Oriolo, F.

Integral large-scale vessel retention experiments have been performed using up to 60 kg of prototypic corium melt (C-30) that is discharged from the electric melting furnace from a height of 1,7 m into a model RPV (Reactor Pressure Vessel) (40cm dia. x 60cm depth) with plasmatrons for decay heating of corium. The experiments on corium retention in the vessel were 1-2 hours. Specific power release in corium was 5-8 W.cm3 and the maximum temperature of the RPV wall was up to 1300°C. The following has been achieved during the project: 1) The technology of the protective coating on the graphite crucibles and on surfaces of plasmatron graphite nozzles has been developed. The plasmatron design now gives improved simulation of decay heat in corium. This has required numerous trials to set up the experimental systems. 2) Calculations of the corium pool and its heating efficiency, distributions of thermal fluxes and temperatures in the RPV have been performed. Validation of the models for the large-scale integral experiments has been conducted by means of specific tests. 3) 4 large-scale experiments with sustained energy release into the molten corium pool in the model RPV using oxidic corium (C-30) and oxidic-metallic corium (C-30+10 wt% stainless steel) have been conducted. 4) Post-test analysis of corium samples and RPV steel has been done. This included sectioning of corium ingot and the RPV wall, XRD, optical metallography and element analysis. It was found during the post-test examination that solidified corium exists both in the form of a continuous, massive ingot and in the form of small fragments located above the ingot. There was insignificant erosion of the steel surface of the RPV wall at the impact point of the corium jet. The results lead us to the following preliminary conclusions: 1) The relatively low thermal fluxes through a RPV model wall could be explained as follows: firstly, the thermal insulation on the RPV external surface results in the redistribution of thermal fluxes normal to, and along, the RPV wall; secondly, there is incomplete dissolution of uranium dioxide by the metallic zirconium melt in the melting furnace and this endothermic dissolution of UO2 continues during the decay heat generation in the corium retained in the RPV; thirdly, the gap caused by differential expansion between the corium crust and the RPV wall reduces heat transfer; fourthly, the layered character of the corium crust effectively reduces the crust's thermal conductivity. 2) Steady-state phenomena during corium retention in the reactor vessel are highly dependent on the previous transient processes of the melt speed dropping onto the lower head, the corium pool formation and the configuration of this pool. The presence of a fragmented debris layer over a massive corium ingot suggests that an optimistic prediction about corium coolability can be made. Here, with a large area for "corium/water" interaction on the top layer of debris, internal flooding & cooling seems probable.

Keywords: In-vessel melt retention; reactor core melt; severe accident research

  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP 2011) Paper 11375, 02.-05.05.2011, Nice, France
    Study of the processes of corium-melt retention in the reactor pressure vessel (INVECOR)

Publ.-Id: 14970

Spin reorientation transition and phase diagram in an He+ ion irradiated ultrathin Pt/Co(0.5 nm)/Pt film

Bergeard, N.; Jamet, J.-P.; Ferré, J.; Mougin, A.; Fassbender, J.

A rich thermal magnetic phase diagram has been determined by magneto-optical Kerr magnetometry and microscopy in a He+ ion irradiated ultrathin Pt/Co0.5 nm/Pt film. The components of the net magnetization and the evolution and disappearance of the ribbonlike magnetic domain pattern have been studied in the perpendicular to in-plane spin reorientation transition temperature region. As observed in a dipolar frustrated ferromagnet, the ribbon pattern blurs progressively with increasing the temperature as due to efficient spatial fluctuations. We emphasize the limitation of present theories for interpreting such a type of dynamic transition.

Keywords: magnetism; ion irradiation; spin reorientation

Publ.-Id: 14969

Measuring the Saturation Magnetization in Samples With Unknown Magnetic Volume

Markó, D.; Lenz, K.; Strache, T.; Kaltofen, R.; Fassbender, J.

Measuring the Saturation Magnetization in Samples With Unknown Magnetic Volume

Keywords: magnetism; ion irradiation; saturation magnetization

Publ.-Id: 14968

Model spectra of organic phosphate-U(VI) and sulfurU(VI) complexes: a study of P k-edge and S k-edge XANES

Li, B.; Foerstendorf, H.; Raff, J.; Rothe, J.; Dardenne, K.

Phoshorylation of serine threonine and tyrosine residues, oxidation of methionine residues and sulfation on the sugar residues are common post translational modification to proteins. And study of protein-U(VI) interaction at mo-lecular level deepens the knowledge of U(VI) influence in the biosphare. P/S k-edge XANES were applied in the protein-U(VI) complexation in order to detect the tiny amount of phosphate-/sulfoxide-/sulfate-U(VI) com-plexes. In this study, model spectra were set up using phosvitin-U(VI), DMSO-U(VI) and sulfate-U(VI) for phosphate-/ sulfoxide-/sulfate-U(VI) complexes, respec-tively. Spectra features to represent the U(VI) complexa-tion have been found.

Keywords: phosphorus sulfur Uranyl protein complexation DMSO XANES

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2010
    ISSN: 1437-322X

Publ.-Id: 14967

Spectroscopic Characterization of Am(III)-Complexes with small organic acids

Müller, M.; Acker, M.; Bernhard, G.

Americium contributes to the activity of radioactive waste to a certain extend. Until now, a little is known about the complexation with organic molecules. We analyzed the complexation of the trivalent ion (Am(III)) with Pyromellitic acid (Pyr) using UV-vis spectroscopy with a Liquid Waveguide Capillary Cell (LWCC) at different temperatures.

Keywords: UV-Vis; LWCC; americium; complex formation

  • Poster
    5th FZD Ph.D. Seminar, 22.-24.09.10, Krögis, Deutschland

Publ.-Id: 14965

Bestimmung der mikrobiellen Diversität von Biofilmen mit Schwerpunkt des Nachweises von eukaryonten Mikroorganismen in Uran kontaminierten Milieus

Zirnstein, I.

The Eukaryote diversity of the biofilms from two uranium-contaminated habitats (uranium mine Königstein in Saxony and the “Gessenhalde” next to the former leaching dump Ronneburg inThuringia) were studied by microscopical and molecular analysis (18S rDNA PCR). In the sulphate- and heavy metal-rich acidic mine drainage water of the uranium mine Königstein biofilms are formed as gelatinous filaments in the drainage channels and as stalactite-like snotites hanging from the ceilings. The results showed a low Eukaryote diversity of the sampled biofilms. Amoebozoa, Ciliophora and Heterolobosea were the dominants species. Fungi, Rotatoria und Flagellates were only present in minor amounts. Apikomplexa and Acari were detected sporadically. The creek of the Gessenwiese next to the former uranium field Ronneburg is characterized by an acid pH and a high concentration of sulphate. The biofilms are formed as thick algae mats are in form of filamentous stream biofilms. The diversity of Eukaryotes of these biofilms is higher in comparison to the biofilms of the uranium mine Königstein due to the environmental influence. The green algae Microspora and Klebsormidium dominated the sampled biofilm of the creek. In addition, Diatoms, Flagellates, Ciliates, Rotatoria, Amoebozoa, Fungi, Cryptophycaea, Heliozoa, Gastrotricha, Chrysophycaea, Insecta and Bryophyta were analyzed. The season-dependent differences between the diversity of Eukaryote groups were low. Algae cultures of the biofilms and algae single-culture of Klebsormidium sp. were analyzed with analytical methods and TEM/EDX using different pH. An accumulation of uranium at the algae cell wall of the single-culture of Klebsormidium sp. was only determined using a pH of 6.57 of the culture medium.

Keywords: microbial diversity; biofilms; uranium

  • Diploma thesis
    TU Dresden, FZD, 2010
    115 Seiten

Publ.-Id: 14964

Sorption of U(VI) onto mineral model systems -An in situ ATR FT-IR spectroscopic study

Gückel, K.; Foerstendorf, H.; Brendler, V.

Motivation, Ziele und erste Ergebnisse der Doktorarbeit

  • Poster
    Doktorandenseminar im Rahmen des Kompetenzzentrums Ost für Kerntechnik, 16.12.2010, Dresden, Deutschland

Publ.-Id: 14963

Report and evaluation of the redox potential measurements during the Intercomparison Exercise of ReCosy

Krawczyk-Bärsch, E.

The redox potential measurements were performed in systems with simple organics, near-natural, and natural ground- and porewater samples (NAT) and in microbial systems (MIC). As an example the results of the natural ground- and porewater samples (NAT), which were obtained by 10 to 19 groups or redox sensors, were interpreted in detail. Nine groups or redox sensors, including FZD, showed similar results. In most cases the measurements varied insignificantly. In some samples a difference of approximately 100 mV between the lowest and the highest value was determined. Accepting the measurement ranges, the results will give a good overview of the redox conditions in the near-natural, and natural ground- and porewater samples. However, in special cases further studies are needed for the interpretation of the measured redox potential, e.g. Extended X-ray Absorption Fine Structure (EXAFS), TEM in combination with Electron Energy Loss Spectroscopy (EELS) and Confocal Laser Scanning Microscopy (CLSM)/Laser Induced Fluorescence Spectroscopy (LIFS).
Unfortunately, only one of the microbial system samples was studied. The results showed clearly that redox potential measurements of microbial systems need much more time for getting a stable signal due to microbially influenced processes.

Keywords: Redox potential; natural ground- and porewater; microbial systems

  • Contribution to external collection
    M. Altmaier, G. Buckau, D. Fellhauer, X. Gaona: ReCosy ICE Report - Assessment of ReCosy Intercomparison Exercise. Intercomparison of Redox Determination Methods on Designed and Near-Natural Aqueous Systems. KIT Scientific Reports 7572., Karlsruhe: KIT Sientific Publishing, 2011, 1-24

Publ.-Id: 14962

Tomography measurements of gas-holdup in rotating foam reactors with Newtonian non-Newtonian and foaming liquids

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

Rotating solid foam reactors have already proven to show high mass transfer rates and to be a potential alternative to slurry reactors. The rotation of a foam block stirrer results in a high mass transfer and in the development of different reactor sections showing specific hydrodynamics and gas holdup distributions. In order to optimize the reactor system the hydrodynamics in a lab scale reactor are studied using gamma-ray tomography, a powerful method to measure the gas holdup in three-phase reactors. The influence of liquid properties, such as viscosity and surface tension, and the rotational speed on the gas/liquid distribution in the different reactor sections is investigated. Especially the viscosity has a strong effect on the entrapment of gas bubbles in the foam block structure, while the surface tension is the dominant parameter in the outer reactor section. The influence of these paramters on the inset of foaming and the collapse of the gas/liquid dispersion is investigated. Conclusions on the mass transfer performance are drawn and recommendations for further optimizations of the reactor design and the operational conditions depending on the liquid properties are developed.

Keywords: multiphase reactors; gas holdup; tomography; solid foam

Publ.-Id: 14961

Advanced Laser Particle Accelerator Development at LANL: From Fast Ignition to Radiation Oncology

Flippo, K. A.; Gaillard, S. A.; Kluge, T.; Bussmann, M.; Offermann, D. T.; Cobble, J. A.; Schmitt, M. J.; Bartal, T.; Beg, F. N.; Cowan, T. E.; Gall, B.; Gautier, D. C.; Geissel, M.; Kwan, T. J.; Korgan, G.; Kovaleski, S.; Lockard, T.; Malekos, S.; Montgomery, D. S.; Schollmeier, M.; Sentoku, Y.

Laser-plasma accelerated ion and electron beam sources are an emerging field with vast prospects, and promise many superior applications in a variety of fields such as hadron cancer therapy, compact radioisotope generation, table-top nuclear physics, laboratory astrophysics, nuclear forensics, waste transmutation, Special Nuclear Material (SNM) detection, and inertial fusion energy. LANL is engaged in several projects seeking to develop compact high-current and high-energy ion and electron sources. We are especially interested in two specific applications: ion fast ignition/capsule perturbation and radiation oncology. Laser-to-beam conversion efficiencies of over 10% are needed for practical applications, and we have already shown inherent efficiencies of >5% from flat foils, on Trident using only a 5th of the intensity [1] and energy of the Nova Petawatt laser [2]. With clever target designs, like structured curved cone targets, we have also been able to achieve major ion energy gains, leading to the highest energy laser-accelerated proton beams in the world [3]. These new target designs promise to help usher in the next generation of particle sources realizing the potential of laser-accelerated beams.

Keywords: laser; proton; ion; plasma; acceleration; pulse duration; intensity; scaling; inertial fusion; warm dense matter; oncology; radiotherapy; trident; cone target

  • Contribution to proceedings
    AIP Conference Proceedings 1299(1) of the 14th Advanced Accelerator Concepts Workshop, AAC2010, 13.-19.06.2010, Annapolis, MD, United States of America
    Advanced Laser Particle Accelerator Development at LANL: From Fast Ignition to Radiation Oncology: AIP, 693-698

Publ.-Id: 14960

Prospects For and Progress Towards Laser-Driven Particle Therapy Accelerators

Cowan, T. E.; Schramm, U.; Burris-Mog, T.; Fiedler, F.; Kraft, S. D.; Zeil, K.; Baumann, M.; Bussmann, M.; Enghardt, W.; Flippo, K.; Gaillard, S.; Harres, K.; Herrmannsdoerfer, T.; Kluge, T.; Nürnberg, F.; Pawelke, J.; Roth, M.; Schmidt, B.; Sobiella, M.; Sauerbrey, R.

Recent advances in laser-ion acceleration have motivated research towards laser-driven compact accelerators for medical therapy. Realizing laser-ion acceleration for medical therapy will require adapting the medical requirements to the foreseeable laser constraints, as well as advances in laser-acceleration physics, beam manipulation and delivery, real-time dosimetry, treatment planning and translational research into a clinical setting.

Keywords: radiotherapy; proton; laser; acceleration; cancer; compact; plasma; dosimetry; beamline

  • Contribution to proceedings
    14th Workshop on Advanced Accelerator Concepts, AAC2010, 13.-19.06.2010, Annapolis, MD, United States of America
    AIP Conference Proceedings, Advanced Accelerator Concepts, 1299: AIP, 721-726
  • Invited lecture (Conferences)
    AAC2010, 15.06.2010, Annapolis, USA

Publ.-Id: 14959

Cluster dynamics study of neutron irradiation induced defects in Fe-12.5at%Cr alloy

Gokhman, A.; Ulbricht, A.; Birkenheuer, U.; Bergner, F.

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 12 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. A saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC and the volume fraction of the Cr precipitates for neutron exposures above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. A specific surface tension of about 0.028 J/m2 between the α matrix and the Cr-rich α' precipitate was found as best fit value for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.

Publ.-Id: 14958

Comparative studies on electrochemical and laser-based fiber-optic oxygen microsensors applied to uranium contaminated biofilms.

Krawczyk-Bärsch, E.; Steinbrück, D.; Arnold, T.; Schmälzlin, E.; Kumke, M.

Dissolved oxygen is one of the key parameters in biofilm systems and may show different O2 concentrations within the biofilm. The O2 concentration may also be influenced by the microbial response to the exposure of heavy metals. Oxygen sensor measurements in such biofilms are a useful tool in interpreting oxygen microprofiles, which are influenced by the microbial respiratory activity. Consequently microsensors help to evaluate on redox processes in biofilms induced by heavy metals. To compare the applicability of electrochemical and laser-based fiber-optical microsensors for microbial ecology studies, oxygen microprofiling measurements in uranium free biofilms and in biofilms exposed to ecologically relevant uranium concentration were performed. The data obtained from both microsensor methods were in good agreement up to a depth of 680 and 480 µm. To avoid the risk of destroying the sensor tip, electrochemical sensor measurements had to be stopped at this depth. In contrast, laser-based sensor measurements were acquired over an additional range of 1 mm down to the biofilm/solid glass slide interface since optodes offer a high stability against consolidated materials. Thus, additional information on the oxygen concentration in lower zones of biofilms were obtained.

Keywords: electrochemical sensor; fiber-optic sensor; biofilm; uranium

  • Contribution to external collection
    in: 2nd Annual Workshop Proceedings of the Collaborative Project "Redox Phenomena Controlling Systems" (7th EC FP CP RECOSY), KIT Scientific Reports 7557, 139-146, 2010., Karlsruhe: KIT Scientific Publishing, Karlsruhe, 2010

Publ.-Id: 14956

Second reporting of the scientific-technical outcome of WP 4.2: - chemical and redox behavior of the investigated radionuclides in the different systems through microbial mediated processes.

Krawczyk-Bärsch, E.

First studies have been carried out in stalactite-like biofilms from the uranium mine Königstein (Germany), where the mining activities had been stopped in 1990 and the uranium mine has been partially flooded for remediation. In the acidic, sulphate-rich waters with high concentration of heavy metals and radionuclides (uranium) as contaminants, biofilms are formed and occur as gelatinous filaments, and as stalactite-like snotites. The analyses of the bacterial diversity of these biofilms showed a dominance of Ferrovum myxofaciens, an acidophilic, autotrophic, iron oxidizing bacteria, which belongs to the Betaproteobacteria. Ferrous iron is oxidized strongly catalyzed by Fe(II)-oxidizing bacteria with the consequence of producing oxidizing conditions within the biofilm with high oxygen concentration. Fiber-optic oxgyen microprofiles, carried out in these snotites are in a good agreement with electro-chemical measurements. The oxygen concentration is decreasing slowly from the edge versus center of the snotite biofilm. Electrochemical redox potential micoprofilings were carried out in these snottite-biofilms by a miniaturized platinum redox electrode with a tip diameter of 10 µm, too. In the bulk solution a redox potential of 728 mV +- 9.5 mV was measured in comparison to an increased redox potential of 834.5 mV +- 10.21 mV within the snottite-biofilm. We guess that the different geochemical conditions are due to the oxidation of ferrous iron catalyzed by Fe(II) oxidizing bacteria and that they will have an influence on the uranium speciations. A pH-Eh diagram for the U-S-O-H-C system at 15 °C was constructed using the geochemical speciation code “Geochemist´s Workbench” Version 8.0.8 / ACT2 Version 8.0.8 and the most recent NEA database for Uranyl Silicates and solid Uranates (Guillaumont et al., 2003), supplemented with solubility data for Uranophane (Nguyen et al., 1992) and CaU2O7.3H2O(s) (Altmaier et al., 2006) and the analytical data of the bulk water for the calculation of the field stability boundaries of different uranium species. The plotting of the measured pH and Eh values into this diagram showed that the theoretical stability fields of U species are defined in areas characterized by higher pH or lower Eh. The measured values indicate that aqueous Uranium(VI) Sulfate Complexations were formed in the biofilm as well as in the bulk solution. Only the changing of the local conditions (e.g. closure of the underground galleries) will lead to substantial changes and the formation of solid uranium(IV) species.

Keywords: Biofilm; uranium; redox potential; sensor measurements

  • Contribution to proceedings
    2nd Annual Workshop Proceedings of the Collaborative Project "Redox Phenomena Controlling Systems" (7th EC FP CP RECOSY), KIT Scientific Reports 7557, 51-54, 2010., 16.-19.03.2010, Larnaca, Cyprus: KIT Scientific Publishing, Karlsruhe

Publ.-Id: 14955

Development of redox determination methods

Steinbrück, D.; Kumke, M.; Neck, V.; Fellhauer, D.; Runke, J.; Grambow, B.; Landesman, C.; Ribert, S.; Krawczyk-Bärsch, E.; Perdicakis, M.

To compare the applicability of an electrochemical and a laser-based fiber-optical microsensor for oxygen determination in biofilm samples, microprofiling measurements in uranium free biofilms and in biofilms exposed to ecologically relevant uranium concentration were performed. For our studies we used a commercial available Clark-type microelectrode and a custom fiber-optic instrument, which was optimized for tip probes < 10 µm (optodes) by use of a diode laser and the so-called two frequency phase modulation technique, to mask interfering background fluorescence.
The data obtained from both microsensor methods in uranium free and uranium contaminated biofilms were in good agreement. Fiber-optic and electrochemical microsensor measurements showed high concentrations of oxygen over the total thickness of the uranium free biofilms. In contrast, biofilms exposed to uranium revealed a much lower oxygen concentration in the upper layers of the biofilm. At a biofilm depth of approximately 750 µm no oxygen was detectable at all.

Keywords: Electrochemical microsensor; fiber-optic sensor; biofilms; uranium

  • Contribution to proceedings
    2nd Annual Workshop Proceedings of the Collaborative Project "Redox Phenomena Controlling Systems" (7th EC FP CP RECOSY) Kit Scientific Reports 7557, 11-26, 2010, 16.-19.03.2010, Larnaca, Cyprus, KIT Scientific Publishing, Karlsruhe

Publ.-Id: 14954

Automated radiosynthesis of the thiol-reactive labeling agent N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide ([18F]FBAM)

Knieß, T.; Kuchar, M.; Pietzsch, J.

The two-step radiosynthesis of N-[6-(4-[18F]fluorobenzylidene)aminooxyhexyl]maleimide ([18F]FBAM) was adapted to a remotely controlled synthesizer module. After optimization of reaction conditions as well as solid phase extraction based purification steps, the final [18F]FBAM was obtained in a decay-corrected radiochemical yield of 29±4% (related to [18F]fluoride, n=12) within a total synthesis time of 40min. The radiochemical purity of [18F]FBAM was in the range of 94-98%, the specific activity was determined with 13.4-17.2 GBq/µmol.

Keywords: 18F-labeling; Positron emission tomography (PET); Michael addition; Maleimide

Publ.-Id: 14953

Neue Ergebnisse zur Komplexbildung und Sorption im System Am(III)/Eu(III)-Modellligand-Opalinuston

Müller, M.; Acker, M.; Schott, J.; Barkleit, A.; Taut, S.; Bernhard, G.

Die Komplexbildung von Am(III) und Eu(III) wurde mittels UV-vis Spektroskopie und TRLFS untersucht. Mit steigender Temperatur konnte ein Anstieg der Eu(III)-Lactat Komplexierung festgestellt werden. Die Stabilität logb des Am(III)-Lactat Komplexes konnte bei Raumtemperatur mit TRLFS, UV-vis mit LWCC und UV-vis mit Standardpfadlänge übereinstimmend auf 2,2 ± 0,2 beziffert werden und liegt damit in der Nähe des Eu(III)-Lactat Komplexes. Vorgestellt wurde außerdem der Einfluss von Temperatur, pH-Wert und Organik auf die Sorption von Eu(III) am Opalinuston im Porenwasser. Es konnte gezeigt werden, dass die Sorption mit steigender Citrat und Tartat Konzentration abnimmt. Über TRLFS konnten Eu(III)-Citrat Spezies im Überstand der Batch-Sorptionsversuche, nicht jedoch am Opalinuston nachgewiesen werden. Die Erhöhung der Temperatur führt zwischen 20 und 60°C zu einer Verstärkung der Sorption. Ein Einfluss der Liganden auf die Sorptionsenthalpie konnte nicht nachgewiesen werden.

Keywords: complex formation; sorption; americium; europium; opalinus clay; UV-vis; TRLFS; temperature dependence

  • Lecture (others)
    9. Workshop zum Verbundprojekt "Wechselwirkungen und Transport von Actiniden im natürlichen Tongestein", 05.-06.10.10, Mainz, Deutschland

Publ.-Id: 14952

On the use of the Serpent Monte Carlo code for few-group cross section generation

Fridman, E.; Leppänen, J.

Serpent is a recently developed 3D continuous-energy Monte Carlo (MC) reactor physics burnup calculation code. Serpent is specifically designed for lattice physics applications including generation of homogenized few-group constants for full-core core simulators.
Currently in Serpent the few-group constants are obtained from the infinite lattice calculations with zero neutron current at the outer boundary. In this study, in order to account for the non-physical infinite-lattice approximation, B1 methodology, routinely used by deterministic lattice transport codes, was considered for generation of leakage-corrected few-group cross sections in the Serpent code. A preliminary assessment of applicability of the B1 methodology for generation of few-group constants in the Serpent code was carried out according to the following steps. Initially, two-group constants generated by Serpent were compared with those calculated by Helios deterministic lattice transport code. Then, 3D analysis of a Pressurized Water Reactor (PWR) core was performed by a nodal diffusion code DYN3D employing two-group cross section sets generated by Serpent and Helios. At this stage thermal-hydraulic (T-H) feedback was neglected. The DYN3D results were compared with those obtained from the 3D full core Serpent MC calculations. Finally, the full core DYN3D calculations were repeated taking into account T-H feedback and assuming Hot Full Power (HFP) conditions.
B1 two-group cross sections and diffusion coefficients generated by the Serpent and Helios codes agree within less than 2.5%. The results of the DYN3D calculations with the Serpent B1 cross-section sets agree very well with those of the Serpent full core MC calculations. The relative difference in keff is below 300 pcm. The maximum and root mean square (RMS) difference in the radial power distribution is 2.7% and 1.1% respectively. The results of the DYN3D full core calculations with T-H feedback obtained with Helios and Serpent generated cross-section libraries show an excellent agreement as well. The estimated critical boron concentration agrees within 5 ppm. The maximum and RMS difference in the core radial power peaking factors is 0.8% and 0.4% respectively.
In this study a Matlab script was used for calculation of the leakage-corrected few-group cross sections, however the B1 methodology has recently been implemented directly in the Serpent code.

Keywords: Monte Carlo; Lattice physics; Few-group cross section generation; Critical spectrum; 3D core analysis

Publ.-Id: 14951

Overview of the FZD and of the Institute of Safety Research / Counter-current flow limitation experiments in a model of the hot leg of a PWR

Vallée, C.

First, an overview of the FZD and of the Institute of Safety Research was presented. This includes in particular the departments of the institute, the main tests facilities and some examples of current research topics.
The second part of the presentation was focused on counter-current flow limitation experiments performed in a model of the hot leg of a pressurised water reactor. The background of this issue in the nuclear safety was introduced. Furthermore, the hot leg model of the TOPFLOW test facility and its particular operation in the pressure chamber were presented. The main results of the counter-current flow limitation experiments were shown in details, including the experimental procedure, a typical experiment performed with steam and saturated water at 50 bar, the method used to determine the flooding characteristics, the length characteristics in the Wallis parameter for channels with rectangular cross-sections and a comparison between air and steam experiments.

Keywords: FZD; hot leg; pressurised water reactor; PWR; counter-current flow limitation; CCFL

  • Lecture (others)
    Young scientists seminar, 08.11.2010, Mihama-cho (Fukui), Japan

Publ.-Id: 14950

Simulation of 1+1 dimensional surface growth and lattices gases using GPUs

Schulz, H.; Ódor, G.; Ódor, G.; Nagy, M. F.

Restricted solid on solid surface growth models can be mapped onto binary lattice gases. We show that efficient simulation algorithms can be realized on GPUs either by CUDA or by OpenCL programming. We consider a deposition/evaporation model following Kardar-Parisi-Zhang growth in 1+1 dimensions related to the Asymmetric Simple Exclusion Process and show that for sizes, that fit into the shared memory of GPUs one can achieve the maximum parallelization speedup (~ ×100 for a Quadro FX 5800 graphics card with respect to a single CPU of 2.67 GHz). This permits us to study the effect of quenched columnar disorder, requiring extremely long simulation times. We compare the CUDA realization with an OpenCL implementation designed for processor clusters via MPI. A two-lane traffic model with randomized turning points is also realized and the dynamical behavior has been investigated.

Keywords: surface growth model; lattice gas; GPU; parallel algorithm

Publ.-Id: 14949

S-layer based concept for the development of nano-structured biosensors

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.

The challenge for new sensor systems is to make them smaller and to achieve higher specifity and sensitivity to one analyte. Most promising, therefore, are bio molecules due to their typical sizes in the nano-meter range, self-assembly properties and the high affinity of biological binding molecules. Here we present a method to construct a nano-structured sensor device, using surface layer (S-layer) proteins as templates, aptamers (short oligonucleotides) as receptors and a dye pair for fluorescence resonance energy transfer (FRET) to detect the binding of one analyte . S-layer proteins are structural proteins, forming the outermost cell envelope of numerous bacteria and almost all archaea. They feature a lot of functions for the microbial cell such as protection, adhesion, filtration or framework. Their oblique, square or hexagonal structure, high content of regular arranged functional groups and the ability of the monomers to self-assembly in aqueous solution qualifies them for various nanotechnological purposes. The functional groups of the side chains of the S-layer proteins can be used for the sequential coupling of aptamers and organic or inorganic fluorescent dyes. In combination with an optical device for detection, a nano-structured sensor system is constructible. Aptamers were chosen as receptor system due to their high specificity, comparable to that of antibodies, and their higher stability against environmental changes. Currently we are working on a sensor system which is able to detect pharmaceuticals in water. Therefore different S-layer, aptamer and dye conformations will be tested to optimize the binding of a target molecule and to maximize the interference of the initial FRET between the two fluorescent dyes. It is expected to generate an optical signal that will allow the detection of very low analyte concentrations. An additional aim for the future is to bind two or more different aptamers to the S-layers, to develop a multiple detection system. Beside the construction of sensory devices, the aptamer-S-layers combination can be used for the construction of filter materials for the specific binding and degradation of toxic organic substances in water. For this purpose, photocatalytic active nanoparticles and aptamers are regularly arranged on the S-layer protein. Bound organic substances can be eliminated by the formation of reactive oxygen species induced by light irradiation.

Keywords: S-layer; aptamers; fluorescence dyes; FRET; biosensor

  • Poster
    Nanofair 2010 - 8th International Nanotechnology Symposium, 06.-07.07.2010, Dresden, Deutschland

Publ.-Id: 14947

Self assembling proteins as matrix for the construction of optical devices

Weinert, U.; Günther, T.; Raff, J.; Pollmann, K.

Self-assembling biomolecules are widespread in nature and attractive for technical purposes due to their size and highly ordered structures in nanometer range. Surface-layer (S-layer) proteins are one of those self-assembling molecules and their chemical and structural properties make them quite attractive for nanotechnical purposes. They possess a high content of functional groups so a sequential coupling of functional devices is possible and their ability to self assemble in aqueous solutions or on surfaces, e. g. SiO2 wafers, qualifies them for nanotechnical applications. In this work, first experiments were done in order to construct a sensory device containing S-layer proteins as matrix to bind optical elements and analytes for detection of specific substances. The S-layer proteins were isolated from the Lysinibacillus sphaericus strain JG-A12 recovered from a uranium mining waste pile in Germany. As optical elements fluorescent dyes or quantum dots can be used. Three different fluorescent dyes which are able to perform a Fluorescence resonance energy transfer (FRET) were used and coupled to the S-layer proteins. As receptor molecule aptamers were chosen due to their high specifity and stability towards many chemicals. Aptamers are short oligonucleotides which are able to bind specific molecules via their three dimensional structure. In this work, a model aptamer was used that is specific towards human thrombin. The aim was to construct a sensor system which is able to detect specific substances in very low concentration ranges in aqueous solutions.

Keywords: S-layer proteins; fluorescent dyes; aptamers

  • Lecture (Conference)
    Design and Nature 2010 Fifth International Conference on Comparing Design in Nature with Science and Engineering, 28.-30.06.2010, Pisa, Italia

Publ.-Id: 14946

Morphology Induced Magnetic Anisotropy of Thin Films Deposited on Nanoscale Ripple Substrates

Körner, M.; Liedke, M. O.; Lenz, K.; Ranjan, M.; Fritzsche, M.; Facsko, S.; Fassbender, J.; von Hörsten, U.; Krumme, B.; Wende, H.

Magnetic properties of thin films are influenced by the morphology of substrates with periodically modulated patterns on the nanometer scale [1]. These well ordered surface modulations (ripple) can be produced by low energy ion beam erosion and are tuneable over a wide range [2]. Thin magnetic films deposited on these ripple surfaces repeat the surface profiles of these patterns and thus an additional uniaxial magnetic anisotropy is induced. This is shown for thin films of Fe, Co as well as the quasi-Heusler compound Fe3Si. The magnetic anisotropy is determined by means of angular- as well as frequency-dependent ferromagnetic resonance measurements using a vector network analyzer. We find a strong uniaxial magnetic anisotropy induced by the ripple surface, which is superimposed on the cubic anisotropy in the case of single crystalline films.
This work is supported by DFG grant FA 314/6-1.
[1] M. Körner et al., Phys. Rev. B 80, 214401 (2009).
[2] J. Fassbender et al., New Journal of Physics 11, 125002 (2009).

  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM) 2011, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 14945

Novel biosensors by combining bacterial S-layers, fluorescent dyes and aptamers

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.

Bacterial surface layer (S-layer) represent the outermost cell envelope of various bacteria and feature a lot of functions such as protection, binding, filtration or framework. From the uranium mining waste pile “Haberland” near Johanngeorgenstadt in Saxony different Bacilli were isolated and their S-layer proteins were investigated. These S-layer proteins are able to self assemble in aqueous solution and form sheets or tubes with a hexagonal, square or oblique paracrystalline structure. By combining S-layers with polyelectrolytes, many technical surfaces, e.g. SiO2 wafers, can be covered with a closed and highly regular protein layer. The so modified materials are very promising for the construction of multifunctional materials, particularly new biosensors. Their high content of different and regularly arranged functional groups such as hydroxyl, amino and carboxyl groups provide a convenient platform for the sequential and defined coupling of sensor elements. So the idea is to construct a sensor system on the basis of S-layer proteins by combining fluorescence dyes with aptamers. Possible fluorescence dyes have an overlapping emission and excitation spectra and therefore the ability to induce a fluorescence resonance energy transfer (FRET). FRET describes a non radiation energy transfer between two chromophores. One chromophore (donor) in its excitated state will transfer energy to another chromophore (acceptor) and as a result the donor emission will decrease while the acceptor emission increases. The latter is detectable and can be used for the construction of the optical device of a sensor. One requirement therefore is the spatial proximity of both chromophores (<10nm), what can be easily achieved by using S-layers as nano-structured polymer with a high density of functional groups. Further components of the sensors are aptamers, working as specific receptors for analytes. Aptamers are short oligonucleotides with a high binding capacity towards a specific analyte, in present case specific pharmaceuticals and biocides. The combination of all three parts will lead to a selective, sensitive and adaptable sensory layer system useful for environmental technologies.

Keywords: S-layer; aptamers; fluorescence dyes; biosensor

  • Poster
    Nanocoatings-International Conference on Functional Nanocoatings, 28.-31.03.2010, Dresden, Deutschland

Publ.-Id: 14944

Entwicklung von sensorischen Schichten auf Basis bakterieller Hüllproteine

Weinert, U.; Günther, T.; Pollmann, K.; Raff, J.

Hüllproteine sind Strukturproteine, welche die äußerste Abgrenzung von zahlreichen Bakterien und fast allen Archaeen darstellen. Isoliert bilden diese Proteine in wässrigen Lösungen und an Grenzflächen regelmäßige parakristalline Gitterstrukturen aus, auf deren Oberfläche sich zahlreiche modifizierbare Carboxyl- und Aminogruppen befinden. Hüllproteine sind daher eine ideale Matrix zur Konstruktion von nanoskaligen sensorischen Schichten, bestehend aus Aptameren und Fluoreszenzfarbstoffen. Aptamere sind kurze Oligonukleotide, welche ähnlich wie Antikörper an Strukturmerkmale anderer Moleküle binden können, jedoch deutlich stabiler sind. Mittels dieser chemischen Antikörper lassen sich eine Vielzahl verschiedener Targetmoleküle spezifisch an die sensorische Schicht binden. Alle Komponenten des Detektionssystems befinden sich durch die regelmäßige Proteinmatrix in räumlicher Nähe, was einen Fluoreszenz Resonanz Energie Transfer zwischen den Fluoreszenzfarbstoffen ermöglicht. Dieser Energietransfer kann durch Binden eines Analyten an das Aptamer gestört werden (Quenching), was die Realisierung eines hochempfindlichen Sensors ermöglicht.

Keywords: S-layer; aptamers; fluorescence dyes; FRET; biosensor

  • Poster
    7. Max-Bergmann-Symposium, 16.11.2010, Dresden, Deutschland

Publ.-Id: 14943

Experimental characterisation of the interfacial structure during counter-current flow limitation in a model of the hot leg of a PWR

Vallée, C.; Nariai, T.; Futatsugi, T.; Tomiyama, A.; Lucas, D.; Murase, M.

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, dedicated experiments were performed in a scaled down model of Kobe University. The structure of the interface was observed from the side of the channel test section using a high-speed video camera. An algorithm was developed to recognise the stratified interface in the camera frames after background subtraction. The evolution of the water level along the hot leg is analysed in function of the liquid and gas flow rates.

Keywords: counter-current flow limitation; CCFL; hot leg; stratified two-phase flow; interfacial structure; image processing

  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14), 25.-29.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), paper 175

Publ.-Id: 14942

1 J white-light continuum from 100 TW laser pulses

Petit, Y.; Henin, S.; Nakaema, W.; Béjot, P.; Jochmann, A.; Kraft, S.; Bock, S.; Schramm, U.; Stelmaszczyk, K.; Rohwetter, P.; Kasparian, J.; Sauerbrey, R.; Wöste, L.; Wolf, J.-P.

We experimentally measured the supercontinuum generation by 3 J, 30 fs laser pulses and measured white-light generation at the unprecedented level of 1 J. Such high energy is allowed by a strong contribution to the continuum by the photon bath, as compared to the self-guided filaments. This contribution due to the recently observed congestion of the filament number density in the beam profile at very high intensity, also results in a wider broadening for positively chirped pulses rather than for negatively chirped ones, similarly to broadening in hollow-core fibers.

Keywords: Beam trapping, self focusing and defocusing, self-phase modulation; Frequency conversion; harmonic generation, including higher-order harmonic generation

Publ.-Id: 14941

Mn-doped Ge and Si: A Review of the Experimental Status

Zhou, S.; Schmidt, H.

Diluted ferromagnetic semiconductors (FMS) are in the focus of intense research due to their potential applications in spintronics and their striking new physical properties. So far Mn-doped III-V compound semiconductors such as GaMnAs are the most important and best understood ones, but they are ferromagnetic only at well below room temperature. An interesting alternative could be magnetic semiconductors based on elemental semiconductors, also owing to their compatibility with Si microelectronics. In the last decades, considerable amount of work has been devoted to fabricate Mn-doped Ge and Si FMS. In this article, the structural, magnetic and magneto-transport properties of Mn-doped Ge and Si will be reviewed.

Keywords: Diluted ferromagnetic semiconductor; Mn doped Si; Mn doped Ge

Publ.-Id: 14940

XAS versus IC-ICP-MS for arsenic-sulfur speciation analysis

Planer-Friedrich, B.; Suess, E.; Scheinost, A. C.; Wallschläger, D.

Modern analytical methods have demonstrated that soluble arsenic-sulfur species constitute a major fraction of dissolved arsenic in sulfidic waters. However, an intense debate is going on about the exact chemical nature of these compounds, with X-ray absorption spectroscopy (XAS) data suggesting thioarsenites, ion chromatographic and mass spectroscopic (IC-ICP-MS) data suggesting thioarsenates. We show here by XAS that thioarsenites are the primary reaction products of arsenite and sulfide which convert rapidly to thioarsenates when exposed to atmospheric oxygen. The predominance of dithioarsenate determined by IC-ICP-MS in arsenite-sulfide solutions is thus an analytical artifact. When eliminating oxygen by conducting the chromatographic separation under anaerobic conditions, thioarsenites convert to arsenite as they are instable in the acidic and alkaline pH-range and undergo competitive dissociation at decreasing SH-:OH- ratios when diluting a sample. As thioarsenites were found to be necessary precursor species for thioarsenate formation, their analysis at environmentally relevant concentrations is a necessity for modern arsenic speciation analysis.

Keywords: arsenic; sulfur; XAS

  • Invited lecture (Conferences)
    11th International Conference on the Biogeochemistry of Trace Elements, 03.-07.07.2011, Florence, Italy

Publ.-Id: 14939

Experimentelle Untersuchung polydisperser Dampf/Wasser-Strömungen mit Phasenübergang in einer vertikalen DN200-Teststrecke

Beyer, M.; Lucas, D.; Szalinski, L.; Pietruske, H.; Schütz, P.; Lindner, K.

Zweiphasenströmungen spielen eine wichtige Rolle bei der Sicherheitsbewertung bzw. Optimierung verfahrenstechnischer Prozesse. Ein wichtiger Anwendungsbereich für Zweiphasenströmungen sind die konventionelle und die Kernkraftwerkstechnik, bei denen in Dampfkesseln, Dampferzeugern aber auch in Siedewasserreaktoren schon im Normalbetrieb unterschiedliche Dampfgehalte und damit verschiedene Strömungsformen auftreten. Für die nukleare Sicherheitsforschung ist die zuverlässige Vorhersage charakteristischer Parameter von Zweiphasenströmungen in Störfallanalysen wichtig. Bei hypothetischen Leck- bzw. Reaktivitätsstörfällen in Siedewasser- oder Druckwasserreaktoren können auf Grund der teilweisen Verdampfung des Kühlmittels komplexe Zweiphasenströmungen auftreten. Auch für solche Fälle muss die Abfuhr der im Kern generierten Nachzerfallswärme nachgewiesen werden.
Eine zweckmäßige Methode zur Modellierung von Mehrphasenströmungen ist die dreidimensionale rechnergestützte Simulation der Strömungsvorgänge mittels CFD (Computational Fluid Dynamics) Programmen. Während diese Programme gegenwärtig für einphasige Strömungen gute Ergebnisse liefern, besteht im Zweiphasenbereich noch Entwicklungsbedarf. Zur Modell-entwicklung und –validierung sind qualitativ hochwertige Daten von Experimenten in praxisrelevanten Geometrien bei hohen Drücken und Temperaturen erforderlich. Ein wesentlicher Teil dieser Datenbasis wird im Rahmen der TOPFLOW Projekte bereitgestellt.
Der Vortrag erläutert die Durchführung von Experimenten mit polydispersen nicht adiabaten Dampf/Wasser-Strömungen und beschreibt die speziell für den Hochtemperaturbereich entwickelte Messtechnik. Ein wesentlicher Bestandteil des Seminars ist die Diskussion von ausgewählten Ergebnissen der Kondensationsversuche, die die Entwicklung der Strömungsstruktur über die Höhe eines vertikalen Rohres sowie die dabei auftretenden Energie- und Stofftrans-portprozesse zwischen den Phasen veranschaulichen.

Keywords: Steam/Water-flow; non adiabatic flow; wire-mesh sensor; gas velocity profiles; bubble size distributions; vertical pipe

  • Lecture (others)
    Institutsseminar, 09.12.10, FZD, Germany

Publ.-Id: 14938

Atom probe characterization of solute atom clustering in decommissioned Greifswald unit 4 weld metal

Nishida, K.; Soneda, N.; Nomoto, A.; Dohi, K.; Bergner, F.; Viehrig, H.-W.

Characterization of irradiation-induced microstructural features in reactor pressure vessel (RPV) materials is essential for the understanding of the mechanisms of RPV embrittlement. Particularly, analyses of materials from decommissioned RPVs are very important because the simulated irradiations in material testing reactors can never be the same as that of actual commercial reactors. In this study, we performed microstructural characterization of the weld metals cut from the decommissioned Greifswald Unit 4 RPV. Atom probe tomography technique was used to characterize the microstructural features in terms of solute atom clustering and segregation. The following conclusions can be drawn: (1) Carbides containing large amount of vanadium with a small size of ~10nm in diameter were observed. (2) Clusters which consist of Cu, Ni, Mn, Si, Cr and P are formed at Layer 4 and 6. (3) At Layer 4, two kinds of solute atom clusters i.e. with and without Cu atoms are observed, whereas almost all clusters contain Cu at Layer 6. (4) Concentrations of Ni, Mn, Si and Cr in the clusters are independent of cluster size. Si concentration is different between Layer 4 and 6. (5) There is a large scatter in the concentrations of Cu and P. However, the sum of Cu and P concentrations in the clusters is almost constant.

Keywords: Reactor pressure vessel steel; Atom probe tomography

  • Lecture (Conference)
    MRS Fall Meeting, 29.11.-03.12.2010, Boston, USA

Publ.-Id: 14937

Exceptional points: Mathematical aspects and Krein space related physics (I + II)

Günther, U.

In the first one-hour lecture some basic mathematical facts are presented on an introductory level. Specifically, we discuss spectral singularities of various types, projective Hilbert space structures at exceptional points (EPs), Krein spaces and PT quantum mechanics (PTQM) as well as gauged PTQM and PTQM Jaynes-Cummings models.
The second one-hour lecture is devoted to Krein space related physics and some concrete applications. The topics of this lecture are higher-order EPs in PT-symmetric Bose-Hubbard models, the PTQM brachistochrone and entanglement dynamics. Additionally, we briefly comment on EPs in MHD dynamo setups.

Keywords: exceptional points; non-Hermitian operators; PT quantum mechanics; Krein space; projective Hilbert space; Bose-Hubbard model; Bose-Einstein condensate; gauged PT quantum mechanics; Jaynes-Cummings models; quantum brachistochrone; entangled states; MHD dynamos

  • Invited lecture (Conferences)
    The physics of exceptional points., 02.-05.11.2010, Stellenbosch, South Africa

Publ.-Id: 14936

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)
    seminar of the Computational Physics Group, Institute of Theoretical Physics, TU Dresden, 26.11.2010, Dresden, Deutschland

Publ.-Id: 14935

Three models of Krein-space-related physics: PT-symmetric Quantum Mechanics, Squire equation and the MHD α²-dynamo

Günther, U.

PT-symmetric Quantum Mechanics, the Squire equation of hydrodynamics and the spherically symmetric α²-dynamo of magnetohydrodynamics (MHD) can be structurally linked and treated in a unified way as spectral problems in Krein spaces. We demonstrate their interrelation explicitly and provide examples for specific parameter dependencies of their spectra. Special emphasis is laid on the physical relevance of transitions between real and complex spectral branches in connection with phase transitions between sectors of exact PT-symmetry and spontaneously broken PT-symmetry in Quantum Mechanics as well as with possible polarity reversals of dynamo maintained magnetic fields of planets. We briefly comment on third order spectral branch points with geometric multiplicity one and algebraic multiplicity three as well as on a dynamo related resonant unfolding of diabolical points (spectral intersection points of geometric and algebraic multiplicity two). Finally, we sketch the general technique of versal deformations as specific unfolding of Jordan-block related singularities.

Keywords: operator theory; Krein space; PT-symmetric Quantum Mechanics; dynamo theory; Squire equation; spectral branch points; diabolical points; phase transition; perturbation theory; resonances; Puiseux expansions; versal deformations; Jordan block; unfolding of singularities

  • Lecture (others)
    weekly seminar of the Krein space group, 05.05.2010, Ilmenau, Deutschland

Publ.-Id: 14934

PT-symmetry, Cartan decompositions, Lie triple systems and Krein space related Clifford algebras

Günther, U.; Kuzhel, S.

Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.

Keywords: PT quantum mechanics; non-Hermitian Hamiltonians; gauge theory; Abelian gauge field; non-Abelian gauge field; Cartan decomposition; compact and noncompact components; Lie triple system; Clifford algebra; ultra-localized potential; Krein space; J-selfadjoint extension; Jaynes-Cummings system; multilevel artificial atoms; cavity QED; transmon states

Publ.-Id: 14933

PT symmetry, Cartan decompositions, Lie triple systems and Krein space related Clifford algebras

Günther, U.; Kuzhel, S.

Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.
The talk is based on arXiv:1006.1134[math-ph]

Keywords: PT quantum mechanics; non-Hermitian Hamiltonians; gauge theory; Abelian gauge field; non-Abelian gauge field; Cartan decomposition; compact and noncompact components; Lie triple system; Clifford algebra; ultra-localized potential; Krein space; J-selfadjoint extension; Jaynes-Cummings system; multilevel artificial atoms; cavity QED; transmon states

  • Lecture (Conference)
    21st International Workshop on Operator Theory and its Applications, 12.-16.07.2010, Berlin, Deutschland

Publ.-Id: 14932

PTQM related involution structures

Günther, U.; Kuzhel, S.

Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions. A Lie-triple structure is found and an interpretation as PT-symmetrically generalized Jaynes-Cummings model is possible with close relation to recently studied cavity QED setups with transmon states in multilevel artificial atoms. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials. Based on: arXiv:1006.1134[math-ph]

Keywords: PT quantum mechanics; non-Hermitian Hamiltonians; gauge theory; Abelian gauge field; non-Abelian gauge field; Cartan decomposition; compact and noncompact components; Lie triple system; Clifford algebra; ultra-localized potential; Krein space; J-selfadjoint extension; Jaynes-Cummings system; multilevel artificial atoms; cavity QED; transmon states

  • Invited lecture (Conferences)
    Pseudo-Hermitian Hamiltonians in Quantum Physics IX, 21.-24.06.2010, Hangzhou, China

Publ.-Id: 14931

PTQM related Cartan and Clifford structures

Günther, U.

Gauged PT quantum mechanics (PTQM) and corresponding Krein space setups are studied. For models with constant non-Abelian gauge potentials and extended parity inversions compact and noncompact Lie group components are analyzed via Cartan decompositions and an underlying Lie-triple structure is described. For models with Abelian gauge potentials a hidden Clifford algebra structure is found and used to obtain the fundamental symmetry of Krein space related J-selfadjoint extensions for PTQM setups with ultra-localized potentials.

Keywords: PT quantum mechanics; non-Hermitian Hamiltonians; gauge theory; Abelian gauge field; non-Abelian gauge field; Cartan decomposition; compact and noncompact components; Lie triple system; Clifford algebra; ultra-localized potential; Krein space; J-selfadjoint extension

  • Invited lecture (Conferences)
    Analytic and algebraic methods VI, 10.-11.05.2010, Prague, Czech Republic

Publ.-Id: 14930

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