Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Development and first experimental tests of Faraday cup array

Prokůpek, J.; Kaufman, J.; Margarone, D.; Krůs, M.; Velyhan, A.; Krása, J.; Burris-Mog, T.; Busold, S.; Deppert, O.; Cowan, T. E.; Korn, G.

A new type of Faraday cup, capable of detecting high energy charged particles produced in a high intensity laser-matter interaction environment, has recently been developed and demonstrated as a real-time detector based on the time-of-flight technique. An array of these Faraday cups was designed and constructed to cover different observation angles with respect to the target normal direction. Thus, it allows reconstruction of the spatial distribution of ion current density in the subcritical plasma region and the ability to visualise its time evolution through time-of-flight measurements, which cannot be achieved with standard laser optical interferometry. This is a unique method for two-dimensional visualisation of ion currents from laser-generated plasmas. A technical description of the new type of Faraday cup is introduced along with an ad hoc data analysis procedure. Experimental results obtained during campaigns at the Petawatt High-Energy Laser forHeavy Ion Experiments (GSI, Darmstadt) and at the Prague Asterix Laser System (AS CR) are presented. Advantages and limitations of the used diagnostic system are discussed.

Publ.-Id: 19734

Internal characterisation of fresh agricultural products using traditional and ultrafast electron beam X-ray computed tomography imaging

Donis Gonzalez, I. R.; Guyer, D. E.; Pease, A.; Barthel, F.

Currently, destructive techniques can be employed to evaluate the internal attributes of fresh fruits, vegetables and nuts. However, clearly not all produce can be evaluated. Thus, there is a need to develop an in vivo non-destructive technique able to assess fresh agricultural commodity internal components, especially disorders. In this study, medical grade computed tomography (CT) was used to obtain transversal two-dimensional (2D) Images from several fresh agricultural product phenomena. CT scanning was performed by placing and securing numbered samples onto a whole polyethylene sheet, placed on the CT scanner table. Phenomena included the internal decay of chestnuts (Castanea spp.), internal defects in pickling cucumbers (Cucumis sativus), translucency disorder in pineapples (Ananas comosus), pit presence in tart cherries (Prunus cerasus var. Montmorency) and plum curculio (Conotrachelus nenuphar ) infestation of tart cherries.
In addition, an ultrafast X-ray CT scanner was also used to visualise internal characteristics of fresh chestnuts. Chestnuts were labelled and packed in a thin plastic hose, which was pulled through the scanning plane. The 2D CT X-ray images and post-processing three-dimensional CT image recon-struction indicate that CT can be used as an accurate in vivo insight of fresh intact agri-cultural products. Results suggest that there is a potential for non-destructive inline sorting of the internal quality of several agricultural products.
The long-term objective is that the fresh and processing product industries will then be able to detect internal quality attributes of fresh agricultural commodities, at a relatively early stage, after validation under commercial conditions.

Publ.-Id: 19733

Temperature dependence of ion-beam mixing in crystalline and amorphous germanium isotope multilayer structures

Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.; Schmidt, B.; Bougeard, D.

Self-atom mixing induced by 310 keV gallium (Ga) ion implantation in crystalline and preamorphized germanium (Ge) at temperatures between 164 K and 623 K and a dose of 1x1015 cm-2 is investigated using isotopic multilayer structures of alternating 70Ge and natGe layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and the ion-beam induced depth-dependent self-atom mixing was determined by means of secondary ion mass spectrometry. Three different temperature regimes of self-atom mixing, i.e., low-, intermediate-, and high-temperature regimes are observed. At temperatures up to 423 K, the mixing is independent of the initial structure, whereas at 523 K, the intermixing of the preamorphized Ge structure is about twice as high as that of crystalline Ge. At 623 K, the intermixing of the initially amorphous Ge structure is strongly reduced and approaches the mixing of the crystalline material. The temperature dependence of ion-beam mixing is described by competitive amorphization and recrystallization processes.

Keywords: germanium; isotope multilayer; ion-beam mixing; thermal spike model

Publ.-Id: 19732

A spectroscopic study of uranyl hydrolysis

Drobot, B.

Short overview of a time resolved laser induced fluorescence spectroscopy (TRLFS) study and mathematical analyzis (PARAFAC).

Keywords: U(VI); Uranium; TRLFS; spectroscopy; PARAFAC

  • Lecture (others)
    Annual PhD seminar, 07.-09.10.2013, Bautzen, Germany

Publ.-Id: 19731

Aspects of Fermiology in correlated metals

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Sino-German (International) Workshop On Kondo and Mott Physics in Correlated Matter, 13.-17.10.2013, Hangzhou, China

Publ.-Id: 19730

World Record Race - Research at High Magnetis Fields

Wosnitza, J.

  • Invited lecture (Conferences)
    Symposium "10 Jahre Mikroaktorik", 11.10.2013, Freiburg, Deutschland

Publ.-Id: 19729

The Dresden High Magnetic Field Laboratory - Recent Research Results

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Seminar at Niigata University, 12.08.2013, Niigata, Japan

Publ.-Id: 19728

Titration curves, column experiments, and reactive transport models

Britz, S. M.; Noseck, U.; Brendler, V.; Stockmann, M.

Surface reactions related to e.g. transport and retardation processes in groundwater systems are correlated with geochemical conditions that vary in time and space. For longterm safety analysis of radioactive waste repositories it is of great interest to better understand and to realistically assess these geochemically driven surface and transport reactions, since they might strongly impact radiation exposure. To get an advanced insight into these processes column experiments are conducted and subsequently modeled with the geochemical speciation code PhreeqC, Version 2.18 (coupled with UCODE_2005). In order to set-up realistic reactive transport models so-called surface complexation parameters (SCP) such as surface site density, specific surface area, and protolysis constants need to be derived from titration experiments of relevant mineral phases. Two different titration techniques are conducted for muscovite and orthoclase: continuous and batch titration. Derived results are compared offering an insight into pHinfluencing reactions that contribute to surface reactions but also to cation exchange and mineral dissolution. In column experiments diffent solids are applied: natural sediments from the Gorleben site, Germany and pure mineral phases (orthoclase, muscovite, quartz). Parameters such as pH, ligands, ionic strength, and cation concentrations are varied in each experiment to reflect realistic enviromental conditions. Moreover, transient pH conditions are applied in selected columns.
Both types of experiments (titration, column experiments) including each geochemical variation provide data to model reactive transport processes of hazardous pollutants more realistically in groundwater-flow driven environments with PhreeqC. Calculations will be conducted and first results offered for discussion.
This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract no. 02 E 11072A and 02 E 11072B.

  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy

Publ.-Id: 19727

Technischer Zwischenbericht: Partikelentstehung und –transport im Kern von Druckwasserreaktoren

Kryk, H.; Hoffmann, W.; Kästner, W.; Alt, S.; Renger, S.; Seeliger, A.

Im borsäurehaltigen Kühlmittelreislauf von Druckwasserreaktoren können nach einem postulierten Kühlmittelverluststörfall während des Sumpfumwälzbetriebs signifikante Konzentrationen an gelöstem Zink auftreten, welche durch Korrosion feuerverzinkter Einbauten des Containments verursacht werden. Bedingt durch die in Batch-Experimenten nachgewiesene abnehmende Löslichkeit der Zink-Korrosionsprodukte (Zink-Borate) mit zunehmender Temperatur ist eine Ausscheidung fester Korrosionsprodukte in heißen Zonen nicht auszuschließen. Die physikochemischen und thermofluiddynamischen Mechanismen der Korrosionsprodukt-Abscheidung wurden am HZDR im Labormaßstab bzw. an der Hochschule Zittau/Görlitz an halbtechnischen Versuchsanlagen untersucht.
Der Beitrag gibt einen Überblick über die bisher im BMWi-Verbundvorhaben „Partikelentstehung und –transport im Kern von Druckwasserreaktoren“ durchgeführten Untersuchungen, die erzielten Ergebnisse sowie die geplanten Arbeiten zur Modellierung der Korrosions- und Ablagerungsprozesse und zu Präventivmaßnahmen.

Keywords: loss-of-coolant accident; LOCA; pressurized water reactor; PWR; corrosion; zinc borate; reactor safety research

  • Other report
    Dresden: HZDR, 2013
  • Lecture (others)
    Sitzung des Projektkomitees „Transienten und Unfallabläufe“, 26.09.2013, Köln, Deutschland

Publ.-Id: 19726

Partikelentstehung und –transport im Kern von Druckwasserreaktoren

Kryk, H.; Kästner, W.

Im borsäurehaltigen Kühlmittelreislauf von Druckwasserreaktoren können nach einem postulierten Kühlmittelverluststörfall während des Sumpfumwälzbetriebs signifikante Konzentrationen an gelöstem Zink auftreten, welche durch Korrosion feuerverzinkter Einbauten des Containments verursacht werden. Bedingt durch die in Batch-Experimenten nachgewiesene abnehmende Löslichkeit der Zink-Korrosionsprodukte (Zink-Borate) mit zunehmender Temperatur ist eine Ausscheidung fester Korrosionsprodukte in heißen Zonen nicht auszuschließen. Die physikochemischen und fluiddynamischen Mechanismen der Korrosionsprodukt-Abscheidung wurden am HZDR im Labormaßstab bzw. an der Hochschule Zittau/Görlitz an halbtechnischen Versuchsanlagen untersucht.
Der Vortrag gibt einen Überblick über die bisher im BMWi-Verbundvorhaben „Partikelentstehung und –transport im Kern von Druckwasserreaktoren“ erzielten Ergebnisse als Unterstützung für Sicherheitsbewertungen durch die Reaktor-Sicherheitskommission und entsprechende Behörden.

Keywords: loss-of-coolant accident; LOCA; pressurized water reactor; PWR; corrosion; zinc borate; reactor safety research

  • Invited lecture (Conferences)
    RSK-Ausschuss Anlagen- und Systemtechnik, 28.11.2013, Bonn, Deutschland

Publ.-Id: 19725

The effect of dual Fe+/He+ ion beam irradiation on microstructural changes in FeCrAl ODS alloys

Chen, C.; Richter, A.; Kögler, R.

Nanostructured ferritic oxide dispersion strengthened (ODS) alloys contain a high density of Y-Al-Ti-O nanoparticles, high dislocation densities and fine grains. Structural analysis with HRTEM shows that the composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles.
Irradiation of these alloys was performed with a dual beam implantation of 2.5 MeV Fe+ and 350 keV He+, either simultaneously or sequentially.
Additionally, the He+ concentration was varied between 18 and 72 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. A clear hardness increase in the irradiated area is observed by nanoindentation in every ion implantation regime. Hardness ratios of irradiated relative to non-irradiated ODS materials and the appearance of hardness maxima close to the surface region are discussed in detail. The irradiation induced hardening effect is stronger for a heat treated HT-ODS alloy than for an as-received one. The large difference in the hardness data of as-received ODS for simultaneous and sequential implantation can be explained by point defect recombination at dislocations and grain boundaries occurring for sequential irradiation.

Publ.-Id: 19724

Visualisierung neurodegenerativer Veränderungen in einem neuen Mausmodell der Alzheimer Erkrankung mittels (+)-[18F]flubatine.

Ullmann, C.

Es ist kein Abstract vorhanden.

  • Master thesis
    Universität Leipzig, 2013
    102 Seiten

Publ.-Id: 19723

Search for supernova-produced 60Fe in the microfossil record

Ludwig, P.; Bishop, S.; Egli, R.; Chernenko, V.; Faestermann, T.; Famulok, N.; Fimiani, L.; Frederichs, T.; Gomez, J.; Hain, K.; Hanzlik, M.; Korschinek, G.; Merchel, S.; Rugel, G.

Material distributed into the interstellar medium by supernova explosions can be incorporated into terrestrial archives. After the discovery of live 60Fe atoms in 2-3 Myr old layers of a Pacifc Ocean ferromanganese crust (Knie et al., 2004), a confirmation of this signal, as well as a mapping of the signal with high time-resolution is desireable. Another reservoir in which the 60Fe signature should have been incorporated in are the fossils of magnetotactic bacteria in ocean sediment. To this end, two sediment cores from the Eastern Equatorial Pacifc were obtained, iron was chemically extracted with high selectivity towards biogenic magnetite, and the extraction procedure was characterized using novel magnetic measurements. The samples were then measured with accelerator mass spectrometry in Garching. Preliminary results for both sediment cores will be reported.

Keywords: accelerator mass spectrometry; AMS; supernova; astrophysics

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19722

Investigation of heavy metals sorption behavior of isolated bacterial cell wall components of Gram-positive bacteria using ICP-MS and TRLFS

Viacava Romo, K. E.

Attention for heavy metal removal and recovery has been increasing as their demand and scarcity increase. The property of certain types of biomass to remove heavy metals from the environment has encouraged the search of novel biosorbents for technology development. In this work the heavy metal biosorption of two Gram-positive bacteria strains Lysinibacillus sphaericus bacterial (JG-A12 and JG-B53) isolated from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) has been investigated. The metal binding capacities of the isolated main three cell wall components (peptidoglycan, lipids and surface-layer proteins) and the heavy metal uptake of the intact bacteria have been studied for eight different heavy metals (palladium, cadmium, platinum, gold, lead, europium and uranium). Lysinibacillus sphaericus JG-B53 probed to have higher heavy metal binding capacities and uptakes. The best biosorbent for both strains was the peptidoglycan and the higher binding capacities were observed for uranium, lead and europium. Finally in order to elucidate the mechanisms involved in the biosorption of metal ions, the Eu3+ was used as a fluorescent probe and investigated with time-resolved laser-induced fluorescence spectroscopy (TRLFS) as it interacted with the different biosorbents. The results although complexed to interpreted due to the inherent complexity of the biosorbents showed clearly the Eu3+-biosorbent binding and are an important basis for further complexation studies.

Keywords: Bacteria; sorption; heavy metals; S-layer; cell wall; lipids; peptidoglycan; ICP-MS; TRLFS

  • Master thesis
    TU Dresden, 2013
    120 Seiten

Publ.-Id: 19721

Direct Observation of Binary Vortex Core States in Magnetic Mutlilayers

Wintz, S.; Im, M.-Y.; Banholzer, A.; Weigand, M.; Raabe, J.; Mattheis, R.; Fischer, P.; Erbe, A.; Fassbender, J.

Topological spin textures such as skyrmions or vortices are attracting significant attention because of their fundamentally interesting magnetostatic and dynamic properties. In particular, magnetic vortices have been studied intensively during the past decade. As shown in Fig. 1(a), such a spin vortex consists of a planar, flux-closing magnetization curl that tilts out of the plane in the central core. Vortices are typically found as the ground state of micron sized ferromagnetic thin film elements, whi- le their nanoscopic cores are being much smaller, with diameters on the order of 10 nm only. Along with fundamental investigations, proposals were also made to apply vortices for memory cells, or as oscillators in data communication devices. In this view, stacking of vortices via nonferromagnetic interlayers [cf. Fig. 1(b)] is an important issue to address, since such geometries allow for the exploitation of GMR/TMR as well as spin-torque effects.

Keywords: magnetic vortex core multilayer x-ray microscopy

  • Poster
    IEEE International Magnetics Conference 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 19720

Synthesis and biological evaluation of a novel non-peptidic brain-penetrant F-18-labeled oxytocin receptor ligand

Wenzel, B.; Mollitor, J.; Kranz, M.; Deuther-Conrad, W.; Günther, R.; Teodoro, R.; Fischer, S.; Ludwig, F.-A.; Smits, R.; Steinbach, J.; Hoepping, A.; Brust, P.

1. Introduction
Oxytocin is a neurohypophysial peptide hormone, synthesized in the hypothalamus and stored in the posterior pituitary gland for release into the bloodstream. It acts as neurotransmitter and neuromodulator to regulate a diverse range of CNS functions including emotional, parental, and sexual behaviors. Its receptor (OTR) is expressed in peripheral organs as well as in specific brain areas related to cognitive function and psychiatric diseases such as schizophrenia and depression. So far, investigation of the distribution of OTR in brain in vivo is hampered by the lack of suitable radiotracers. Thus, the development of a brain-penetrant PET ligand with high affinity and selectivity to the OTR would promote the development of non-invasive and quantitative imaging of OTR expression in healthy and diseased brain. Therefore, we synthesized a series of fluorinated non-peptidic OTR ligands and performed radiofluorination of one selected candidate to investigate its in vivo properties by organ distribution and dynamic PET imaging studies in mice and pigs.

2. Materials & Methods
Binding affinities of the novel compounds to the human OTR were determined by radioligand displacement studies using stably transfected hOTR-HEK293 cells and [3H]oxytocin. The radiosynthesis of the selected candidate [18F]ABX163 was performed in a two-step procedure using the methoxymethyl (MOM)-protected tosylate precursor ABX185. 18F was incorporated using K[18F]F-Kryptofix 222-carbonate complex at 90°C in ACN within 15 min followed by removal of the two MOM protecting groups with 1M HCl at 90°C within 15 min. The radiotracer was isolated by semi-preparative HPLC (Reprosil-Pur AQ column, 250x10mm), ACN/aqu. 20 mM NH4OAc) followed by final purification with a Sep-Pak C18 Plus light cartridge and formulation in isotonic saline containing 10% ethanol. Specific binding of [18F]ABX163 was assessed by in vitro autoradiography on mouse brain slices. Metabolism and organ distribution of the radiotracer were studied in female CD-1 mice at 30 and 60 min p.i. Dynamic PET scans were performed in mice (animal PET/MR; 60 min) and in one female piglet (PET; 120 min), the latter one accompanied by chromatographic analysis of plasma radio-metabolites.

3. Results
Based on the biphenyl-benzopyrrolodiazepine derivative WAY-162720, described as OTR selective and brain-penetrant ligand [1], three fluoro-containing reference compounds were synthesized which retained high affinity towards the OTR (Ki=14-22 nM). Radiolabeling of the selected candidate [18F]ABX163 was obtained in a two-step radiosynthesis with a RCY(DC) of 20-25%, radiochemical purity >98%, and specific activity of 35-133 GBq/µmol.[18F]ABX163 was stable for at least 60 min in saline, PBS, and pig plasma at 37°C. A logDoctanol/PBS value of 2.9 ± 0.2 (n=3) was determined by shake flask method.
Both organ distribution and dynamic PET imaging studies revealed limited uptake of the radiotracer in mouse brain (mean SUV value of 0.04). Besides, significant uptake in the pituitary gland was observed (SUV=0.85 at 55 min p.i.), which indicates target-specific binding of [18F]ABX163. By a dynamic PET study in one piglet, a mean SUV of 0.43 was estimated for whole brain at 120 min p.i. Most remarkable was the elevated uptake in the olfactory bulb with SUV120=0.73, a region with high expression of OTR. Metabolite analysis of pig plasma by radio-HPLC demonstrated moderate metabolism of [18F]ABX163 with non-metabolized tracer accounting for 44% of total radioactivity at 30 min p.i.

4. Discussion & Conclusion
Radiofluorination of a novel non-peptidic oxytocin receptor ligand [18F]ABX163 was achieved with appropriate radiochemical yield and specific activity. Evidence was obtained, that uptake of [18F]ABX163 in the pituitary gland of mouse brain and olfactory bulb of pig brain reflects target-specific binding. Differences in brain uptake between mice and pigs may be caused by species-specific expression of efflux transporters in the blood-brain barrier. With the development and evaluation of [18F]ABX163 we could demonstrate for the first time the potential of non-peptidic oxytocin receptor ligands for imaging of OTR in brain by PET. To further improve brain uptake, we are currently working on structural modifications of [18F]ABX163.

[1] Ring RH, Malberg JE, Potestio L, Ping J, Boikess S, Luo B, Schechter LE, Rosenzweig-Lipson S, [2006] Psychopharmacology 218-225.

  • Lecture (Conference)
    ESRR'2014 - 17th European Symposium on Radiopharmacy and Radiopharmaceuticals, 24.-27.04.2014, Pamplona, Spain

Publ.-Id: 19719

Comparative evaluation of two novel fluorine-18 PET radiotracers for the alpha7 nicotinic acetylcholine receptor (α7nAChR)

Teodoro, R.; Deuther-Conrad, W.; Rötering, S.; Scheunemann, M.; Patt, M.; Donat, C. K.; Wenzel, B.; Peters, D.; Sabri, O.; Brust, P.

Objectives :
The α7nAChR plays an important role in mediating cholinergic transmission, and is considered as biomarker for inflammatory processes and certain types of cancer. [18F]NS14490 (1), and [18F]DBT10 (2) showed high in vitro binding affinity and selectivity (Ki,α7= 2.5 and 0.3 nM, Ki,α3β4= 102 and 5000 nM, respectively, and Ki,α3β2both > 800 nM). Here, we report automated radiosyntheses and in vivo PET evaluation in pigs of 1 and 2.

Methods : Syntheses of 1 and 2 were performed in one-step procedure using OTs and NO2 precursors, respectively, in automated module (Tracerlab FX F-N). Dynamic PET studies (4 h) were performed in anesthetized female juvenile pigs after injection with ~300-400 MBq of 1 or 2 (n=6 each). Blocking studies were performed in 3 pigs each by bolus injection/constant infusion of NS6740 (7 mg/kg), a highly selective α7nAChR ligand. Metabolite-corrected plasma input functions were used for 2-tissue-compartment modeling (2TCM) to determine binding parameters of 1 and 2 in 24 brain regions.

Results : 1 and 2 were synthesized in high radiochemical purities (>92%, >95%), and high specific activities (> 150 GBq/μmol, EOS) with a RCY of 24-36% and 45-50%, respectively. Maximum brain SUVs of 1 (0.54) and 2 (1.89) were reached at 3 and 11.5 min p.i., respectively. Metabolism of 1 and 2 is comparable. At 60 min p.i. about 25% of 1 and 24% of 2 accounted for total radioactivity in plasma. 2TCM of 1 and 2 allowed reliable estimates of k3 of 1 (-46%) and BP, respectively (Table). NS6740 significantly reduced (* p<0.05) mean k3 of 1 (-46%) and mean BP of 2 (-75%).

Conclusions : 1 and 2 are promising PET tracers for imaging α7nAChR. Because of higher affinity, brain uptake and specific binding [18F]DBT10 (2) is selected for further evaluation to obtain approval for translational clinical validation in human beings.

Research Support: DFG (DE 1165/2-1)

  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1099


Publ.-Id: 19718

Materials research at the Dresden High Magnetic Field Laboratory

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Seminar at the Départment de Physique, Université de Montréal, 22.07.2013, Montreal, Canada

Publ.-Id: 19717

Recent developments in superconductivity in organic materials

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    10th International Symposium on Crystalline Organic Metals, Superconductors and Magnets (ISCOM 2013), 14.-19.06.2013, Montreal, Canada

Publ.-Id: 19716

Die Jagd nach dem Weltrekord - Materialforschung an der Grenze des Machbaren

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Dresdner Lange Nacht der Wissenschaften, 05.07.2013, Dresden, Deutschland

Publ.-Id: 19715

Materials research at high magnetic fields

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Kick Off Meeting for the Helmholtz International Beamline for Extreme Fields (HIBEF), 02.-05.06.2013, Hamburg, Deutschland

Publ.-Id: 19714

The Fulde-Ferrell-Larkin-Ovchinnikov state in quasi-two-dimensional organic superconductors

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    IV International Symposium on Strong Nonlinear Vibronic and Electronic Interactions in Solids, 01.-03.05.2013, Tartu, Estonia

Publ.-Id: 19713

Probing magnetic exchange interactions in rare-earth intermetallic compounds by high-field measurments

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    International Conference on Rare-Earth Materials: Advances in Synthesis, Studies and Applications, 26.-28.04.2013, Wroclaw, Poland

Publ.-Id: 19712

High-magnetic-field properties of frustrated magnets

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Invited lecture (Conferences)
    Kick-off meeting of the Helmholtz Virtual Institute "New States of Matter and their Excitations", 22.-24.04.2013, Berlin, Deutschland

Publ.-Id: 19711

Infrared images of single electrons

Winnerl, S.; Helm, M.

Scattering-type near-field optical microscopy (s-SNOM) is a powerful technique to image nano objects. It can be employed in a broad spectral range, namely the complete infrared region spanning from the terahertz range up to the visible range. In this article we describe a system which utilizes a free-electron laser as a spectrally narrow and widely tunable source of infrared radiation. This system was employed to study electrons confined in self-assembled InAs quantum dots. We spatially resolved single quantum dots upon resonant excitation of transitions between discrete energy levels of the confined electrons.

Keywords: near-field microscopy; terahertz nano-spectroscopy; single quantum dots

  • Open Access Logo Imaging & Microscopy 15(2013)1, 40-42

Publ.-Id: 19709

The novel fluorine-18 PET radiotracer [18F]NS14490 allows in vivo investigation of alpha7 nicotinic acetylcholine receptor (α7-nAChR) expression on brain vasculature

Bucerius, J.; Rötering, S.; Deuther-Conrad, W.; Donat, C. K.; Fischer, S.; Xiong, G.; Mottaghy, F. M.; Wildberger, J. E.; Cumming, P.; Brust, P.

Objectives :
The α7nAChR plays an important role in the pathophysiology of atherosclerosis, where it is known to mediate the deleterious effects of nicotine. Recently, [18F]NS14490 was described as radioligand with high in vitro binding affinity and selectivity towards α7nAChR (Ki, α7=2.5), Ki, α3β4=102, Ki, α4β2>800 nM) [BMC 21(2013), 2635]. Here, we report in vivo investigation of α7nAChR in brain blood vessels of pigs using [F]NS14490 and PET.

Methods : The synthesis of [18F]NS14490 and pig studies were performed as reported [Teodoro et al. this volume]. Baseline (n=3) and blocking studies with NS6740 (n=3) were done. Volumes of interest for the left carotid artery (LCA) and Circle of Willis (CW) were drawn with reference to T1-weighed MR images aligned to a summed PET image. Metabolite-corrected plasma input functions were used for 2-tissue-compartment (2TC) modelling to determine receptor parameters. Parametric maps of the distribution volumes (VT) were calculated for baseline and blocking conditions.

Results : Reduction of VT on brain vasculature was clearly visible in parametric maps of [18F]NS14490.
Maximum SUV in LCA (1.4±0.2) and CW (1.3±0.2) was reached at 4 and 2 min p.i., respectively. At 4 h after blockade, the SUV in LCA was reduced by 36%, with lesser declines in CW. Using an 2TC irreversible binding model, we found a [18F]NS14490 k3 of 0.0023 min-1 in LCA, which was 40% blocked by NS6740.

Conclusions :
The study provides first evidence for the detection of α7nAChRs by PET in the pig brain vasculature, notably in the LCA. This further elucidates the feasibility of PET to non-invasively image vascular image vascular α7nAChRs.

Research Support: Support from DFG (DE 1165/2-1, Dan Peters (DanPET AB) and Matthias Scheunemann is gratefully acknowledged.
References: 1.Rötering S., Scheunemann M., Fischer S. et al. (2013) Radiosynthesis and first evaluation in mice of [(18)F]NS14490 for molecular imaging of α7 nicotinic acetylcholine receptors. Bioorg Med Chem 21, 2635
2. Teodoro R, Deuther-Conrad W, Rötering S, et al. (2013) Comparative evaluation of two novel fluorine-18 PET radiotracers for the alpha7 nicotinic acetylcholine receptor (α7nAChR), submitted

  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1695


Publ.-Id: 19708

Broadband fast terahertz detector based on graphene

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.

Some sources of pulsed intense terahertz radiation such as free-electron lasers and gas lasers pumped by high-pressure CO2 lasers exist already for relatively long time. More recent developments like THz-generation via nonlinear processes in plasmas or lithiumniobate crystals as well as novel accelerator-based sources for coherent synchrotron radiation have greatly advanced the field of nonlinear terahertz optics [1,2]. Robust, simple and fast detectors are highly desirable for experiments at these sources, in particular if they are not naturally synchronized to a pulsed near-infrared laser. We present a graphene-based detector operated at room temperature featuring a rise time of 50 ps. It was tested at the free-electron laser FELBE in the frequency range from 1.3 THz to 38 THz.
The detector is based on an exfoliated graphene flake on Si/SiO2 coupled to a broadband logarithmic periodic antenna. The temporal resolution of the detector (rise time ~50 ps) is limited by the electronic circuitry. We show that high-resistive substrates are of crucial importance to keep RC-time constants short. The responsivity is about 5 nA/W in the investigated spectral range. While a linear dependence of the detector signal was found for small pulse energies, significant saturation occurred for larger pulse energies. We demonstrate that the nonlinearity provided by the saturation can be exploited in autocorrelation measurements. In this type of measurement the detector response is limited by the intrinsic carrier relaxation time but not by the electronic circuit, resulting in a temporal Resolution below 10 ps [3]. The high temporal resolution combined with room-temperature operation and high damage threshold makes the detector attractive for pulse diagnostics of intense THz sources. Furthermore the broadband response, which possibly can be extended towards the visible and UV spectral region by using different substrate materials, is ideal for characterizing the timing of pulses in multicolor experiments.
[1] M. C. Hoffmann and J. A. Fülöp, J. Phys. D: Appl. Phys. 44, 083001 (2011).
[2] H. Hirori, Hideki and K. Tanaka, IEEE J. Sel. Top. Quantum Electron. 19, 8401110 (2013).
[3] M. Mittendorff, S. Winnerl, J. Kamann, J. Eroms, D. Weiss, H. Schneider, and M. Helm, Appl. Phys. Lett. 103, 021113 (2013).

Keywords: fast detector; terahertz

  • Lecture (Conference)
    6th Workshop on Terahertz Technology and Applications 2014, 11.-12.03.2014, Kaiserslautern, Deutschland

Publ.-Id: 19707

Longitudinal fields in focused terahertz beams

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

In textbooks electromagnetic waves are often described as infinitely extended plane waves, which are of purely transverse character. For beams of finite size, however, also longitudinal fields are expected. In case of focused radially polarized beams, the longitudinal fields can actually be stronger as compared to the transverse components. This has been found in experiments recording the intensity of near-infrared beams. In our study we directly record the electric field of single cycle terahertz pulses of radial and linear polarization. This enables us to reveal the phase relation between longitudinal and transverse fields. The obtained value of pi/2 is of universal nature as it does not depend on the type of mode, frequency or focusing condition. Additionally we demonstrate that the longitudinal components of radially polarized beams exhibit superior focusing properties.

Keywords: radially polarized fields; longitudinal electromagnetic fields; terahertz radiation

  • Lecture (Conference)
    DPG-Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19706

Relaxation dynamics in graphene close to the Dirac point

Winnerl, S.

The carrier relaxation in graphene is of strong interest for understanding carrier-carrier and carrier-phonon interactions in this fascinating material as well as for optoelectronic applications such as detectors, and saturable absorbers. Here we give an overview on our investigations on the dynamics in the energetic vicinity of the Dirac point, which is explored by pump-probe experiments with mid-infrared and terahertz radiation [1]. We compare our experimental results with microscopic theory and discuss the role of optical phonons, acoustic phonons and carrier-carrier scattering. For excitations slightly above and below the Fermi edge an interesting change in sign of the pump-probe signals is observed, which can be explained by an interplay of intraband and interband excitation. Furthermore we present recent results on the dynamics in Landau quantized graphene, where a strong dependence of the pump-probe signals on the state of circular polarization of both pump and probe radiation is found. The results indicate the importance of Auger-type processes in this regime.
S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).

Keywords: graphene; carrier dynamics; ultrafast spectroscopy

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19705

Relaxation dynamics in graphene in the terahertz spectral range

Winnerl, S.

The relacation dynamics in graphene in the infrared spectral range is reviewed. In particular the range of terahertz energies, i.e. excitation in proximity of the Dirac point, is discussed.

  • Lecture (others)
    SFB Kolloquium, 14.11.2013, Konstanz, Deutschland

Publ.-Id: 19704

Graphene investigated in the THz range: ultrafast dynamics and device perspectives

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

The carrier relaxation dynamics in graphene in energetic proximity to the Dirac point is studied. In particular we discuss the role of optical phonon scattering and the interplay of interband and intraband excitations. The potential to make use of the ultrafast dynamics of graphene, in particular under terahertz excitation, in saturable absorbers and fast detectors is highlighted. A room-temperature operated ultra-broadband graphene-based detector is presented.

  • Invited lecture (Conferences)
    21st International Conference on Applied Electromagnetics and Communications, 14.-16.10.2013, Dubrovnik, Croatia

Publ.-Id: 19703

Relaxation dynamics of graphene investigated in the mid-infrared and THz spectral range

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

The unique band structure of graphene results in optical properties, which are promising with respect to graphene applications in detectors, saturable absorbers and frequency mixers. For these applications the knowledge of the carrier dynamics is essential. However, while the relaxation dynamics in graphene is extensively studied in pump-probe experiments involving pumping with near-infrared photons, only few studies exist for pumping in the mid-infrared and THz spectral range [1,2]. Here we present results of single-color pump probe experiments on epitaxial graphene on SiC studied in a wide range of photon energies (8 – 245 meV). A significant slowing down of the carrier relaxation is observed when the photon energy is reduced to values below the optical phonon energy of ~200 meV. For photon energies below twice the value of the Fermi energy (Ef ≈ -13 meV) negative pump-probe signals, i.e. induced absorption is observed. This is associated with intraband absorption contributions at energies, where interband absorption is initially not possible. Our experimental results are compared to microscopic calculations based on the density matrix formalism. Comparison of experiment and theory reveals the role of scattering via optical and acoustic phonons as well as contributions from Auger scattering processes. Applying a magnetic field perpendicular to the graphene layers leads to a not equidistant Landau-level splitting. Using circularly polarized radiation for pump-probe experiments allows one to selectively measure individual Landau-level transitions. The pump-probe signals exhibit a strong dependence on the polarization state of both pump and probe radiation.
[1] S. Winnerl et al. Phys. Rev. Lett. 107, 237401 (2011).
[2] S. Tani, F. Blanchard, and K. Tanaka, Phys. Rev. Lett. 109, 166603 (2012).

Keywords: graphene; carrier dynamics; ultrafast spectroscopy

  • Poster
    International Workshop on Terahertz Science and Technology, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 19702

Longitudinal THz fields and their phase relation with respect to transverse fields

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

Radiation with significant longitudinal components of the electric field is of interest for excitation of systems with a dipole moment in the direction of propagation of the radiation. Another special feature of longitudinal fields occurring in the focus of radially polarized radiation is their superior focusing property as compared to transverse fields of linearly polarized beams. In contrast to previous studies in the near infrared spectral range, where the intensity distribution was recorded, our terahertz study provides direct access to the electric field. Consequently, the phase relation between longitudinal and transverse field components can be addressed. We present results for the field distribution in the focal plane for both radially and linearly polarized single cycle THz pulses generated by photoconductive emitters. In both cases a phase shift of pi/2 between transverse and longitudinal field components is found. We show that this phase shift is of universal nature as it does not depend on the type of mode, the focussing condition and the frequency [1]. The universal phase shift is a fundamental consequence Maxwell’s law div E = 0 and symmetry properties of the beams. We also show that the longitudinal field components of a radially polarized beam can be focussed to a smaller spot as compared to the transverse components of linearly polarized radiation. This is valid even for moderate focusing conditions, where the transverse fields are stronger than the longitudinal field components. Implications of the findings for imaging applications and for studies of light-matter interaction in case of vanishing Poynting vector will be discussed.
[1] S. Winnerl, R. Hubrich, M. Mittendorff, H. Schneider, and M. Helm, New J. Physics 14, 103049 (2012).

Keywords: vector beams; Bessel-Gauss beams; terahertz radiation

  • Lecture (Conference)
    International Workshop on Terahertz Science and Technology, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 19701

Ultrafast graphene-based terahertz detector

Winnerl, S.; Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.

The gapless band structure, universal interband absorption and considerably strong intraband absorption make graphene attractive for applications in the terahertz frequency range [1]. Furthermore the high mobility and fast carrier relaxation [2] enable a fast response when graphene is used a material for terahertz detection. Graphene-based fast bolometers [3] and rectifying transistors [4] have been reported recently. We demonstrate an ultrafast broadband detector operated at room temperature. Response times of 50 ps are observed in the wavelength range from 30 µm to 220 µm.
The detector is based on an exfoliated graphene flake on Si/SiO2, which is coupled to a logarithmic-periodic planar antenna. In the center of the antenna interdigitated electrodes provide the electrical contacts between the antenna arms and the graphene flake (cf. Fig. 1). The response of the detector to picosecond terahertz radiation pulses from a free-electron laser was studied. A responsivity of ~5 nA/W and a signal rise time of 50 ps was found for the spectral range from 30 µm to 220 µm. The linear detection range is followed by region of saturation for high pulse powers. The characteristic pulse energy E_sat for the onset of saturation is ~10 nJ for lamda = 220 µm. With decreasing wavelength the saturation regime shifts towards higher pulse energies (E_sat ≈ 150 nJ for lamda = 30 µm). Comparing detectors fabricated on either intrinsic or doped silicon we find that a high substrate resistivity is crucial for the short response time. We attribute this to large RC time constants occurring for the conductive substrates.
These easy-to-use detectors are well suited for monitoring the timing of terahertz pulses. We will discuss several physical mechanisms, which may be involved in the detection process. As an outlook we suggest that the detector principle allows one to produce detectors covering an even larger spectral range, namely from the UV to THz range. To this end appropriate non-absorbing substrates have to be used.

[1] B. Sensale-Rodriguez, R. Yan, M. M. Kelly, K. Tahy, W. S. Hwang, D. Jena, L. Liu, and H. G. Xing, Nature Commun. 3 (2012) 780.
[2] S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. AMlic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider, and M. Helm, Phys. Rev. Lett. 107 (2011) 237401.
[3] J. Yan, M.-H. Kim, J. A. Elle, A. B. Shukov, G. S. Jenkins, H. M. Milchberg, M. S. Fuhrer, and H. D. Drew, Nat. Nanotechnol. 7 (2012) 472.
[4] L. Vicarelli, M. S. Vitiello, D. Coquillat, A. Lombardo, A. C. Ferrari, W. Knap, M. Poloni, V. Pellegrini, and A. Tredicussi, Nat. AMterials 11 (2012) 865.

Keywords: terahertz detection; ultrafast detector; metal-graphene-metal device

  • Poster
    Graphene Week, 02.-07.06.2013, Chemnitz, Deutschland

Publ.-Id: 19700

Carrier dynamics in graphene near the Dirac point

Winnerl, S.

The relaxation dynamics of charge carriers in graphene is characterized by interesting properties such as impact ionization resulting in carrier multiplication [1,2]. Apart from the fundamental interest, knowledge about the carrier dynamics is important for the development of graphene-based electronic and optoelectronic devices. In our study we apply picosecond mid-infrared and terahertz pulses to explore the carrier dynamics in the vicinity of the Dirac point. In particular the role of carrier-phonon and carrier-carrier scattering is discussed. The carrier dynamics was studied in single-color pump-probe experiments in a wide spectral range (photon energies: 10 meV – 245 meV). A significant increase of the relaxation time was observed as the photon energy was decreased to values below the optical phonon energy of about 200 meV [3]. Microscopic modelling based on the density matrix formalism revealed a suppression of optical-phonon scattering for low photon energies, however, this process is still more efficient than scattering via acoustic phonon [3,4].
The pump-probe study was extended to graphene in magnetic fields (B = 4.2 T, photon energy 75 meV), where the Landau level (LL) transitions LL-1 -> LL0 and LL0 -> LL1 were resonantly excited. Applying circularly polarized radiation allows one to distinguish between these energetically degenerate transitions. Pump-probe signals for all four different combinations of left- and right-circularly polarized radiation are characterized by complex dynamics involving positive and negative signals as well as fast and slow components. An analysis of the results indicates that the carrier occupation of the three LLs is strongly influenced by Auger-type scattering processes. In particular situations the population change by Auger scattering even dominates over the change induced by optical pumping. In summary the role of carrier-phonon scattering in graphene in the energetic vicinity of the Dirac point is clarified by a joint experiment-theory study. Furthermore we report strong evidence for efficient Auger-type scattering in Landau-quantized graphene. M. Mittendorff, H. Schneider, M. Helm, M. Orlita, and M. Potemski planned and performed the experiments, T. Winzer, F. Wendler, E. Malic, and A. Knorr carried out the microscopic modelling. The samples were grown by M. Sprinkle, C. Berger, and W. A. de Heer.

Keywords: graphene; relaxation dynamics; ultrafast spectroscopy

  • Invited lecture (Conferences)
    The 18th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures, 22.-26.07.2013, Matsue, Japan

Publ.-Id: 19699

Longitudinal fields in focused terahertz beams

Winnerl, S.; Hubrich, R.; Mittendorff, M.; Schneider, H.; Helm, M.

We measure transverse as well as longitudinal terahertz field components in the focus of both radially and linearly polarized beams. A phase shift of pi/2 between the transverse and longitudinal field contributions is found in both cases for all frequency components. Furthermore tighter focusing of the longitudinal components of the radially polarized beam as compared to the transverse components of the linearly polarized beam is demonstrated.

Keywords: terahertz; vector beams; radial polarization

  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665517

Publ.-Id: 19698

One-Group Cross Sections Generation for Monte Carlo Burnup Codes

Kotlyar, D.; Shwageraus, E.; Fridman, E.

Allowing Monte Carlo (MC) codes to perform fuel cycle calculations requires coupling to a point depletion solver. In order to perform depletion calculations, one-group (1-g) cross sections must be provided in advance. This paper focuses on generating accurate 1-g cross section values that are necessary for evaluation of nuclide densities as a function of burnup. The proposed method is an alternative to the conventional direct reaction rate tally approach, which is more computationally expensive. The method presented here is based on the multi-group (MG) approach(1), in which pre-generated MG sets are collapsed with MC calculated flux. In our previous studies(2), we showed that generating accurate 1-g cross sections requires their tabulation against the background cross-section (σ0) to account for the self-shielding effect. However, in previous studies, the model that was used to calculate σ0 was simplified by fixing Bell and Dancoff factors. This work demonstrates that 1-g values calculated under the previous simplified model may not agree with the tallied values. Therefore, the original background cross section model was extended by implicitly accounting for the Dancoff and Bell factors. The method developed here reconstructs the correct value of σ0 by utilizing statistical data generated within the MC transport calculation by default. The proposed method was implemented in BGCore code system. The 1-g cross section values generated by BGCore were compared with those tallied directly from the MCNP code. Very good agreement (<0.05%) in the 1-g cross values was observed. The method does not carry any additional computational burden and it is universally applicable to the analysis of thermal as well as fast reactor systems.

  • Contribution to proceedings
    The 27th Conference of the Nuclear Societies in Israel, 11.-13.02.2014, Daniel Dead Sea Hotel, Israel
    Proceedings of the 27th Conference of the Nuclear Societies

Publ.-Id: 19697

Beyond the Liu limit: Extending the range of low-Pm magnetorotational instabilities

Kirillov, O. N.; Stefani, F.

The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is ist questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile. This way we further show how the formerly known lower Liu limit of the critical Rossby number connects naturally with the upper Liu limit.

Keywords: Magnetorotational instability; accretion disk; WKB approximation

  • Lecture (Conference)
    3rd workshop on Rotational fluid dynamics for planetary and stellar applications, 29.-30.05.2013, Exeter, United Kingdom

Publ.-Id: 19696

Ziegler-Bottema dissipation-induced instability and related topics

Kirillov, O. N.

Abstract: Exactly 60 years ago Ziegler [1] observed (I) that viscous dissipation can move pure imaginary eigenvalues of a Lyapunov stable time-reversible non-conservative mechanical system (Ziegler’s pendulum loaded by a follower force) to the right half of the complex plane and (II) that the threshold of asymptotic stability generically does not converge to the threshold of the Lyapunov stability of the non-damped system when dissipation coefficient tends to zero. In 1956 Bottema [2] related the structurally unstable situation (II) to the Whitney umbrella singularity [3] of the stability boundary. I will show the examples of Hamiltonian, reversible and PT -symmetric systems of physics and mechanics with the similar effects of dissipation-induced instabilities and non-commuting limits of vanishing dissipation. I will discuss the relation of these effects to the multiple non-derogatory eigenvalues occurring both on the stability boundary and inside the domain of asymptotic stability, show the connection to the spectral abscissa minimization [4] and in the Hamiltonian case will demonstrate that a suitable combination of damping and nonconservative positional forces can destabilize the eigenvalues with both positive and negative Krein (symplectic) signature of the unperturbed system [5-7].
1. H. Ziegler, Die Stabilit¨atskriterien der Elastomechanik, Ing.-Arch. 20, 49-56 (1952).
2. O. Bottema, The Routh-Hurwitz condition for the biquadratic equation, Indagationes Mathematicae, 18, 403-406 (1956).
3. W. F. Langford, Hopf Meets Hamilton Under Whitney’s Umbrella, in IUTAM Symposium on Nonlinear Stochastic Dynamics. Proceedings of the IUTAM Symposium, Monticello, IL, USA, Augsut 2630, 2002, Solid Mech. Appl. 110, edited by S.N. Namachchivaya et al. (Kluwer, Dordrecht, 2003), pp. 157-165.
4. J. V. Burke, A. S. Lewis and M. L. Overton, Optimal Stability and Eigenvalue Multiplicity, Foundations of Computational Mathematics 1, 205-225 (2001).
5. O. N. Kirillov, Gyroscopic stabilization in the presence of nonconservative forces, Dokl. Math. 76(2), 780-785 (2007).
6. O. N. Kirillov and F. Verhulst, Paradoxes of dissipation-induced destabilization or who opened Whitney’s umbrella? Z. Angew. Math. Mech., 90(6), 462-488 (2010).
7. O. N. Kirillov, Stabilizing and destabilizing perturbations of PT -symmetric indefinitely damped systems. Phil. Trans. R. Soc. A (2012).

Keywords: Dissipation-induced instabilities; nonconservative systems; flutter; modulational instability

  • Lecture (Conference)
    Third Conference on Particle-Based Methods (PARTICLES 2013), Invited Session “Instability Mechanisms, from Particles to Structures”, 18.-20.09.2013, Stuttgart, Germany

Publ.-Id: 19695

Inductionless Magnetorotational Instabilities: From Lab Tests To Accretion Disks

Kirillov, O. N.; Stefani, F.; Fukumoto, Y.

How stars and black holes are able to form from rotating matter is one of the big questions of astrophysics. What is known is that magnetic fields figure prominently into the picture via the mechanism of magnetorotational instability (MRI). However, the current understanding is that it only works if matter is electrically well conductive – but in rotating disks this is not always the case. In areas of low conductivity like the dead zones of protoplanetary disks or the far-off regions of accretion disks that surround supermassive black holes, the MRI’s effect is numerically difficult to comprehend and is thus a matter of dispute. Simulation of the MRI in a liquid metal experiment with an exclusively vertically oriented magnetic field requires that this field has to be rather strong. At the same time, since the rotational speed has to be very high, these types of experiments are extremely involved and thus far success has eluded them. By adding a circular magnetic field to a vertical one it became possible to observe the helical MRI at substantially smaller magnetic fields and rotational speeds. Very recently, the azimuthal MRI with m=1 has also been observed in the PROMISE facility in Dresden. However, one of the blemishes of these inductionless versions of MRI is the fact that they only act to destabilize rotational profiles that are relatively precipitous towards the periphery, which for now did not include rotation profiles obeying Kepler’s law. In this talk we present a study of the stability of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence characterized by an appropriate magnetic Rossby number. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive case, our main focus is on the limit of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We rigorously demonstrate that the inductionless versions of MRI extend well to the Keplerian case if only the azimuthal field slightly deviates from its field-free profile.

Keywords: Magnetorotational instability; accretion disks; WKB

  • Lecture (Conference)
    Workshop "Putting Accretion Theory to the Test", 04.-06.11.2013, Annapolis, Maryland, United States

Publ.-Id: 19694

Singular divergence instability thresholds of kinematically constrained circulatory systems

Kirillov, O. N.; Challamel, N.; Darve, F.; Lerbet, J.; Nicot, F.

Static instability or divergence threshold of both potential and circulatory systems with kinematic constraints depends singularly on the constraintsʼ coefficients. Particularly, the critical buckling load of the kinematically constrained Zieglerʼs pendulum as a function of two coefficients of the constraint is given by the Plücker conoid of degree n=2. This simple mechanical model exhibits a structural instability similar to that responsible for the Velikhov–Chandrasekhar paradox in the theory of magnetorotational instability.

Keywords: Ziegler pendulum; Static instability; Kinematic constraints; Non-commuting limits; Magnetorotational instability; Material instabilities

Publ.-Id: 19693

Magnetization Reversal Mechanisms in Co-Antidot Arrays

Langer, M.; Bali, R.; Kowalska, E.; Neudert, A.; Lenz, K.; Potzger, K.; Kostylev, M.; Lindner, J.; Adeyeye, A.; Fassbender, J.

Co-antidots with holes arranged in the form of a square lattice, with lattice parameter of 415 nm and hole diameter d = 145 to 255 nm were fabricated using DUV photolithography. For arrays with film thickness of 50 nm, the angular dependence of the saturation field Hs shows presence of four-fold anisotropy with the hard axes along the <01> directions and easy axes was along the diagonal <11> directions. Spikes in the Hs were measured along the intermediate <12> directions. Kerr microscopy suggests that the reversal mechanism along the <01> is domain-wall (DW) depinning followed by propagation within the continuous channels along the <01>, whereas along the <11> the mechanism tends towards nucleation and growth. We postulate that the Hs-spikes occur because DW-propagation requires domino-like spin-reorientations through the continuous channels, whereas nucleation can only occur when a coherent region is formed with the spins oriented along the applied field. The frustration caused by the two possible spin-reorientation paths results in the larger Hs. We attempt to model these mechanisms using OOMMF and investigate the influence of varying d.

  • Poster
    DPG Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19692

Dependence of Ferromagnetic Resonance Behaviour on Chemical Disorder in Fe60Al40 Thin Films

Bali, R.; Schneider, T.; Gollwitzer, J.; Meutzner, F.; Boucher, R.; Potzger, K.; Bauch, J.; Fassbender, J.; Lenz, K.; Lindner, J.

We report on the influence of chemical disorder in Fe60Al40 thin films on their ferromagnetic resonance. Chemical disorder leads to increased nearest neighbour Fe-Fe magnetic interactions and plays a crucial role in inducing ferromagnetism. The saturation magnetization increases from 20 kA/m-1 for the chemically ordered film to 780 kA/m for disordered films. Disorder was induced by irradiation of Ne+ ions, and the depth-distribution of disorder was controlled by adjusting the ion-energy and -fluence. For moments aligned within the film plane, the resonant linewidth decreases with increasing ion-energy in the range from 2.5 to 30 keV, for a fixed ion-fluence. In-plane magnetic anisotropy is negligible in all cases. The linewidths for in-plane moment alignment are much larger than in materials that do not exhibit disorder induced ferromagnetism. These results may be explained by enhanced two-magnon scattering due to the presence of random defects, and help in preparing thin films with tailored spin-wave dynamic properties.

  • Poster
    DPG Frühjahrstagung 2014, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 19691

Printing Nearly-Discrete Magnetic Patterns using Chemical Disorder Induced Ferromagnetism

Bali, R.; Wintz, S.; Meutzner, F.; Huebner, R.; Boucher, R.; Uenal, A. A.; Valencia, S.; Neudert, A.; Potzger, K.; Bauch, J.; Kronast, F.; Facsko, S.; Lindner, J.; Fassbender, J.

We show that sub-50 nm ion-induced lateral patterning of magnetic structures can be enabled by disorder induced ferromagnetism.[1] Disorder is induced through exposure of the chemically ordered alloy to energetic ions; collision cascades formed by the ions knock atoms from their ordered sites and the concomitant vacancies are filled randomly via thermal diffusion of atoms at room temperature. Here we consider the case of Fe60Al40 wherein the chemically ordered B2 structure is paramagnetic, and chemical disordering leads to the formation of the A2 structure which is ferromagnetic.[2] This ion-induced transition can be exploited to induce ferromagnetism in localized regions by ion-irradiation through lithographed shadow masks. We show that this technique may be useful for fabricating novel spin-transport devices.
First we demonstrate the disorder-induced increase in saturation magnetization, Ms, in continuous films. Fe60Al40 films of 40 nm thickness were deposited on SiO2(150 nm)/Si(001) substrates by magnetron sputtering. The films were annealed at 773 K in vacuum to form the chemically ordered B2 phase structure. Hysteresis loops were measured using a vibrating sample magnetometer (VSM). Figure 1a shows that the B2 film is weakly ferromagnetic with a saturation magnetization of Ms = 20 kA m-1.
The chemically ordered films were irradiated with 6 x 1014 ions cm-2 of Ne+-ions at 10 and 30 keV respectively. After irradiation, the Ms increases to 480 and 780 kA m-1, respectively for the 10 and 30 keV samples. The Ms of the 30 keV Ne+ sample is a factor of 40 larger than that of the annealed sample. Figure 1b shows X-ray Diffraction measurements around the 100 reflection for the sample after annealing, and after subsequent 10 keV Ne+-irradiation. The 100 reflection is allowed for the B2 superstructure but vanishes for the disordered A2 phase and this transition is clearly observed since the reflection initially present in the B2 film vanishes for the 10 keV sample.
Magnetic patterning was performed on a 10 μm wide and 400 μm long wire of chemically ordered Fe60Al40 (Figure 2a). The wire was covered with a 150 nm thick resist layer, and patterned using e-beam lithography. Simulations based on the binary collision approximation (TRIM) showed that the 150 nm thick resist layer is sufficient to block impinging 10 keV Ne+-ions.[3]
Lithography was used to carve out stripe like openings of 0.5 and 2 μm widths respectively. As shown in the micrograph in Figure 2b, the stripe-openings were separated by ~ 40 nm wide (and 150 nm high) resist walls, thereby stopping the impinging Ne+ ions reaching the areas directly underneath the resist. These areas can be expected to retain chemical order after exposure to Ne+, however, only if the lateral scattering of ions is restricted. The wire covered by the shadow-mask was exposed to 10 keV Ne+-ions at a fluence of 6 x 1014 ion cm-2. Figure 2c shows the magnetic contrast image, obtained using Kerr Microscopy on the sample prior to application of saturating magnetic fields. Striped magnetic regions are clearly observed possessing random magnetic orientations.
Magnetic contrast was captured whilst sweeping the field to obtain hysteresis loops shown in Figure 2d, on a set of 32 (0.5 μm/spacer/2 μm/spacer) stripe-pairs. Magnetization reversal occurs via a two-staged process; the first reversal step occurs at ≈ ±3 mT and the second step at ≈ ±7 mT. The magneto-optic intensity changes by 80% in the first reversal step, indicating that the 2 μm wide stripes reverse collectively at the smaller field. In the stripe geometry, the internal demagnetizing field increases with the stripe width. Reversal of the 2 μm wide stripes therefore occurs at smaller externally applied field as compared with the 0.5 μm stripes, resulting in selective reversal.
Magnetic contrast images were captured at remnant points of the above hysteresis loops and are shown in Figure 2e – h. Stripes with magnetization pointing towards the left or right appear as dark and bright contrast, respectively. Images captured after applying the saturating field of +/-18 mT followed by reduction to zero field show that the parallel magnetization configuration is preserved in remanence (Figure 2e and f). The antiparallel configuration is obtained after applying a reverse field of -/+5 mT to the saturated stripes and returning to zero field. Figure 2g and h show alternating light and dark contrast of the antiparallel state in remnant fields.
Spin-resolved Photo-Emission Electron Microscopy (SPEEM) measurements were performed to observe magnetic contrast with high spatial resolution of ~ 50 nm. The SPEEM micrographs are shown in Figure 2e and g as magnified equivalent regions of the Kerr-images. The color scale varies from red to blue for magnetic moments pointing left or right respectively. Straight, low-contrast regions are found to separate the 500 nm and 2 μm wide high-contrast regions that correspond to the magnetic stripes.
The straight low-contrast regions are unresponsive to the magnetic field and occur for both parallel and anti-parallel states. Since the straight low-contrast lines also exactly follow the pattern of the shadow mask, it can be concluded that these lines correspond to the 40 nm wide un-irradiated regions. Neighboring 500 nm and 2 μm magnetic stripes are therefore isolated by a continuous weakly magnetic spacer of 40 nm nominal width.
Thus, parallel and antiparallel magnetization configurations can be programmed using the magnetic field history and are non-volatile i.e., stable when the field is switched off. Selective reversal and the existence of binary magnetic states namely is a prerequisite for spin-valves and advantageous in devices for storing data bits. In particular with respect to spin-transport devices, it is also necessary to ensure that the magnetic regions are separated by narrow spacers of zero or low magnetization. Showing that discrete magnetic nanostructures can be prepared by ion-irradiation has important consequences not previously considered in literature, such as the possibility of laterally patterned spin-transport devices – our results are a step in this direction.

[1] R. Bali et al., Nano Letters 2013 (accepted). [2] J. Fassbender, et al., Phys. Rev. B 2008, 77, 174430. [3] J. F. Ziegler et al., Nucl. Instrum. Methods B 2010, 268, 11-12, 1818.

  • Lecture (Conference)
    Intermag 2014, 04.-08.05.2014, Dresden, Germany
  • Poster
    Joint European Magnetism Symposia, 25.-30.08.2013, Rhodos, Greece
  • Poster
    International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium
  • Lecture (Conference)
    59th Annual Magnetism and Magnetic Materials (MMM), 03.-07.11.2014, Honolulu, USA
  • Invited lecture (Conferences)
    Sixth Joint BER II and BESSY II User Meeting, 03.-05.12.2014, Berlin, Deutschland
  • Poster
    Joint European Magnetism Symposia 2012, 09.-14.09.2012, Parma, Italy

Publ.-Id: 19690

Draco The Dresden Laser Acceleration Source recent setups measurement techniques future perspectives

Bock, S.

The presentation depicts the recent setup and techniques we use to characterize the pulse properties of the lasersystem Draco. Also the upgrade of Draco is shown and its impact on the new diagnostics setup.

Keywords: Draco; diagnostic techniques

  • Lecture (Conference)
    Characterisation of ultra-short high energy laser pulses, 23.-24.09.2013, Abingdon, United Kingdom

Publ.-Id: 19689

The enduring secret of Meissen Porcelain

Neelmeijer, C.; Pietsch, U.; Ulbricht, H.

Prior to their restoration the porcelain bulks of 34 pieces from various 18th century authentic Meissen objects were studied by proton beam analysis. In either case attention was paid that the proton beam touches only the area of fracture. Thus, possible contributions from residues of surface glaze to the measured spectra were excluded. The chemical compositions obtained by light element (Na-Si) plus heavier element analysis represent quiet consistent mixtures of porcelain primary material. This finding reflects the consistent keeping of recipes and raw materials for Meissen porcelain production already at that time. The technology of surface glazing, by contrast, makes use of modified ingredients. It is shown that non-destructive analysis of intact glazed porcelain does not stand for the bulk material composition, hence may pretend wrong conclusions if bulk analysis is of interest.
The proton beam of 4 MeV-energy (Rossendorf 5 MV Tandem accelerator) leaves the vacuum beam line onto air and may hit unique objects without sampling. Extremely low beam intensities and short irradiation times ensure non-destructive analysis of the valuable objects. The chemical elements of the irradiated material respond emitting characteristic radiations. They are detected simultaneously in order to get non-destructive and complete composition analysis using the established ion beam techniques PIXE (Particle induced X-ray Emission), PIGE (Particle Induced Gamma-ray emission) and RBS (Rutherford Backscattering Spectrometry).

Keywords: Porcelain; chemical analysis; Ion beam Analysis; PIXE; PIGE

  • Lecture (Conference)
    38th International Symposium on Archaeometry, 10.-14.05.2010, Tampa, USA

Publ.-Id: 19688

Effect of the solidified shell thickness on the impact of an electromagnetic brake on the flow in the continuous casting mould

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

This paper presents numerical investigations with respect to the fluid flow in the continuous casting process under the influence of a ruler-type EMBR. The impact of the DC magnetic field on the outlet flow from the Submerged Entry Nozzle has been studied up to Hartmann numbers of about 400. 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 numerical results were validated by flow measurements carried out in the small-scale mockup mini-LIMMCAST using the eutectic alloy GaInSn. The electrical wall conductance ratio was identified as an important parameter, which has a serious influence on the mould flow just as it is exposed to an external magnetic field. In a real casting process the solidifying shell plays the role of a conducting wall. The wall conductance ratio increases with growing thickness of the shell. It turns out that the solidifying shell has a considerable impact on the magnetic damping of the flow. An increasing wall conductance ratio improves the efficiency of the magnetic damping effect.

Keywords: Continous casting; EMBR; RANS-SST; MHD turbulence model

  • Lecture (Conference)
    SteelSim 2013 conference, 10.-12.09.2013, Ostrava, Czech Republic

Publ.-Id: 19687

Comparative study of thermo-stimulated luminescence and electron emission of nitrogen nanoclusters and films

Boltnev, R. E.; Bykhalo, I. B.; Krushinskaya, I. N.; Pelmenev, A. A.; Khmelenko, V. V.; Lee, D. M.; Khyzhniy, I. V.; Uyutnov, S. A.; Savchenko, E. V.; Ponomaryov, A. N.; Gumenchuk, G. B.; Bondybey, V. E.

We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those detected from N2 films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates.

  • Low Temperature Physics 39(2013), 451-455
    Online First (2013) DOI: 10.1063/1.4807150

Publ.-Id: 19686

New evidence for the mixing length concept in a narrow bubble column operated in the transition regime

Nedeltchev, S.; Schubert, M.; Donath, T.; Rabha, S.; Hampel, U.

Different scales of liquid mixing exist in bubble columns and it is very important to determine the prevailing mixing scale in each flow regime. Two independent parameters were found to exhibit a monotonous decline in the transition flow regime, which could be attributed to the decrease of the mixing length values L. In this work, a new parameter called ‘maximum number of visits in a region’ Nv max and the Kolmogorov entropy (KE) were extracted from the gas holdup time series (60 000 points). The latter were recorded at a high sampling frequency (2000 Hz) by a wire-mesh sensor. The measurements were performed in a narrow bubble column (0.15 m in ID, clear liquid height = 2 m) equipped with a perforated plate distributor (14 holes, Ø 4 × 10-3 m). Both parameters were capable of identifying concordantly the two main transition velocities at Utrans = 0.022 and 0.112 m/s, which delineate the boundaries of gas maldistribution, transition and churn-turbulent regimes, respectively.

Keywords: Narrow Bubble Column; Wire-Mesh Sensor; Gas Holdup Fluctuations; Mixing Length; Transition Flow Regime; Maximum Number of Visits; Kolmogorov Entropy

  • Open Access Logo Journal of Chemical Engineering of Japan 47(2014)9, 722-729

Publ.-Id: 19685

Anomalous low-temperature “post-desorption” from solid nitrogen

Savchenko, E. V.; Khyzhniy, I. V.; Uyutnov, S. A.; Ponomaryov, A. N.; Gumenchuk, G. B.; Bondybey, V. E.

Anomalous low-temperature post-desorption (ALTpD) from the surface of nominally pure solid nitrogen pre-liminary irradiated by an electron beam was detected for the first time. The study was performed using a combi-nation of activation spectroscopy methods — thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL) — with detection of the ALTpD yield. Charge recombination reactions are considered to be the stimulating factor for the desorption from pre-irradiated α-phase solid nitrogen.

Keywords: solid nitrogen; exoelectron emission; thermoluminescence; desorption

  • Low Temperature Physics 39(2013)5, 446-450
    Online First (2013) DOI: 10.1063/1.4807046

Publ.-Id: 19684

Lattice and orbital fluctuations in TiPO4

Wulferding, D.; Möller, A.; Choi, K.-Y.; Pashkevich, Y. G.; Babkin, R. Y.; Lamonova, K. V.; Lemmens, P.; Law, J. M.; Kremer, R. K.; Glaum, R.

In the s = 1/2 antiferromagnetic spin chain material TiPO4, the formation of a spin gap takes place in a two-step process with two characteristic temperatures, T = 111 K and T SP = 74 K. We observe an unusual lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a high-energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different from other spin-Peierls materials.

Publ.-Id: 19683

Long waves from short bunches: Concepts and applications of super-radiant THz sources

Gensch, M.

  • Invited lecture (Conferences)
    Kolloquium der Fakultät für Physik, KIT, 31.01.2014, Karlsruhe, Deutschland

Publ.-Id: 19682

Investigations of the Magnetic Properties in the Pyrochlore Ho2Ti2O7

Schönemann, R.; Herrmannsdörfer, T.; Green, E. L.; Skrotzki, R.; Wang, Z.; Kaneko, H.; Suzuki, H.; Wosnitza, J.

Pyrochlore compounds such as R2Ti2O7 (where R is Ho or Dy) have an highly degenerate ground state where the R3+ moments obey the "ice rules". This provides access to study extraordinary physical phenomena, like the formation of magnetic monopoles. Recent publications evidence monopoles which can be probed using high frequency (adiabatic) susceptibility measurements [1]. We performed ac susceptibility measurements on a single-crystal Ho2Ti2O7 sample at low temperatures down to 30 mK and magnetic fields up to 14 T. Based on isothermal frequency sweeps we were able to determine spin relaxation rates. Both the real and imaginary parts of the temperature-dependent magnetic susceptibility measurements show the spins freezing below 1 K and provide insight into the magnetic-monopole density.

  • Poster
    DPG Frühjahrstagung, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19681

Multimodal imaging of a novel pheochromocytoma tumor model

Bergmann, R. K.; Ullrich, M.; Ziegler, C. G.; Kniess, T.; Ehrhart-Bornstein, M.; Schally, A. V.; Eisenhofer, G.; Bornstein, S.; Steinbach, J.; Pietzsch, J.

Objective. Pheochromocytoma (PHEO) is a rare but potentially lethal neuroendocrine tumor arising from catecholamine producing chromaffin cells. Available treatment strategies are limited and, if the tumor has metastasized, not very effective. The abundant expression of peptide hormone receptors on endocrine tumor cells allows specific targeting and imaging by radioactive and highly effective anti-tumor peptide analogs. The present study focuses on the preclinical imaging and evaluation of potential therapies in the treatment of pheochromocytoma targeting peptide hormone receptors. Design and method. Somatostatin receptor 2 (SSTR2), luteinizing hormone-releasing hormone receptor (LHRH-R) and growth hormone-releasing hormone receptors (GHRH-R) were characterized by both RT-PCR and immunohistological analysis in a mouse pheochromocytoma (MPC) cell line . Based on these data, we evaluated the effects of cytotoxic peptide hormone analogs on cell viability, apoptosis, and necrosis on MPC cells. For in vivo studies, we furthermore established a new MPC mCherry transfected cell line and produced a subcutaneous mouse model of PHEO. The tumors were evaluated by multimodal imaging using PET, MRI, CT and optical imaging. Results. Our data reveal significant anti-tumor effects mediated by the cytotoxic peptide hormone analogs AN-162 and AN-238 targeting SSTR2, by the antagonist Cetrorelix targeting LHRH-R and by the cytotoxic analog AN-152 targeting as well as by the antagonist MIA-602 targeting growth GHRH-R on MPCs. Furthermore, using our newly established mouse model, we were able to visualize the growth, perfusion, metabolism, and hypoxia of MPC cell-derived subcutaneous PHEO in vivo by multimodal molecular imaging including SSTR2 PET. Additionally, histological ex vivo tumor characterization demonstrated unaltered functional peptide hormone receptor expression during in vivo tumor growth in mice. Conclusion. Our current investigation provides strong evidence for a possible future treatment of malignant PHEO using targeted peptide hormone receptor therapy. Support. This work was supported by the Deutsche Forschungsgemeinschaft (Grants BE-2607/1 (R.B. & J.P.), and ZI-1362/2-1 (C.G.Z.&G.E.).

  • Poster
    World Molecular Imaging Congress, 18.-21.09.2013, Savannah, USA

Publ.-Id: 19680

Super-radiant THz sources: Perspectives

Gensch, M.

  • Invited lecture (Conferences)
    Workshop on "The Science and Technology of Accelerator-based THz Lightsources", 18.-19.11.2013, Upsala, Sweden

Publ.-Id: 19679

"Material Science „at Home“ and at the Synchrotron"

Grenzer, J.

  • Invited lecture (Conferences)
    Institutskolloquium, 21.01.2013, Freiberg, Germany

Publ.-Id: 19678

Numerical study of MHD instabilities in Liquid Metal Batteries

Weber, N.; Barry, L.; Galindo, V.; Grants, I.; Stefani, F.; Weier, T.

Nowadays, liquid metal batteries (LMBs) are considered as one promising device for storing electricity on the short and medium time scale. Built as a stable density stratification of two metals separated by a liquid salt electrolyte, liquid metal batteries offer comparatively very high current densities as well as a potentially superior live time, compared to solid batteries. Bearing in mind the low material price, LMBs may provide cheap power as well as energy, by simply upscaling the battery. This is where magnetohydrodynamics come into play. Currents in the order of kilo-amperes will induce fluid instabilities with the potential of short-circuiting the fully liquid battery. Beside of thermal convection and electro-vortex flows, surface instabilities, as known from aluminum smelters, and the kink-type Tayler instability (TI) are of particular significance.

We present a numerical model, based on the open source CFD library OpenFOAM which is able to simulate the Lorentz force induced fluid flow in LMBs. Starting with single phase simulations, the model shows good correspondence with a recent Tayler instability experiment. Further studies lead to a comprehensive characterization of the TI in liquid metal batteries and to a number of countermeasures for taming it. The influence of the current collectors and feeding cables of the battery is investigated, as well. Finally, first results of multiphase simulation are presented, particularly with regard to the deformation of the thin electrolyte layer.

Keywords: OpenFOAM Tayler instability simulation liquid metal battery

  • Lecture (Conference)
    9th PAMIR International Conference, 16.-20.06.2014, Riga, Lettland
  • Contribution to proceedings
    9th PAMIR International Conference, 16.-20.06.2014, Riga, Lettland

Publ.-Id: 19677

Nanoindentation on ion-irradiated Fe-Cr alloys

Heintze, C.; Hernández Mayoral, M.; Bergner, F.

Ferritic/martensitic high-chromium steels are candidate structural materials for future nuclear applications such as fusion and generation IV fission reactors. Nevertheless these steels suffer hardening and embrittlement due to neutron irradiation. Ion irradiation is an efficient tool to simulate neutron irradiation effects without the drawbacks of producing radioactive material. In the present work ion-irradiation in combination with nanoindentation has been applied to study the irradiation-induced hardening of binary Fe-Cr alloys. The details of the approach are specified and the effects of Cr content and irradiation conditions including both single-beam and dual-beam irradiations are considered. Transmission electron microscopy is used to characterize irradiation-induced defects. Ion-irradiation-induced hardening is compared to hardening observed after neutron irradiation at similar conditions and dominant hardening mechanisms are identified.

Keywords: ion irradiation; Fe-Cr alloys; nanoindentation; TEM; radiation hardening

  • Lecture (Conference)
    5th Workshop on Nuclear Fe Alloys: Modeling and Experiment, 28.-29.11.2013, Roma, Italia

Publ.-Id: 19676

In-situ X-ray Scattering & Diffraction: Studying the Formation of Nanostructures using ion beam techniques

Grenzer, J.; Facsko, S.; Holy, V.; Bähtz, C.; Roshchupkina, O.

  • Lecture (Conference)
    Workshop „Ionenstrahlen – Forschung und Anwendung“ 2013, 12.-14.06.2013, Leipzig, Germany

Publ.-Id: 19675

In-situ Ionen-Experimente @ ROBL-MRH

Grenzer, J.

  • Lecture (others)
    FWIZ Statusklausur 2013 am Institut für Ionenstrahlphysik und Materialforschung; Ionenstrahlzentrum, 10.-11.07.2013, HZDR, Germany

Publ.-Id: 19673

Structure dependent magnetic properties of Co implanted TiO2

Yildirim, O.; Cornelius, S.; Vinnichenko, M.; Butterling, M.; Wagner, A.; Smekhova, A.; Potzger, K.

Magnetic and structural properties of amorphous and anatase TiO2 thin films implanted with Co ions have been investigated. Implantation induced defects have been characterized using positron annihilation spectroscopy (PAS) while for magnetic chracterization we have used magnetometry. Up to a doping level of 2.5 at.%, only a paramagnetic contribution has been detected. The susceptibility strength , however, depends on the structure of the unimplanted film. Results on the formation of secondary phases at higher doping level will also be presented.

This work is supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz-Russia Joint Research Group HRJRG-314, and the Russian Foundation for Basic Research, RFBR #12-02-91321-SIG_а, Start: 01.02.2012

  • Lecture (Conference)
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany

Publ.-Id: 19672

Erzeugung funktionaler Schichten auf Basis von bakteriellen Hüllproteinen

Weinert, U.

Die hier vorliegende Arbeit beschäftigt sich mit Eignung bakterieller Hüllproteine als Bindungsmatrix für die Kopplung funktionaler Moleküle mit dem Ziel, sensorische Schichten zu erzeugen. Bakterielle Hüllproteine sind biologische SAMs, an deren Oberfläche sich modizierbare COOH-, NH2- und OH-Gruppen benden. Die Ausbildung polymerer Strukturen erfolgt dabei in wässrigen Systemen und auf Oberflächen. Im Zuge der boomenden Entwicklung von Biosensoren werden insbesondere Biotemplate gesucht, die zwischen biologischer Komponente und Sensoroberfläche vermitteln. Bakterielle Hüllproteine stellen eine solche Zwischenschicht dar. Als Anwendungsbeispiel wurden die Proteine daher mit einem FRET-Paar und Thrombin- und Kanamycin-Aptameren modiziert. Hierbei wurden das FRET-Paar H488 und H555 an die bakteriellen Hüllproteine der beiden Haldenisolate A12 und B53 mittels EDC mit einer Modifizierungsrate von 0,54 mol_Farbsto/mol_Protein kovalent gebunden. Bei der vorhandenen p4-Symmetrie bedeutet dies, dass ein FRET-Paar pro Einheitszelle vorhanden war. Der Nachweis eines Energietransfers zwischen den beiden am Protein gebundenen Fluoreszenzfarbstoffen H488 und H555 erfolgte mittels statischer und zeitaufgelöster Fluoreszenzmessung. Die Ergebnisse zeigten, dass ein Energietransfer nur möglich war, wenn die Proteine in polymerer Form vorlagen, unabhängig davon, ob sich die Proteine immobilisiert an einer Oberfläche oder in wässriger Lösung befanden. Mittels Variieren des Donor-Akzeptor-Verhältnisses konnte ein maximaler Energietransfer von 40 % generiert werden, wenn das Verhältnis der Fluoreszenzfarbstoffe von Donor und Akzeptor 4 betrug. Die Fluoreszenzintensität der Fluorophore wurde durch die Bindung an die Proteine nicht verringert oder gelöscht. Dies legt nahe, dass die Farbstoffe in den hydrophoben Poren immobilisiert wurden und die Poren die Fluoreszenzfarbstoffe schützen. Um weitere Aussagen über die Lage der gebundenen Fluoreszenzfarbstoffe zu erhalten, wurden die bakteriellen Hüllproteine der Stämme A12 und B53 enzymatisch verdaut und die Fragmente mittels SEC und SDS-PAGE untersucht. Dabei zeigten sich je nach Enzym und Protein unterschiedliche Bandenmuster bezüglich modifizierter und nativer Hüllproteine. Dies belegt, dass die Fluoreszenzfarbstoffe an NH2- und COOH-Gruppen der Proteine gebunden wurden und so teilweise den enzymatischen Verdau hinderten. Die SEC deutet an, dass die Fluoreszenzfarbstoffe an verschiedenen Stellen am Protein gebunden wurden. In einem zweiten Beispiel wurde das bakterielle Hüllprotein von A12 mit einem Aptamer modiziert. Aptamere sind kurze einzelsträngige Oligonukleotide, die u. a. mittels ihrer ausgebildeten 3D-Struktur spezifisch Zielstrukturen reversibel binden können. Die hier verwendeten Aptamere binden spezifisch Thrombin und Kanamycin. Die Aptamere wurden mit Hilfe einer der beiden Vernetzer PMPI oder Sulfo-SMCC an die bakteriellen Hüllproteine kovalent gebunden. Nach dem Modifizieren der Proteine wurden diese auf entsprechenden Sensorchips immobilisiert und die Aktivität des gekoppelten Aptamers mittels Affinitätsmessungen, SPR-Spektroskopie und QCM-D-Messungen analysiert. Die Funktion des gebundenen Thrombinaptamers konnte mittels Affinitätsmessungen und QCM-D nachgewiesen werden und entspricht in beiden Fällen einer Bindung von 2 nmol Thrombin pro Quadratzentimeter. Die Funktionalität des Kanamycinaptamers sollte mittels SPR bestimmt werden, jedoch konnte keine Funktionalität des gekoppelten Kanamycinaptamers nachgewiesen werden. Alle Messungen bestätigten jedoch, dass die Bindungsmatrix aus bakteriellen Hüllproteinen keinerlei oder nur ein sehr geringes Hintergrundsignal liefert. Werden nun beide Komponenten, FRET-Paar und Aptamere, an das Protein gebunden, ist es möglich, eine sensorische Schicht zu erzeugen. Die Zielstruktur, welche detektiert werden soll, wird an das Aptamer gebunden und so in räumliche Nähe zur Sensorfläche gebracht. Stellt die Zielstruktur einen Fluoreszenzlöscher dar, so wird der Energietransfer durch die räumliche Nähe des Fluoreszenzlöscher gestört. Die Detektion des Zielmoleküls erfolgt nun über die Änderung von Fluoreszenzintensitäten. Die hier vorgelegte Arbeit soll einen Grundstein legen für die Entwicklung eines solchen Sensors und insbesondere die Detektion eines Energietransfers optimieren und Schwachstellen in der Detektion nachweisen. Die systematische Untersuchung der Fluoreszenzfarbstoffe auf dem Protein ermöglichen es, in zukünftigen Arbeiten einen FRET zweifelsfrei zu detektieren. Die Modifizierung von bakteriellen Hüllproteinen von A12 mit Aptameren und die Detektion der Funktionalität der Aptamere mittels verschiedener Methoden zeigte auf, dass die bakteriellen Hüllproteine als universelle Bindungsmatrix für sensorische Moleküle dienen können, bei denen Affinitätsmessungen, SPR- oder QCM-D-Messungen genutzt werden. Besonders hervorzuheben ist, dass bakterielle Hüllproteine nahezu kein Hintergrundsignal liefern und aufgrund ihrer dünnen Monolage von etwa 6 - 9 nm die Sensitivität der Messungen nur gering beeinträchtigen.

Keywords: S-layer Proteins; sensors; aptamers; FRET; Protein modification

  • Doctoral thesis
    TU Dresden, 2013
    180 Seiten

Publ.-Id: 19671

S-layers as multifunctional templates for nanotechnology

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

Surface-layer (S-layer) proteins are biomolecules which can self-assemble in aqueous solutions and on surfaces. Those polymers form highly ordered two dimensional structures with unit cell sizes of few nanometers. On surface of such protein polymers one can find a high amount of modifiable groups like COOH-, NH2- and OH-groups. The latter and its nanostructuring make S-layers a perfect platform for nanotechnology.
Therefore S-layers can work as biotemplate to build biosensors consisting of fluorescence dyes and aptamers. Thereby fluorescence dyes will work as signal transducer system by performing a Foerster Resonance Energy Transfer (FRET) between each other. Aptamers serve as receptor for one specific analyte. Analyte binding by the aptamer leads to a detectable signal change because of a disturbed FRET. An idealized design of such a biosensor is shown in Fig. 1a. In a recent published work a FRET-pair was chemically linked to S-layers and showed an energy transfer efficiency of 40 % [1]. In further work aptamers will be chemically linked to the S-layer-FRET-system to reach proof of concept.
Another application for those S-layer proteins can be the development of catalytic materials based on highly ordered nanoparticles. Thereby nanoparticles of platinum or palladium are synthesized in the pores of S-layers. Fig. 1b shows an idealized scheme. After removal of the organic matrix nanoparticles are arranged on the surface having a defined size and order. These materials can now work as catalysts for e.g. organic synthesis or metallization of polymers.

Keywords: S-layer; nanotechnology; surface modification; sensors; aptamer; nanoparticles

  • Lecture (Conference)
    COST Action "Bio-inspired nanotechnologies: from concepts to applications", 08.-09.10.2013, Leipzig, Deutschland

Publ.-Id: 19670

Bakterielle Hüllproteine als Matrix für die Entwicklung funktionaler Schichten

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

Sensoren für spezifische Substanzen, wie z.B. Medikamente und Umweltgifte, gewinnen mit dem wachsenden Umweltbewusstsein der Gesellschaft und der Industrie z.B. in Bereichen wie der Wasserüberwachung und -aufbereitung immer mehr an Bedeutung. Die vorliegende Arbeit beschäftigt sich daher mit der Konzipierung einer sensorischen Schicht, bestehend aus bakteriellen Hüllproteinen, Fluoreszenzfarbstoffen und Aptameren, die es ermöglichen soll, kleinste Mengen an Schadstoffen im Wasser zu detektieren. Bakterielle Hüllproteine sind selbstassemblierende Proteine, die in wässrigen Systemen und an Oberflächen ebenmäßige Gitterstrukturen ausbilden und an deren Oberfläche zahlreiche modifizierbare funktionelle Gruppen, wie z. B. COOH- und NH2-Gruppen, zu finden sind. Sie stellen damit eine nahezu perfekte Bindungsmatrix für die sequentielle Kopplung sensorischer Komponenten dar, die mit wenigen Nanometern Abstand zueinander auf eine Oberfläche fixiert werden sollen. Die vorliegende Arbeit nutzt ein FRET-Paar als optische Komponente und Aptamere als Rezeptor-Moleküle. Die räumliche Nähe aller Komponenten zueinander soll gewährleisten, dass nach der Bindung des zu detektierenden Analyten, der Energietransfer zwischen den beiden Fluoreszenzfarbstoffen unterbunden wird. Das veränderte optische Signal kann dann einfach mittels Fluorometer detektiert und ausgewertet werden. Die nachfolgende Abbildung soll schematisch und idealisiert einen möglichen Aufbau der sensorischen Schicht darstellen. Die derzeitigen Arbeiten beschäftigen sich mit der erfolgreichen Funktionalisierung von bakteriellen Hüllproteinen mit einem FRET-Paar und Aptameren.

Keywords: FRET; aptamer; sensor; surface-layer Proteins; modification

  • Poster
    8. Deutsches BioSensor Symposium, 10.-13.03.2013, Wildau, Deutschland

Publ.-Id: 19669

X-ray diffraction and grazing-incidence diffraction

Grenzer, J.

  • Invited lecture (Conferences)
    9th Autumn School on X-ray Scattering from Surfaces and Thin Layers, 25.-28.09.2013, Smolenice Castle, Slovakia

Publ.-Id: 19668

Material Science at „Home“ and at the Synchrotron: Investigations of nanocrystalline films

Grenzer, J.

"Material Science at „Home“ and at the Synchrotron: Investigations of nanocrystalline films"

  • Invited lecture (Conferences)
    Firma PANalytical B.V., 12.09.2013, ALMELO, The Netherlands

Publ.-Id: 19667

Inter-sublevel dephasing in quantum dots

Teich, M.; Schneider, H.; Bhattacharyya, J.; Winnerl, S.; Wilson, L.; Helm, M.

We use the Dresden Free-Electron-Laser (FELBE) to investigate intersublevel coherence times in semiconductor quantum dots (QDs) by degenerate four-wave mixing (DFWM) spectroscopy. We know from pump-probe measurements1 on a series of quantum dot samples with varying intersublevel energy that intersublevel relaxation times of the s-p intersublevel transition can become very long (up to 1.5 ns). Due to the discrete nature of these sublevels, intersublevel coherence times should exhibit similar time constants at low temperatures where “pure dephasing” is suppressed.

Keywords: semiconductor quantum dot; inter-sublevel transition; terahertz free-electron laser; degenerate four-wave mixing; homogeneous and inhomogeneous broadening

  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665455
  • Poster
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland

Publ.-Id: 19666

Extra-long hole spin relaxation time in InGaAs/GaAs quantum wells probed by cyclotron resonance spectroscopy

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

We report a long, ms range, spin relaxation time of holes in InGaAs/GaAs quantum wells probed by cyclotronresonance spectroscopy in pulsed magnetic fields up to 60 Tesla. We found a strong hysteresis in the spectral weights of the cyclotron resonance absorption when a rapidly changing magnetic field is used for the experiment, while the hysteresis vanishes when a much slower changing magnetic field is used. We attribute this behavior to a long, comparable to the magnetic-field rise time, energy relaxation time between the two lowest spin-split hole Landau levels, i.e., a long hole spin relaxation time.

Keywords: cyclotron resonance spectroscopy; hole spin relaxation; pulsed magnetic fields; InGaAs/GaAs quantum well

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665921

Publ.-Id: 19665

Plasmonic focusing on metal and semiconductor disks under radially polarized terahertz illumination

Kaltenecker, K. J.; Wallauer, J.; Waselikowski, S.; Hodapp, J.; Fischer, C.; Winnerl, S.; Schneider, H.; Fischer, B. M.; Walther, M.

Optimal focusing of surface plasmon polaritons in the center of a metal disc illuminated by radially polarized terahertz pulses is demonstrated. Due to the cylinder symmetrical structure surface plasmons can be excited along the entire circumference, which interfere constructively in the center of the disk forming a sharp frequency-depended focal spot. We map the field distribution on the disk by THz near-field microscopy and compare our result to numerical simulations. For comparison, behavior under linearly polarized THz illumination is characterized. Furthermore, first results of semiconducting plasmonic lenses are presented.

Keywords: Terhertz radiation; plasmon polaritons; radial polarization

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665612

Publ.-Id: 19664

Krein space related physics: from mathematical structures towards experiments

Günther, U.

A compact overview is given about physical systems with antilinear symmetries as they have been intensively studied during the past 15 years and as they are currently still under intensive investigation worldwide. Starting from a few comments on the historical background, the underlying basic mathematical structures are sketched. This especially concerns the properties of the corresponding effective Hamiltonians, their non-selfadjointness in usual Hilbert spaces with positive definite (Euclidean type) inner products and their selfadjointness in Hilbert spaces with indefinite inner products, so called Krein spaces. Specific properties of these Hamiltonians like non-diagonalizability at spectral branch-points, hidden Jordan block structures, perturbation theory in terms of Puisseux series expansions instead of Taylor expansions as well as related group structures will be briefly discussed. Realizations of the antilinear symmetries are demonstrated for physical systems with simultaneous time-reversal and parity-inversion symmetries (PT symmetries). Specific physical effects like PT phase transitions and exciting new features of these systems are illustrated on simulations for various optical waveguide systems, Bose-Einstein condensates (BECs), microwave cavities, systems of coupled oscillators etc. Finally, a brief overview is given about recent experimental implementations as well as about a couple of promising new directions of research with interconnections to other areas of active research in theoretical and experimental physics.

Keywords: PT physics; PT phase transitions; operator theory; Krein spaces; branch points; Jordan blocks; Puisseux series expansions; Bose-Einstein condensates; optical waveguide systems; microwave cavities

  • Lecture (others)
    Lecture presented at the Physics Department, College of Sciences, Koc University, Istanbul, 16.12.2013, Istanbul, Turkey

Publ.-Id: 19663

Stabilite des systemes non conservatifs et algebra lineaire

Lerbet, J.; Aldowaji, M.; Challamel, N.; Kirillov, O.; Nicot, F.; Darve, F.

Investigations about linear stability of nonconservative systems with non symmetric stiness matrices lead to linear algebra results that are unusual in mechanics. It may also lead to original linear algebra developments. It is illustrated about linear divergence stability when adding kinematic constraints on the nonconservative system. The original concept of m-positive definite matrices is proposed, the main result is given and some mathematical open problems are suggested.

Keywords: nonconservative systems; kinematic constraints

  • Open Access Logo Contribution to proceedings
    21eme Congres Francais de Mecanique, 26.-30.08.2013, Bordeaux, France
    Congrès Francais de Mécanique, 39/41 rue Louis Blanc, 92400 Courbevoie, France: AFM, Maison de la Mécanique

Publ.-Id: 19662

Robust stability at the swallowtail singularity

Kirillov, O. N.; Overton, M. L.

Consider the set of monic fourth-order real polynomials transformed so that the constant term is one. In the three-dimensional space of the coefficients describing this set, the domain of asymptotic stability is bounded by a surface with the Whitney umbrella singularity. The maximum of the real parts of the roots of these polynomials is globally minimized at the Swallowtail singular point of the discriminant surface of the set corresponding to a negative real root of multiplicity four. Motivated by this example, we review recent works on robust stability, abscissa optimization, heavily damped systems, dissipation-induced instabilities, and eigenvalue dynamics in order to point out some connections that appear to be not widely known.

Keywords: abscissa; optimization; overdamping; asymptotic stability; Whitney umbrella; Swallowtail; caustic; eigenvalue dynamics

Publ.-Id: 19661

In Vivo Imaging of Microglia Cells Activated by LPS-Induced Systemic Inflammation in Mouse

Mathe, D.; Futo, I.; Veres, D.; Horvath, I.; Semjeni, M.; Kovacs, N.; Tóth, M.; Bergmann, R. K.; Szigeti, K.

Introduction: The role of microglia cells in the pathogenesis of inflammations and chronic neurodegenerative disorders in the central nervous system (CNS) is an active research field in recent years. The ramified form of microglia cells is activated via inflammation markers (e.g. IL-1b, TNF-alpha). The activated form of microglia cells as a key player of the innate immune system in the CNS present MHC II and release antiinflammatory agents. The activation status of the microglial benzodiazepine (BZD) receptor system could be used to monitor the process of neuroinflammation. Methods: Healthy (n=6) and LPS induced inflamed (n=4) C57BL/6 mice were used. The activation of the microglia cells was induced by systemic injection of 0.3 g/bw kg lipopolysaccharide (LPS) 5h before the in vivo measurements. We used NanoSPECT/CT Plus and nanoScan PET/MRI (Mediso Ltd, Hungary) multimodal in vivo imaging systems. To detect dynamics and localization of microglia activation we used a micro dose partial inverse BZD agonist ( 125-I - Iomazenil). The change of the general metabolic state in the CNS was monitored by 18-F-FDG PET. 99m-Tc-HMPAO (hexamethylpropylene-amino-oxime) was used for the detection of altered regional cerebral perfusion. The segmentation of different mouse regions was first based on MRI measurements of the animals and for aims of standardization coregistered with an MRI atlas. Results: FDG uptake was increased by systemic LPS in every region of the brain (p<5%). HMPAO uptake was decreased in several brain regions (p<5%). We found that the activity concentration of 125-I-Iomazenil was increased in the hippocampus and cerebellum but not in the cortex after systemic induction of neuroinflammation. Conclusions: FDG uptake increase indicates an increased metabolic rate due to induced brain inflammation. HMPAO uptake change could show glutathione depletion generated decrease of HMPAO fixation induced by reactive oxygen species (ROS) generated by activated inflammatory cells. The surprising result of selective Iomazenil uptake increase could be attributed to a higher amount of an activated but already resident microglia cell pool in the hippocampus as an early step of acute systemic inflammation in the brain. Based on our results the LPS induced changes in the BZD system should be further monitored in neuroinflammation in concordance with ROS status and the time course of the inflammatory changes in this general neuroinflammatory model in mice. A multi-modal imaging approach combining detailed structural and functional approaches elucidates important unknown details of neuroinflammation monitoring. This work was supported in part by INMiND (HEALTH.2011.2.2.1-2 No.278850) of FP7.

  • Poster
    World Molecular Imaging Congress, 18.-21.09.2013, Savannah, USA

Publ.-Id: 19660

Preparation of PW-class laser driven radiation sources for radiation oncology and structural analysis

Schramm, U.

Over the last decade laser particle acceleration has made such progress that first applications in special fields can be envisioned. Prominent examples are radiation therapy with laser accelerated ion beams as well as the generation of pulsed X-ray sources.
In this presentation the status of the joint activities of the Dresden groups at HZDR running the high power laser Draco and at Oncoray, the national center for radiation research in oncology, will be discussed. Emphasis will be given to the energy scaling of proton bunches accelerated in the TNSA regime with and during ultra-short pulses, potential instabilities in the process, methods for online monitoring, and to the status of the ongoing upgrade of Draco to PW power level. This topic will be complemented by a presentation of the recently achieved results on X-ray generation via Thomson back-scattering.

Keywords: Laser plasma acceleration

  • Invited lecture (Conferences)
    Institutsseminar HI Jena, 11.12.2013, Jena, Deutschland

Publ.-Id: 19659

Status of the PW laser at the HZDR Dresden

Schramm, U.

Status of the HZDR PW laser project with respect to the upcoming installations in Salamanca.

Keywords: PW laser

  • Invited lecture (Conferences)
    Third User Meeting of the Spanish Pulsed Laser Center CLPU, 02.-03.12.2013, Salamanca, Spanien

Publ.-Id: 19658

Diffusion Processes in the Sintering of Zirconia-Based Nanomaterials

Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.; Konstantinova, T.; Danilenko, I.

In the present work, zirconia-based nanomaterials with various stabilizers were prepared by a co-precipitation technique. Defects in these nanomaterials were characterized by positron annihilation spectroscopy which is a non-destructive technique with a high sensitivity to open volume defects and atomic scale resolution. It was found that zirconia-based nanomaterials contain vacancies and also nano-scale and meso-scale pores. Diffusion processes which occur in the nanomaterials sintered at elevated temperatures were investigated by depth sensitive positron annihilation studies on a variable energy slow positron beam. It was found that sintering causes intensive grain growth and residual porosity is removed from samples by diffusion to the surface.

Keywords: Yttria-stabilised zirconia; nanopowders; sintering; porosity; positron annihilation

Publ.-Id: 19657

Hydrogen absorption in thin ZnO films prepared by pulsed laser deposition

Melikhova, O.; Cizek, J.; Lukac, F.; Vlcek, M.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Connolly, J.; Mccarthy, E.; Krishnamurthy, S.; Mosnier, J.-P.

ZnO films with thickness of ~80 nm were grown by pulsed laser deposition (PLD) on MgO(100) single crystal and amorphous fused silica (FS) substrates. Structural studies of ZnO films and a high quality reference ZnO single crystal were performed by slow positron implantation spectroscopy (SPIS). It was found that ZnO films exhibit significantly higher density of defects than the reference ZnO crystal. Moreover, the ZnO film deposited on MgO substrate exhibits higher concentration of defects than the film deposited on amorphous FS substrate most probably due to a dense network of misfit dislocations. The ZnO films and the reference ZnO crystal were subsequently loaded with hydrogen by electrochemical cathodic charging. SPIS characterizations revealed that absorbed hydrogen introduces new defects into ZnO.

Keywords: ZnO; thin films; hydrogen; positron annihilation; defects

Publ.-Id: 19656

GISAXS Messungen am Labor-Diffraktometer

Grenzer, J.; Gateshki, M.; Holz, T.; Kharchenko, A.

Die Entwicklung neuer Materialien geht meistens einher mit der Schaffung neuer funktionalisierter Nanostrukturen. Strukturuntersuchungen sind dabei der Schlüssel, um eine Verbindung zwischen der Funktion und den strukturellen Eigenschaften, welche diese Funktion generieren, herstellen zu können. Dieses Wissen macht es möglich neuartige Materialien mit genau vorbestimmten Eigen-schaften zu entwerfen. Dünne nanostrukturierte Schichten können Ober- und Grenzflächen-eigenschaften derart beeinflussen, dass die Materialeigenschaften von konventionellen Werkstoffen optimal an die jeweilige Aufgabe angepasst werden können. Dabei wird die Funktion von Nanostrukturen nicht nur von deren innerer Struktur sondern zu einem großen Teil durch Ihre Morphologie und Oberfläche bestimmt.
Kleinwinkel-Röntgenstreuung im streifenden Einfall (GISAXS - Grazing incidence small angle scattering) hat den Vorteil gegenüber bildgebenden mikroskopischen Methoden (TEM, SEM), dass in der Regel keine aufwendige Probenpräparation notwendig ist und größere Probenvolumina untersucht werden können. GISAXS erlaubt es die Morphologie von oberflächennahen Strukturen als auch deren (innere) Elektronendichteverteilung zu ermitteln. GISAXS-Untersuchungen wurden lange fast ausschließlich an spezialisierten Synchrotronstrahllinien durchgeführt, da die Anforderungen an die Strahlqualität, Detektor und Experimentierfläche (sehr lange Strahllinie) mit konventionellen Laborgeräten gar nicht oder nur schlecht zu erfüllen waren. Seit einigen Jahren kann man beobachten, dass die Kleinwinkelstreuung Einzug in das Labor hält. Die Entwicklung von Mikrofokusquellen in der Kombination von leistungsfähigen Optiken und vor allem die Entwicklung neuer Halbleiter-flächendetektoren etabliert GISAXS-Untersuchungen zunehmend an Laborgeräten.

  • Invited lecture (Conferences)
    7. PRORA 2013 - Fachtagung Prozessnahe Röntgenanalytik, 21.-22.11.2013, Berlin, Germany

Publ.-Id: 19655

New structural constraints on the southern Provence thrust belt (France): evidences for an Eocene shortening event linked to the Corsica-Sardinia subduction

Andreani, L.; Loget, N.; Rangin, C.; Pichon, X. L.

We reply to the comments of J. Philip regarding the structure of La Nerthe range (southern Provence, France) and the timing of the deformation. We first agree with J. Philip on the structural independence of La Nerthe and L’Etoile ranges. We then discuss the allochthonous and autochthonous models. The allochthonous model mainly relies on a reactivation of a N-verging thrust during the Oligocene. There are no evidences for a Middle Rupelian thrusting event and the interpretation of the Oligocene series in southern Provence area was entirely revised. J. Philip’s Argumentation is solely based on the existence of steep dipping Rupelian limestones. However we demonstrate that they could be tilted along normal faults as it is the case in the Marseille basin. Recent works clearly show that the Oligocene Marseille and Saint-Pierre basins have a similar tectonic history resulting from two main extensional events. The last point debated by J. Philip is the age of the strike-slip faults. As it is pointed in our contribution the strike-slip fault planes cut folded strata and were reactivated during an extensional event. This strike-slip faulting event occurred between the latest stages of the main Bartonian compressional event and the beginning of the Early Rupelian extensional tectonics. As pointed by J. Philip the E-trending faults of Saint-Pierre basin acted as normal faults during the Oligocene. We however suggest that these faults were inherited from the Late Eocene strike-slip tectonics and reactivated during the Oligocene.

Keywords: Tectonics; Southern Provence; La Nerthe range; Paleogene; Neogene

Publ.-Id: 19654

Deep-Sea Astronomy with Accelerator Mass Spectrometry

Feige, J.; Wallner, A.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Accelerator Mass Spectrometry (AMS) is a highly sensitive method to measure extremely low isotopic ratios of long-lived radionuclides relative to its stable isotope. Inspired by findings of an excess of 60Fe in a ferromanganese crust approximately 2 Myr ago, which was interpreted to be of supernova-origin, we use this method to determine concentrations of a variety of radionuclides in deep-sea sediment samples covering a time range from 1.7 to 3.2 Myr.
An international collaboration of different AMS facilities is utilized to search for signatures of 26Al, 53Mn, and 60Fe above terrestrial background production and extraterrestrial influx. In addition, the cosmogenic radionuclide 10Be is measured to confirm existing magnetostratigraphic dating of the samples and for comparison with atmospheric production ratios of 26Al/10Be. All 10Be and 26Al measurements arefinished, 53Mn and 60Fe is in progress. Measurement results and the influence of different background sources on a potential supernova signature will be presented and discussed.

Keywords: accelerator mass spectrometry; AMS; cosmogenic radionuclide; astronomy; supernova

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19653

Hydrogen interaction with defects in nanocrystalline, polycrystalline and epitaxial Pd films

Čížek, J.; Melikhova, O.; Vlček, M.; Lukáč, F.; Vlach, M.; Dobroň, P.; Procházka, I.; Anwand, W.; Brauer, G.; Wagner, S.; Uchida, H.; Gemma, R.; Pundt, A.

Hydrogen interaction with defects and structural development of Pd films with various microstructures were investigated. Nanocrystalline, polycrystalline and epitaxial Pd films were prepared and electrochemically loaded with hydrogen. Structural changes of Pd films caused by absorbed hydrogen were studied by in-situ X-ray diffraction combined with acoustic emission and measurement of electromotorical force. Development of defects during hydrogen loading was investigated by positron annihilation spectroscopy. It was found that hydrogen firstly fills open volume defects existing already in the films ans subsequently it occupies also interstitial sites in Pd lattice. Absorbed hydrogen causes volume expansion, which is strongly anisotropic in thin films. This introduces high stress into the films loaded with hydrogen. Acoustic emission measurements revealed that when hydrogen-induced stress achieves certain critical level rearrangement of misfit dislocations takes place. The stress which grows with increasing hydrogen concentration can be further released by plastic deformation and also by detachment of the film from the substrate.

Keywords: hydrogen; palladium; thin films; defects; positron annihilation; acoustic emission; X-ray diffraction

Publ.-Id: 19652

Forschungsprojekt am Helmholtz-Institut Freiberg für Ressourcentechnologie zum Rohstoffrecycling in der GaAs-Waferfertigung

Eichler, S.; Reinhold, T.; Zeidler, O.

Der Vortrag gibt einen Überblick zur Fertigung und Anwendung von GaAs Wafern. Durch den hohen Preisdruck für Wafer bei gleichzeitig schwankenden Gallium-Preisen und einer begrenzter Rohstoffverfügbarkeit ist das Unternehmen auf die Erschließung bisher ungenutzter Recyclingpotentiale angewiesen. Zusammen mit dem Helmholtz-Institut Freiberg wurde ein umfassendes Konzept für ein ökonomisches Recycling auf Grundlage von Membranverfahren entwickelt.

  • Invited lecture (Conferences)
    9. Sächsischer Kreislaufwirtschaftstag, 21.-22.11.2013, Freiberg, Deutschland

Publ.-Id: 19651

Revisiting magnetic stripe domains - anisotropy gradient and stripe asymmetry

McCord, J.; Erkartal, B.; von Hofe, T.; Kienle, L.; Quandt, E.; Grenzer, J.; Roshchupkina, O.

The thickness dependent generation of magnetic stripe domains in NiFe films is investigated by in-depth magnetic domain and micromagnetic analysis, as well as complementary analysis of the microstructure by x-ray diffraction and transmission electron microscopy. A gradient of perpendicular magnetic anisotropy with film thickness is found. Micromagnetic simulations show that the anisotropy gradient results in an asymmetric stripe domain configuration. Columnar grain coarsening and texture development with thickness are derived from the microstructural investigations. The variations correspondingly lead to the gradient of magnetic anisotropy and to an asymmetric magnetic stripe domain structure.

Publ.-Id: 19650

Neutron capture cross section measurements for 197Au from 4 to 80 keV at GELINA

Massimi, C.; Becker, B.; Dupont, E.; Kopecky, S.; Lampoudis, C.; Massarczyk, R.; Moxon, M.; Pronyaev, V.; Schillebeeckx, P.; Sirakov, I.; Volev, K.; Wynants, R.

Neutron induced capture cross section measurements for 197Au have been performed in the energy region between 4 keV and 80 keV. The experiments have been carried out at the time-of-flight facility GELINA. The prompt capture gamma-rays were detected by two C6D6 liquid scintillators, placed at 12.5 m distance from the neutron source. The shape of the neutron flux was measured with a 10B-loaded double Frisch-gridded ionization chamber based on the 10B(n,alpha) reaction. The total energy detection principle in combination with the pulse height weighting technique was applied. The data have been normalized to the well-isolated and saturated 197Au resonance at 4.9 eV. Special procedures have been applied to reduce bias effects due to the weighting function, normalization, dead time and background corrections. Uncertainties due to normalization, neutron flux and weighting function are 1.0 %. An additional uncertainty of 0.5 % results from the correction for self-shielding and multiple interactions, which have been verified by experiment. Resonance fluctuations have been studied by additional measurements at a 30 m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to a standard evaluation of the 197Au(n,gamma) cross section that was based on a least squares fit of experimental data available in the literature prior to this work and are fully consistent with the latest average capture cross section obtained in a quasi-Maxwellian spectrum at 25 keV.

Keywords: neutron capture; neutron resonances; neutron cross section

Publ.-Id: 19649

Novel scintillators - new ways at ELBE

Massarczyk, R.; Schwengner, R.; Junghans, A.; Wagner, A.

Nuclear resonance fluorescence experiments are a suitable tool to measure photo-absorption cross sections, from which one can determine the electromagnetic photon-strength functions. These strength functions are one of the main ingredients in network calculations for the nucleosynthesis in supernovae as well as in simulations concerning future nuclear power facilities. However, with the new orientation of these power plants from pure power production to a site where the transmutation of nuclear waste becomes more and more important, new kinds of data sets are needed.
The talk will show how we started to use the unique characteristics of LaBr3 detectors in experiments at the ELBE accelerator in Dresden-Rossendorf.
Experiments with positrons, neutrons and photons are presented and potential improvements are pointed out, which show how these experiments can benefit from the developments in the field of novel scintillators.

Keywords: LaBr3; detector techniques; nuclear structure; dipole strength functions

  • Invited lecture (Conferences)
    Physics with Large Arrays of Novel Scintillators, 15.-16.01.2014, Dublin, Ireland

Publ.-Id: 19648

Dose enhancement and localisation by combining reduced mass targets and a pulsed solenoid for radiobiological effectiveness studies of laser accelerated protons

Kroll, F.; Kluge, T.; Bussmann, M.; Cowan, T. E.; Herrmannsdörfer, T.; Kraft, S. D.; Metzkes, J.; Sauerbrey, R.; Schmidt, B.; Schramm, U.; Zeil, K.; Zier, M.; Zherlitsyn, S.

Proton beams by means of the well-confined dose deposition in matter are a promising tool for improving radiotherapy of cancer. Wider clinical use, however, is limited by the complexity and expense of current proton accelerators. Compact laser-driven proton therapy accelerators are a potential alternative, yet require substantial development in reliable beam generation, transport and dosimetric monitoring as well as validation in radiobiological studies.

In vitro cell irradiations with laser-accelerated protons show radiobiological effectiveness similar to conventionally accelerated protons. In vivo animal irradiations – the next step in the translational research chain towards laser-driven proton therapy of cancer – are currently restricted by the low proton yield and energy at the irradiation site.

We report on systematic investigations of the ultrashort pulse laser-driven acceleration of protons from thin targets of narrow lateral dimension, so-called reduced mass targets (RMTs). A robust maximum energy enhancement (almost doubled) was found when compared to reference irradiations of plain foils of same thickness and material. Combining RMTs with a pulsed high-field solenoid for particle capturing, as developed at Helmholtz-Zentrum Dresden-Rossendorf, gives the potential to enhance and localise the dose per pulse applied to the tumour, thus making further radiobiological studies on volumetric tumours feasible in the future.

  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Elba, Italien

Publ.-Id: 19647

Nuclear structure - photon strength functions and nuclear level densities

Massarczyk, R.

Overview talk on investigations in nuclear structure today and their relation to astrophysical topics.

Keywords: nuclear structure; dipole strength

  • Invited lecture (Conferences)
    XLIV Arbeitstreffen Kernphysik in Schleching, 21.-28.02.2013, Schleching, Deutschland

Publ.-Id: 19646

Neutrons and Photons at ELBE - Contribution to the transmutation Project ERINDA

Massarczyk, R.; Schwengner, R.; Beyer, R.; Elekes, Z.; Ferrari, A.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Wagner, A.

Contribution of experiments with neutrons and gamma rays at the radiation source ELBE to transmutation related projects like ERINDA

Keywords: transmutation; nuclear reaction

  • Poster
    11th International Topical Meeting on Nuclear Applications on Accelerators, 05.-08.08.2013, Brugge, Belgien

Publ.-Id: 19645

Depth profiling of Fe-implanted Si(100) by means of X-ray reflectivity and extremely asymmetric X-ray diffraction

Khanbabaee, B.; Biermanns, A.; Pietsch, U.; Grenzer, J.; Facsko, S.

This article reports on surface density variations that are accompanied by ion-beam-induced pattern formation processes on Si. The density profiles perpendicular to Si(100) surfaces were investigated after off-normal implantation with 5 keV Fe+ ions at fluences ranging from 1 x 10(16) to 5 x 10(17) ions cm(-2). Ripple formation was observed for ion fluences above 1 x 10(16) ions cm(-2). X-ray reflectivity (XRR) revealed the formation of a nanometre subsurface layer with incorporated Fe. Using XRR, no major dependence of the surface density on the ion fluence could be found. In order to improve the surface sensitivity, extremely asymmetric X-ray diffraction was applied. Depth profiling was achieved by measuring X-ray rocking curves as a function of the decreasing incidence angle down to 0 degrees using this noncoplanar scattering geometry. The density information was extracted from the dynamical Bragg shift of the diffraction peak caused by refraction of the X-ray beam at the air-sample interface.
Simulations based on the dynamical theory of X-ray diffraction revealed a decrease of density for increasing ion fluence in a region close to the surface, caused by the amorphization and surface roughening.

Publ.-Id: 19644

Broadband, diode pumped Yb:SiO2 multicomponent glass laser

Roeser, F.; Loeser, M.; Reichelt, A.; Albach, D.; Siebold, M.; Schwuchow, A.; Litzkendorf, D.; Grimm, S.; Schramm, U.

The spectroscopic properties and laser performance of a Yb:SiO2 multicomponent glass has been investigated. A maximum slope efficiency of 51%, an optical to optical efficiency of 42% and a tuning range of 80nm was realized.

Keywords: Lasers, solid-state; Laser materials; Lasers, ytterbium

  • Poster
    Ultrafast Optics 2013, 04.-08.03.2013, Davos, Switzerland

Publ.-Id: 19643

Progress at DREsden AMS

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Renno, A. D.; Ziegenrücker, R.

The combination of a mass spectrometer with an accelerator allows very sensitive detection limits for many applications. At the Helmholtz-Zentrum Dresden-Rossendorf an AMS (accelerator mass spectrometry) facility, DREsden AMS (DREAMS), with a 6-MV tandem accelerator has been successfully installed [1]. DREAMS has its applications in many scientic fields by determining 10Be, 26Al, 36Cl and 41Ca. We made progress to develop a negative ion source for volatile elements like chlorine or iodine by reducing the memory effect [2]. The range of isotopes is broaden to higher masses by the first experiments with actinides. A time-of-flight beam line will enable the measurement at higher count rates and of additional isotopes. Another focus is the combination of a commercial SIMS (CAMECA 7f Auto) with the accelerator. For this so called Super-SIMS the CAMECA 7f is utilized as ion source and low energy mass spectrometer. By complete destruction of molecules in the stripping process at the terminal of the accelerator detection limits some orders of magnitude better than for traditional dynamic SIMS are expected, i.e. ~10-9-10-12, see e.g. [3]. The Focus of applications will be geological samples in the framework of resource technology research. Ref.: [1] S. Akhmadaliev et al., NIMB 294 (2013) 5. [2] S. Pavetich et al., this conference. [3] C. Maden, Dissertation ETH Zürich 2003.

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19642

HZDR pulsed power developments for laser plasma applications and the LIGHT collaboration

Kroll, F.; Cowan, T. E.; Herrmannsdörfer, T.; Masood, U.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Schlenvoigt, H.-P.; Schramm, U.; Zherlitsyn, S.

Since the mid-1950s, pulsed (iron-free) high-field magnets have become a common, versatile research tool. Applications in solid state physics have promoted the development of sophisticated magnets that nowadays can achieve fields above 90 T repeatedly.

We report here another area of application for pulsed power magnet technology in combination with high-intensity lasers; namely the use of pulsed magnets as research tools in laser-based laboratory astrophysics and as effective optical devices for laser-accelerated particle beams. Pulsed power solenoids for focusing of laser-accelerated particle beams might allow for the use of these new radiation qualities in medical radiation therapy or could function as a crucial part of a compact, laser-based ion source.

The talk gives a survey of developments at Helmholtz-Zentrum Dresden-Rossendorf in portable pulse generator technology and pulsed high-field magnets, especially designed to match the requirements of different laser-plasma physics environments. The beam optical properties of a capacitor-driven air core solenoid are derived from experimental data and most recent experimental results collected within the LIGHT collaboration at the PHELIX laser system at GSI, Darmstadt are presented.

Keywords: High-field magnet; laser; plasmas; beam optics; astrophysics

  • Lecture (Conference)
    LaB 2013 - Exploring the coupling between intense magnetic fields and high-power lasers, 02.-04.12.2013, Palaiseau, France

Publ.-Id: 19641

Algorithm for fluid velocity field quantification from image sequences in complex geomaterials

Korn, N.; Lippmann-Pipke, J.

For reactive transport modelling in geosciences a velocity field v(xi,t) with i = 1, 2, or 3 is required. This velocity field can be a) obtained by definition, b) calculated on the basis of a given geometry, a set of partial differential equations and initial and boundary conditions or, c) obtained from observations:
By now, various tomographic methods have been applied to observe fluid flow also in dense geological material under realistic conditions. These are magnetic resonance imaging (MRI, e.g. (Greiner et al., 1997), neutron transmission tomography (e.g. (Pleinert and Degueldre, 1995), X-ray computed tomography (CT) (e.g. (Goldstein et al., 2007; Klise et al., 2008), electrical resistivity tomography (ERT), e.g. (Bowling et al., 2006; Gheith and Schwartz, 1998) and last but not least positron emission tomography (PET), e.g. (Khalili et al., 1998; Kulenkampff et al., 2008; Richter et al., 2005). Still, the extraction of quantitative velocity fields from observed concentrations fronts that pass through complex geological media is not a trivial task.
One option to solve this kind of problem is to inject a tracer pulse into a sample, record image sequences of the tracer's flow through the sample and generate local break through curves (BTC). Numerical simulations – e.g. on the basis of finite difference methods (e.g. (Yoon et al., 2008) – may then vary hydraulic conductivity, porosity and dispersivity values within appropriate ranges and evaluate the model fits of the data over different scales. The authors conclude that predicting water flow at fine scales (relative to permeability variations) is very challenging and that this may have large implications for modelling reactive transport, where reactant residence time and mixing can be greatly impacted by water flowpaths.

To overcome such problems that accompany the fitting of parameter values such as hydraulic conductivity, porosity or dispersivity in 3D numerical flow models, we designed, implemented and tested a new algorithm. It is conceptualized for application to real-world 3D PET image series of transport process observation in geological media that may be affected to some degree by noise, image artifacts and detection limits. Our algorithm does not need prior information about the internal geometry of the sample, but only the global flow rate and the geometric boundaries of the sample.
Still, the foundation of the algorithm is the continuity equation. Its validity serves as an optimization criterion to fit segments of flow paths to the images. In this way, the network of flow paths is recovered and the velocity can be computed using a robust and universal approach.
We model the flow path network inside a rock sample as a network of flow path segments. Each segment is a straight and typically a short part of a single flow path. For these segments, we assume that the fluid is incompressible and that there are no sinks and sources within a segment. These assumptions are typically true for water in a closed flow path.
As a first step, the algorithm identifies regions that show a significant increase in mass at some point in time (maxima in a BTC). At such regions nodes are placed, that are to be connected later with segments of the flow path network.
For each straight flow path segment, it is sufficient to use a 1D model, which greatly reduces computation time without sacrificing much accuracy, and makes the algorithm more robust against noise. For the algorithm, a segment is represented by a cylindrical tube that completely covers the flow path. Because there are no sinks and sources, the flow rate is constant when the tube covers exactly one flow path, but varies when it does not. Therefore, we can use the variation of the flow rate as an optimization criterion to decide where to place a tube, i.e. which of the aforementioned nodes to connect.
Finally, we can compute the velocity field from the flow rate and cross-sectional area of the tube.

Results & Discussion
For validating the algorithm we simulated a non-reactive tracer experiment in COMSOL Multiphysics® on a synthetic fracture network as a benchmark model for the algorithm. (Later, the image sequences obtained from the transport simulation are to be replaced by the PET image sequences). A velocity field (derived using the cubic law) was used to simulate transport of a conservative tracer. The resulting image sequence was provided to our new algorithm, which then computed the underlying velocity field.

Here we introduced our new algorithm (work in progress) that estimates velocity distributions from image sequences. It is robust against noise and static image artefacts, and requires no prior knowledge about the, possibly complex geometry of the sample. The current run-time for the example shown is well under ten seconds . These properties make the new algorithm universally suitable for tracer experiments for a wide range of applications.
The obtained velocity distributions (fig. 2, left) can directly be used for further reactive transport modelling.

Bowling, J.C., Zheng, C., Rodriguez, A.B. and Harry, D.L., 2006. Geophysical constraints on contaminant transport modeling in a heterogeneous fluvial aquifer. Journal of Contaminant Hydrology, 85(1–2): 72-88.
Gheith, H.M. and Schwartz, F.W., 1998. Electrical and visual monitoring of small scale three-dimensional experiments. Journal of Contaminant Hydrology, 34(3): 191-205.
Goldstein, L., Prasher, S.O. and Ghoshal, S., 2007. Three-dimensional visualization and quantification of non-aqueous phase liquid volumes in natural porous media using a medical X-ray Computed Tomography scanner. Journal of Contaminant Hydrology, 93(1–4): 96-110.
Greiner, A., Schreiber, W., Brix, G. and Kinzelbach, W., 1997. Magnetic resonance imaging of paramagnetic tracers in porous media: Quantification of flow and transport parameters. Water Resources Research, 33(6): 1461-1473.
Khalili, A., Basu, A.J. and Pietrzyk, U., 1998. Flow visualization in porous media via positron emission tomography. Physics of Fluids, 10: 1031-1033.
Klise, K.A., Tidwell, V.C. and McKenna, S.A., 2008. Comparison of laboratory-scale solute transport visualization experiments with numerical simulation using cross-bedded sandstone. Advances in Water Resources, 31(12): 1731-1741.
Kulenkampff, J., Richter, M., Gründig, M. and Seese, A., 2008. Observation of transport processes in soils and rocks with Positron Emission Tomography. Geophysical Research Abstracts, 9: 02754.
Pleinert, H. and Degueldre, C., 1995. Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study. Journal of Contaminant Hydrology, 19(1): 29-46.
Richter, M., Gründig, M., Zieger, K., Seese, A. and Sabri, O., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochimica Acta, 93: 643-651.
Yoon, H., Zhang, C., Werth, C.J., Valocchi, A.J. and Webb, A.G., 2008. Numerical simulation of water flow in three dimensional heterogeneous porous media observed in a magnetic resonance imaging experiment. Water Resources Research, 44: W06405.

  • Lecture (Conference)
    TRePro III 2014, 05.-07.03.2014, Karlsruhe, Deutschland

Publ.-Id: 19640

AER Working Group D on VVER safety analysis – report of the 2013 meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 22th meeting in Paris, France, during the period April 10-11, 2013. The meeting was hosted by the OECD/NEA and was held in conjunction with the fifth workshop on the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and the seventh workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modeling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 17 participants attended the meeting of the working group D, 12 from AER member organizations and 5 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:

  • Code development and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
  • Safety analyses methods and results
  • Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.
  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 417-422
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia

Publ.-Id: 19639

Charakterisierung von Mineralen, Laugungsüberständen und Mikroorganismen mittels Raman-Spektroskopie

Kostudis, S.; Kutschke, S.; Pollmann, K.

Heute erfahren die regionalen Kupferschiefervorkommen nach dem Ende der 800jährigen Bergbauära im Jahr 1990 eine Wiederentdeckung. Der moderate Kupfergehalt fordert den Einsatz alternativer umweltschonender und effizienter Abbauprozesse. Ziel unserer Arbeit ist daher die Etablierung von Biolaugungsprozessen mit heterotrophen Mikroorganismen zu Kupfergewinnung. Bio-induzierte Veränderungen auf Mineraloberflächen, der Laugungsüberstände sowie Veränderungen der Biomasse durch Wechselwirkungen mit dem Laugungsmaterial sollen unter anderem mithilfe von Raman-Spektroskopie analysiert werden.
Als Grundlage für die Zuordnung der Minerale zu den Raman-Spektren wird die Polarisationsmikroskopie genutzt. Dasselbe mikroskopierte Areal wird mithilfe der zweidimensionalen Scanfunktion des mit einem Mikroskop gekoppelten Raman-Spektrometers analysiert. Aus den erhaltenen Daten ist die bildgebende Differenzierung zwischen den Hauptmineralen Chalkopyrit (CuFeS2) und Bornit (Cu5FeS4) im Kupferschiefer unter Verwendung univariater Datenanalyse möglich. Der Vergleich der Spektren von Chalkopyrit und Bornit zeigt, dass sich die verschiedenen Kristallgitter und Anteile von Kupfer, Schwefel und Eisen in unterschiedlichen Bandenintensitäten widerspiegeln.
Bei der Untersuchung der Laugungsüberstände können die von der Probe erhaltenen Spektren mithilfe von Referenzmessungen zugeordnet werden. Im Vergleich zu den abiotischen Komponenten des Laugungssystems sind deutliche Unterschiede in den Spektren der eingesetzten Biomasse sichtbar.

  • Poster
    Aufbereitung und Recycling, 13.-14.11.2013, Freiberg, Deutschland

Publ.-Id: 19638

Investigation of the hydrophobization of silicate ore minerals using a Force Mapping Method combining Non contact Atomic Force Microscopy and Raman Spectroscopy

Rudolph, M.; Peuker, U. A.

The Helmholtz-Institute Freiberg (HIF) founded in 2011 conducts research on innovative techniques for the enhanced processing of strategic metal containing resources. Flotation has been identified as the most essential process in the minerals processing department to be focusing research on. In this paper we introduce a force mapping technique based on non-contact colloidal probe atomic force microscopy where a cantilever with an attached hydrophobic sphere is oscillating above a planarized ore sample in the aqueous environment including dissolved collector molecules. The physical background of force-distance conversion from amplitude- and phase-distance evaluations is presented to point out the opportunities when compared to conventional AFM force spectroscopy. Raman spectroscopy is used in combination to identify the mineral phase localized at the cantilever position. The method is applied on samples of a rare earth containing silicate ore from southern Sweden made up of feldspars, aegirine, nepheline and the rare earth containing eudialyte.

  • Lecture (Conference)
    Flotation '13, 18.-21.11.2013, Cape Town, South Africa

Publ.-Id: 19637

Highly efficient all diode pumped burst mode laser system for ultra-short pulses

Körner, J.; Hein, J.; Liebtrau, H.; Seifert, R.; Klöpfel, D.; Kahle, M.; Loeser, M.; Siebold, M.; Schramm, U.; Kaluza, M.

Concept and first results on an all diode pumped cryogenically cooled Yb:CaF2 based burst mode laser system are presented. Output parameters are designed to be 5J per burst of 1000 350fs pulses at 1MHz.

  • Contribution to proceedings
    Advanced Solid State Lasers (ASSL), 27.10.-01.11.2013, Paris, France
    Conference Papers ASSL, 978-1-55752-982-4, ATu3A.63
    DOI: 10.1364/ASSL.2013.ATu3A.63

Publ.-Id: 19636

Direct Observation of Waterglass Impregnation of Fractured Salt Rock with Positron Emission Tomography

Bittner, L.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Enzmann, F.

Sealing with waterglass is one option of technical improvement of the geological barrier. The process of injection is rather involved, because it depends on the kinetics of reaction of the injected waterglass with salt and brines, on the nature of the fractures and the injection velocity. Generally, up to now only the final result of this impregnation could be tested with injection tests and tomographic methods.
We already applied PET process monitoring as laboratory method in a large number of studies of conservative and reactive flow, as well as diffusion experiments, in different geological materials. PET enables to observe the propagation of radiolabelled substances with ultimate sensitivity and with a reasonable spatial resolution of 1 mm. We now developed a method to observe the process of waterglass impregnation into salt rock with PET. Labelling of waterglass is possible by simply adding a small portion of [18F]KF solution, with an activity of around 100 MBq. During the injection of the labelled waterglass into the salt rock we acquire a sequence of PET scans which yield a sequence of the spatial activity distribution in the sample. The activity per voxel is proportional to the volume fraction of waterglass.
The method was tested on small volumes of salt grit and a drill core, which was previously damaged with a geomechanical test and characterized with CT-imaging. These first examples were conducted at a low entry pressure, which limited the achievable depth of penetration and thus the achieved permeability reduction. However, PET-monitoring of the flow process before and after the waterglass injection showed significant alterations of the flow field.
Generally, this method is applicable also with other impregnation agents and matrices. Our approach, where we combine numerical process simulation based on CT-imaging with direct experimental process observation with PET is suited to improve fundamental process understanding and to verify the underlying assumptions and model codes.

Keywords: PET; pet; reactive transport; tracer; flow experiments; geological barrier; nuclear waste disposal

  • Lecture (Conference)
    International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, 06.-07.02.2014, Hannover, Deutschland

Publ.-Id: 19635

Ressourcentechnologie ‚Made in Germany‘ -Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF)-

Birtel, S.; Klossek, A.; Gutzmer, J.

Die exportorientierte Industrie in der Bundesrepublik Deutschland ist in ihrer derzeitigen Ausrichtung nahezu vollständig abhängig von metallischen und mineralischen Rohstoffen, die auf dem Weltmarkt erworben und importiert werden müssen. Die Gründung des Helmholtz-Instituts Freiberg für Ressourcentechnologie im August 2011 war daher motiviert durch den raschen Anstieg und die starke Fluktuation der Rohstoffpreise des letzten Jahrzehnts und der damit einhergehenden Sorge möglicher Versorgungsengpässe. Das Helmholtz-Institut ist organisatorisch an das Helmholtz-Zentrum Dresden-Rossendorf angegliedert und wird von diesem gemeinsam mit der Technischen Universität Bergakademie Freiberg aufgebaut. Die Forschung im Helmholtz-Institut fokussiert sich hauptsächlich auf interdisziplinäre und tech-nologieorientierte Projekte zur energie- und ressourceneffizienten Nutzung einer Auswahl von Hochtechnologierohstoffen (insbes. Seltene Erden, Indium, Germanium und Gallium), aber auch die Nutzung von anderen Hochtechnologiemetallen. Es werden sowohl Technologien zur primären Rohstoffnutzung als auch für das Recycling erforscht. Forschungsprojekte werden gemeinsam mit Partnern in Konsortien auf regionaler, nationaler und internationaler Ebene initiiert und durchgeführt. Nicht zuletzt leistet das Helmholtz-Institut einen signifikanten Beitrag zur Ausbildung einer neuen Generation hochqualifizierter Wissenschaftler und Techniker für die deutsche Industrie und den Hochschulsektor.

Keywords: Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF); Rohstoffstrategie; Rohstoffabkommen; Zusammenarbeit mit Industrie und Forschung

  • Other report
    Santiago: AHK Chile, 2014

Publ.-Id: 19634

Effect of compounding principles on thermal, mechanical and magnetic performance of soft magnetic polymethylmethacrylate/Fe3O4 nanocomposites

Xie, L.; Kirchberg, S.; Rudolph, M.; Ziegmann, G.; Peuker, U.

In this study, the effect of compounding principles on the properties of Polymer Bonded Soft Magnetic Nanocomposites (PBSMNs) was discussed. The polymethylmethacrylate /Fe3O4 magnetic nanocomposites (Fe3O4: 30 wt%) were prepared by the in situ process based on the solution and spray drying method, as well as by the ex situ process based on the kneading machine. As reference, the process combining these two compounding principles was also carried out for the PBSMN preparation, named as in-between process. The morphology structures, thermal, mechanical and magnetic properties of the magnetic nanocomposites achieved with different compounding principles were characterized. The results show that compounding principles have significant influence on the properties of the magnetic polymer nanocomposites. In the end, their contributions to the power electronic applications were discussed as well.

Keywords: compounding process; in situ polymerization; Polymer composites; soft magnetic composites

Publ.-Id: 19633

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