Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34757 Publications

Investigating fluorinated cycloalkyl groups for increased metabolic stability using a Tyrosine model system

Franck, D.; Kniess, T.; Steinbach, J.; Zitzmann-Kolbe, S.; Friebe, M.; Dinkelborg, L. M.; Graham, K.

The aim was to investigate whether fluorocyclobutyl rings can be introduced into targeting probes to improve metabolic stability, while maintaining its binding affinity, using tyrosine as a model system for the LAT transporters.

The precursor, cis-cyclobutane-1,3-diol ditosylate, its corresponding F-19 reference compound trans-3-fluorocyclobutanol (FCB), along with the cis-(3-fluorocyclobutyl)-tyrosine (3FCBT), were synthesized using standard organic chemistry methodologies. The non-radioactive 3FCBT was tested in competition and efflux stimulation cell assays using A549 human lung carcinoma cells with [3H]-D-Tyrosine. The metabolic stability of reference compound 3FCBT was studied in both rat hepatocytes and human plasma. Radiosynthesis methods using standard radiofluorination of the prosthetic group [18F]FCB and its conjugation to tyrosine gave the desired 3[18F]FCBT after chromatographic purification. In vitro studies were performed in A549 cells using 3[18F]FCBT and incubated at 37°C for 10, 20, 30 and 60 minutes with and without inhibitors fluoroethyl-tyrosine (FET) and non-radioactive

The syntheses of cis-cyclobutane-1,3-diol ditosylate, trans-3-fluorocyclobutanol (FCB), along with the cis-(3-fluorocyclobutyl)-tyrosine (3FCBT) were established. 3FCBT was shown to block the uptake of [3H]-D-tyrosine in the competition cell assay and could stimulate the release of 3H]-D-Tyrosine from the cell in an efflux stimulation cell assay. 3FCBT showed very high stability in both rat hepatocytes (> 95%) and human plasma (> 95%). The unoptimized radiosynthesis gave the desired 3[18F]FCBT, via the prosthetic group [18F]FCB, in moderate yield (12%) with high radiochemical purity (> 99%). The cell uptake showed an increase of 3[18F]FCBT over time and reached a plateau of 5.87% after 30 minutes.

The radiosynthesis of the prosthetic group [18F]FCB and its conjugation to tyrosine to give 3[18F]FCBT were successfully established. The introduction of 3[18F]FCBT into the LAT-targeting vector D-Tyr was characterized by a significant in vitro uptake in A549 cells and was actively transported into these cells. The encouraging results warrant further investigations of this tracer in the in vivo setting.

  • Lecture (Conference)
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, USA

Publ.-Id: 15453

Experiments on evaporating pipe flow

Lucas, D.; Beyer, M.; Szalinski, L.

Evaporating two-phase flows were investigated in an 8 m long vertical pipe with an inner diameter of 195.3 mm. The phase transfer was induced by depressurization of the pipe starting from 1, 2, 4 and 6.5 MPa. The pressure relief was done for an upward liquid flow in the test section as well as for stagnant liquid. These experiments complete the extensive CFD-grade database obtained at the same test section for adiabatic two-phase flows and flows with bubble condensation along the pipe. Detailed information on the structure of the steam-water interface was obtained using a pair of wire-mesh sensors. The established database is suitable for the development and validation of CFD.

Keywords: poly-disperse flow; evaporation; pressure relief; phase transfer; bubble size

  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, paper NURETH14-061, 25.-30.09.2011, Toronto, Ontario, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), paper 061
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Ontario, Canada

Publ.-Id: 15452

Measurement of two-phase flow parameters with multi-channel gamma densitometry and local void probes at the INKA test facility

Schleicher, E.; Bieberle, A.; Tschofen, M.; Hampel, U.; Lineva, N.; Maisberger, F.; Leyer, S.

In the integral test facility "INKA" at AREVA NP GmbH in Karlstein, Germany, different passive safety systems of the boiling water reactor concept "KERENA" are being tested. One of these systems is the emergency condenser (EC) which starts automatically in case of a loss of coolant accident with the descent of the filling level in the reactor pressure vessel causing fast heat dissipation. For the exact balance and description of the processes in the emergency condenser a more precise understanding of the two-phase flow in the EC pipes is essential. In this paper we describe the instrumentation of the EC bundle itself as well as the condensate line with thermo needle probes to determine the phase distribution and phase temperatures with high temporal resolution of 10 kHz along the EC circuit. The needle probes have been designed for fast local measurement of void fraction and temperature under extreme conditions like water-steam ambience under 310°C and 9 MPa. The phase measurement is realized by use of an electrical conductivity signal measured at the probe tip. A micro-sheath thermocouple serves as the measuring electrode, hence the conductivity and the temperature signal can be measured simultaneously exactly at the same position in the flow. With this technology it is possible to differentiate between steam and non-condensable gases. Additionally, the EC return pipe has been instrumented with a multichannel gamma densitometer to measure the cross-sectional gas fraction in the condensate line. The gamma densitometer measures the ray attenuation of gamma rays from a Cs137 source along 34 single beams through the 200 mm steel pipe at 10 Hz sampling rate. From these attenuation data the cross-sectional void fraction can be calculated with an accuracy of about 3 %. The paper gives a short overview of the passive safety concept of the KERENA system, the development of the special instrumentation and measuring techniques for extreme temperatures and pressure and discusses the first experimental results in the INKA test facility in Karlstein.

Keywords: nuclear thermal hydraulics instrumentation; needle probes; gamma densitometry

  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14 , 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    NURETH-14, 25.-29.09.2011, Toronto, Canada, 25.-30.09.2011, Toronto, Canada

Publ.-Id: 15451

Radiation exposure by (-)-F18-NCFHEB, a new PET tracer for imaging of cerebral alpha4beta2 nicotinic acetylcholine receptors (nAChRs)

Sattler, B.; Wilke, S.; Starke, A.; Patt, M.; Hoepping, A.; Graef, S.; Schoenknecht, P.; Hegerl, U.; Brust, P.; Sabri, O.

Objectives : (-)-[F-18]Norchloro-fluoro-homoepibatidine ((-)-NCFHEB) is a new tracer for neuroimaging of alpha4beta2 nAChRs with PET. To assess the radiation risk after application of the radioligand, the biodistribution, organ doses (OD) and the effective dose (ED) were determined in a phase 0/1 trial.
Methods : Whole body dosimetry of (-)-NCFHEB was performed in 3 healthy volunteers (59.6±3.9a; weight 74.3±3.1kg; 2m, 1f). The subjects were sequentially imaged up to 7h post i.v. injection of 353.7±10.2 MBq of (-)-NCFHEB on a SIEMENS Biograph16 PET/CT-system with 9 bed positions (BP) per frame, 1.5-6min/BP, CT-attenuation correction and iterative reconstruction. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity-data. The ODs were calculated using the adult male model with OLINDA. The ED was calculated using tissue weighing factors as published in the ICRP 103/2007.
Results : The highest OD was received by the urinary bladder (80.2±37.8), followed by liver (44.7±5.4) and kidneys (38.6±5.1). The highest contribution to the ED was by the lungs (3.7±0.6) and the urinary bladder (3.2±1.5). The ED by i.v. application of (-)-NCFHEB is 22.9±0.7 (all in [μSv/MBq]).
Conclusions : The ED after i.v. application of 300 MBq (-)-NCFHEB is 6.8±0.2mSv. This corresponds to values obtained with other [F-18]-labeled compounds. These favorable dosimetry data encourage the further development of (-)-NCFHEB as a clinical tool for imaging of alpha4beta2 nAChRs with PET.

  • Poster
    SNM 58th Annual Meeting, 04.-08.06.2011, San Antonio, Texas, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 52(2011), 1459

Publ.-Id: 15450

Plasma immersion implantation for the corrosion protection of lead in pipe organs

Skorupa, W.; Cherkouk, C.; Prucnal, D.; Henke, S.; Reuter, H.; Hahn, A.; Skorupa, K.; Jehmlich, R.; Werner, H.; Pfeiffer, D.; Eule, A.-C.

A new technique for the corrosion protection of lead in pipe organs is presented using plasma immersion implantation of nitrogen. A 20 nm surface layer protects against a massive acetic acid impact leading without protection to a strong etching effect which destroys the lead surface quality.

Keywords: plasma immesion implantation; nitrogen acetic acid impact; corrosion protection

  • Invited lecture (Conferences)
    2. Internationale Konferenz des Instituts für Orgel und Orgelbau an der Hochschule für Künste Bremen, 17.-19.03.2011, Lemgo, Deutschland

Publ.-Id: 15449

CFD studies on the phenomena around counter-current flow limitations of gas/liquid two-phase flow in a model of a PWR hot leg

Deendarlianto; Höhne, T.; Lucas, D.; Vallée, C.; Montoya, G.

In order to improve the understanding of counter-current two-phase flow and to validate new physical models, CFD simulations of a 1/3rd scale model of the hot leg of a German Konvoi pressurized water reactor (PWR) with rectangular cross section were performed. Selected counter-current flow limitation (CCFL) experiments conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX using the multi-fluid Euler-Euler modelling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model.

In the simulation, the drag law was approached by a newly developed correlation of the drag coefficient (Höhne & Vallée, 2010) in the Algebraic Interfacial Area Density (AIAD) model. The model can distinguish the bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicate also a quantitative agreement between calculations and experimental data for the CCFL characteristics and the water level inside the hot leg channel.

Keywords: Algebraic interfacial area density (AIAD) model; Drag coeficient; Countercurrent flow limitations (CCFL); Pressurized water reactor (PWR); Hot leg

Publ.-Id: 15448

Aptamer modifizierte bakterielle Oberflächenstrukturen für die Entwicklung neuer Sensoren

Pollmann, K.


  • Poster
    BIONA Statusseminar, Industriekongress, 16.-17.04.11, Berlin, Deutschland

Publ.-Id: 15446

Die zunehmende Bedeutung von biotechnologischen Innovationen für angrenzende Branchen

Pollmann, K.

Biotechnologie in angrenzenden Branchen

  • Invited lecture (Conferences)
    6. Innovationsbörse Sachsen, 30.03.11, Görlitz, Deutschland

Publ.-Id: 15445

Cholinergic markers are altered in two different models of traumatic brain injury

Donat, C. K.; Hoffmeister, P.-G.; Walter, B.; Deuther-Conrad, W.; Schuhmann, M. U.; Voigt, C.; Bauer, R.; Meixensberger, J.; Brust, P.

Traumatic brain injury (TBI) is the leading cause of death and disability in childhood, adolescence and early adulthood and often results in cognitive impairments. There is evidence from behavioural animal experiments and patient studies that those cognitive deficits are related to functional alterations within the cholinergic system. The present study was performed to investigate cholinergic markers in two different animal models of TBI with emphasis on the time-course of posttraumatic events and critical brain regions. The identification of sensitive targets within the cholinergic system is a precondition for the development of radioligands for neuroimaging of TBI patients with Positron-Emission-Tomography (PET).

Male Sprague-Dawley rats were randomized into three groups (post-TBI survival time: 2 h, 24 h and 72 h), anaesthetized and subjected to sham injury (control, n = 8) or controlled cortical impact injury (CCI) (n = 8) with 2 mm depth of impact at a velocity of 4 m/sec.
Thirteen newborn piglets (post-TBI survival time: 6 h) underwent fluid percussion (FP) injury (n = 7) or sham operation (n = 6) with an impact pressure of 3.8 ± 0.3 atmospheres.
For both species, cryostat brain sections were cut (rat 12 µm, pig 20 µm) and density of nicotinic (nAChR; α7, α4*/α3*), muscarinic (mAChR; M1-M5) acetylcholine receptors and the vesicular acetylcholine transporter (vAChT) were assessed with in vitro autoradiography. Additionally, histochemical staining of the acetylcholinesterase (AChE) was performed.

A significant decline in the receptor density of the α4*/α3* nAChR up to -33% was found in injured rats within brain regions critical for cognitive processes (thalamus, basal forebrain). In contrast, the brains of injured piglets did not reveal significant changes in receptor density.
The α7 nAChR density was drastically reduced (up to -47%) in injured rats at all time points and in piglets. Rats showed early decline of receptor density in 14 of 15 investigated brain regions (including hippocampus, thalamus, basal forebrain and cortex), while in piglets impairment was found especially in the hippocampus.
The mAChR showed smaller (~-20%), time-dependent reductions in injured rats and in piglets. However, almost identical brain regions were affected as found for α4*/α3* nAChR.
Histochemical staining indicated region-dependent increases and decreases in AChE activity in rats after TBI (~+/-20%) in contrast to injured piglets where only increased AChE-activity (+20%) was found.

In conclusion, cholinergic markers are significantly altered after experimental TBI independently of species, age and model. Even though differences in methodology do not allow direct comparisons between both models, results indicate common mechanisms of cholinergic changes after TBI. Considering the role of cholinergic markers for cognition in the brain, it seems likely that these alterations contribute to attention and memory deficits. Identifying the underlying mechanisms, for instance with PET, could help to ameliorate deficits in TBI-patients.

Keywords: traumatic brain injury; acetylcholine system; rat; pig; newborn; autoradiography

  • Poster
    9th Göttingen Meeting, 23.-27.03.2011, Göttingen, Deutschland

Publ.-Id: 15444

Phase fraction distribution measurement of oil-water flow with capacitance wire-mesh sensor

Da Silva, M. J.; Hampel, U.; Rodriguez, I. H.; Rodriguez, O. M. H.

In this article, a novel wire-mesh sensor based on permittivity (capacitance) measurements is applied to generate images of phase fraction distribution and investigate the flow of viscous oil and water in a horizontal pipe. Phase fraction values were calculated from the raw data delivered by the wire-mesh sensor using different mixture permittivity models. Furthermore, these data were validated against quick-closing valve measurements. Investigated flow pattern were dispersion of oil in water (Do/w) and dispersion of oil in water and water in oil (Do/w&w/o). Maxwell-Garnett mixing model is better suited for Dw/o and Logarithimc model for Do/w&w/o flow pattern. Images of time-averaged cross-sectional oil fraction distribution along with axial slice images were used to visualize and disclose some details of the flow.

Keywords: wire-mesh sensor; liquid-liquid flow; viscous oil; phase fraction measurement; flow visualization

  • Measurement Science and Technology 22(2011)10, 104020

Publ.-Id: 15443

Compact magnetospectrometer for pulsed magnets based on infrared quantum cascade lasers

Drachenko, O.; Winnerl, S.; Schneider, H.; Helm, M.; Wosnitza, J.; Leotin, J.

In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron–resonance studies under pulsed magnetic fields up to 60 T.

Keywords: cyclotron resonance; infrared spectrometers; lasers

  • Review of Scientific Instruments 82(2011)3, 033108-1-033108-6
    DOI: 10.1063/1.3556441

Publ.-Id: 15442

FISH based analysis of 10 kV and 25 kV soft X-ray induced DNA damage in 184A1 human mammary epithelial cells

Beyreuther, E.; Dörr, W.; Lehnert, A.; Leßmann, E.; Pawelke, J.

Over the past years, several in vitro studies have been performed on DNA damage induced by soft X-rays, especially in the energy range below 50 keV. Radiation effects originating from such low-energy photons are relevant in the context of medical diagnostics, e.g. mammography, or of accidental exposure to scattered radiation. The present study was initiated to investigate the X-ray energy dependent induction of stable and unstable chromosomal aberrations in the human mammary epithelial cell line 184A1. Three colour fluorescence in situ hybridisation was applied to identify chromosomal damage in chromosomes 1, 8 and 17, induced by 10 kV or 25 kV soft X-rays as well as by 200 kV X-rays as a reference quality.
Based on dose dependencies in the range of 0.5 to 5 Gy, RBE values of 0.84 ± 0.09 and 1.45 ± 0.18 were found for stable translocations induced by 25 kV and 10 kV X-rays, respectively, using 200 kV X-rays as reference. Moreover, the analysis of the minimum number of breaks, as required to form the visible chromosomal damage, resulted in similar RBE values of 0.93 ± 0.07 for 25 kV X-rays and 1.25 ± 0.10 for 10 kV X-rays relative to 200 kV X-rays. In addition, non-DNA-proportional contributions of chromosomes 8 and 17 to the whole DNA damage and deviations from the expected 1:1 ratio of translocations and dicentrics were revealed for the mammary epithelial cell line 184A1.

Keywords: RBE; soft X-rays; chromosomal aberrations; 184A1; FISH; mammary epithelial cells

  • Radiation and Environmental Biophysics 51(2012), 33-42
    DOI: 10.1007/s00411-011-0396-3
  • Poster
    12th International Wolfsberg Meeting on Molecular Radiation Biology / Oncology 2011, 25.-27.06.2011, Wolfsberg Castle/Ermatingen, Schweiz
  • Contribution to proceedings
    12th International Wolfsberg Meeting on Molecular Radiation Biology / Oncology 2011, 25.-27.06.2011, Wolfsberg Castle/Ermatingen, Schweiz
    Proceedings Book Molecular Radiation Biology/Oncology, Vol. 9, 3-9808819-6-2

Publ.-Id: 15441

Overview of laser cooling of relativistic C3+ ion beams at ESR

Bussmann, M.; Kroll, F.; Loeser, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F. A.; Beck, T.; Rein, B.; Walther, T.; Birkl, G.; Nörtershäuser, W.; Kühl, T.; Novotny, C.; Kozhuharov, C.; Geppert, C.; Steck, M.; Dimopoulou, C.; Nolden, F.; Ma, X.; Stöhlker, T.

We present an overview of the setup for all-optical cooling and beam diagnostics for relativistic C3+ ion beams at the Experimental Storage Ring (ESR) at GSI. With new optical diagnostics it is foreseen to improve the measurement of the longitudinal momentum spread of the beam by at least an order of magnitude. The new optical diagnostics together with the new Schottky diagnosis and beam profile monitor available at ESR will allow to access the complete phase space evolution of the beam inside the storage ring. With new laser systems developed for cooling beams with an initially large energy spread it will be possible to replace the electron cooler that was used to reduce the initial momentum spread of the ion beam.

Keywords: laser cooling; ion beam; relativistic energy; diagnostics; optical detection; beam parameters; phase space

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

Publ.-Id: 15440

PIConGPU - A scalable GPGPU implementation of the particle-in-cell algorithm

Bussmann, M.; Burau, H.; Berninger, F.; Kluge, T.; Debus, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Widera, R.; Hönig, W.; Juckeland, G.; Nagel, W.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.; Ragan-Kelley, B.; Verboncoeur, J.

We present PIConGPU, an efficient and scalable implementation of the particle-in-cell algorithm for GPGPUs. We discuss the main building blocks of PIConGPU, the data access patterns used for both particle and field data and the communication model that allows to hide the large latency of network communication between GPGPU nodes on a cluster. PIConGPU provides a general framework which can be used to study both relativistic and nonrelativistic plasmas. We show first results on relativistic laser wakeeld acceleration of electrons in underdense plasmas and on the progress of integrating new physics models. The fast response time of the code makes it possible to receive results in hours compared to weeks with particle-in-cell codes running on mid-size commodity clusters. With this increase in computational
speed extensive parameter scans become possible even for large physical systems.

Keywords: particle-in-cell; pic; gpu; algorithm; latency; wakefield; acceleration; electron

  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland
  • Lecture (Conference)
    DPG Frühjahrstagung Kiel, Plasmaphysik und Kurzzeitphysik, 28.-31.03.2011, Kiel, Deutschland

Publ.-Id: 15439

Enhanced laser ion acceleration from mass-limited foils

Kluge, T.; Enghardt, W.; Kraft, S. D.; Zeil, K.; Schramm, U.; Cowan, T. E.; Bussmann, M.

We have performed an analysis of ultra-intense laser interaction with solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020W=cm2) laser pulses with targets of diameter down to 1 micron is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. We developed an analytical model which enables us to predict the electron energy distribution of an MLT. Our results suggest that the most signicant ion energy enhancement should be expected for MLT with diameter below the laser focal spot
size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.

Keywords: mass-limited targets; electron recirculation; particle-in-cell; simulation; pic; foil; electron sheath; heating; ion energy; coulomb explosion

  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15438

Electron acceleration mechanisms in cone targets - scaling up the energy of laser accelerated ions

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

In 2009, at the LANL Trident laser facility a new world record in laser accelerated proton energy has been set, exceeding 65 MeV, using hollow conical targets. We performed 2D collissional PIC simulations and identify two novel electron acceleration mechanisms that have not been considered before to enhance ion acceleration: the direct acceleration of electrons comoving with the driving laser along the the cone-wall inner surface (DASE) and the acceleration of electrons in surface plasma waves (PWA). We nd that they are responsible for a signicant increase in both electron number and energy in the case of a grazing laser incidence onto the inner cone wall surface compared to regular flat foils. We study the scaling of the electron and ion energies for various target and laser parameters.

Keywords: cone target; laser; proton; acceleration; beam; maximum energy; electron dynamics; heating; simulation; particle-in-cell; pic

  • Lecture (Conference)
    DPG Frühjahrstagung Münster, Hadronen und Kerne, 21.-25.03.2011, Münster, Deutschland

Publ.-Id: 15437

Interaction of intersubband transitions and ponderomotive responce in doped GaAs/AlGaAs multiple quantum wells at the THz regime

Baudisch, M.; Wagner, M.; Helm, M.; Stehr, D.

In the present work we investigate the line shape of the broadband terahertz (THz) response in doped multiple quantum wells by means of field-resolved detection. In an optically excited structure we recently observed a Fano-like shape of the THz response [1]. This results from the superposition of the broad continuous ponderomotive response and the sharp intersubband transition. The first originates from the force that takes effect on carriers in an oscillating electromagnetic field. The applied spectroscopy technique is time-resolved ultrabroadband THz spectroscopy. The THz radiation is generated by phase-matched optical rectification of 10 fs near-infrared pulses in 50 μm thin GaSe crystals. The pulses are tuneable in a range from 15 to 40 THz with a width (FWHM) of up to 15 THz. The field-resolved detection is done by phase-matched electro optic sampling. The applied detection method is crucial for observing the effect since the ponderomotive current can only be seen as a lossless phaseshift of the transmitted THz radiation while the intersubband transition leads to an absorption. Thus we are able to observe directly the superposition of ponderomotive current and intersubband transition in the time-domain.
[1] D. Golde et al., Phys. Rev. Lett. 102, 127403 (2009).

Keywords: Terahertz; intersubband transition; fano; ponderomotive

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

Publ.-Id: 15436

Phonon contribution to the thermodynamics of pure and mixed clusters in bcc-Fe

Talati, M.; Posselt, M.; Bonny, G.; Al-Motasem, A. T.; Bergner, F.

The irradiation-enhanced nanostructural evolution in reactor pressure vessel steels is a multiscale phenomenon. It can be effectively studied by rate theory for which necessary parameters must be obtained through atomistic simulations. The present work focuses on the phonon contribution to the thermodynamics of nanoclusters consisting of vacancy and/or Cu. In all calculations the most recent Fe-Cu interatomic potential developed by Pasianot and Malerba is employed. The vibrational density of states determined by the dynamical matrix method is used to calculate the phonon contribution to free energy of formation and free binding energy of the clusters. Pure bcc-Fe and pure fcc-Cu are used as references in the calculation of the free energy of formation. The vibrational contribution to the total free energy of these metals determined in this work is compared with available CALPHAD data and with literature data obtained by first-principle methods or interatomic potentials. In the case of pure vacancy clusters and for many mixed vacancy-Cu clusters the absolute value of the total free binding energy decreases with increasing temperature. Pure Cu clusters show the opposite behavior.

Keywords: Vibrational Density of States; Total free energy; Free binding energy; bcc-Fe; Thermodynamics; Molecular Dynamics Simulation

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

Publ.-Id: 15435

Tribological Aspects of Carbon-Based Nanocoatings - Theory and Simulation

Kunze, T.; Gemming, S.; Posselt, M.; Seifert, G.

Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. An important example are diamond-like carbon (DLC) films, which exhibit high mechanical stability depending on their deposition process. We present an introduction to this field of tribology by giving a short overview on DLC films, on the influence of lubricants from a theoretical point of view and in a broader sense, on basic principles of modeling tribological processes with molecular dynamic methods.

Publ.-Id: 15434

Direct observation of antiferromagnetically oriented spin vortex states in magnetic multilayer elements

Wintz, S.; Strache, T.; Körner, M.; Fritzsche, M.; Markó, D.; Mönch, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; McCord, J.; Erbe, A.; Fassbender, J.

We report on the coupling of spin vortices in magnetic multilayer elements. The magnetization distribution in thin film disks consisting of two ferromagnetic layers separated by a nonmagnetic spacer is imaged layer- resolved by using x-ray microscopy. We directly observe two fundamentally different vortex coupling states, namely antiferromagnetic and ferromagnetic orientation of the flux directions. It is found that these states are predetermined for systems that involve a sufficiently strong interlayer exchange coupling, whereas for the case of a purely dipolar interaction both states are transformable into each other.

Keywords: magnetic vortex; vortex coupling; magnetic multilayer; magnetic microscopy

  • Applied Physics Letters 98(2011), 232511

Publ.-Id: 15433

Structure and energetics of nanoclusters in bcc-Fe containing vacancies, Cu, and Ni

Al-Motasem, A. T.; Posselt, M.; Bergner, F.; Birkenheuer, U.

Reactor pressure vessel (RPV) steels consist of polycrystalline bcc-Fe containing Cu, Ni and other foreign atoms. The continuous irradiation by fast neutrons leads to supersaturation of vacancies and self-interstitials and enhances the diffusion of Cu and Ni which occurs via the vacancy mechanism. These processes favor the formation of nanoclusters consisting of vacancies, Cu and Ni. The interaction of dislocations with these precipitates is considered to be the main cause of hardening and embrittlement of the RPV steels. In order to model the evolution of the precipitates under irradiation by rate theory, the energetics and thermodynamics of the clusters must be known. These data are hardly obtainable by experiments, however, they can be provided by atomic-level computer simulations. In the present work a combination of on-lattice Monte Carlo simulations and off-lattice Molecular Dynamics calculations is employed to determine structure and energetics of the nanoclusters. The atomistic simulations show that ternary clusters exhibit a shell structure with a core consisting of vacancies followed by a shell of Cu and an outer shell of Ni. Binary vacancy-Cu and Ni-Cu clusters show a similar shell structure, whereas the atomic configuration of vacancy-Ni agglomerates is completely different.

Keywords: LMMC; MD; binding energy

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

Publ.-Id: 15431

Expression, purification and fluorine-18 radiolabeling of recombinant S100A4: a potential probe for molecular imaging of receptor for advanced glycation endproducts in vivo?

Wolf, S.; Haase-Kohn, C.; Lenk, J.; Hoppmann, S.; Bergmann, R.; Steinbach, J.; Pietzsch, J.

Data concerning the pathophysiological role of extracellular S100A4, a member of the multigenic family of Ca2+-modulated S100 proteins, and its interaction with the receptor for advanced glycation endproducts (RAGE) or other putative receptors in tumorigenesis, metastasis, and inflammatory processes in vivo are scarce. One reason is the shortage of suitable radiotracer methods. We report a novel methodology using recombinant human S100A4 as potential probe for molecular imaging and functional characterization of this interaction. Therefore, human S100A4 was cloned as GST fusion protein in the bacterial expression vector pGEX-6P-1 and expressed in E. coli strain BL21. Purified recombinant human S100A4 was radiolabeled with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radioligand [18F]fluorobenzoyl-S100A4 (18F-S100A4) was used in cell binding experiments in RAGE-bearing human melanoma cells and endothelial cells in vitro, and in both biodistribution experiments and small animal positron emission tomography (PET) studies in normal rats in vivo. The cellular association and tissue-specific distribution of 18F-S100A4 in vitro and in vivo correlated well with the protein expression and anatomical localization of RAGE, e.g., in the vascular system and in lung. Compared to other S100 RAGE radioligands, the overall findings of this study indicate that extracellular S100A4 in vivo shows only a moderate interaction with RAGE and, furthermore, exhibits a substantially faster metabolic degradation. On the other hand, the approach allows the use of quantitative small animal PET and provides a novel probe to both delineate functional expression and differentiate multiligand interaction of RAGE under normal and pathophysiological
conditions in rodent models of disease.

Keywords: Endothelial cells; Melanoma cells; Molecular imaging; Multiligand receptors; Protein radiolabeling; Small animal positron emission tomography (PET); S100 proteins

  • Amino Acids 41(2011), 809-820

Publ.-Id: 15430

Dedicated 3D list-mode reconstruction for whole-body PET

Lougovski, A.; Langner, J.; Hofheinz, F.; Brüning, E. M.; van den Hoff, J.

Although all currently available PET scanners support 3D acquisition protocols, full 3D image reconstruction is only rarely available in clinical PET. Usually, Fourier rebinning is used to reduce the image reconstruction to a set of independent 2D problems. Nowadays, faster computer systems allow to consider real 3D reconstruction as superior approach even for clincial routine, especially for whole body investigations. We report on our work on a dedicated whole-body image reconstruction using a 3D list-mode-based algorithm.

We implemented a 3D Ordinary Poisson List-mode Ordered Subsets Expectation Maximization algorithm (3D-LMOSEM) with on-the-fly calculation of the system matrix. Matrix elements are considered to be proportional to the intersection volume of voxels with Lines-of-Response (LORs) having a finite cross section. Two assumptions were used in this calculation:
i) the voxel grid is considered to consist of overlapping spheres, where the sphere volume is taken to be equal to that of the corresponding cubic voxel,
ii) LORs are cylinders whose axes connect the centers of the contributing detectors and the radii are calculated from the initial LOR volume.
This procedure reduces the complexity of system matrix computation considerably. The reconstruction is performed simultaneously for all bed positions. This bears the following advantage:
i) count loss in overlap regions is avoided leading to improved image quality,
ii) simultaneous reconstruction of all bed positions enables improved scatter calculation.
The new reconstruction was evaluated by comparison with the standard sinogram-based attenuation weighted OSEM-reconstruction (AW-OSEM) available with our Siemens EXACT HR+ scanner. The evaluation addressed these parameters: i) quantitative accuracy; ii) spatial resolution (FWHM comparison), iii) artifacts and noise characteristics.

Quantitative analysis yielded differences of mean values in selected regions-of-interest below a few percent. 3D-LMOSEM shows much better resolution (4.05 mm in brain and 4.35 mm in whole-body) compared to AW-OSEM (5.65 mm and 5.98 mm, respectively) with less inhomogeneity artifacts and noise. Typical 3D-LMOSEM reconstruction time for a FDG whole-body scan (7 bedpos; 6 min each) is 220 min using 80x2.3 GHz cores.

Compared to AW-OSEM the 3D-LMOSEM provides improved image resolution while decreasing overall noise level. The possibility to reconstruct all bed positions in one run prevents count loss and allows for a more accurate Out-of-FOV scatter correction. Due to the use of multi-threading and distributed computing techniques reconstruction times are approaching a level which will allow use of 3D-LMOSEM in clinical routine in the near future.

  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A29
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15429

Locally adaptive image filtering for noise reduction in PET

Langner, J.; Hofheinz, F.; Lougovski, A.; Brüning, E. M.; Oehme, L.; Beuthien-Baumann, B.; van den Hoff, J.

As well known, the signal-to-noise ratio (SNR) of PET images can be low. This is especially true for whole body examinations of heavy patients, for respiratory-gated studies, and dynamic studies with short frames. In these cases linear smoothing filters (LF) such as a Gaussian filter are usually applied in order to achieve an acceptable SNR. Image resolution is, however, reduced by these LFs. This affects detectability and quantification of small structures. Interesting alternatives to LFs are non-linear, locally adaptive filters (NLF), which enable noise reduction while preserving strong edges in the data. It was the aim of this study to investigate the performance of a special NLF (bi-lateral filter, BF) when applied to low SNR images in PET.

The BF consists of the product of a spatially dependent part and an intensity dependent part. In one spatial dimension the filter weights are defined as W(n-n0) = S * exp(-(n-n0)2/2/sn2) * exp(-(I(n)-I(n0))2/2/sI2) where n0 is the index of the target voxel, n is the index of neighboring voxels, sn is the spatial standard deviation, I(n), I(n0) are the intensities of n and n0, sI is the intensity standard deviation, and S normalizes the sum over all weights to unity. Due to the intensity dependence this filter is not invariant but adjusted individually for each choice of n0, thus it is locally adaptive. The filter works by penalizing voxels, which are distant from n0 either in the spatial or the intensity domain. The latter property leads to preservation of sharp edges. To quantify the effects of this filter, phantom measurements were performed with F-18 using a cylinder phantom (∅=20 cm, h=18 cm; 6 spheres with 2.7 - 27 ml). Three different sphere-to-background ratios were investigated in list-mode in order to assess different SNR levels. The image data were filtered, both with the BF and a LF. The filtered data were analyzed for changes in noise level, resolution, and signal recovery. Furthermore, clinical respiratory-gated whole body studies were investigated with BF and compared to LF filtered images.

In the phantom studies the BF is able to preserve the spatial resolution of the original data near the edges of the spheres while improving the noise characteristics. Signal recovery even of small spheres is not significantly reduced. Using the LF seriously compromises spatial resolution and leads to unacceptable reduction of signal recovery. The positive properties of the filter were also apparent when applying the BF to single gates of respiratory-gated studies, which otherwise were not suitable for visual inspection.

NLF is a powerful alternative to LF, especially for studies with high noise. Its performance, however, critically depends on a sensible choice of the intensity standard deviation sI. Further work will show whether the filter is suitable for clinical use.

  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A92
  • Poster
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15428

Accuracy of MR-based attenuation: first experience with a whole-body PET/MR system

Brüning, E. M.; Langner, J.; Hofheinz, F.; Will, E.; Beuthien-Baumann, B.; Oehme, L.; Platzek, I.; Steinbach, J.; Laniado, M.; Kotzerke, J.; van den Hoff, J.

Combined PET/MR systems for whole body investigations have been developed recently and are now starting to become available. One of the first of these systems (Gemini TF PET/MR, Philips) has been installed at our site. PET/MR is expected to provide new possibilities, notably in the area of quantitative bimodal functional imaging.
Quantitative PET imaging requires attenuation correction (AC), which is straightforward for PET/CT but not for PET/MR. In order to ensure quantitative accuracy of the PET data in the absence of a measured AC, one needs to use MR-based AC (MRAC), which relies on a combination of templates and accurate segmentation and tissue type identification of a suitable MR scan. Here, we report on a first evaluation of MRAC in phantoms as well as in patient investigations with the new system.

Methodik/Methods: A NEMA IEC Body Phantom was used. Data were evaluated regarding quantitative accuracy of background and sphere activity as well as homogeneity of the background. Reconstructed resolution was assessed as well. Evaluation of MRAC in patients is performed by direct comparison of MRAC with a transmission based AC (TMAC) acquired with an ECAT Exact HR+ (Siemens).

Ergebnisse/Results: Background inhomogeneity was found to be < 4% across the whole phantom. The reconstructed activity in the sphere inserts deviates from the known true values by < 5%. No artifacts related to erroneous AC could be observed in these measurements. The reconstructed resolution (FWHM) in these measurements was determined to be (5.01 - 5.48) mm. Patient studies will be performed in the coming months and evaluated as described above. The corresponding results will be reported.

Schlussfolgerungen/Conclusions: The vendor provided MRAC algorithms yielded very good results in our first phantom measurements both with respect to quantitative accuracy as well as regarding general image quality. The upcoming patient investigations will show whether these findings can be confirmed in whole body applications as well.

  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A49
  • Lecture (Conference)
    Gemeinsame Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaften für Nuklearmedizin 2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15427

Thioantimonates in geothermal waters

Planer-Friedrich, B.; Scheinost, A. C.

The formation of aqueous antimony sulfide complexes upon dissolution of stibnite (Sb2S3) and their importance for geothermal antimony transport has often been stressed. All the more surprising, up to date only laboratory studies and theoretical calculations support the existence of these thioantimony species1-5. We successfully applied alkaline chromatographic separation and detection by inductively coupled plasma mass spectrometry (AEC-ICP-MS) previously used for thioarsenates6, for the determination of two antimony-sulfur species in synthetic solutions and natural geothermal waters. Based on their S/Sb ratios of 3.08 ± 0.28 and 4.05 ± 0.32 they were provisionally assigned as tri- and tetrathioantimonate. Using X-ray absorption spectroscopy (XAS), the identity of tetrathioantimonate was confirmed based on shell fits by about 4 Sb-S paths (CN 4.2-4.3) and the characteristic pentavalent Sb-S binding length of 2.33-2.34 Å. Aqueous trithioantimonate concentrations were too low for structural characterization.
XAS analyses further confirmed that the initial species formed from antimonite in the presence of excess sulfide under anoxic conditions is not a pentavalent thioantimonate, but the trivalent trithioantimonite (CN 3.4-3.7, binding length 2.40-2.41 Å). However, this species is highly instable and rapidly transforms either to tetrathioantimonate in the presence of oxygen or antimonite at excess OH- versus SH- concentrations. Thioantimonites thus escape chromatographic detection even in complete absence of oxygen.
In natural geothermal waters from Yellowstone National Park, where oxygen concentrations > 0.2 mg/L render the presence of thioantimonites highly unlikely, tri- and tetrathioantimonate were detected. In accordance with our own laboratory studies and previous observations1-5 their share increased at increasingly alkaline pH and with increasing sulfide and decreasing oxygen concentrations to a maximum of 30 and 9% of total antimony, respectively. However, given the large S/Sb ratio (100 to 10,000) almost quantitative transformation of antimony to thioantimonates would have been expected based on results in synthetic pure antimony solutions. We postulate that the presence of arsenic and direct competition for a limited source of sulfide affects thioantimonate formation in natural waters. In the same samples, thioarsenate formation at S/As ratios of 2 to 4 is much higher (> 80% of total arsenic) and corresponds to results from synthetic pure arsenic solutions. Sulfur might therefore be a key species in helping to resolve different results and an ongoing controversy on similar 7, 8 or dissimilar 9, 10 behavior of arsenic and antimony in the environment.

[1] Tossell, J.A., 1994: Geochimica et Cosmochimica Acta 58, 5093. [2] Wood, S.A., 1989: Geochimica et Cosmochimica Acta 53, 237. [3] Mosselmans, J. F. W. et al., 2000: Applied Geochemistry 15, 879. [4] Helz, G. R. et al., 2002: Environmental Science and Technology 36, 943. [5] Sherman, D. M. et al., 2000, Chemical Geology 167, 161. [6] Planer-Friedrich, B. et al., 2007: Environmental Science & Technology 41, 5245. [7] Vink, B.W., 1996: Chemical Geology 130, 21. [8] Sakamoto, H. et al., 1988: Bulletin of the Chemical Society of Japan 61, 3471. [9]. Stauffer, R.E.; Thompson, J.M., 1984: Geochimica et Cosmochimica Acta 48, 2547. [10] Landrum, J.T. et al., 2009: Applied Geochemistry 24, 664.

Keywords: Antimony; EXAFS; thio-S

  • Lecture (Conference)
    Antimony 2011: 2nd International Workshop on Antimony in the Environment, 21.-24.08.2011, Jena, Germany

Publ.-Id: 15426

Zwei oder vier Stunden [18F]FMISO-PET in Kopf-Hals-Karzinomen: Wann ist der Bildkontrast am höchsten?

Abolmaali, N.; Haase, R.; Koch, A.; Zips, D.; Steinbach, J.; Baumann, M.; Kotzerke, J.; Zöphel, K.

Die [18F]Fluormisonidazol-Positronenemissionstomographie (FMISO-PET) ist ein nicht invasives Bildgebungsverfahren, das hypoxische Subvolumina in Tumoren detektieren kann. Die FMISO-PET kann dynamisch oder statisch nach unterschiedlichen Uptakezeiten post injectionem (p.i.) akquiriert werden, hat aber ein vergleichsweise niedriges Signal zu Rausch Verhältnis (SNR). Ziel dieser Studie war es für spätere Analysen zu klären, ob der Bildkontrast in statisch aufgenommenen Untersuchungen nach einer Uptakezeit von zwei Stunden (MISO2) oder vier Stunden (MISO4) p.i. höher ist. Patienten, Methoden: Bei einer Subgruppe von 23 Patienten einer prospektiven Studie zur kurativen Radiochemotherapie (RCT) von Plattenepithelkarzinomen des Hals-Nasen-Rachen-Raumes (HNSCC) wurden vor und während der Therapie [18F]Fluordeoxyglukose (FDG-)PET-Untersuchungen durchgeführt. Zusätzlich wurden bei diesen Patienten FMISO-PET-Aufnahmen zwei und vier Stunden p.i. nach Strahlentherapiedosen von im Mittel 11Gy, 23Gy und 57Gy während der RCT akquiriert. Nach Koregistrierung aller PET- und CT-Datensätze wurde die Rover-Software (ABX, Radeberg) verwendet, um das aus der FDG-PET abgeleitete „gross tumour volume“ der Primärtumoren festzulegen. Diese Volumina wurden in die FMISO-Datensätze kopiert um Hypoxie innerhalb des Primärtumors zu definieren. Der Kontrast zwischen hypoxischen Regionen in den Aufnahmen MISO2 und MISO4 wurde untersucht und mit dem Wilcoxon-Rangsummen-Test auf signifikante Unterschiede geprüft. Ergebnisse: Der mittlere SUVmax der Primärtumoren aller Untersuchungen war 2.2 (stdev: 0.4, min: 1.3, max: 3.4) nach 2 h p.i. und 2.4 (stdev: 0.7, min: 1.1, max: 4.4) nach 4 h p.i.. Der mittlere SUVmax in der Nackenmuskulatur war zwei und vier Stunden p.i. 1.5 und der mittlere SUVmean fiel von 1.2 nach 2 h auf 1.1 nach 4 h ab. Diese geringen Veränderungen bedingten aber einen steigenden Kontrast von MISO2 nach MISO4. Für die unterschiedlich definierten Kontraste ergab der Wilcoxon-Rangsummen-Test signifikant höhere Werte in den Untersuchungen vier Stunden p.i. (p < 0.002). Schlussfolgerung: Die Datenakquisition für die [18F]FMISO-PET sollte vorzugsweise vier Stunden p.i. erfolgen, da der Kontrast zwei Stunden p.i. schlechter ist. Diese Datensätze eignen sich deshalb besser für weitere Analysen, z. B. für die verbesserte Definition hypoxischer Tumorsubvolumina zur Strahlentherapieplanung.

Keywords: FMISO PET; Kopf/Hals-Tumoren; Tumor-zu-Muskel-Signalverhältnis; Kontrast-zu-Rausch-Verhältnis; Bioimaging; Strahlentherapieplanung

Publ.-Id: 15425

Subharmonic Resonant Optical Excitation of Confined Acoustic Modes in a Free-Standing Semiconductor Membrane at GHz Frequencies with a High-Repetition-Rate Femtosecond Laser

Bruchhausen, A.; Gebs, R.; Hudert, F.; Issenmann, D.; Klatt, G.; Bartels, A.; Schecker, O.; Waitz, R.; Erbe, A.; Scheer, E.; Huntzinger, J.; Mlayah, A.; Dekorsy, T.

We propose subharmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a subharmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.

Keywords: Piezo-optical; elasto-optical; acousto-optical; and photoelastic effects; Time resolved reflection spectroscopy; Mechanical modes of vibration

Publ.-Id: 15424

Low-dimensional compounds containing cyanido groups. XXI. Crystal structure, spectroscopic, thermal and magnetic properties of two polymorphous modifications of [Cu(men)2Pt(CN)4]n complex (men = N-methyl-1,2-diaminoethane)

Vavra, M.; Potocnak, I.; Cizmar, E.; Kajnakova, M.; Dusek, M.; Schmidt, H.; Ozerov, M.; Zvyagin, S.; Dlhan, L.; Boca, R.

Violet (1) and blue (2) polymorphous modifications of [Cu(men)2Pt(CN)4]n (men = N-methyl-1,2-diaminoethane) have been prepared and investigated by IR and UV–vis spectroscopy, thermal analysis, measurement of magnetic data and X-ray structural analysis. Both modifications are formed by similar but differently packed zigzag chains, which consist of [Cu(men)2]2+ moieties bridged by two trans arranged cyanido groups of [Pt(CN)4]2- units. The Cu(II) atoms in both structures are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate men ligands with the average Cu–N(Me) and Cu–N(H2) bond lengths of 2.046(8) and 2.008(8) Å, respectively, and by two nitrogen atoms from bridging cyanido groups in the axial positions at average distance of 2.50(7) Å. Broad nearly symmetric bands observed in the UV–vis spectra of 1 and 2 of 2B1g -> 2Eg transitions are consistent with a deformed octahedral coordination of the CuN6 chromophoric groups. One and two nu(C-N) absorption bands observed in the IR spectra of 1 and 2, respectively, are in agreement with different local symmetries of [Pt(CN)4]2- units and different Cu–N(cyanido) bond lengths in these polymorphs and are subject of discussion on the spectral–structural correlations in 1D compounds. The complexes are stable up to 238 °C when their two-stage thermal decompositions start and ending up with a mixture of CuO and metallic Pt as the most probable final thermal decomposition products. The temperature dependence of the magnetic susceptibility suggests the presence of a weak antiferromagnetic exchange coupling between Cu(II) atoms in 1, J/hc = -0.17 cm-1 and in 2, J/hc = -1.3 cm-1.

Publ.-Id: 15423

The impact of atmospheric carbonate on the sorption of actinyl(V/VI) ions onto gibbsite studied by in situ ATR FT IR spectroscopy

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

The migration behavior of heavy metal contaminants like actinyl ions (U, Np) is mainly controlled by sorption processes at water-mineral interfaces [1]. Hence, the investigation of the interactions of actinides with metal oxides such as Al(OH)3, Fe(OOH)x, TiO2, or SiO2, serving as model phases for more complex, naturally occurring minerals in aqueous solution, becomes essential for the safety assessment in the near and far field of nuclear repositories.

In this study, gibbsite is used as a mineral model system because it the most common crystalline aluminum hydroxide and an ubiquitous weathering product of aluminosilicate minerals. Furthermore, the structure of gibbsite, Al(OH)6 octahedrons, occurs as parts of the structure of important clays like kaolin [2]. Gibbsite is very stable under environmental conditions and is capable to sorb anions and metal cations as well on its surface [3].

Spectroscopic data of surface complexes of uranium(VI) on gibbsite were obtained from batch samples by by time-resolved laser-induced fluorescence spectroscopy [4] and X-ray absorption spectroscopy [5]. From these studies, the formation of a bidendate mononuclear inner-sphere surface complex was derived. In case of Np(V), no spectroscopic data of surface complexes on gibbsite are available up to now. However, the formation of inner-sphere complexes of NpO2+ ion was suggested from batch experiments [6].

Attenuated total reflection Fourier-transform (ATR FT-IR) spectroscopy is a powerful technique for in situ investigations of U(VI) and Np(V) sorption processes in a micro molar actinyl concentration range [7]. Structural information of the molecular complexes occurring during the sorption processes of actinide ions on the solid-liquid interface of mineral phases can be obtained [8]. In this work we focus on the sorption behavior and the formed complexes of uranium(VI) on synthetic gibbsite. The experiments were performed in the presence and absence of atmospheric carbonate in order to illustrate the impact of carbonate ions on the sorption processes. In the absence of carbonate, only one inner-sphere complexes are formed at the mineral surface. In addition, surface precipitation was observed after prolonged sorption which can be derived from a characteristic absorption band at 942 cm−1 (Fig. 1). In the presence of carbonate, two different surface species were derived from the spectra: an inner-sphere U(VI) complex and a ternary carbonate containing uranyl surface complex. The inner-sphere complex is suggested from the significantly shifted frequency of the antisymmetric stretching vibration ν3(UO2) (~ 913 cm−1) compared to the aqueous U(VI)-species (~ 923 cm−1). A much more red-shifted absorption band (903 cm−1) is observed in ambient atmosphere which is obviously due to the formation of a carbonate containing uranyl complex (Fig. 1).

The sorption of a pentavalent actinyl ion, that is Np(V), onto gibbsite was investigated to gain information of the migration behavior of pentavalent actinide ions. The results obtained from first sorption experiments performed at pH 7.6 in the absence of atmospheric carbonate suggest the formation of stable surface species, most probably an inner-sphere complex, which can be derived from the significant shift of the band representing the antisymmetric stretching vibration ν3 of the NpO2+ ion to lower frequencies.

This study provides a first comparative insight into the course of the surface complex formation of U(VI) and Np(V) onto gibbsite on a molecular level.

[1] Choppin, G.R. (2007). “Actinide speciation in the environment.” J. Radioanal. Nucl. Chem. 273, 695-703
[2] Wu, T. et al. (2009). “Neptunium(V) sorption onto gibbsite.” Radiochim. Acta 97, 99-103
[3] A. Karamalidis, D.A. Dzombak (2010). “Surface complexation modelling- gibbsite.” J. Wiley and Sons, Inc., Hoboken, New Jersey
[4] N. Baumann et al. (2005). “Uranyl sorption onto gibbsite studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)” J. Colloid Interface Sci 290, 318–324
[5] Hattori et al. (2009). “The structure of monomeric and dimeric uranyl adsorption complexes on gibbsite: A combined DFT and EXAFS study.” Geochim. Cosmochim. Acta 73, 5975-5988
[6] Wu et al. (2009). “Neptunium (V) sorption onto gibbsite.” Radiochim. Acta 97, 99-103
[7] Müller et al. (2009) “Sorption of Np(V) onto TiO2, SiO2, and ZnO: An in situ ATR FT-IR spectroscopic study.” Environ. Sci. Technol. 43, 7665–7670
[8] Lefèvre (2004). “In situ Fourier-transform spectroscopy studies of inorganic ions adsorption on metal oxides and hydroxides.” Adv. Colloid Interface Sci. 107, 109-123.

  • Poster
    Migration 2011,13th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 19.-23.09.2011, Peking, China

Publ.-Id: 15422

Generation of tuneable narrowband terahertz pulses using large-area photoconductive antennas

Krause, J.; Wagner, M.; Winnerl, S.; Helm, M.; Stehr, D.

Photoconductive antennas, driven by ultrafast optical pulses, are frequently used as broadband terahertz sources. Due to water vapour absorption in ambient air, these sources are less suitable for free space imaging or addressing small spectral regions. Amongst other techniques, narrow-band THz generation via difference frequency generation in ZnTe crystals [1] and photoconductive antennas [2] were demonstrated, the latter reaching frequencies of only 900 GHz. In this work we generate tuneable narrow-band terahertz pulses from a large-area photoconductive antenna by means of difference frequency generation with two up to 3.3 ps long time-delayed chirped optical pulses. The source is a 250 kHz regenerative Ti:sapphire amplifier. It’s output is split into three beams, where one is compressed for field resolved detection. The other two pulses are sent to a Michelson interferometer and get – with an adjustable time delay – recombined and are focussed on the antenna.
By using this technique we generated THz pulses tuneable from 0.35 to 2.5 THz with adjustable spectral widths (FWHM) of 200 to 500 GHz.

Keywords: terahertz; photoconductive antenna

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

Publ.-Id: 15421

Intraexciton terahertz nonlinear optics in quantum wells

Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Teich, M.; Helm, M.; Andrews, A. M.; Schartner, S.; Strasser, G.

Terahertz (THz) light is not only used to probe low-energy material excitations in a spectral region that has become accessible only during the last decades, but at high field strengths it can also induce nonlinear optical effects and enrich our understanding of light-matter interaction. In our contribution we investigate experimentally nonlinear optical effects related to excitonic transitions in undoped GaAs/AlGaAs semiconductor quantum wells. Excitons as bound electron-hole pairs show an energy structure analogous to the hydrogen atom, however, the binding energy is scaled down by a factor of 1000 and lies in the THz spectral range. We make use of the intra-excitonic 1s to 2p transition to explore two basic concepts of nonlinear optics, i.e. the perturbative effect of sideband generation and the non-perturbative Autler-Townes effect. In sideband generation a near-infrared (NIR) laser beam is mixed with the THz beam to generate sidebands at the sum- and difference-frequencies around the NIR frequency. The Autler-Townes or AC Stark effect refers to a splitting of an energy level that is resonantly coupled via intense radiation to an adjacent level. Both effects with their large distinct signatures in the sample’s optical response could find applications in future optical modulators.

Keywords: AC Stark; Autler-Townes; free-electron laser; intraexcitonic; exciton; terahertz

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

Publ.-Id: 15420

A 7-(2-[F-18]Fluoroethoxy)-6-Methoxy-Pyrrodinylquinazoline for PET Imaging of PDE10A: Radiosynthesis and Evaluation in vivo and in vitro

Funke, U.; Schwan, G.; Maisonial, A.; Scheunemann, M.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Egerland, U.; Nieber, K.; Briel, D.; Sträter, N.; Brust, P.; Steinbach, J.

Pharmacological treatment of the enzymatic activity of phosphodiesterase 10A (PDE10A) is a potential approach in the therapy of several neuropsychiatric disorders such as schizophrenia and psychoses. For improved treatment1 and diagnosis2 thereof, the development of potent and selective brain penetrable PDE10A inhibitors is forced. Based on a 6,7-dimethoxy-4-pyrrolidinylquinazoline (Ki = 4 nM1) we developed a 7-[18F]fluoroethoxy-derivative [18F]V as a potential PET radiotracer for imaging PDE10A in brain. Its non-radioactive analogue V showed strongest PDE10A inhibition (Ki = 53 nM) and selectivity in enzyme activity studies and was chosen for radiolabelling, initially performed via two-step-reaction. Therefore the conversion of 1,3-bistosyloxyethane I into [18F]fluoroethyltosylate II, using the [18F]KF-K2.2.2-carbonate complex, was followed by direct etherification of deprotonated 7-hydroxy-derivative III to afford [18F]V (3.5-4.5 h, based on [18F]F- aqueous solution; RCY 18-29%, radiochemical purities 92-99%). Next, an improved one-step radiosynthesis was developed by direct substitution of the 7-tosyloxy-analogue IV with n.c.a. [18F]fluoride (3-4 h, RCY 17-40%, radiochemical purity ≥ 99%, specific activities 110-1110 GBq/µmol). Purification of [18F]V was performed by SPE and semi-preparative HPLC with sample monitoring by radio-TLC and -HPLC. In vitro homologous competition assays on PDE10A transfected SF21 cells showed a high PDE10A affinity of [18F]V (KD = 14 nM). By HPLC as well as shake-flask methods a moderate lipophilicity of [18F]V was determined (logD7.0-7.4 ~ 2.6). In vivo biodistribution studies of [18F]V in female CD-1 mice revealed a high initial brain uptake of 2.3%ID/g at 5 min p.i. in striatum. Nevertheless, the baseline uptake of [18F]V in striatum(1.14%ID/g 60 min p.i.) was not inhibited by blocking with V (1.3%ID/g) as well as highly PDE10A specific inhibitor MP-10 (1.4%ID/g). Screening of metabolism in vivo showed, that ~ 70% and 96% of the radioactivity corresponded to native radioligand in plasma and brain at 30 and 60 min p.i., respectively, and no defluorination of the radioligand was observed. Finally, despite promising in vitro outcome and convenient radiosynthesis, results obtained in vivo show necessity of structural optimization of [18F]V to make it suitable for neuroimaging of PDE10A with PET.

  • Lecture (Conference)
    TurkuPET2011, 28.-31.05.2011, Turku, Finland

Publ.-Id: 15419

Neutrino pair emission off electrons in a strong electromagnetic wave field

Titov, A. I.; Kämpfer, B.; Takabe, H.; Hosaka, A.

The emission of νν̅ pairs off electrons in a polarized ultraintense electromagnetic (e.g., laser) wave field is analyzed. We elaborate on the significance of nonlinear electrodynamics effects (i.e., multiphoton processes) and the peculiarities of neutrino production. Special attention is devoted to the convergence of the reaction probabilities as a function of the number of absorbed photons. Expressions for large field intensities are provided. The asymmetry between the probabilities of electron and μ+τ neutrino production depends on initial conditions such as energy of the wave field photons and the field intensity. These findings differ from the lowest-order perturbative calculation of the reaction γ+e→e′+νν̅ .

Publ.-Id: 15418

Intraoperative Sonography: A Technique for Localizing Focal Forms of Congenital Hyperinsulinism in the Pancreas

von Rohden, L.; Mohnike, K.; Mau, H.; Eberhard, T.; Mohnike, W.; Blankenstein, O.; Empting, S.; Koch, M.; Füchtner, F.; Barthlen, W.


Der kongenitale Hyperinsulinismus (CHI), Synonym Nesidioblastose, ist die häufigste Ursache persistierender, rezidivierender Hypoglykämien im Säuglingsalter. Ein Drittel der Patienten weist einen umschriebenen Fokus auf. Die Enukleation und vollständige Entfernung aller betroffenen β-Zellen ist die Therapie der Wahl. Gesundes Gewebe muss soweit als möglich geschont, intrapankreatischer Choledochus sowie Ductus pancreaticus major intakt bleiben. Diagnostischer Goldstandard ist das [18F] F DOPA PET/CT. Die Sonografie wird durchgeführt, um den im präoperativen PET/CT lokalisierten Fokus während der Operation korrekt in situ darzustellen. Bei 5 Patienten im Alter von 3½ - 14 Monaten erfolgte 3 - 20 Tage nach PET/CT die Enukleation des Herdes. Die intraoperative Ultraschalluntersuchung wurde mit Hochleistungsgeräten verschiedener Hersteller unter Verwendung von Breitbandschallköpfen (9 - 14 MHz) vorgenommen. Bei allen 5 Patienten mit fokaler CHI ist, gemessen an PET/CT, intraoperativem Lokalbefund und Histologie mithilfe des intraoperativen Ultraschalls, der Herd korrekt lokalisiert und von den Ductus choledochus et pancreaticus major sicher abgegrenzt worden. 3 von 5 Patienten wurden durch komplette Fokusenukleation geheilt. Problematisch ist die vollständige intraoperative Darstellung stark segmentierter Herde. Sonografische Charakteristika des CHI-Fokus sind: konstante Hypoechogenität, variable homogene/inhomogene Gewebetextur, unscharfe, unregelmäßige Begrenzung ohne Kapsel, filiforme, lobuläre Fortsätze und insuläre Absiedlungen in das umgebende Gewebe. Die intraoperative hochauflösende Sonografie hilft dem Kinderchirurgen, Größe, Konfiguration und Topografie eines CHI-Fokus zu bestimmen.


Congenital hyperinsulinism (CHI), syn. nesidioblastosis, is the most frequent cause of persistent, recurrent hypoglycemia in infancy. One third of patients show a single circumscribed focus. Enucleation of the focus and the removal of all affected β-cells with preservation of healthy tissue is the treatment of choice. The intrapancreatic choledochus as well as the ductus pancreaticus major must remain intact. The diagnostic gold standard is 18F-DOPA-PET/CT. Intraoperative sonography is carried out to correctly visualize the focus preoperatively localized by PET/CT in situ during the operation. The enucleation of the focus was carried out 3 - 20 days after PET/CT in 5 patients at an age of 3.5 - 14 months. Intraoperative ultrasound was carried out with high-capacity devices of different manufacturers under use of broadband probes (9 - 14 MHz). The localization by intraoperative ultrasound was accurate in all 5 patients with focal CHI, with regard to the intraoperative localization as previously described by PET/CT and histology. D. choledochus and D. pancreaticus major were separated intraoperatively by ultrasound. 3 of 5 patients were cured by complete enucleation of the focus. Nevertheless, the entire intraoperative identification of the segmented focus is still problematic. Characteristic sonographic features of a CHI focus are: hypoechogenicity, variable homogeneous and inhomogenous texture, blurred, irregular limitation without capsule, filiform, lobular processes, and insular dispersal into the surrounding tissue. Intraoperative high-resolution sonography helps the pediatric surgeon to determine size, configuration and topography of a CHI focus.

Keywords: congenital hyperinsulinism; pancreas; intraoperative; ultrasound; PET-CT

Publ.-Id: 15417

Seltene Metalle in der Hochtechnologie

Fassbender, J.

Der Vortrag gibt einen Überblick über die Aktivitäten des HZDR im Bereich der technologischen Anwendungen von Materialien, die seltene Metalle verwenden. Insbesondere wird die Möglichkeit der Substitution von verschiedenen Materialklassen eingegangen.

Keywords: rare earth; metal; ressources; application; TCO; ITO; hard magnets

  • Invited lecture (Conferences)
    1. Freiberger Ressourcen Technologie Symposium, 14.-15.02.2011, Freiberg, Deutschland

Publ.-Id: 15416

Determination of residence time distributions in different high pressure gasification processes

Ortwein, A.; Jentsch, T.; Zeuner, A.; Zeissler, R.; Seifert, P.; Meyer, B.; Schlichting, H.

The production of synthesis gas is one of the first steps in the conversion of different feedstocks to liquid fuels like methanol or gasoline. Feedstocks might be gaseous (e.g. natural or flare gas), liquid (e.g. heavy oil residues) or solid (e.g. coal or biomass). At TU Bergakademie Freiberg in Germany, a test plant with 5 MW thermal power has been installed and operated together with Lurgi GmbH (part of Air Liquide Group) for the conversion of gaseous and liquid fuels. It is designed for three different modes: the so-called ATR-mode (Autothermal Reforming), the Gas-POX-mode (Partial Oxidation of natural gas) and the MPG-mode (Multi-Purpose Gasification). The first one is a process for the catalytical conversion of natural gas and can be run at pressures of up to 70 bar(g). The Gas-POX-mode is also used for natural gas processing, but no catalyst is used and pressures may reach up to 100 bar(g). In MPG-mode, high-viscosity liquids can be gasified at pressures of up to 100 bar(g). In all modes, the feedstock is processed with oxygen and steam.
Because of high investment costs for such processes, design studies with the help of computational fluid dynamics (CFD) are of increasing importance. Validation of such studies is very complicated due to high pressures and temperatures within the reactor and the poor accessibility of measurement equipment. The usage of radioactive tracer material has been determined as a possible way for obtaining information on flow conditions within the reactor. Experiments have been conducted for all three modes explained above.
The radioactive isotope 41Ar (half-life 1.83 hours) has been used for the measurements. Scintillation counters were installed outside of the reactor at different heights to measure gamma radiation. The method of momentum (MOM) was used to derive residence time distributions out of the measured values.
The quality of measurement of residence time is different for the three processes. In ATR-mode, a large reactor volume and height in combination with the homogenization of the flow by the catalyst bed make it possible to determine the residence time distribution of the complete reactor. In Gas-POX- and MPG-mode, the reactor dimensions were strongly reduced for these experiments. Additionally, due to the lack of homogenization, the actual velocities within the reactor are much higher compared to the ATR-mode. Thus, measuring accuracy is considerably reduced.
CFD calculations were also performed. The CFD model was validated by comparing the residence time calculated with the experimentally measured one. A reasonable agreement was found, however, some problems with the accuracy of the experiments were found - besides some other parameters - in dependence of the operation mode of the gasifier. As a conclusion, the radiotracer method in general is well suited for investigation of high pressure gasification processes.

Keywords: Multi-Purpose Gasification; Radiotracer Method; Residence Time Measurement; Argon-41

  • Poster
    Tracer 6 - Sixth International Conference on Tracers and Tracing Methods, 06.-08.06.2011, Oslo, Norge

Publ.-Id: 15415

Fast propagation of weakly-pinned domain walls and current-assisted magnetization reversal in He+-irradiated Pt/Co/Pt nanotracks

Cormier, M.; Mougin, A.; Ferré, J.; Jamet, J.-P.; Weil, R.; Fassbender, J.; Baltz, V.; Rodmacq, B.

Current developments of magnetic data storage and processing technologies make highly desirable to control fast and reproducible magnetic-domain-wall motion in narrow magnetic tracks, using either magnetic field or electrical current. For this purpose, nanotracks defined in ultrathin magnetic films with out-of-plane anisotropy seem to be particularly interesting. However, in most of the out-of-plane metallic nanosystems which were studied up to now, domain-wall pinning was shown to still play a predominant role, which resulted in low domain-wall velocities, as compared to the ones observed in plain magnetic films [1].
Using magneto-optical microscopy, we show that in an etched Pt/Co/Pt nanotrack with out-of-plane anisotropy, where pinning has been artificially reduced by He+-irradiation [2], weakly-pinned domain-walls can propagate as fast and under magnetic fields as low as in the corresponding plain irradiated film (Fig. 1) [3]. Moreover, when magnetic-field and electrical-current pulses are simultaneously applied to the track, a considerably faster magnetization reversal is observed, which is due to a Joule-heating-induced thermomagnetic effect [3].
This work was partially supported by the EU-“Research Infrastructures Transnational Access” program “Center for Application of Ion Beams in Materials Research” under contract no. 025646, and by the French ANR-07-NANO-034 “Dynawall” project.
* now at Radboud University Nijmegen, Institute for Molecules and Materials, Netherlands
[1] F. Cayssol et al., Phys. Rev. Lett. 92, 107202 (2004).
[2] C. Chappert et al., Science 280, 1919 (1998).
[3] M. Cormier et al., submitted (2011).

Keywords: magnetism; ion irradiation; microscopy; magnetic anisotropy; domain walls; dynamics

  • Poster
    Magnetics and Optics Research International Symposium 2011, 21.-24.06.2011, Nijmegen, The Netherlands
  • Journal of Physics D: Applied Physics 44(2011)21, 215002
    DOI: 10.1088/0022-3727/44/21/215002

Publ.-Id: 15414

The influence of microbes on the uranium speciation under aerobic and anaerobic conditions

Frost, L.; Moll, H.; Bachvarova, V.; Geißler, A.; Selenska-Pobell, S.; Bernhard, G.

Bacteria belong to the most widely spread organisms in nature. Besides archaea, these organisms represent the only form of life which can inhabit hostile like designated nuclear waste disposal sites. Since bacteria are known to have a considerable impact on radionuclide migration, it is of importance to characterize the U(VI) interaction with dominant bacterial strains isolated from such sites.
In this study, as microbial representatives from actually discussed potential geological formations for nuclear waste storage, one isolate from granite rock (Äspö Hard Rock Laboratory, Sweden) and another bacterial strain from clay (Mont Terri Rock Laboratory, Switzerland), which we have recently isolated and been able to cultivate, are investigated. Concretely, the Gram-negative obligate aerobic Äspö strain P. fluorescens and a species of the Gram-positive facultative anaerobic genus Paenibacillus are examined regarding their interaction with uranium and compared.
Following results will be presented for both mentioned strains:
a) U(VI) accumulation in dependence on [U(VI)]initial, [dry biomass] and pH, b) U(VI) speciation determined by TRLFS, c) phosphate liberation in dependence on [U(VI)], and d) potentiometric titration. Furthermore this work differentiates between metabolically active and rather inactive cells. In addition, the influence of different cell wall structures and oxygen availability on U(VI) interaction will be assessed.
The results on direct interactions of U(VI) with the Äspö strain P. fluorescens will finally be compared with our previous studies exploring indirect U(VI) interactions with pyoverdine-siderophores secreted by this strain. Through this, the influence of indirect U(VI) interactions in comparison to direct interaction mechanisms can be judged.

This work was funded by the BMWi under contract number: 02E10618.

Keywords: Uranium; Accumulation; Speciation; Pseudomonas fluorescens; Paenibacillus sp; TRLFS; Potentiometric Titration

  • Poster
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere 2011, 18.-23.09.2011, Beijing, China

Publ.-Id: 15412

Vector-magneto-optical generalized ellipsometry

Mok, K. M.; Du, N.; Schmidt, H.

We present the setup of a variable-angle vector-magneto-optical generalized ellipsometer (VMOGE) in the spectral range from 300 to 1100 nm using an octupole magnet, and demonstrate VMOGE measurements of the upper 3 × 4 submatrix of the Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. New “field orbit” measurements can be performed without physically moving the sample, which is useful to study magnetic multilayer or nanostructure samples. A 4 × 4 matrix formalism is employed to model the experimental VMOGE data. Searching the best match model between experimental and calculated VMOGE data, the magneto-optical dielectric tensor εMO of each layer in a multilayer sample system can be determined. In this work, we assume that the nonsymmetric terms of εMO are induced by an external magnetic field and depend linearly on the sample magnetization. Comparison with vector magnetometer measurements can provide the anisotropic magneto-optical coupling constants Qx , Qy, Qz .

Keywords: Mueller matrix; generalized ellipsometry; magneto optics

  • Review of Scientific Instruments 82(2011)0 33112

Publ.-Id: 15411

CFD analysis of a void distribution benchmark of the NUPEC PSBT tests

Krepper, E.; Rzehak, R.

The paper presents CFD calculations using CFX-12.1 on the void distribution tests of the PSBT benchmark. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross-sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of void distribution cross-sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model which is able to resolve the secondary flows is able to reproduce at least qualitatively the void distribution images.

Keywords: CFD; two phase flow; boiling; turbulence

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

Publ.-Id: 15410

Liquid metal experiments with a swirling-flow submerged entry nozzle

Wondrak, T.; Eckert, S.; Galindo, V.; Gerbeth, G.; Stefani, F.; Timmel, K.; Peyton, A.; Yin, W.; Riaz, S.

The influence of a swirling flow inside the submerged entry nozzle on the structure and the stability of a liquid metal flow in a physical model of a slab-casting mold is investigated. For visualization of the flow the Contactless Inductive Flow Tomography (CIFT) is applied. As expected and desired, the swirling flow leads to a stronger upward fluid motion along the walls. At the same time, however, the oscillatory character of the flow becomes stronger. These flow features obtained with CIFT are shown to be in reasonable agreement with independent measurements using Ultrasonic Doppler Velocimetry (UDV). Preliminary results of numerical simulations show a similar behaviour, too.

Publ.-Id: 15409

Vector-Magneto-Optical Generalized Ellipsometry applied to magnetically anisotropic multilayer and metamaterial samples

Mok, K.; Du, N.; Schmidt, H.

Magneto-optical generalized ellipsometry is the most general approach to characterize the magneto-optical response of magnetically anisotropic materials [1]. We extended this experimental approach to Vector-Magneto-Optical Generalized Ellipsometry (VMOGE) in the IR-UV spectral range, by combining a generalized spectroscopic ellipsometer with a 3D vector magnet [2]. VMOGE measures the upper 3 x 4 submatrix of the 4 x 4 Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. Searching the best match model between experimental and calculated VMOGE data, the complex-valued magneto-optical dielectric tensor is determined. Comparison with vector magnetometry measurements can provide the complex and anisotropic magneto-optical coupling constant Qx, Qy, Qz. We have determined the wavelength dependence of the isotropic Qx and Qy of ferromagnetic Co, Fe, and Ni films. Besides, VMOGE is also employed to study Co nanowires [3] with very strong anisotropic optical response. Having knowledge of the magneto-optical coupling constant Q, one can design magneto-optical devices, e.g., ferromagnetic thin film and nanowire structures, with a strong magneto-optical response for a selected wavelength.

[1] D. Schmidt, T. Hofmann, C.M. Herzinger, E. Schubert, and M. Schubert, Appl. Phys. Lett. 96 (2010) 091906.
[2] K. Mok et al. ‘Vector-Magneto-Optical Generalized Ellipsometry’, Rev. Sci. Instrum., submitted
[3] M. Ranjan et al. ‘Optical properties of silver nanowire arrays with 35 nm periodicity’ Optics Letters 35 (2010) 2576.

Keywords: Mueller matrix; generalized ellipsometry; ferromagnetic; magneto optics

  • Lecture (Conference)
    6th workshop ellipsometry, 21.-24.02.2011, Berlin, Germany

Publ.-Id: 15408

Single crystal strontium titanate surface and bulk modifications due to vacuum annealing

Hanzig, J.; Abendroth, B.; Hanzig, F.; Stöcker, H.; Strohmeyer, R.; Meyer, D. C.; Lindner, S.; Grobosch, M.; Knupfer, M.; Himcinschi, C.; Mühle, U.; Munnik, F.

Vacuum annealing is a widely used method to increase the electric conductivity of SrTiO3 single crystals. The induced oxygen vacancies act as intrinsic donors and lead to n-type conductivity. Apart from the changed electric properties, however, also structural modifications arise from this treatment. The present paper provides a survey of the real structure of commercially available SrTiO3 single crystals and the changes to the real structure induced by reducing vacuum heat-treatment. Used characterization methods include atomic force microscopy, transmission electron microscopy, X-ray diffraction, spectroscopic ellipsometry, infrared and photoluminescence spectroscopy. Beside the expected variation of bulk properties, especially surface modifications have been detected. The intrinsic number of near-surface dislocations in the samples was reduced by vacuum annealing. Furthermore, X-ray photoelectron spectroscopy proves the existence of a contamination layer on the surface which disappears upon increased annealing time and affects the workfunction. Also, the interaction between adsorbates and surface point defects as well as laser
annealing due to local oxygen absorption are discussed.

Publ.-Id: 15407

Advanced EXAFS analysis: Examples from mineral/water interface redox reactions

Scheinost, A. C.; Rossberg, A.

Depending on their oxidation state, actinides and other metal/metalloid radionuclides show a great variety of hydrolysis constants, solubility, complexation behavior, and sorption/precipitation reactions. Redox conditions have therefore a great impact on the migration behavior of radionuclides and the safety of nuclear waste repositories. The redox conditions of such repositories are often determined by Fe(II) and mixed Fe(II,III) (hydr)oxides, which are naturally widespread in host rocks or form as corrosion products on steel containers. Furthermore, they catalyze metal/metalloid reduction processes at their surfaces, thereby speeding up reaction kinetics which would otherwise be extremely slow. In spite of their relevance, such interfacial redox processes are still poorly understood, since they proceed through complex reaction schemes, and are commonly far from thermodynamic equilibrium.
X-ray absorption spectroscopy encompassing the methods XANES and EXAFS is in principle ideally suited to elucidate such processes by deciphering in situ the oxidation state and short range structure of radionuclides at reactive surfaces. However, the inherent shortcomings of the two methods, like limited energy resolution for XANES, and distal and angular resolution, non-Gaussian disorder as well as limited elemental resolution of backscattering atoms for EXAFS, make the data interpretation with conventional analysis methods often difficult and do not allow the derivation of unequivocal conclusions. I will therefore demonstrate the usefulness of a range of advanced XAFS analysis methods, including (1) Iterative transformation factor analysis (2), (2) Monte-Carlo analysis (see Fig. 1) (3), (3) wavelet analysis (4,5), and (4) Landweber-iteration to derive the pair distribution function from EXAFS spectra.

KEYWORDS: XAFS modeling, wavelet, factor analysis, PDF, Landweber

(1) Kirsch, R.; Fellhauer, D.; Altmaier, M.; Neck, V.; Rossberg, A.; Fanghänel, T.; Charlet, L.; Scheinost, A. C. Oxidation state and local structure of plutonium reacted with magnetite, mackinawite and chukanovite. Environ. Sci. Technol. 2011, online published.
(2) Rossberg, A.; Reich, T.; Bernhard, G. Complexation of uranium(VI) with protocatechuic acid - application of iterative transformation factor analysis to EXAFS spectroscopy. Anal. Bioanal. Chem. 2003, 376, 631-638.
(3) Rossberg, A.; Scheinost, A. C. Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo simulations and target transformation factor analysis. Anal. Bioanal. Chem. 2005, 383, 56-66.
(4) Funke, H.; Scheinost, A. C.; Chukalina, M. Wavelet analysis of extended X-ray absorption fine structure data. Phys. Rev. B: Condens. Matter 2005, 71, 094110.
(5) Funke, H.; Chukalina, M.; Scheinost, A. C. A new FEFF-based wavelet for EXAFS data analysis. J Synch. Rad. 2007, 14, 426-432.

Keywords: actinides; EXAFS; factor analysis; Monte Carlo; PDF

  • Invited lecture (Conferences)
    J-ACTINET Computational Science School 2011, 05.-06.09.2011, Tokyo, Japan

Publ.-Id: 15406

Actinide redox reactions at the solid-water interface probed by XAFS

Scheinost, A. C.

Fe(II)-bearing phases are naturally occuring in most anoxic aquifers, and form also at the surface of corroding steel containers under typical nuclear waste repository conditions. Due to their ability to reduce metal and metalloid contaminants, they are expected to play a key role for the migration behaviour of a wide range of radionuclides, including actinides and fission products. Using X-ray absorption spectroscopy as main tool, we have studied reaction end products, mechanisms and kinetics of redox processes at a range of water/mineral interfaces, including magnetite, green rust, mackinawite, chukanovite, and Fe2+-sorbed clays, but also in more redox-inert systems like cement.
Our results show that the electron transport within mineral structures and at the surface is controlling the extent and the kinetics of multi-electron redox reactions. Examples that I will show include: (1) The reduction of Pu(V) to Pu(III), which then forms a highly ordered inner-sphere sorption complex at the 111 face of magnetite, instead of the expected precipitation of PuO2 clusters. (2) The reduction of Pu(V) to PuO2 by chukanovite, and by chukanovite to a mixture of Pu(III) and PuO2. (3) The reduction of U(VI) to mixed U(IV/VI) surface complexes on Fe(II)-sorbed montmorillonite. (4) The conservation of the tetravalent oxidation state of Np in fresh and degrading cement phases and its local structure in the cemet phases. The results highlight the need for direct spectroscopic investigation of such processes, which are difficult to predict by thermodynamic methods, in order to provide reliable risk assessments.

(1) Kirsch, R.; Fellhauer, D.; Altmaier, M.; Neck, V.; Rossberg, A.; Fanghänel, T.; Charlet, L.; Scheinost, A. C. Oxidation state and local structure of plutonium reacted with magnetite, mackinawite and chukanovite. Environ. Sci. Technol. 2011, 45, 7267–7274.

(2) Chakraborty, S.; Boivin, F. F.; Banerjee, D.; Scheinost, A. C.; Mullet, M.; Ehrhardt, J.-J.; Brendle, J.; Vidal, L.; Charlet, L. U(VI) Sorption and Reduction by Fe(II) Sorbed on Montmorillonite. Environ. Sci. Technol. 2010, 44, 3779–3785.

(3) Gaona, X.; Daehn, R.; Tits, J.; Scheinost, A. C.; Wieland, E. Uptake of Np(IV) by C-S-H phases and cement paste: an EXAFS study. 2011, accepted fro publication.

Keywords: nuclear waste; redox; Fe(II) minerals; actinides; fission products; cement

  • Invited lecture (Conferences)
    J-ACTINET Meeting, 01.-02.09.2011, Tokyo, Japan

Publ.-Id: 15405

Solving the Bethe-Salpeter Equation in Euclidean Space

Dorkin, S. M.; Kaptari, L. P.; Ciofi Degli Atti, C.; Kämpfer, B.

Different approaches to solve the spinor–spinor Bethe–Salpeter (BS) equation in Euclidean space are considered. It is argued that the complete set of Dirac matrices is the most appropriate basis to define the partial amplitudes and to solve numerically the resulting system of equations with realistic interaction kernels. Other representations can be obtained by performing proper unitary transformations. A generalization of the iteration method for finding the energy spectrum of the BS equation is discussed and examples of concrete calculations are presented. Comparison of relativistic calculations with available experimental data and with corresponding non relativistic results together with an analysis of the role of Lorentz boost effects and relativistic corrections are presented. A novel method related to the use of hyperspherical harmonics is considered for a representation of the vertex functions suitable for numerical calculations.

Publ.-Id: 15404

Heavy pseudoscalar mesons in a Schwinger-Dyson--Bethe-Salpeter approach

Dorkin, S. M.; Hilger, T.; Kaptari, L. P.; Kämpfer, B.

The mass spectrum of heavy pseudoscalar mesons, as quark–antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum-dependent masses of the constituents. This dependence is prior found by solving the Schwinger-Dyson equation for quark propagators in rainbow-ladder approximation. Such approximation is known to provide fast convergence of numerical methods and accurate results for lightest mesons. However, as the meson mass increases, the method becomes less stable and special attention must be devoted to details of means of solving the corresponding equations. We focus on the pseudoscalar sector and show that our numerical scheme describes fairly accurately the π, K, D, D s and η c ground states. The excited states are considered as well. Our calculations are directly related to future physics at FAIR.

Publ.-Id: 15403

Microstructure analysis at the interface of Er decorated Ge nanocrystals in SiO2

Kanjilal, A.; Gemming, S.; Rebohle, L.; Muecklich, A.; Gemming, T.; Voelskow, M.; Skorupa, W.; Helm, M.

Using scanning transmission electron microscopy and aberration-corrected high-resolution transmission electron microscopy the existence of Er around Ge nanocrystals (NCs) is established. In fact, Ge NCs with Er-rich graded interfaces are proposed experimentally and validated by theoretical modeling using a supercell structure that consists of compounds determined by x-ray diffraction. The local electronic structure of the proposed interface geometry is found to be in accordance with the hypothesis behind the inverse energy transfer process from the Er3+ to Ge related oxygen-deficiency centers.

Keywords: nanocluster; silicon dioxide; luminescence; erbium; TEM; DFT; germanium; core-shell

Publ.-Id: 15402

Development of the coupled 3D neutron kinetics/thermal-hydraulics code DYN3D-HTR for the simulation of transients in block-type HTGR

Rohde, U.; Baier, S.; Duerigen, S.; Fridman, E.; Kliem, S.; Merk, B.

The Light Water Reactor (LWR) dynamics code DYN3D is extended and adopted for the application to block-type High Temperature Gas-Cooled Reactor (HTGR). A procedure for the cross section generation for the HTGR core calculations was developed. The modified Reactivity-Equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in the deterministic lattice calculations. A full core analysis of the reference simplified HTGR core is performed with DYN3D using macroscopic nodal cross sections provided by HELIOS.
The SP3 transport approximation is integrated into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method was developed for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes.
A 3D heat conduction module coupled with a channel-type coolant flow model is implemented into the code. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.

Keywords: high temperature gas cooled reactor; reactor dynamics; double heterogeneity; nuclear cross section data; neutron transport methods; heat conduction model

  • Kerntechnik 76(2011)3, 166-173

Publ.-Id: 15401

A 18F-labeled Fluorobutyl-substituted spirocyclic piperidine derivative as a selective radioligand for PET imaging of sigma1 receptors

Maisonial, A.; Große Maestrup, E.; Fischer, S.; Hiller, A.; Scheunemann, M.; Wiese, C.; Schepmann, D.; Steinbach, J.; Deuther-Conrad, W.; Wünsch, B.; Brust, P.

In this study we synthesized and evaluated a new spirocyclic piperidine derivative (3), bearing a 4-fluorobutyl side chain, as PET radioligand for neuroimaging of σ1 receptors. In vitro, 3 displayed a high affinity for σ1 receptors (Ki = 1.2 nM) and high selectivity. [18F]3 radiosynthesis was performed from corresponding tosylate precursor, with high radiochemical yield (45-51%), purity (> 98%) and specific activity (> 201 GBq/μmol). The metabolic stability of [18F]3 in the brain of CD-1 mice was verified and no penetration of peripheral radiometabolites into the cerebral tissue was observed. Results of ex vivo autoradiography revealed that the distribution of [18F]3 in brain corresponded to regions with high σ1 receptor density. The highest target-to-nontarget tissue ratio (2.83) was determined in the facial nucleus. Biodistribution study indicated a rapid and high brain uptake of [18F]3 (2.2% ID/g at 5 min p.i.). Pre-administration of haloperidol significantly inhibited [18F]3 uptake into the brain and in σ1 receptor expressing organs, supporting the in vivo target specificity.

Keywords: fluorinated ligands; spirocyclic piperidines; sigma1 receptors; positron emission tomography; radiochemistry

Publ.-Id: 15400

S-layer supported Pt-nanoparticles as catalyst for the asymmetric hydrogenation

Steinfeldt, N.; Sebek, M.; Günther, T.; Jähnisch, K.; Pollmann, K.; Raff, J.

Biomimetic approaches to material chemistry provide new possibilities to fabricate nanostructured materials for a wide variety of applications including catalysis.[1] In particular, two dimensional high symmetrical S-layer architectures can be considered as a promising template for the synthesis of precious metal nanoparticles with well-defined size and shape in a highly dispersed state. Most studies carried out on such materials focus on the synthesis and characterization of the S-layer structures and the templated metallic particles. Here we report on first results where Pt-nanoparticles supported on S-layer were applied to asymmetric hydrogenation.

Keywords: S-layer; catalyst; nanoparticles

  • Poster
    44. Jahrestreffen Deutscher Katalytiker mit Jahrestreffen Reaktionstechnik, 16.-18.03.2011, Weimar, Deutschland

Publ.-Id: 15399

Comparison of PVD, PECVD & PEALD Ru(-C) films as Cu diffusion barriers by means of bias temperature stress measurements

Wojcik, H.; Merkel, U.; Jahn, A.; Richter, K.; Junige, M.; Klein, C.; Gluch, J.; Albert, M.; Munnik, F.; Wenzel, C.; Bartha, J. W.

The diffusion barrier properties of PVD Ru and PECVD / PEALD Ru-C films, deposited by RuEtcp2 precursor and N2/H2 plasma, were compared on the basis of bias temperature stress measurements. An MIS test structure was used to distinguish between thermal diffusion induced by annealing and a Cu field drift due to applied electric fields. BTS-CV, TZDB and TDDB measurements revealed that the barrier performance is significantly better for PEALD and PECVD Ru-C films. This improvement is associated with carbon impurities in the Ru films with a concentration in the order of several percent according to ToF-SIMS and ERDA. The TDDB mean time to failure at 250 °C, +5 MV/cm was 7 s for PVD Ru samples, ~500 s for PECVD Ru-C, ~800 s for PEALD Ru-C and >3600 s for PVD TaN. Triangular voltage sweep measurements at 300 °C, 0.1 V/s confirmed the presence of Cu ions inside the SiO2 for degraded dots, in contrast to the Al reference sample and to PVD TaN, which performed best among all the Cu barriers under test. XRD data suggests that PEALD and PECVD Ru-C films are only weakly crystalline.

Keywords: Ru-C; Bias temperature stress; Triangular voltage sweep; Diffusion barrier; PEALD

Publ.-Id: 15398

The application of microsensors for the determination of redox processes in biofilms from uranium contaminated acidic mine drainage waters

Krawczyk-Bärsch, E.; Arnold, T.; Eisbein, E.; Brendler, V.; Jenk, U.; Zimmermann, U.

Microsensors were used in order to perform profiles of redox potential and pH within biofilms, which have formed in small drainage channels of uranium contaminated acidic mine drainage (AMD) waters from an underground uranium mine in Saxony (Germany). The results clearly showed significant differences between the redox potential and pH of the AMD water in comparison to the measured values in the biofilm, indicating that the biofilms have built up their own microenvironment. The redox potential of 921 ± 17 mV inside the biofilm was approximately 200 mV higher than in the surrounding water. The pH of the biofilm was characterized by a pH of 1.9 ± 0.1, whereas the pH of the AMD water showed a higher pH of 2.6 ± 0.1. The results were plotted into the pH-Eh diagram for the U-S-O-H-C system, which was constructed by using the analytical data of the drainage water for the calculation of the predominance fields of different uranium species. It clearly shows that an aqueous uranium(VI) sulfate complex exists in the biofilm as well as in the water under the ambient conditions. Laboratory experiments, simulating the first state of flooding of the uranium mine by increasing the pH of the AMD water, showed the influence of the Ferrovum myxofaciens dominated biofilms on the migration of uranium. Due to homeostatic mechanisms the microbes maintain their intracellular pH even when the pH of the water is increased. Consequently, an immobilization of uranium in the biofilms as well as in the AMD water is inhibited as long as Ferrovum myxofaciens will be the dominant bacteria of the biofilms.

Keywords: biofilms; uranium; AMD water; microsensors

  • Contribution to proceedings
    3rd Annual Workshop of the Collaborative Project "Redox Phenomena Controlling Systems" (7th EC FP CP RECOSY), 21.-24.03.2011, Balaruc-les-Bains, Frankreich
    3rd Annual Workshop Proceedings of the Collaborative Project "Redox Phenomena Controlling Systems" (7th EC FP CP RECOSY), KIT Scientific Reports KIT-SR 7603, Karlsruhe: KIT Scientific Publishing, Karlsruhe, 2011, 978-3-86644-756-1, 117-122

Publ.-Id: 15397

Gold nanoparticle arrays generated by modified Electron Beam Lithography and their applicability to plasmonic sensors

Derenko, S.; Grebing, J.; Härtling, T.

Gold nanoparticle arrays manufactured by a modified Electron Beam Lithography method are presented. The method allows to write highly ordered dot structures with a dot size of 50 nm and total area of 4 x 4 mm in a reasonable time.

The arrays are evaluated with respect to the desired application as plasmonic sensors. Therefore the uniformity of the particles created by the modified method is investigated. Using far-field optical spectroscopy the sprectral position and FWHM of the surface plasmon resonance (SPR) of the arrays are determined. Influences of plasmonic coupling effects on the SPR properties of closely packed array structures are elucidated by comparing the results to single particle SPR spectra. The experiments are conducted on arrays with different interparticle spacings.

Keywords: electron beam lithography; nano dots; sensors; spectroscopy

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

Publ.-Id: 15395

Dielectron production in Ar+KCl collisions at 1.76A GeV

Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Epple, E.; Fabbbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Gilardi, C.; Golubeva, M.; Gonzalez-Díaz, D.; Guber, F.; Gumberidze, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krasa, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Liu, K.; Lapidus, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Moriniere, E.; Mousa, J.; Müntz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Pechenov, V.; Pechenova, O.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y.

We present results on dielectron production in Ar+KCl collisions at 1.76A GeV. For the first time $\omega$ mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The omega multiplicity has been extracted and compared to the yields of other particles, in particular of the phi meson. At intermediate e+e- invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for a pair cocktail dominated at intermediate masses by delta Dalitz decays.

Publ.-Id: 15394

Effects of Secondary Phase Formation on Dielectric Function of Al-doped ZnO Thin Films

Vinnichenko, M.; Cornelius, S.; Kolitsch, A.

Recent investigations of Al-doped ZnO (AZO) thin films using techniques based on synchrotron radiation show that formation of metastable homologous phase (ZnO)3Al2O3 is the reason for the observed deterioration of the film electrical properties at deposition temperatures higher than certain optimum value [1]. The effect of this phase formation on the AZO film optical properties has not been studied yet. Moreover, little is known about optical properties of ZnO-Al2O3 solid solutions in general and (ZnO)3Al2O3 phase in particular, although this information might facilitate in situ diagnostics of the film properties evolution. The present work is focused on characterization of AZO and undoped ZnO films by spectroscopic ellipsometry in a wide spectral range (0.73-5.8 eV). For selected samples, ellipsometric measurements were combined with reflection and transmission measurements. The films with defined Al concentrations (cFAl=0-20 at.%) grown by reactive pulsed magnetron sputtering at temperatures ranging from RT to 550 °C were investigated.

The complex dielectric function of AZO films was obtained using a general oscillator model which combines Drude term in order to account for the free electron absorption with parameterized semiconductor oscillator model (PSEMI) [2] to account for interband transitions. The comparison of undoped ZnO and AZO films with the highest crystallinity shows that an addition of ~1 at.% of Al leads to the lowest electrical resistivity and to substantial decrease of the refractive index in the whole spectral range. This is accompanied by broadening of the PSEMI oscillator around the fundamental transition energies. It is characteristic of ZnO with high defect concentrations and is consistent with observed presence of the (ZnO)3Al2O3 phase-related peaks in x-ray absorption near edge structures (XANES) of Al K-edge. 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.

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. It is observed that these films have significantly lower amplitude and a blue-shifted PSEMI oscillator compared to conductive AZO 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 is explained in analogy to optical properties of the metastable wurtzite Mg(x)Zn(1-x)O alloys.

[1] M. Vinnichenko, R. Gago, S. Cornelius, N. Shevchenko, A. Rogozin, A. Kolitsch, F. Munnik, and W. Möller, Appl. Phys. Lett. 96, 141907 (2010).
[2] B. Johs, C.M. Herzinger, J.H. Dinan, A. Cornfeld, and J.D. Benson, Thin Solid Films 313-314, 137 (1998).

Keywords: spectroscopic ellipsometry; ZnO-Al2O3 solid solution; transparent conducting oxides

  • Poster
    6th Workshop Ellipsometry, 21.02.-24.03.2011, Berlin, Deutschland

Publ.-Id: 15393

Terahertz investigations on semiconductor quantum structures

Schneider, H.

This seminar gives an overview on recent experimental studies involving terahertz (THz) and mid-infrared radiation from photoconducting antennae and from the free-electron laser in Dresden, Germany. In particular, microstructured scalable antennae for photoconductive THz emitters and semiconductor quantum well detectors for quadratic autocorrelation of pulsed THz and mid-infrared radiation will be discussed. The final part of my talk will concentrate on nonlinear THz spectroscopy, in particular THz sideband generation and coherent dynamics of excitons dressed by strong THz beams.

Keywords: Terahertz spectroscopy; semiconductor quantum well; free-electron laser

  • Lecture (others)
    Seminar, Jet Propulsion Laboratory, Pasadena CA (USA), 10.02.2011, Pasadena, CA, USA

Publ.-Id: 15392

Numerical simulations of single- and two-phase flow liquid metal model experiments of the steel casting process

Miao, X.; Lucas, D.; Galindo, V.; Ren, Z.; Eckert, S.; Gerbeth, G.

The LIMMCAST program at HZDR models the flow fields in mould, tundish and nozzle using low-melting liquid metals. It provides detailed flow measurements which may serve for the validation of related codes. Here we present numerical simulations using the CFX code for the influence of an electromagnetic brake on single- and two-phase flows in the mould. These simulations are done in close relation to LIMMCAST experiments. Contrary to the expectation, the local flow around the jets was intensified remarkably and lead to an asymmetric flow at the center plane in the presence of the magnetic field in case of electrically insulating mould walls. For electrically conducting walls, the jet becomes rather stable. It turns out that the electrically conducting boundary conditions have a great impact on the flow structure with the imposition of an external static magnetic field. For the two-phase case of injected argon bubbles, the model problem of a rising bubble driven flow in an external magnetic field is considered.

Keywords: continuous casting; SST turbulence model; EMBR; bubbly flow

  • Lecture (Conference)
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland
  • Contribution to proceedings
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland

Publ.-Id: 15391

Influence of spectral history on PWR full core calculation results

Bilodid, I.; Mittag, S.

The few-group cross section libraries, used by reactor dynamics codes, are affected by the spectral history effect – a dependence of fuel cross sections not only on burnup, but also on local spectral conditions during burnup. A cross section correction method based on Pu-239 concentration was implemented in the reactor dynamic code DYN3D.
This paper describes the influence of a cross section correction on full-core calculation results. Steady-state and burnup characteristics of a PWR equilibrium cycle, calculated by DYN3D with and without cross section corrections, are compared. A study has shown a significant influence of spectral history on axial power and burnup distributions as well as on calculated cycle length. An impact of the correction on transient calculations is studied for a control rod ejection example.

Keywords: cross section library; history effects; spectral history; burnup; DYN3D

  • Open Access Logo Contribution to proceedings
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany
    Proceedings of the 21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, Budapest, 978-963-372-646-4, 127-138
  • Lecture (Conference)
    21st SYMPOSIUM of AER on VVER Reactor Physics and Reactor Safety, 19.-23.09.2011, Dresden, Germany

Publ.-Id: 15390

Field-induced gap in a quantum spin-1/2 chain in a strong magnetic field

Zvyagin, S. A.; Cizmar, E.; Ozerov, M.; Wosnitza, J.; Feyerherm, R.; Manmana, S. R.; Mila, F.

Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsed-field electron-spin-resonance spectroscopy. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the density matrix renormalization group calculations for a spin-1/2 Heisenberg chain with a staggered transverse field.

  • Physical Review B 83(2011), 060409(R)

Publ.-Id: 15388

Magnetic torque evidence for the Fulde-Ferrell-Larkin-Ovchinnikov state in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2

Bergk, B.; Demuer, A.; Sheikin, I.; Wang, Y.; Wosnitza, J.; Nakazawa, Y.; Lortz, R.

We present magnetic-torque measurements of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 for inplane magnetic fields up to 32 T. In this layered two-dimensional compound the superconductivity can persist even in fields above the Pauli limit of about 21 T. There, a pronounced upturn of the upper-critical-field line occurs and the superconducting phase-transition line splits and forms an additional high-magnetic-field phase. κ-(BEDT-TTF)2Cu(NCS)2 is a spin-singlet superconductor; therefore, such a superconducting high-field phase beyond the Pauli limit can originate only from Cooper pairing with finite center-of-mass momentum. The measurements are discussed in connection with a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in accordance with earlier specific-heat observations. The torque experiments allow us to investigate the high-magnetic-field phase diagram and the FFLO state of κ-(BEDT-TTF)2Cu(NCS)2 in great detail.

  • Physical Review B 83(2011), 064506

Publ.-Id: 15387

New solid state detectors

Ilgner, C.

Contemporary particle accelerators for fundamental research in particle physics like Fermilab's Tevatron and CERN's Large Hadron Collider (LHC) provide researchers with higher and higher luminosities. This sets the pace for the need for radiation hard detector materials for both beamline instrumentation and the physics experiments themselves.
Silicon pixel and silicon microstrip detectors are well developed devices for tracking applications in these high-energy physics experiments. However, these detectors are expected to reach the end of their lifetime within a few years due to their exposure to harsh radiation, of which the yearly level amounts to up to several 1014 hadrons/cm2 during the foreseen 10 years of operation in the case of LHC experiments.
In order to protect sensitive experimental devices from adverse beam conditions, chemical vapor deposition (CVD) diamond, an artificially generated diamond material, is more and more being used in systems called Beam Condition Monitors
(BCM). The radiation level these sensors are exposed to is even higher than in the case of position sensitive tracking detectors. An example are the CVD diamond sensors of the BCM of the LHCb experiment at CERN, which is meant to withstand 1015 hadrons/cm2 during 10 years.
Preparation of CVD diamond sensors for BCM applications are discussed in detail, together with the properties of this new material as a candidate for position sensitive devices in high energy physics experiments, addressing also operational questions like the appearance of erratic dark currents in polycrystalline diamond bulks. Other new materials for position sensitive devices such as CdZnTe and CdTe are discussed as well and compared to the well established silicon, together with a compilation of their properties relevant to particle detection.
Recent advances in the field of passive radiation monitors, where thermoluminescent sensors made from lithium fluoride now cover a dynamic range from several µGy up to 105Gy, are also discussed briefly.

Keywords: diamond detector; chemical vapor deposition diamond; polycrystalline diamond; radiation damage; erratic dark currents; cadmium telluride; cadmium zinc telluride; particle detection; lithium fluoride; thermoluminescence; solid state detector; metalization; Beam Conditions Monitor; beamline instrumentation

  • Book chapter
    Grupen, Claus; Buvat, Irène: Handbook of Particle Detection and Imaging, Heidelberg: Springer, 2011, 978-3-642-13270-4, 519-533

Publ.-Id: 15386

Ziele der Forschung am Large Hadron Collider

Ilgner, C.; Trefzger, T.

Ausgehend von Fragen wie „Was ist Masse?“ oder „Was passierte beim Urknall?“ erläutert der Beitrag Ziele und Methoden der Forschung am Large Hadron Collider (LHC). CERN, das Europäische Labor für Teilchenphysik, betreibt diesen größten Teilchenbeschleuniger der Welt in der Nähe von Genf. Angereichert mit zahlreichen Fakten wird dabei einerseits der bisherige Kenntnisstand dargestellt, andererseits aber auch die Theorien, welche man momentan am CERN der experimentellen Prüfung unterzieht. In zusätzlichen Info-Kästen wird genauer auf das Standardmodell der Elementarteilchenphysik, die einzelnen Experimente LHC und die Physik des Higgs-Bosons eingegangen. Eine umfangreiche Literaturliste, die sowohl neue Bücher als auch Webseiten mit Bezug zum Thema enthält, rundet den Artikel ab.

Keywords: mass; big bang; Large Hadron Collider; CERN; Higgs boson; fundamental research; particle physics

  • Praxis der Naturwissenschaften Physik in der Schule 2/60(2011), 5-16

Publ.-Id: 15385

Evidence for Pauli-limiting behaviour at high fields and enhanced upper critical fields near T-c in several disordered FeAs based superconductors

Fuchs, G.; Drechsler, S.; Kozlova, N.; Bartkowiak, M.; Behr, G.; Nenkov, K.; Klauss, H.; Freudenberger, J.; Knupfer, M.; Hammerath, F.; Lang, G.; Grafe, H.; Buchner, B.; Schultz, L.

We report resistivity and upper critical field Bc2 (T) data for disordered (As-deficient) LaO0.9F0.1 FeAs1-delta in a wide temperature and high field range up to 60 T. These samples exhibit a slightly enhanced superconducting transition at Tc = 28.5 K and a significantly enlarged slope dBc2/dT = -5.4 T/K near Tc which contrasts with a flattening of Bc2(T) starting near 23 K above 30 T. The latter evidences Pauli-limiting behaviour (PLB) with Bc2(0) approximate to 63 T. We compare our results with Bc2(T)-data from the literature for clean and disordered samples. Whereas clean samples show almost no PLB for fields below 60-70 T, the hitherto unexplained pronounced flattening of Bc2(T) for applied fields H vertical bar ab observed for several disordered closely related systems is interpreted also as a manifestation of PLB. Consequences are discussed in terms of disorder effects within the frames of (un)conventional superconductivity, respectively.

Publ.-Id: 15383

Coordination of uranium(VI) with functional groups of bacterial lipopolysaccharide studied by EXAFS and FT-IR spectroscopy

Barkleit, A.; Foerstendorf, H.; Li, B.; Rossberg, A.; Moll, H.; Bernhard, G.

The complexation of uranyl ions with lipopolysaccharide (LPS), the main component of the cell wall of Gram-negative bacteria, was investigated on a molecular level with U LIII edge extended X-ray absorption fine structure (EXAFS) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy over a wide pH range (2.6 to 7.0). For the first time, structural determinations of uranyl complexes with cell wall compounds were extended from acidic up to neutral pH. The main functionalities responsible for uranyl binding are phosphoryl and carboxyl groups. At an excess of LPS, related to environmental conditions, the uranyl ion is mainly complexed by phosphoryl groups four-fold monodentately coordinated in the equatorial plane of the uranyl dioxo cation UO2 2+ showing great homologies to the uranyl mineral phase meta-autunite in the EXAFS spectra. At equimolar ratios of uranyl and functional groups of LPS, according to a slight deficit of phosphoryl groups, additional carboxyl coordination in a bidentate manner becomes important as it is shown by IR spectroscopy. From the vibrational spectra, a mixed coordination of UO2 2+ with both phosphoryl and carboxyl groups is derived. The coordination of uranyl ions to the LPS molecule is obviously mainly controlled by the U/LPS concentration ratio, and the influence of pH is only of minor significance at the investigated range.

Publ.-Id: 15381

Uranium(VI) speciation in natural waters determined by TRLFS

Baumann, N.

Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS) is a very helpful tool with an extremely low detection limit for analyzing speciation of certain radioactive heavy metal ions like uranium (VI). Thus this technique is preferential appropriate for detection of speciation from that ions in environmental relevant concentrations. So TRLFS can be useful in safety assessment concerning migration behaviour of radioactive elements.
In this presentation is shown, that the uranium speciation in natural occurring seepage water samples, and in soil water samples, all samples collected from test site “Gessenwiese” close to Ronneburg in Eastern Thuringia (Germany), were analyzed by TRLFS. This test site was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of recultivated former uranium mining heaps.
The TRLFS measurements on water samples collected within test site Gessenwiese revealed that the uranium speciation in that seepage water is dominated by the hydrolyzed and monomer uranium (VI) sulfate species UO2SO4(aq). This results presented here are a convincing example for the suitability of TRFLS in analyzing the speciation of uranium from natural occurring water samples with pH values between 3.2 and 4.0.

Keywords: uranium; environment; TRLFS; safety assessment

  • Poster
    The 12th Conference on Nuclear Science and Technology, 01.-02.07.2011, Bangkok, Thailand

Publ.-Id: 15380

Role of Coulomb blockade and spin-flip scattering in tunneling magnetoresistance of FeCo-Si-O nanogranular films

Kumar, H.; Ghosh, S.; Bürger, D.; Li, L.; Zhou, S.; Kabiraj, D.; Avasthi, D. K.; Grötzschel, R.; Schmidt, H.

In this work we report the effect of FeCo atomic fraction (0.33 < x < 0.54) and temperature on the electrical, magnetic and tunneling magnetoresistance (TMR) properties of FeCo-Si-O granular films prepared by atom beam sputtering technique. GAXRD and TEM studies reveal that films are amorphous in nature. The dipole-dipole interactions (particle-matrix mixing) is evident from Zero-field cooled (ZFC) and field-cooled (FC) magnetic susceptibility measurements and the presence of oxides (mainly Fe- related) is observed by XPS analysis. The presence of Fe-oxides is responsible for the observed reduction of saturation magnetization and rapid increase in coercivity below 50 K. TMR has been observed in a wide temperature range and a maximum TMR of -4.25 % at 300 K is observed for x = 0.39 at a maximum applied field of 60 kOe. The fast decay of maximum TMR at high temperatures and lower TMR values at 300 K as compared to , where PFeCo is the spin polarization of FeCo are in accordance with a theoretical model that includes spin-flip scattering processes. The temperature dependent study of TMR effect reveals a remarkably enhanced TMR at low temperatures. The TMR value varies from -2.1% at 300 K to -14.5% at 5 K for x = 0.54 and a large MR value of -18.5% at 5 K for x = 0.39 is explained on the basis of theoretical models involving Coulomb blockade effects. Qualitatively particle-matrix mixing and presence of Fe-oxides seems to be the source of spin-flip scattering, responsible for fast decay of TMR at high temperatures. A combination of higher order tunneling (in Coulomb blockade regime) and spin flip scattering (high temperature regime) explains the temperature dependent TMR of these films.

Keywords: Tunneling Magnetoresistance; Granular films; Spin-flip scattering; Coulomb blockade

Publ.-Id: 15378

Natural analogs of synthetic reference materials: Assessing the limits of homogeneity testing at the picogram scale

Michalak, P. P.; Renno, A. D.; Merchel, S.; Munnik, F.; Wiedenbeck, M.

The demand for certified reference materials for chemical and structural microanalysis of geological samples is growing continuously. The fact that there are no certified materials currently available, for which the chemical homogeneity has been documented at the micrometer- and submicrometer level [1] reinforces the need of producing them. A collaboration involving several German scientific institutions has now received funding from the Free State of Saxony and the European Union Social Fund with the objective of providing synthetic, adequately homogeneous minerals with appropriate contents of economically important trace elements that could be certified as reference materials for methods employing sub-ng sampling masses.

Due to such geological processes as crystallization, metasomatism and weathering, specific elemental exchange vectors and substitution mechanisms may be triggered [2, 3] (as shown in Fig. 1), causing elements in minerals to be spatially, heterogeneously distributed at the micrometer scale [4] (e.g. zonation, see Fig. 2). An awareness of naturally occurring solid solutions as well as different structural characters in the lattice of minerals must, therefore, form a foundation for any attempt at producing synthetic mineral materials, which according to this project’s objective, should be free of any compositional and structural inhomogeneities at such a sampling scale.

Prior to the synthesis of any minerals, a thorough crystal-chemical characterization of their natural analogs should be performed. A certain spatial variation in the concentration of major and trace elements in natural mineral samples may be revealed using microanalytical techniques of varied sensitivity. One way to perceive homogeneity is as the function of the size of the studied analytical volume, which is largely determined by the spatial resolution of the probe. For example, a material rated homogenous by optical microscopy and EPMA may demonstrate inhomogeneity when tested using nanoSIMS because of the better spatial resolution and detection limits provided by this method. On the other hand, an isotopically homogenous material may exhibit heterogeneity in the major and/or trace element distributions [5].

In order to test such variances and relationships in selected natural analogs of synthetic reference materials as a function of analytical method, we designed a series of chemical and structural homogeneity–check measurements of sanidine, tantalite, columbite and pyrite. We are using several different imaging and spectroscopic techniques, starting from optical polarizing and reflected microscopy, BSE and CL imaging, EBSD, IR, Raman, EPMA, µPIXE coupled with µPIGE, SIMS and synchrotron µXRF. Establishing a rapid, economical and robust homogeneity testing procedure is essential for achieving the overall goals of this project. In order to meet these criteria, a reasonable sequence of measurements is devised starting from simple techniques (i.e., optical microscopy) and move toward the more complex (i.e. SIMS and µXRF). This first phase will contribute towards optimizing our homogeneity testing procedure, assuring that our approach will be suitable for our ultimate certification plan.

  • Poster
    Microscopy & Microanalysis 2011, 07.-11.08.2011, Nashville, USA

Publ.-Id: 15377

Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape

Kumar, H.; Ghosh, S.; Avasthi, D. K.; Kabiraj, D.; Mücklich, A.; Zhou, S.; Schmidt, H.; Stoquert, J. P.

Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

Keywords: Magnetic nanoparticles; swift heavy ions

Publ.-Id: 15376

Heavy liquid metal network: HeLiMnet project overview

Ricci, E.; de Grandis, S.; Briceno, D.; Di Gabriele, F.; Tarantino, M.; Fazio, C.; Schuurmans, P.; Latge, C.; Wagner, W.; Eckert, S.; Bucenieks, I.; Karbojan, A.; Abella, J.

The international development of the Lead-cooled Fast Reactor (LFR) had an early start in the Soviet Union in the 1960s where reactors cooled by Lead-Bismuth Eutectic (LBE) were developed and deployed for use in submarine propulsion. More recently, the Generation IV International Forum (GIF) Technology Roadmap identified the LFR as a technology with great promise to provide small-unit electricity generation as well as large, grid-connected power. Since then, considerable effort has been devoted to the development of new concepts.

Keywords: Transmutation; lead -cooled fast reactor; generation IV; accelerator-driven systems

  • Lecture (Conference)
    ICAPP 2011 "Performance & Flexibility: The Power of Innovation", 02.-05.05.2011, Nice, France
  • Contribution to proceedings
    ICAPP 2011 "Performance & Flexibility: The Power of Innovation", 02.-05.05.2011, Nice, France

Publ.-Id: 15375

Intermittent behaviour caused by surface oxidation in a liquid metal flow driven by a rotating magnetic field

Zhang, C.; Shatrov, V.; Priede, J.; Eckert, S.; Gerbeth, G.

The focus of the experimental and numerical study presented here is on the bulk flow within a swirling liquid metal column driven by a rotating magnetic field (RMF), whereas the free surface of the melt was covered by a distinct oxide layer. Flow measurements revealed an anomalous behaviour of the flow: Pronounced oscillations of both the primary swirling and the secondary recirculating flow occur spontaneously. This peculiarity can be attributed to the influence of the oxide layer at the surface of the metal. The motion of the covering layer is determined by the strength of the fluid flow and the properties of the layer and may exhibit three different states of motion: permanent rotation, intermittent rotation or the quiescent state. The regime of an intermittent oxide layer rotation reveals a striking influence on the bulk flow of the liquid metal. The amplitude of the velocity oscillations observed appears to be at least one order of magnitude larger than those of turbulent fluctuations in a steady RMF-driven flow. Essential features of the phenomenon observed were reproduced by a simple numerical model.

Keywords: Electromagnetic stirring; rotating magnetic field; oxide layer; ultrasound Doppler velocimetry

Publ.-Id: 15374

Liquid metal modelling of continuous steel casting - the LIMMCAST programme

Gerbeth, G.; Eckert, S.; Timmel, K.; Miao, X.; Lucas, D.; Stefani, F.; Wondrak, T.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications. Water model experiments are of limited value, particularly in the cases of strong temperature gradients, two-phase flows or flows exposed to electromagnetic fields. We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up Mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. First results from LIMMCAST and Mini-LIMMCAST will be presented covering the following phenomena: fully contactless electromagnetic tomography of the flow in the mould, mould flow monitoring by a multitude of ultrasonic sensors and analysis of the flow in the mould under the influence of an electromagnetic brake: intensification of the flow turbulence contrary to the expected flow damping, injection of argon bubbles through the stopper rod: occurrence of pressure oscillations. In addition, numerical simulations using ANSYS-CFX will be presented which basically confirm the measuring results.

Keywords: Continuous casting; liquid metal model; mould flow; flow measurements; two-phase flow; magnetic flow tomography; ultrasound Doppler method; numerical simulation

  • Lecture (Conference)
    7th European Continuous Casting Conference (ECCC), 27.06.-01.07.2011, Düsseldorf, Deutschland
  • Contribution to proceedings
    7th European Continuous Casting Conference (ECCC), 27.06.-01.07.2011, Düsseldorf, Deutschland
    Proceedings of the 7th European Continuous Casting Conference (ECCC)

Publ.-Id: 15373

Model experiments on two-phase flows occurring in the continuous casting process

Timmel, K.; Wondrak, T.; Stefani, F.; Eckert, S.; Gerbeth, G.; Terzija, N.; Yin, W.; Peyton, A.

We present model experiments with low melting point liquid metal two-phase flows using the setup of the Mini-LIMMCAST facility at HZDR. Argon gas was injected at the tip of the stopper rod. The flow field and the gas distribution were measured in the submerged entry nozzle (SEN) and in the mould by means of electromagnetic and/or ultrasonic techniques. Data sets were recorded for the pressure at the gas injection point and for the levels of the liquid metal surface in the tundish and the mould, respectively. The investigations showed that not all the gas injected forms bubbles or slugs within the SEN. In all likelihood, gas layer were formed around the stopper rod and a part of the gas escapes along the stopper rod towards the free surface in the tundish. The flow experiments delivered a strong indication for the occurrence of a slug flow inside the SEN manifested by simultaneous, coherent oscillations of the pressure at the injection point and the liquid metal level in the mould. Further systematic experiments are necessary to figure out the occurrence of different flow regimes in the SEN depending on the ratio of liquid and gas flow rates.

Keywords: Continuous casting; liquid metal model; mould flow; flow measurements; two-phase flow; magnetic flow tomography; ultrasound Doppler method

  • Lecture (Conference)
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland
  • Contribution to proceedings
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland
    Proceedings of the 4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim)

Publ.-Id: 15372

Experimental modelling of the impact of a DC magnetic field on the melt flow in a continuous casting mould

Timmel, K.; Miao, X.; Lucas, D.; Eckert, S.; Gerbeth, G.

This paper is concerned with experimental and numerical investigations focusing on the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Systematic measurements of the mould flow were carried out using the eutectic alloy GaInSn inside a plexiglass model at room temperature. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mould. The ultrasound Doppler velocimetry (UDV) was applied to obtain a detailed experimental data base with respect to the mean values and transient properties of the velocity fields occurring in the mould. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The comparison between our numerical calculations and the experimental results displays a very well agreement. An important result of our study was the feature that a static magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations.

Keywords: continuous casting; liquid metal model experiment; mould flow; flow measurements; DC magnetic field; electromagnetic brake

  • Lecture (Conference)
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland
  • Contribution to proceedings
    4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim), 27.06.-01.07.2011, Düsseldorf, Deutschland
    Proceedings of the 4th International Conference on Modelling and Simulation of Metallurgical Processes in Steelmaking (SteelSim)

Publ.-Id: 15371

Solidification of a binary metal alloy driven by a radial heat flux in presence of a rotating magnetic field: numerics vs. experiments

Travnikov, V.; Nikrityuk, P. A.; Eckert, K.; Räbiger, D.; Eckert, S.

Rotating magnetic fields (RMF’s) are meanwhile widely used in metallurgy. The RMF eliminates flow asymmetries and allows for the control of heat and mass transfer, and hence of the evolving microstructure during solidification processes. In an extension of previous works, devoted to the unidirectional solidification in both constant and temporarily modulated RMF’s, we now analyze the solidification driven by a radial heat flux. The model geometry is a cylinder filled with a binary aluminum-silicon alloy. The outer walls of the cylinder are held on a constant temperature of 20°C while its lower surface is adiabatic. The top surface of the alloy is free.
The numerical simulations employ a hybrid solidification model which is implemented into a 2D Navier-Stokes solver based on the SIMPLE algorithm. We first re-investigate the spin-up problem, given by the simultaneous start of both cooling and acceleration of the melt, for different thermal conditions. Second, we compare the numerical results with corresponding experiments in the same model geometry which have been performed at the Helmholtz-Zentrum HZDR.

Keywords: solidification; melt flow; electromagnetic stirring; hybrid solidification model

  • Poster
    3rd International Conference on Advances in Solidification Processes (ICASP3), 07.-10.06.2011, Aachen, Deutschland

Publ.-Id: 15370

Observation of segregation freckle formation under the influence of melt convection

Shevchenko, N.; Boden, S.; Eckert, S.; Gerbeth, G.

An undesired phenomenon associated with natural convection in the mushy zone is the formation of segregations channels, the so-called chimneys. We investigated the influence of melt flow on the solidification of a Ga-25wt.In alloy, if the buoyancy-driven flow is interfered by a much stronger electromagnetically-driven flow. For visualizing the process we apply the X-ray radiography which enables a general intuitional understanding of the interaction between solidification and melt flow. The main effect of the flow is determined by the flow-induced redistribution of solute concentration. The consequences are a change of the grow direction of the dendrites and the preference of secondary arm branches for and accelerated and decelerated growth, respectively. The present study demonstrates that a dominating electromagnetic stirring may provoke a unidirectional solute transport in the mushy zone which in turn causes the formation of spacious segregation pattern.

Keywords: solidification; melt flow; forced convection; segregation; freckle formation; X-ray radiography

  • Lecture (Conference)
    3rd International Conference on Advances in Solidification Processes (ICASP3), 07.-10.06.2011, Aachen, Deutschland
  • Open Access Logo Journal of Physics: Conference Series 27(2011), 012085
    DOI: doi:10.1088/1757-899X/27/1/012085

Publ.-Id: 15369

Flow control during solidification of SnPb-Alloys using time-modulated AC magnetic fields

Räbiger, D.; Leonhardt, M.; Eckert, S.; Gerbeth, G.

Electromagnetic stirring during solidification has been proved to be a striking method for achieving a purposeful alteration of the microstructure of casting ingots, such as grain refinement or the promotion of a transition from a columnar to an equiaxed dendritic groth (CET). However, the imposition of a rotating (RMF) or a travelling magnetic field (TMF) also causes problems like the occurrence of typical segregation pattern or a deflection of the upper free surface. A permanent radial inward (RMF and downward TMF) or outward (upward TMF) flow along the solidification front is responsible for the transport of solute to the axis or the wall of the ingot resulting in typical freckle segregation pattern filled with alloy of eutectic composition. It was shown, that modulated AC magnetic fields are appropriate to overcome these problems.
This present study examines the directional solidification of SnPb alloys from a water cooled copper chill. Time-modulated combinations of rotating and travelling magnetic field are used to agitate the melt. Our results reveal the potential of modulated magnetic fields to realize an effective flow control for achieving grain refinement without the formation of segregation freckles.

Keywords: solidification; melt flow; electromagnetic stirring; grain refinement; segregation

  • Lecture (Conference)
    3rd International Conference on Advances in Solidification Processes (ICASP3), 07.-10.06.2011, Aachen, Deutschland
  • Open Access Logo Journal of Physics: Conference Series 27(2011), 012053
    DOI: doi:10.1088/1757-899X/27/1/012053

Publ.-Id: 15368

The impact of melt flow on the grain orientation in solidifying metal alloys

Eckert, S.; Räbiger, D.; Zimmermann, G.; Mathes, M.

The kinetics of solidification as well as the resulting microstructure are significantly affected by convection occurring in the liquid phase. Therefore, the application of electro-magnetic fields to control solidification processes has received a growing interest. We study the grain growth in various metal alloys under the influence of a rotating magnetic field (RMF) which generates a melt flow aligned mainly perpendicular to the solidification front. Previous investigations showed an inclination of the columnar structure towards the incident flow. The tilting of the columnar grains can be explained by the transport of solute, however, the influence of the flow on the crystal orientation has not been examined so far.
Within the present study directional solidification experiments were performed in PbSn and AlSi alloys applying a sudden onset of the electromagnetic force. Just be-fore and after the initiation of the magnetic field the grain structure was analyzed. Electrolytical etching was used to identify grains having different orientations and related EBSD measurements provided quantitative values for the crystallographic orientation of the grains. Whereas a distinct asymmetric grain growth or a deflection of the columnar grains becomes obvious in case of forced melt flow, a perceivable modification of the crystal orientation cannot be detected by our measurements.

Keywords: solidification; melt flow; rotating magnetic field; grain orientation; EBSD

  • Lecture (Conference)
    3rd International Conference on Advances in Solidification Processes (ICASP3), 07.-10.06.2011, Aachen, Deutschland
  • Open Access Logo Journal of Physics: Conference Series 27(2011), 012051
    DOI: doi:10.1088/1757-899X/27/1/012051

Publ.-Id: 15367

An Approach for IT Service Management of Research Institutes

Konrad, U.; Lemke, C.

In times of scarce resources and increasing demands, an optimum IT support requires a greater service orientation and a more systematic description and management. While IT Service Management (ITSM) previously in the industry has become a standard, there are so far, only few best practice examples at universities and research institutions. The essential characteristic of this paradigm shift in the way of IT provisioning is to align IT with the specific business processes of the organization.

This paper proposes an approach to ITSM for research institutes that achieves an IT and business alignment in the context of an IT service orientation, based on ITIL v3. Starting with a description of the business processes in the context of research institutions the required IT services structure can be derived. A draft of a generic business process map providing the basis for the definition and design of IT services has been found. The resulting IT service and IT function catalogues combine the business and technical view. This provides the first step towards the development of a standardized and efficient implementation reference model for ITSM in the research area. The goal of this ongoing project is to develop a practical framework for the ITSM of research institutes and an IT management information system prototype.

Keywords: IT Service Management; ITIL v3; IT service orientation; business alignment

  • Contribution to proceedings
    Innovation Information Technologies: Theory and Practices, 08.-13.04.2011, Ufa, Russia
    Proceedings of the International Workshop "Innovation Information Technologies: Theory and Practice", 978-5-4221-0159-7, 1-4

Publ.-Id: 15366

Uranium – transfer from soil to plant cells

Geipel, G.; Günther, A.; Viehweger, A.; Bernhard, G.

Uranium exist in low concentrations overall in the environment. Despite this ground level of uranium distribution the use of this metal in nuclear industry, agriculture, and as depleted uranium in weapons caused widespread additional contamination of this element in the environment. Depleted uranium ammunition can form uranium minerals by weathering, which later decompose and may increase the uranium concentration in the ground water [1].
This dissolved uranium may be bio-available and can be incorporated by microorganism, biofilms, algae, fungi and plants. In this way uranium reaches the food chain and can be incorporated also by the human.
Due to the extraordinary properties of uranium it is possible to study the speciation of this element under natural conditions and up to extremely low concentrations of about 50 ng/L by time-resolved laser-induced fluorescence spectroscopy.
We could show that the uranium speciation in compartments of living organism differ strongly. As example we follow the theoretical way of the uranium from the mineral phases after weathering to cell compartments of Arabidopsis halleri, grown on a mine tailing pile in Johanngeorgenstadt.
We could show that the uranium speciation changes from the uranium mineral phase like sabugalit to carbonate species in the aqueous environment. This dissolved uranium may be up taken by roots of plants and transported into the plant cells [2]. Compounds with phosphate and carboxylate ligands in different compartments of the living organisms were expected. By fractionation of the plant cells the uranium speciation in the several compartments was studied. Other bioligands play an additional role by reducing the hexavalent uranium .

[1] Schimmack, W.; Gerstmann, U.; Schultz, W.; Geipel, G.: Radiation and Environmental Biophysics 46(2007), 221-227
[2] Viehweger, K.; Geipel, G.: Environmental and Experimental Botany 69(2010), 39-46

Keywords: uranium; transfer; soil; plant cells; speciation

  • Contribution to proceedings
    UMH Freiberg, 18.-22.09.2011, Freiberg, Deutschland
    The New Uranium Mining Boom, Heidelberg: Springer, 978-3-642-22121-7, 821-826

Publ.-Id: 15365

Relaxation dynamics of graphene in magnetic fields close to the Dirac point

Mittendorff, M.; Winnerl, S.; Plochocka, P.; Kossacki, P.; Schneider, H.; Orlita, M.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.; Helm, M.

The relaxation dynamics in graphene is of key importance for understanding the basic material properties as well as for high-frequency electronic and opto-electronic device applications. In addition to single colour pump-probe experiments in the THz range (photon energy: 14-30 meV) without magnetic field, we performed experiments at a photon energy of 18 meV in magnetic fields up to 1.34 T. For photon energies larger than twice the Fermi energy (approx. 10 meV) positive pump-probe signals were observed while for smaller photon energies pump-induced absorption occurred due to carrier heating. Relaxation times were around 30 ps. At magnetic fields around 0.23 T the pumpprobe signal increases by a factor of 2.5. At this field the splitting of the zeroth to first Landau level is resonant with the photon energy.

  • Lecture (Conference)
    DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15364

Influence of organic ligands and temperature on U(VI) sorption and diffusion in the system Opalinus Clay/Opalinus Clay pore water

Schmeide, K.; Joseph, C.; Steudtner, R.; Bernhard, G.

In addition to salt and crystalline rock, argillaceous rock is investigated as potential host rock and backfill material for nuclear waste repositories. For safety assessment, knowledge on the migration behavior of potentially released actinides in these environments is required. Clay rock contains natural organic matter. Low molecular weight organic acids such as acetate, lactate, propionate and formate as well as fulvic and humic acids can be released from clay under certain conditions [1, 2]. In continuation of our former study where the retention properties of the natural clay rock Opalinus Clay (Mont Terri, Switzerland) towards U(VI) were investigated [3], we studied the influence of various organic ligands on the sorption of U(VI) (1•10-6 M) onto Opalinus Clay under aerobic conditions applying synthetic Opalinus Clay pore water (I = 0.36 M, pH 7.6 [4]) as background electrolyte. It was found that the low U(VI) sorption onto Opalinus Clay in the absence of ligands (Kd = (0.0222 ± 0.0004) m3/kg [3]) further decreases with increasing concentration of low molecular weight organic acids (1•10-5 to 1•10-2 M) due to complex formation in aqueous solution. The mobilizing effect of the organic ligands on U(VI) increases in the following sequence: formate < lactate ~ acetate ~ propionate < tartrate < citrate. For instance, in the presence of citrate (1•10-2 M), which has been identified as important ligand in radioactive waste problems, the Kd value for U(VI) amounts to only (0.0011 ± 0.0003) m3/kg. The influence of the organic ligands on the U(VI) sorption onto Opalinus Clay correlates with the stability of the respective U(VI) complexes. In contrast, humic acid (< 50 mg/L) does not change U(VI) sorption [3]. A reduction of U(VI) to U(IV) was not detected.
Since elevated temperatures are expected for the disposal of high-level nuclear waste in clay formations, the influence of temperature on the U(VI) sorption onto Opalinus Clay was studied in the temperature range from 10 to 60°C. In the absence of organic ligands, the U(VI) sorption increases with increasing temperature. For U(VI), the apparent endothermic sorption enthalpy amounts to 34 ± 1 kJ/mol. The temperature dependence of the U(VI) sorption onto Opalinus Clay is almost not influenced by lactate and humic acid (50 mg/L), however, slightly changed by citrate, when present in the concentration range from 1•10-5 to 1•10-2 M.
For interpretation of the sorption results, the U(VI) speciation in aqueous solution has to be known. Therefore, we studied the U(VI) complexation by lactic acid (pH 3) and citric acid (pH 1-10) in the temperature range from 7 to 65°C. Species distribution and complex formation constants were determined by means of UV-Vis and time-resolved laser-induced fluorescence spectroscopy. The complex formation between U(VI) and these ligands was found to be endothermic and entropy-driven.
Finally, the diffusion of U(VI) (1•10-6 M) in intact bore core samples was studied under anaerobic conditions in the absence and presence of humic acid (10 mg/L) both at 25°C and at 60°C. After three months of diffusion time, the U(VI) and humic acid diffusion profiles were determined. Both an influence of the temperature and of humic acid on U(VI) diffusion was detected. Currently, diffusion and distribution coefficients are determined by fitting the U(VI) and humic acid diffusion profiles using the modeling software COMSOL Multiphysics 3.3 [5].
The results show that the sorption and diffusion behavior of U(VI) in the system Opalinus Clay/Opalinus Clay pore water is influenced by natural organic matter and temperature. Especially strongly complexing low molecular weight organic acids can enhance the mobility of U(VI) in clay.

[1] Courdouan, A., Christl, I., Meylan, S., Wersin, P., Kretschmar, R.: Characterization of dissolved organic matter in anoxic rock extracts and in situ pore water of the Opalinus Clay. Appl. Geochem. 22, 2926-2939 (2007).
[2] Claret, F., Schäfer, T., Bauer, A., Buckau, G.: Generation of humic and fulvic acid from Callovo-Oxfordian clay under high alkaline conditions. Sci. Total Environ. 317, 189-200 (2003).
[3] Joseph, C., Schmeide, K., Sachs, S., Brendler, V., Geipel, G., Bernhard, G.: Sorption of uranium(VI) onto Opalinus Clay in the absence and presence of humic acid in Opalinus Clay pore water. Chem. Geology 284, 240-250 (2011).
[4] Pearson, F.J.: Opalinus Clay experimental water: A1Type, Version 980318, PSI Internal Report TM-44-98-07. Paul Scherrer Institut, Villigen, Switzerland (1998).
[5] Finite-element software package.

Keywords: Uranium(VI); sorption; diffusion; complexation; organic ligands

  • Contribution to proceedings
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, China
  • Poster
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, China

Publ.-Id: 15363

Measurement of the in-medium phi-meson width in proton-nucleus collisions

Polyanskiy, A.; Hartmann, M.; Kiselev, Y. T.; Paryev, E. Y.; Büscher, M.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Gebel, R.; Hejny, V.; Kämpfer, B.; Keshelashvili, I.; Koptev, V.; Lorentz, B.; Maeda, Y.; Merzliakov, S.; Mikirtytchiant, S.; Nekipelov, M.; Ohm, H.; Schade, H.; Serdyuk, V.; Sibirtsev, A.; Stein, H. J.; Ströher, H.; Trusov, S.; Valdau, Y.; Wilkin, C.; Wüstner, P.

The production of phi mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles has been measured via the phi→K+K decay using the COSY-ANKE magnetic spectrometer. The phi meson production cross section follows a target mass dependence of A0.56±0.03 in the momentum region of 0.6–1.6 GeV/c. The comparison of the data with model calculations suggests that the in-medium phi width is about an order of magnitude larger than its free value.

Publ.-Id: 15362

Dilepton production studied with the HADES spectrometer

Rustamov, A.; Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A. V.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; 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.; Gumberidze, M.; 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.; Krasa, 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.; Sadovsky, A.; Salabura, P.; Schmah, A.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Vasiliev, T.; Wagner, V.; Weber, M.; Wüstenfeld, J.; Yurevich, S.; Zanevsky, Y. V.

With the HADES spectrometer at GSI we have studied dilepton production in various collision systems from elementary N+N, over p+A, up to the medium-heavy Ar+KCl system. We have confirmed the puzzling results of the former DLS collaboration at the Bevalac. While we have traced the origin of the excess pair yield in C+C collisions to elementary p+p and n+p processes, we find a significant contribution from the dense phase of the collision in larger Ar+KCl system. From recently obtained e+e- pair spectra in p+p and p+Nb interactions at 3.5 GeV kinetic beam energy the inclusive production cross sections for neutral pions, η , ω and ρ mesons are extracted for the first time at this beam energy. Furthermore, the production mechanisms of the vector mesons, which are not known at these energies, are investigated. The direct comparison of p+p and p+Nb data allows us to investigate in-medium mass modifications of vector mesons at nuclear ground state density.

Publ.-Id: 15361

Single and double pion production in np collisions at 1.25 GeV with HADES

Kurilkin, A. K.; Agakishiev, G.; Balanda, A.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Díaz, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; 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.; Krása, A.; Krizek, F.; Krücken, R.; Kuc, H.; Kühn, W.; Kugler, A.; Kurepin, 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.

The preliminary results on charged pion production in np collisions at an incident beam energy of 1.25 GeV measured with HADES are presented. The np reactions were isolated in dp collisions at 1.25 GeV/u using the Forward Wall hodoscope, which allowed to register spectator protons. The results for np -> pppi-, np -> nppi+pi- and np -> dpi+pi- channels are compared with OPE calculations. A reasonable agreement between experimental results and the predictions of the OPE+OBE model is observed.

  • Contribution to WWW
    Proc. XXth Int. Baldin Seminar on High Energy Physics Problems "Relativistic Nuclear Physics and Quantum Chromodynamics", JINR, Dubna, Russia, October 4-9, 2010:

Publ.-Id: 15360

Λp femtoscopy in collisions of Ar+KCl at 1.76A GeV with HADES

Kotte, R.

Results on Λp femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A GeV, the reaction Ar+KCl was studied with HADES at SIS18/GSI. A high-statistics and high-purity Λ sample was collected, allowing for the investigation of Λp correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the Λp emission source. The Λp radius is found significantly smaller than that for Au+Au/Pb+Pb collisions in the AGS, SPS and RHIC energy domains, but larger than that for electroproduction from He. Taking into account all available data, we find the Λp source radius to increase almost linearly with the number of participants to the power of one-third.

  • Physics of Particles and Nuclei Letters 8(2011), 969

Publ.-Id: 15359

Oxidation State and Local Structure of Plutonium Reacted with Magnetite, Mackinawite, and Chukanovite

Kirsch, R.; Fellhauer, D.; Altmaier, M.; Neck, V.; Rossberg, A.; Fanghänel, T.; Charlet, L.; Scheinost, A. C.

Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-LIII-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous 242Pu(III) and 242Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO2 phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalent PuO2 for environmental risk assessment. Our results also demonstrate the necessity to support thermodynamic calculations with spectroscopic data.

Keywords: plutonium; redox; magnetite; mackinawite; chukanovite; EXAFS; XANES

Publ.-Id: 15358

Super-homogenisation factors in pinwise calculations by the reactor dynamics code DYN3D

Grundmann, U.; Mittag, S.

Super-homogenisation (SPH) factors were generated by a modified version of the code DYN3D for PWR fuel assemblies in hot-zero-power states defined in the OECD MOX/UO2 Benchmark. SPH factors averaged for each pin-material type and factors for each individual pin position were produced. The application of the SPH factors improves the accuracy of DYN3D calculations, especially for configurations with control rods inserted.

Keywords: LWR; reactor core model; multigroup; simplified P3 approximation (SP3); pinwise; super-homogenisation (SPH)

  • Annals of Nuclear Energy 38(2011), 2111-2119

Publ.-Id: 15357

Sensitivity and Uncertainty Analysis Applied to Radionuclide Sorption onto Single Minerals and Sediments

Brendler, V.; Ekberg, C.; Ödegaard-Jensen, A.; Schikora, J.; Noseck, U.

Sorption is one of the key retardation processes considered in safety assessment of radioactive waste repositories. Whereas most often conventional distribution coefficients (KD values) are utilized, additionally taking credit from mechanistic sorption models (Surface Complexation Models, SCM) helps to increase confidence both in the underlying basic chemical processes and in their numerical representation. Quality-assurance of long-term safety assessment studies requires the identification of the most sensitive geochemical and thermodynamic model input parameters [1] by means of sensitivity analysis (SA) and uncertainty analysis (UA). Such an approach is tested here rigorously for a variety of test cases: Se(IV/VI) sorption onto goethite, Np(V) sorbed onto hematite, and U(VI) sorption onto a simplified aquifer material resembling the overburden of a salt-rock repository.

In each case KD computations were based on a 1-site, 2pK Diffuse Double Layer Model. A component-additivity approach was used for the simplified aquifer. The mineral characterization comprised selected values for the specific surface area (SSA, typically following a log-normal error distribution function − EDF) and the surface site protolysis constants pK1 and pK2. The data selection was based on the mineral-specific sorption database RES³T [2] as were the decisions about the most relevant surface species and their formation constants. All surface reaction constants were assumed to be Gaussian distributed and were normalized to a reference site density of 2.31 sites/nm². The aqueous speciation of selenate and selenite (basically the hydrolysis steps of H2SeO4 and H2SeO3) as well as the more complex aqueous speciation for Np and U was based on the respective NEA TDB reviews [3,4].

Computations for the single-mineral systems were performed with the code FITEQL [5] as the innermost routine for calculating the speciation and subsequently deriving KD values. The outermost shell was a specially programmed tool to generate the necessary parameter variations and to derive statistical evaluations, namely variances as a function of the input parameter set, from the associated Kd distribution. There is also an option available to introduce correlated variables in the form of a correlation matrix. The coupling between these two codes is performed by UCODE [6]. The simplified aquifer was analysed by a combination of PhreeqC [7] for the geochemical speciation, interfaced by UCODE with the SimLab package [8] for SA/UA.

The SCM for the case of Se sorption onto goethite used an of 44.0 ± 2.8 m²/g, pK1 = 7.04 ± 0.15 and pK2 = 9.41 ± 0.24. Based on the available literature, for both Se oxidation states a protonated and an unprotonated inner-sphere surface complex was selected as most probable species: »Fe SeO3 , »Fe HSeO3, »Fe SeO4 , and »Fe HSeO4 with the following respective formation constants log K: 13.79 ± 0.40, 20.36 ± 0.24, 7.69 ± 0.39, and 14.36 ± 0.60. SA and UA were performed on six different pH levels (4 – 9), for two total selenium concentrations (10-4 M and 10-7 M), and for two redox scenarios (+300 mV and +800 mV), the solid-liquid ratio was set to 10 g/L, and atmospheric carbonate was excluded. Sensitivity analysis of its sorption onto goethite revealed that namely the uncertainty of the unprotonated inner-sphere surface complexes affects the overall uncertainty of the distribution coefficient KD, independent from the redox state. Moreover, the uncertainty of the computed KD values is in the order of about 5-30 %.

The system Np(V)-hematite was investigated based on the following parametrization: SSA = 22.5 ± 1.9 m²/g, pK values of 7.23 ± 0.40 and 9.49 ± 0.44 for the 1st and 2nd surface protolysis steps, and complex formation constants of -2.61 ± 0.21, -4.57 ± 0.18, 3.64 ± 0.28, and -10.53 ± 0.9 for the surface species »Fe–O–NpO2, »Fe–O–COO−, »Fe–O–COOH, and »Fe–O–NpO2(HCO3)22−, respectively. Total Np(V) concentration was set to 10−7 M and the geochemical environment characterized as oxidizing with ambient air and temperature, with a pH stepping from 4 to 9. It turned out that log K for the formation of the ternary surface complex »Fe O NpO2 is the input parameter influencing strongest the overall KD values in this system.

Concerning the most complex case, the aquifer model (composition: 85% quartz, 10% feldspar, 0.5% muscovite, 0.5% gibbsite, 0.5% goethite, 2% calcite, and 1.5% kaolinite) the varied input factors for the KD computations were solely geochemical parameters (contrary to the above cases), namely the pH value, the carbonate content, the ionic strength, the total concentrations of calcium, aluminium, and of uranium. Whereas the first two parameters followed a trigonal EDF, the latter four were log-trigonal distributed (all based on geochemical analyses of more than hundred samples). The most influential factors were identified to be the pH, the Ca content, and the carbonate content.

Based on these examples and further test cases, a generalization of application areas and limits for SA and UA applied to sorption phenomena will be discussed, considering both thermodynamic and environmental parameters.

[1] Ochs, M., Payne, T.E., Brendler, V. (2011). Thermodynamic Sorption Modeling in Support of Radioactive Waste Disposal Safety Cases, NEA Report, Paris.
[2] Brendler, V., Vahle, A. Arnold, T. Bernhard, G. and Fanghänel, T. (2002). „RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics“, J. Contam. Hydrol. 61, 281-291.
[3] Olin, Å., Noläng, B. Öhman, L.-O. Osadchii, E., Rosén, E., (2005). Chemical thermodynamics of selenium. Chemical Thermodynamics Vol. 7 (OECD NEA ed.), Elsevier, Amsterdam.
[4] Guillaumont, R., Fanghänel, T., Fuger, J., Grenthe, I., Neck, V., Palmer, D.A., Rand, M.H (2003). Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium. Chemical Thermodynamics Vol. 5 (OECD NEA ed.), Elsevier, Amsterdam.
[5] Herbelin, A. L. et al. (1999). FITEQL 4.0 Report 99-01, Dept. Chemistry, Oregon State University, Corvallis.
[6] Poeter, E.P.; Hill, M.C. (1998). Documentation of UCODE, a computer code for universal inverse modeling: U.S.G.S. Water-Resources Investigations Report 98-4080, 122 p.
[7] Parkhurst, D.L.; Appelo, C.A.J. (1999). User’s guide to PHREEQC (Version 2) - A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S.G.S. Water-Resources Investigations Report 99-4259, 312 p.
[8] Saltelli, A., Tarantola, S. SimLab,

Financial support through the NEA Sorption Project Phase III and the German Federal Ministry of Economics (Contract 02 E 10528) is gratefully acknowledged.

Keywords: Sorption; surface complexation; modeling; safety assessment; sensitivity analysis; uncertainty analysis; prediction; radionuclides; waste disposal

  • Lecture (Conference)
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products (MIGRATION 2011), 18.-23.09.2011, Beijing, China

Publ.-Id: 15356

Complexation, Computational, Magnetic, and Structural Studies of the Maillard Reaction Product Isomaltol Including Investigation of an Uncommon π Interaction with Copper(II)

Heine, K. B.; Clegg, J. K.; Heine, A.; Gloe, K.; Karsten, G.; Henle, T.; Bernhard, G.; Cai, Z.-L.; Reimers, J. R.; Lindoy, L. F.; Lach, J.; Kersting, B.

The metal complexation properties of the naturally occurring Maillard reaction product isomaltol HL2 are investigated by measurement of its stability constants with copper(II), zinc(II), and iron(III) using potentiometric pH titrations in water, by structural and magnetic characterization of its crystalline complex, [Cu(L2)2] 3 8H2O, and by density functional theory calculations. Strong complexation is observed to form the bis(isomaltolato)copper(II) complex Zincorporating copper in a typical (pseudo-)square-planar geometry. In the solid state, extensive intra- and intermolecular hydrogen bonding involving all three oxygen functions per ligand assembles the complexes into ribbons that interact to form two-dimensional arrays; further hydrogen bonds and π interactions between the furan moiety of the anionic ligands and adjacent copper(II) centers connect the complexes in the third dimension, leading to a compact polymeric three-dimensional (3D) arrangement. The latter interactions involving copper(II), which represent an underappreciated aspect of copper(II) chemistry, are compared to similar interactions present in other copper(II) 3D structures showing interactions with benzene molecules; the results indicate that dispersion forces dominate in the π system to chelated copper(II) ion interactions.

Publ.-Id: 15355

THEREDA: Providing quality-assured thermodynamic data for waste management assessment

Brendler, V.; Altmaier, M.; Marquardt, C.; Moog, H.; Richter, A.; Scharge, T.; Voigt, W.; Wilhelm, S.; Wollmann, G.

The THEREDA project develops a consistent and quality assured thermodynamic reference database for modeling geochemical processes in waste disposal sites. It offers evaluated thermodynamic data for all relevant elements, covering both radioactive waste and chemo-toxic substances, see table 1 for a detailed list. All host rocks currently discussed as candidates for waste repositories in Germany are considered. Thus, parameters for a variety of models describing interactions in mixed phases are included. Here, namely the Pitzer- and SIT-formalisms to describe activity coefficients of hydrated ions and molecules are supported. Provision is made to include parameters for solid solution models and non-ideal gas models at a later stage. Both thermodynamic and interaction parameters can be described by (flexible) temperature functions.
An essential topic in the context of nuclear waste is public confidence building on scientific responsibility. This is addressed by a detailed scheme of quality assurance (QA), incorporating elements such as data categorization (review quality, original publication type, experimental category, and uncertainty level), validity limits, full bibliographic tracking, formalized data evaluation procedures, internal consistency checks (coupled to the concepts of dependent data sets and alternatives), data audits, benchmark test cases, and finally external feedback enabled through free access ( combined with a variety of communication tools. Each part of THEREDA and its accompanying QA, as well as all technologic details, are fully documented.
Another important topic is that THEREDA strives for a broad coverage of all relevant reactions and species by making use of estimation methods, ranging from chemical analogy to LFER and fractional group algorithms. Such values are clearly labeled, also carry uncertainties, and have validity limits assigned.
To ease the use of the THEREDA data pool both “fixed” complete and consistent databases (updated twice a year) as well as user-specified ones can be downloaded directly form the project’s webpage. Available formats are a generic ASCII type, and formats as required by the geochemical speciation codes PhreeqC, EQ3/6, ChemApp and Geochemist’s workbench.

  • Invited lecture (Conferences)
    Volker Neck Memorial Session, 20.05.2010, Karlsruhe, Deutschland

Publ.-Id: 15354

Actinide Sorption Database

Brendler, V.; Richter, A.

wird nachgereicht

  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt-Based Repository (ABC-SALT) International Workshop, 15.-17.09.2010, Carlsbad, New Mexico, USA

Publ.-Id: 15353

Atomic structure of ion-implanted SOI-structures with bonding interfaces

Popov, V. P.; Cherkov, A. P.; Tyschenko, I. E.; Voelskow, M.

Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of Silicon-On-Insulator SOI structures in the current planar CMOS technology. The formation of heterostructures-on-insulator is a way to increase the carrier mobility in the nanometer-scale layers. We have already shown that formation of Ge/Si on SiO2 heterostructure leads to increasing of holes mobility [1]. It is known that electron mobility in bulk InSb is about 77000 cmy2/Vs. This is about 50 times more than that in bulk silicon. The formation of Si/InSb on insulator heterostructures may provide an increase of effective electron mobility in the nanometer scale SOI films. The main goal of this work was a study of nucleation and growth of monocrystalline indium antimonide thin film at the Si/SiO2 grain boundary.

Keywords: SOI; CMOS; InSb; RBS

  • Lecture (Conference)
    Autumn School on Materials Science and Electron Microscopy 2007 "Microscopy - advanced tools for tomorrow's materials", 08.-11.10.2007, Berlin, Germany

Publ.-Id: 15352

Development and verification of the coupled 3D neutron kinetics/thermal-hydraulics code DYN3D-HTR for the simulation of transients in block-type HTGR

Rohde, U.; Baier, S.; Duerigen, S.; Fridman, E.; Kliem, S.; Merk, B.

DYN3D is a nodal diffusion code for 3D steady-state and transient analysis of Light Water Reactor (LWR) cores with hexagonal or square fuel element geometry. In addition to the neutron kinetics, it comprises of a thermal-hydraulics model for flow in parallel coolant channels. Macroscopic cross section data libraries generated with variation of burn-up, reactor poisons concentrations and thermal-hydraulic feedback parameters are linked to the code. Two-group and multi-groups versions of the code are available.
Currently, at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the DYN3D code is being extended and adopted for the application to block-type High Temperature Gas-Cooled Reactors (HTGR). In this paper, we give an overview of the latest developments of DYN3D concerning block-type HTGR.
The simplified P3 (SP3) transport approximation is implemented into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method previously implemented into DYN3D for square fuel element geometry of LWR is being extended for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes to be able to perform a systematic mesh refinement.
One of the main challenges in cross section generation for the HTGR core calculations is the treatment of the so-called “double heterogeneity”. The modified Reactivity-Equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in the deterministic lattice calculations. The main steps of the RPT method are described. The use of the method for the cross section generation of a simplified HTGR core including its verification is presented.
A 3D heat conduction module coupled with a channel-type coolant flow model is implemented to take the temperature reactivity feedback to neutronics physically correctly into account. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.

Keywords: high temperature gas-cooled reactor; reactor dynamics; double heterogeneity; neutron transport methods; SP3 approximation; heat conduction model; transient analysis

Publ.-Id: 15351

THEREDA – The Thermodynamic Reference Database for a Nuclear Waste Disposal in Germany

Richter, A.

The disposal of nuclear waste including the assessment of long-term safety is still an open question in Germany. In addition to the still pending decision about the repository host rock (salt, granite, or clay) the basic necessity of a consistent and obligatory thermodynamic reference database persists. Such a database is essential to assess potential failure scenarios accurately and to make well founded predictions about the long-term safety. Specific needs for waste repository and remediation projects in Germany are comprehensive datasets also covering high temperatures and high salinities. Against this background, available databases do not suffice and are limited in their use, partly because of high restrictions and resulting incompleteness of reactions. Other databases rely on heterogeneous and therefore inconsistent data leading to incorrect model calculations. Due to these deficiencies THEREDA, a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany, was started in 2006 [1,2].
THEREDA contains a relational databank whose structure has been designed in a way that promotes the internal consistency of thermodynamic data. Data considered cover the needs of Gibbs Energy Minimizers and Law-of-Mass-Action programs alike. Parameters for a variety of models describing interactions in mixed phases are included. Namely the Pitzer- and SIT-parameters to describe activity coefficients of hydrated ions and molecules are considered. Provision is made to include parameters for solid solution models and non-ideal gas models at a later stage. Both thermodynamic and interaction parameters can be described by temperature functions.
THEREDA offers evaluated thermodynamic data for all compounds (solid phases, aqueous species, or constituents of the gaseous phase) of elements, which according to the present state of research are relevant. In particular, all oxidation states expected for disposal site conditions are covered.
The guidelines developed by the NEA form the basis for those for THEREDA. They were extended to cover also areas such as nomenclature, interaction coefficients, temperature and pressure functions, and quality assurance (QA). The latter contains an internal review where correctness, plausibility an completeness of documentation are checked.
An important step is the data assessment. It involves subdividing the data according to

  • Class: distinction between “real” datum, chemical analogue, or estimated value
  • Category: type of experiment from which the datum was derived
  • Quality: reliability of the datum derived from its numerical uncertainty
  • Source: type of literature from which the value was adopted (international reviews, based on the analysis of many papers, internal value…)
Parameter files are created from the databank in a variety of formats (generic ASCII type, and formats required by the geochemical speciation codes PhreeqC, EQ3/6, ChemApp and Geochemist’s Workbench). They are also used for internal benchmark calculations – another essential element of the QA scheme. The results are documented and provided to the user.
THEREDA is accessible via internet through This is not only a portal to the database, but shall also serve as an information and discussion platform on issues concerning the database. Thus we are confident to generate helpful feedback from the anticipated user community.
[1] Altmaier, M.; Brendler, V.; Hagemann, S.; Herbert, H.-J.; Marquardt, C.; Moog, H.; Neck, V.; Richter, A.; Voigt, W.; Wilhelm, S. (2008). „THEREDA - Ein Beitrag zur Langzeitsicherheit von Endlagern für nukleare und nichtnukleare Abfälle.“ ATW 53, 249-253.
[2] W. Voigt, V. Brendler, K. Marsh, R. Rarey, H. Wanner, M. Gaune-Escard, P. Cloke, Th. Vercouter, E. Bastrakov, S. Hagemann (2007), „Quality assurance in thermodynamic databases for performance assessment studies in waste disposal”, Pure Appl. Chem. 79, 883-894.

Keywords: THEREDA; thermodynamic reference database; long-term safety; quality assurance; internet access; repository; actinides; hexary system of oceanic salts; cementitious phases; matrix elements

  • Poster
    Migration 2011 - 13th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission products in the Geosphere, 18.-23.09.2011, Beijing, China

Publ.-Id: 15350

2C2D-PIV Messungen einer turbulenten Kanalströmung zur Quantifizierung des Strömungsgebietes

Banowski, M.

An einem Gas-Aerosol-Versuchsstand wurden die Strömungseigenschaften mit dem Messverfahren Particle Image Velocimetry (PIV) untersucht. Die Experimente erfolgten jeweils bei den drei Reynolds-Zahlen Re = 8 900, 27 950 und 44250 an einem Windkanal (d = 10 cm) ohne und mit Einbauten. Für die Strömung ohne Kanaleinbauten wurde die Strömungsentwicklung untersucht und dokumentiert. Dabei konnte festgestellt werden, dass ab der Strömungslänge von x = 15 d die Gesetzmäßigkeiten einer voll entwickelten Strömung anwendbar sind. Als Kanaleinbauten wurden periodische Stufen der Höhe H = 10 mm und Breite B = 100 mm mit einem Abstand von P = 100 mm sowie Zylinderstümpfe mit der Höhe H = 10 mm und Durchmesser d = 20 mm in Noppenstruktur (Vierecksanordnung, Abstand zueinander 20 mm) am Kanalboden verwendet. An verschiedenen Positionen im Bereich der Strömungshindernisse wurden die Geschwindigkeiten in den Strömungsfeldern gemessen und dargestellt. Im Vergleich mit publizierten Daten wurden für die ungestörte Strömung und die Umströmung von Stufen sehr gute Übereinstimmungen gefunden. Die dargestellten Ergebnisse können als Referenz für die weitere Erforschung des Depositions- und Resuspensionsverhaltens von Graphitstaub verwendet werden.
Die Messungen erfolgten mit einem 2C2D-PIV-Messystem. Die ermittelten Messunsicherheiten für die Geschwindigkeit beträgt etwa vier Prozent des Messwertes bei einer messkonfurationsabhängigen Ortsauflösung des Vektorfeldes zwischen 0,4 und 0,8 mm.

Keywords: turbulent flow; obstacled flow; periodic steps; cylindrical stumps; square duct

  • Diploma thesis
    TU Dresden, 2011
    84 Seiten

Publ.-Id: 15349

2C2D-PIV Measurements of a Turbulent Square Duct Flow at Reynolds Numbers up to 42 000

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

The turbulent flow was studied in small-scale gas-aerosol test facility using a particle image velocimetry (PIV) system. The experiments were conducted at Reynolds numbers Re = 8900, 27950 and 44250 in a square duct (d = 10 cm) without and with generic obstacles. The flow formation in the inlet was measured and documented without obstacles. It could be shown that the laws of a well developed turbulent boundary layer are applicable downstream of x = 15 d. Periodic steps (height H = 10 mm, channel width, pitch P = 100 mm) and cylindrical stumps (Ø 20 cm, H = 10 cm, P = 20 cm, square structure) were mounted on the bottom of the channel in order to study more complex flow phenomena. The time averaged mean flow field was illustrated at miscellaneous positions around the obstacles. It agrees well with published data. The showed results can be used for fundamental research on deposition and resuspension of aerosol particles.
The measurement uncertainty of the 2C2D-PIV-system tots up for about 4 percent of the measured value. The resolution of the vector field accounts between 0,4 and 0,8 mm.

Keywords: turbulent flow; obstacled flow; square duct; periodic steps; cylindrical stumps

  • Lecture (Conference)
    THINS Students Course & Workshop, 07.-11.02.2011, Zurich, Swiss

Publ.-Id: 15348

Sorption of uranium(VI) by selected bacteria, algae and fungi and characterization of uranyl biomass species using different microscopic and spectroscopic methods

Günther, A.; Vogel, M.; Raff, J.; Kothe, E.; Bernhard, G.

Microorganisms like bacteria, algae and fungi have a significant influence on the immobilization, mobilization and transport of radionuclides like uranium and other heavy metals in the biological and geological environment via the soil and water path. To understand the mechanisms of uptake, transport, deposition, degradation and the behavior of actinides in different biological and geological systems structural knowledge about the formed actinides species are of great importance and are essential for a reliable assessment of these processes.
Arthrobacter (bacteria), Chlorella vulgaris (green algae) and Schizophyllum commune (fungi) interact in different ways with uranium and are therefore used as model organisms to study different interaction mechanisms and binding forms of uranium, including possibly also so far unknown uptake processes into living cells. Hence the aim of this study was to localize the uranium(VI) on/inside the cells using microscopic methods. Furthermore, experiments with a combination of different spectroscopic techniques were performed to obtain first information about the kind and structure of the formed uranium species and to identify the functionalities, which are responsible for the binding of uranium on/inside the living cells.
All investigated organisms bind significant amounts of uranium(VI) in the pH range from 4 to 7 and contact time of 48 hours. Arthrobacter oxygen and A. nicotinae have binding capacities of 50 – 95 mg U/g biomass dry weight at a uranium concentration of 1∙10-4 M and are thus comparable with that of Schizophyllum cells binding 75 mg U/g bio dry weight independent of the pH value. In contrast to this, metabolic active Chlorella cells bind only up to 30 mg U/g dry biomass under the same experimental conditions. At a more environmentally relevant uranium concentration of 5∙10-6 M in mineral medium and during ongoing cultivation, a mobilization of the algae-bound uranium occurred. At uranium concentrations higher than 1∙10-4 M algal cells died, whereas fungal cells tolerated even high uranium concentrations and were able to accumulate up to 280 mg U/ g biomass dry weigth at pH 5 and 6. At pH 4 and 7, Schizophyllum cells bound only 130 to 150 mg U/ g biomass dry weight. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with EDX analyses were used for the localization of formed uranyl species in the biomass of all investigated organisms. TEM micrographs of thin sections of uranium containing Arthrobacter and Chlorella cells show uranium mainly bound on parts of the cell wall. In some cases uranium containing accumulates were found inside the cells. However, it remains to be resolved if these cells are still alive and possess intact cell walls. In contrast, SEM pictures of transparent fungal cells clearly show uranium containing accumulates inside originally living cells and on their cell surface. Therefore, further research is needed to identify involved uptake mechanisms.
For the determination of the functionalities, which are important for the immobilization of uranium, the interaction of uranium(VI) with metabolic active bacterial, algal and fungal cells was investigated by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption fine structure spectroscopy (EXAFS). The measured luminescence spectra of uranyl containing cell species of all investigated organisms show bathochromic shifts of the uranyl emission bands in comparison to the corresponding emission signals of the uranyl species in the initial solution independent of the uranium concentration and the pH value of the solution (Fig. 1). Obtained results demonstrated a change of the uranyl speciation during the sorption processes. The carboxylic and organic/inorganic phosphate groups are responsible for uranium binding on the biomass with varying contributions dependent on the microbial biomass, cell status and uranium concentration in the initial sorption solution. The dominant interaction of uranium(VI) with organic/inorganic phosphate groups could be verified by EXAFS investigations.

Keywords: Uranium(VI); bacteria; algae; fungi; TRLFS; EXAFS; REM; TEM

  • Lecture (Conference)
    13th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere, 18.-23.09.2011, Beijing, China

Publ.-Id: 15347

MEMS Sensor with giant piezoresistive effect using metall-semiconductor hybrid structure

Ngo, H.-D.; Schiffer, M.; Kurniawan, W.; Mukhopadhyay, B.; Fritz, M.; Vu, T. C.; Kolitsch, A.; Lang, K.-D.; Tekin, T.

The piezoresistance effect of silicon has been widely used in MEMS sensors [1-3]. Strain engineering is now considered to be the one of the most promising strategies for developing high performance sub-10-nm silicon devices [4]. Strain silicon sensors show typically a gauge factor of below 100, depending on temperature, orientation, doping level and stress direction. Interesting electromechanical properties have been observed in silicon nanowires [5] and carbon nanotubes [6]. This new materials show an unusual large piezoresistance effect compared with bulk silicon. One of disadvantages of using this new materials is the complicated and expensive manufacturing. In this paper we report on the first realized pressure sensor approach, which uses the proposed metal-semiconductor (silicon) hybrid structures in order to achieve higher Kfactor.

Keywords: piezoresistive effect; metall-semiconductor hybrid structure; MEMS; pressure sensor

  • Open Access Logo Contribution to proceedings
    Transducers 11 - The 16th International Conference on Solid-State Sensors, Actuators and Microsystems, 05.-09.06.2011, Beijing, China

Publ.-Id: 15346

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