Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35810 Publications

Gender differences in color processing in mice as revealed with functional PET

Kranz, M.; Njemanze, P.; Amend, M.; Wehrl, H.; Brust, P.

OBJECTIVES: Color processing is a central component of mammalian vision. Noninvasive functional transcranial Doppler ultrasound has recently revealed gender-related differences of color processing which include right hemisphere pattern for Blue/Yellow chromatic opponency by men while a left hemisphere pattern was found for women. In the present study, 18F-FDG was used to investigate a similar paradigm in mice with functional PET.
METHODS: Ten anaesthetized CD-1 mice were repeatedly injected on different days with 12 MBq 18F-FDG and subjected in random order to separate monocular stimulation of the left and right eye with white, blue and yellow lights, respectively, for 20 min. A gelatin-(Wratten)-filters-containing chromatoscope was specially designed for that purpose. Subsequently a whole body T1 weighted MR (gradient echo sequence) was performed for anatomical orientation. The SUV of 18F-FDG was determined at 27.5, 32.5, 37.5 and 42.5 min p.i. in the whole cortex and in the left and right visual cortex. Data were analyzed with MANOVA and t-test.
RESULTS: Male mice have significantly higher SUV than female mice in the cortical area, right and left visual cortex in dark baseline condition and during stimulation with white, blue and yellow lights through the right eye but not left (Table). In male mice, the change in SUV was responsive to Blue/Yellow pairs, while in female mice, the response was only to Blue. In male mice, the SUV was highest during Blue stimulation in the left visual cortex through the right eye compared to right visual cortex. Similarly, the SUV was highest during Yellow stimulation in the left visual cortex through the right eye compared to the right visual cortex. Conversely, in female mice, the SUV was highest during Blue stimulation in the right visual cortex through the left eye compared to left visual cortex (Figure). In female mice, there was no change during stimulation with Yellow.
CONCLUSION: The observation in mice is opposite to that in humans where right hemisphere cognitive style for Blue/Yellow opponency was found in men, but a left hemisphere style in women. It is postulated, that the ontogenetic and phylogenetic evolutionary trends for cerebral dominance for color underwent a change during mammalian evolution to humans, perhaps related to left hemisphere dominance for language in most subjects.

  • Poster
    Annual Meeting of the Society of Nuclear Medicine, 10.-15.06.2016, San Diego, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)2, 141P

Publ.-Id: 23537

Preclinical PET/MR: Defining novel roles for phosphodiesterase 10A in brain and brown adipose tissue (BAT) in the regulation of energy homeostasis

Kranz, M.; Hankir, M. K.; Wagner, S.; Deuther-Conrad, W.; Teodoro, R.; Fenske, W. K.; Brust, P.

OBJECTIVES: Phosphodiesterase type 10A (PDE10A) is highly enriched in the striatum and a potential therapeutic target for brain diseases. It is suggested that PDE10A is also involved in the regulation of food intake. By using the novel selective radioligand 18F-AQ28A [1] we evaluated expression of PDE10A in brain and BAT of lean, diet-induced (DIO) and genetically obese mice. As BAT activation could be visualized by using small animal PET/MR using 18F-FDG [2], we also assessed whether inhibition of PDE10A modulates BAT activity.
METHODS: Female CD1 and C57BL/6 mice were studied with either 18F-AQ28A or 18F-FDG. After anesthesia (1.8% isoflurane in 60%O2/40% air) and i.v injection of the tracer, a 1 h PET/MR scan was done for all groups. After image coregistration volumes of interest were created for striatum, hypothalamus, interscapular BAT and skeletal muscle. The selectivity of 18F-AQ28A towards PDE10A was proven by baseline (n=3) and blocking (n=3) experiments with the PDE10A inhibitor MP-10. DIO in CD1 mice was achieved by 16 weeks free access to a high-fat, high-sugar diet. Leptin-deficient ob/ob C57BL/6 mice (n=5) were used as a genetic model of obesity. The first set of CD1 mice (n=10) was divided into lean (n=5) and DIO (n=5) and received 18F-AQ28A. A second group (n=10) of lean CD1 mice were fasted and housed overnight under thermoneutral conditions and received either i.p. injection of MP-10 (n=5) or vehicle (n=5) followed 30 min later by i.v. injection of FDG. After a recovery period, the second group received either an i.p. injection of MP-10 (n=5) or vehicle (n=5) and 2 h later were sacrificed and BAT, hypothalamus and striatum were collected. Relative mRNA expression of PDE10A and thermoregulatory genes in BAT and neuropeptides in striatum and hypothalamus as well as the indirect neuronal activity marker Fos were analyzed by real-time quantitative PCR.
RESULTS: Blocking with MP-10 showed selectivity of 18F-AQ28A towards PDE10A (SUV15min striatum blocking/baseline: 0.54±0.08/1.02±0.19; p<0.01). A 7-fold higher mRNA expression of PDE10A in striatum compared to hypothalamus was found (p<0.001). In lean mice, 18F-AQ28A showed selective symmetrical accumulation in BAT (SUV55min: 0.44±0.04) with low uptake in the adjacent skeletal muscle (SUV55min: 0.20±0.02; p<0.01). Higher PDE10A levels (p<0.05) in striatum and BAT were found for DIO (SUV15min:1.36±0.10 / SUV55min:0.82±0.08) and for ob/ob mice (SUV15min:1.91±0.08 / SUV55min:0.77±0.04) compared to normal weight mice. Acute administration of MP-10 to lean mice resulted in significantly higher FDG uptake by BAT (SUV55min: 0.40±0.01) compared to vehicle administration (SUV55min: 0.25±0.02; p<0.01) and an increase in Pgc1alpha (2-fold), Ucp1 (1.6-fold) and Cidea (1.6-fold) mRNA expression (p<0.01, p<0.05 and p<0.05, respectively) was found. In striatum, acute administration of MP-10 increased expression of Fos (4-fold) and preproenkephalin (2.9-fold) (p<0.0001 and p<0.05 respectively) whereas in hypothalamus there were no changes in gene expression found.
CONCLUSION: A novel thermoregulatory role for PDE10A was demonstrated and related to obesity. PDE10A selectively regulates gene expression in striatum. The data suggest that PDE10A inhibitors offer the potential to treat obesity by increasing thermogenesis and reducing hedonic feeding through recruiting BAT and striatal circuits.

  • Lecture (Conference)
    Annual Meeting of the Society of Nuclear Medicine 2016, 11.-15.06.2016, San Diego, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)2, 200P

Publ.-Id: 23536

Varying Chirality Across Nicotinic Acetylcholine Receptor Subtypes: Selective Binding of Quinuclidine Triazole Compounds

Sarasamkan, J.; Scheunemann, M.; Apaijai, N.; Palee, S.; Parichatikanond, W.; Arunrungvichian, K.; Fischer, S.; Chattipakorn, S.; Deuther-Conrad, W.; Schüürmann, G.; Brust, P.; Vajragupta, O.

The novel quinuclidine anti-1,2,3-triazole derivatives T1-T6 were designed based on the structure of QND8. The binding studies revealed that the stereochemistry at the C3 position of the quinuclidine scaffold plays an important role in the nAChR subtype selectivity. Whereas the (R)-enantiomers are selective to α7 over α4β2 (by factors of 44-225) and to a smaller degree over α3β4 (3-33), their (S)-counterparts prefer α3β4 over α4β2 (62-237) as well as over α7 (5-294). The (R)-derivatives were highly selective to α7 over α3β4 subtypes compared to (RS)- and (R)-QND8. The (S)-enantiomers are 5−10 times more selective to α4β2 than their (R) forms. The overall strongest affinity is observed for the (S)-enantiomer binding to α3β4 (Ki, 2.25-19.5 nM) followed by their (R)-counterpart binding to α7 (Ki, 22.5-117 nM), with a significantly weaker (S)-enantiomer binding to α4β2 (Ki, 414-1980 nM) still above the very weak respective (R)-analogue affinity (Ki, 5059-10436 nM).

Keywords: Nicotinic acetylcholine receptor; positron emission tomography; quinuclidine anti-1; 2; 3-triazole; click chemistry

Publ.-Id: 23535

Prediction and compensation of magnetic beam deflection in MR-integrated proton therapy: A method optimized regarding accuracy, versatility and speed

Schellhammer, S. M.; Hoffmann, A. L.

The integration of magnetic resonance imaging (MRI) and proton therapy for on-line image-guidance is expected to reduce dose delivery uncertainties during treatment. However, the proton beam experiences a Lorentz force induced deflection inside the magnetic field of the MRI scanner, and several methods have been proposed to quantify this effect. We analyze their structural differences and compare results of both analytical and Monte Carlo models. We find that existing analytical models are limited in accuracy and applicability due to critical approximations, especially including the assumption of a uniform magnetic field. As Monte Carlo simulations are too time-consuming for routine treatment planning optimization and on-line plan adaption, we introduce a new method to quantify and correct for the beam deflection, which is optimized regarding accuracy, versatility and speed. We use it to predict the trajectory of a mono-energetic proton beam of energy E 0 traversing a water phantom behind an air gap within an omnipresent uniform transverse magnetic flux density B 0. The magnetic field induced dislocation of the Bragg peak is calculated as function of E 0 and B 0 and compared to results obtained with existing analytical and Monte Carlo methods. The deviation from the Bragg peak position predicted by Monte Carlo simulations is smaller for the new model than for the analytical models by up to 2 cm. The model is faster than Monte Carlo methods, less assumptive than the analytical models and applicable to realistic magnetic fields. To compensate for the Bragg peak dislocation, a numerical optimization strategy is introduced and evaluated. It includes an adjustment of both the proton beam entrance angle and the energy of up to 25° and 5 MeV, depending on E 0 and B 0. This strategy is shown to effectively reposition the BP to its intended location in the presence of a magnetic field.

Keywords: proton therapy; image-guided radiotherapy; IGPT; magnetic resonance imaging; MR guidance; beam trajectory prediction


Publ.-Id: 23534

The strange implications of electron-electron scattering in graphene

Helm, M.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Winnerl, S.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.

Electron-electron scattering in graphene gives rise to some unexpected behavior in the electron dynamics, as observed by pump-probe measurements.
When excited with a near-infrared femtosecond laser pulse, the pump-probe signal depends on the angle between the linear polarization of the pump and the probe pulse, which is due to preferential excitation of electrons perpendicular to the laser electric field. This indicates an anisotropic distribution function in momentum space that is preserved by electron-electron scattering, since it mainly occurs collinearly along the Dirac cone. Only after 150 fs the distribution function is rendered isotropic through optical-phonon scattering. The effect is even more pronounced when exciting at small photon energies (88 meV), below the optical-phonon energy: In this case the anisotropic distribution function survives for as long as 5 ps, when it is finally thermalized by non-collinear Coulomb scattering. These results challenge the common view of ultrafast thermalization by electron-electron scattering.
When a magnetic field is applied to graphene, Landau levels are formed that can be selectively excited by circular-polarized radiation. In a pump-probe experiment, exciting and probing all possible transitions between the n=-1, n=0 and n=+1 Landau levels in slightly n-type graphene, we observe an unexpected sign reversal of the n=0 →1 probe signal when pumping the -1→0 transition. This directly reflects the fact that the n=0 Landau level is depleted by electron-electron Auger-type scattering, even though it is optically pumped at the same time.
Both effects can be quantitatively reproduced by a microscopic calculation based on the graphene Bloch equations, and shed new light on the possibility of infrared and THz devices based on hot carriers in graphene.

Keywords: graphene; pump-probe; free-electron laser; Landau levels

  • Invited lecture (Conferences)
    International Conference on Terahertz Emission, Metamaterials and Nanophotonics (TERAMETANANO 2016), 03.-10.04.2016, Cartagena, Colombia

Publ.-Id: 23533

Prompt γ-ray based proton range verification: From experiments to clinical application

Priegnitz, M.; Nenoff, L.; Barczyk, S.; Golnik, C.; Hotoiu, L.; Keitz, I.; Smeets, J.; Trezza, A.; Vander Stappen, F.; Werner, T.; Fiedler, F.; Prieels, D.; Baumann, M.; Enghardt, W.; Pausch, G.; Richter, C.

no abstract available

  • Poster
    National Center for Radiation Oncology 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland

Publ.-Id: 23531

Comparison of in silico, electrochemical, in vitro and in vivo metabolism of a homologous series of (radio)fluorinated sigma1 receptor ligands designed for positron emission tomography

Wiese, C.; Große Maestrup, E.; Galla, F.; Schepmann, D.; Hiller, A.; Fischer, S.; Ludwig, F. A.; Deuther-Conrad, W.; Donat, C. K.; Brust, P.; Büter, L.; Karst, U.; Wünsch, B.

The imaging of σ1 receptors in the brain by fluorinated radiotracers will be used for the validation of σ1 receptors as drug targets as well as for differential diagnosis of diseases in the central nervous system. The biotransformation of four homologous fluorinated PET tracers 1′-benzyl-3-(ω-fluoromethyl to ω-fluorobutyl)-3H-spiro[2]benzofuran-1,4′-piperidine] ([18F]1–4) was investigated. In silico studies using fast metabolizer (FAME) software, electrochemical oxidations, in vitro studies with rat liver microsomes, and in vivo metabolism studies after application of the PET tracers [18F]1–4 to mice were performed. Combined liquid chromatography and mass spectrometry (HPLC–MS) analysis allowed structural identification of non-radioactive metabolites. Radio-HPLC and radio-TLC provided information about the presence of unchanged parent radiotracers and their radiometabolites. Radiometabolites were not found in the brain after application of [18F]2–4, but liver, plasma, and urine samples contained several radiometabolites. Less than 2 % of the injected dose of [18F]4 reached the brain, rendering [18F]4 less appropriate as a PET tracer than [18F]2 and [18F]3. Compounds [18F]2 and [18F]3 possess the most promising properties for imaging of σ1 receptors in the brain. High σ1 affinity (Ki=0.59 nm), low lipophilicity (logD7.4=2.57), high brain penetration (4.6 % of injected dose after 30 min), and the absence of radiometabolites in the brain favor the fluoroethyl derivative [18F]2 slightly over the fluoropropyl derivative [18F]3 for human use.

Keywords: Homologous fluorinated sigma1 receptor ligands; positron emission tomography; biotransformation; electrochemical oxidation; rat liver microsomes; in vivo metabolism

Publ.-Id: 23530

Beta-Amyloid-PET-Bildgebung des Gehirns - DGN-Handlungsempfehlung

Barthel, H.; Meyer, P. T.; Drzezga, A.; Bartenstein, P.; Boecker, H.; Brust, P.; Buchert, R.; Coenen, H. H.; Fougère, C. L.; Gründer, G.; Grünwald, F.; Krause, B. J.; Kuwert, T.; Schreckenberger, M.; Tatsch, K.; Langen, K. J.; Sabri, O.

Seit Kurzem sind mehrere Radiopharmaka für die klinische Positronen-Emissions-Tomographie (PET) von mit der Alzheimer-Krankheit assoziierten zerebralen beta-Amyloid(Aß-Plaques zugelassen. Mit der zunehmenden Verbreitung dieser Methode entsteht der Bedarf für entsprechende Handlungsanweisungen. Diese S1-Leitlinie der Deutschen Gesellschaft für Nuklearmedizin beschreibt die adäquate Vorgehensweise bei der Aß-Plaque-PET-Bildgebung. Maßnahmen zur Patientenvorbereitung, zur Anamnese-Erhebung und zu Vorsichtsmaßnahmen werden ebenso vorgestellt wie die betreffenden Radiopharmaka, Maßnahmen zur PET-Daten-Gewinnung, -Verarbeitung, -Analyse und -Befundung. Damit soll ein Beitrag zur Qualitätssicherung in der Nuklearmedizin in Deutschland geleistet werden.

Keywords: beta-Amyloid; Plaques; Positronen-Emissions-Tomographie; PET; Leitlinie

Publ.-Id: 23529

Rational Structure-Based Rescaffolding Approach to de Novo Design of Interleukin 10 (IL-10) Receptor-1 Mimetics

Ruiz-Gómez, G.; Hawkins, J. C.; Philipp, J.; Künze, G.; Wodtke, R.; Löser, R.; Fahmy, K.; Pisabarro, M. T.

Tackling protein interfaces with small molecules capable of modulating protein-protein interactions remains a challenge in structure-based ligand design. Particularly arduous are cases in which the epitopes involved in molecular recognition have a non-structured and discontinuous nature. Here, the basic strategy of translating continuous binding epitopes into mimetic scaffolds cannot be applied, and other innovative approaches are therefore required. We present a structure-based rational approach involving the use of a novel customized PROSITE-based regular expression syntax to define minimal descriptors of geometric and functional constraints signifying relevant unctionalities for recognition in protein interfaces of non-continuous and unstructured nature. These descriptors feed a search engine that explores the currently available three-dimensional chemical space of the Protein Data Bank (PDB) in order to identify in a straightforward manner regular architectures containing the desired functionalities, which could be used as templates to guide the rational design of small natural-like scaffolds mimicking the targeted recognition site. The application of this rescaffolding strategy to the discovery of natural scaffolds incorporating a selection of functionalities of interleukin-10 receptor-1 (IL-10R1), which are relevant for its interaction with nterleukin-10 (IL-10) has resulted in the de novo design of a new class of potent IL-10 peptidomimetic ligands.

Keywords: de novo design; peptidomimetics; IL-10 receptor mimetic; 3D functional descriptors; proteinprotein interactions

Publ.-Id: 23528

Liquid velocity determination using thermal anemometry in two-phase flows: new developments

Neumann, M.; Bieberle, A.; Hampel, U.

This article is intended to give an overview of novel approaches to apply thermal anemometry measuring technique for the determination of gas and liquid velocities in two-phase flows, which are currently being pursued at Helmholtz-Zentrum Dresden-Rossendorf. Thermal anemometers are commonly used for determination of local fluid velocities within single phase flows. Because of their high temporal resolution they are also capable of determining velocity fluctuations, as they are common in highly turbulent flows in technical applications and devices. These experimental data are, amongst others, required for validation and development of CFD codes. However, since turbulent two-phase flows (e.g. bubbly flows) are predominant in technical applications, the application of thermal anemometers is highly desired there as well. But, interpretation of those measurement signals is rather complex, since they contain information of both phases, e.g. liquid and gas respectively. To overcome these difficulties, application-oriented adoptions of this measurement technique have to be made. The here presented approaches comprise sophisticated design modifications of the probe itself as well as a novel operation mode. It is intended to utilize such a probe especially for the velocity measurement of the liquid phase in two-phase flows within complex geometries at high temporal resolution.

Keywords: Thermal anemometry; two-phase flow

  • Contribution to proceedings
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH) 2016, 15.-17.06.2016, Livorno, Italia
    Liquid velocity determination using thermal anemometry in two-phase flows: new developments, Pisa, Italy: Grafiche Caroti, 978-88-902391-9-9, 3-73
  • Lecture (Conference)
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH) 2016, 15.-17.06.2016, Livorno, Italia

Publ.-Id: 23527

Production and purification of no-carrier-added 139Ce at the Leipzig cyclotron CYCLONE® 18/9

Mansel, A.; Franke, K.

The global demand for the lanthanides has dramatically increased. Therefore, a detailed understanding of ore chemistry and separation methods is needed. To study these processes, the use of the radiotracer technique is a marvellous method to observe the chemical behaviour of such elements. 139Ce (T1/2 = 137.6 d, Eγ = 166 keV, Iγ = 80%) was chosen as a representative element (radionuclide) for the lanthanide elements. We produced 139Ce using the nuclear reaction 139La(p,n)139Ce by means of irradiation of a few tens mg [natLa]La2O3 at the Leipzig cyclotron CYCLONE® 18/9[1]. At an irradiation time of 3 h, an effective proton current of 2.9 µA and a maximal proton energy of 12.5 MeV, an activity of ~0.5 MBq 139Ce was achieved. The irradiated La2O3 was dissolved in conc. nitric acid and fumed to dryness. For the separation of the radionuclide from the target material, we used the tetravalent oxidation state of cerium by means of an oxidative application with a mixture of dichromate/sulfate in 9 M nitric acid. For the first time, UTEVA® Resin was used to separate the tetravalent cerium (Ce4+) in no-carrier-added (n.c.a.) form from the trivalent lanthanum (La3+) by ion exchange chromatography in column technique, as used for plutonium (Pu4+) separations from trivalent actinides (e.g. Am3+)[2]. The 139Ce4+ ions were washed from the column by 1 mM nitric acid. After evaporation of the combined cerium fractions, the 139Ce was dissolved in 1 mM nitric acid to give a stock solution with an activity concentration of ~1 MBq/ml. The radiochemical yield of n.c.a. 139Ce was 94% ± 5%. With a detection limit of 10 Bq/ml, a concentration range down to ~0.3 pmol/l n.c.a. 139Ce can be achieved. From the dissolution of the irradiated target until preparation of the stock solution, only 5 h are necessary. The chemical purity of the stock solution was evaluated by ICP-MS.
By a weekly in-house production of n.c.a. 139Ce, we can use this radionuclide in our institute (or cooperation partners) for actual studies in liquid-liquid extraction by means of calixarenes or radiolabelling of CeO2-nanoparticles.
[1] C. Vermeulen et al. (2007) Nucl. Instr. Meth. B 255, 331. [2] E. P. Horwitz et al. (1992) Anal. Chim. Acta 266, 25.

Keywords: Lanthanides; No-carrier-added Cerium-139; Proton induced nuclear reaction; Radiochemical separation; UTEVA® Resin

  • Poster
    9th International Conference on Nuclear and Radiochemistry NRC9, 29.08.-02.09.2016, Helsinki, Finland

Publ.-Id: 23526

Two-Phase Flow Studies in Complex Geometries

Neumann, M.; Bieberle, A.; Hampel, U.

In many industrial applications, two-phase flows are predominant and consist often of a liquid and a gaseous phase. Especially in nuclear power plants, those multiphase flow regimes are heavily linked to safety related issues, e.g. behavior of vapor phase in BWRs, nucleate boiling at fuel rods or steam generator tubes as well as loss of coolant accident. One approach for the safety evaluation of nuclear facilities and the prediction of hazardous conditions is the utilization of numerical models and CFD tools. Unfortunately, these methods still need a high number of empirical correlations as closure models up to now, which makes a safe prediction nearly impossible.
Additionally, most of the components in industrial applications provide complex geometries, which create pronounced three-dimensional flow phenomena, e.g. in bends, valves, junctions or heat exchangers. Especially the numerical description of those two-phase flow fields is a challenging task, which requires further experimental data for the development and validation of existing models. At the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) studies in a vertical pipe have already been performed [1]–[3]. In these studies, a movable obstacle was used to create three-dimensional flow phenomena, which was analyzed applying wire-mesh sensor technique. Both, the motion unit of the obstacle and the wire-mesh sensor were thereby located in the flow channel, disturbing the flow field. Furthermore, the wire-mesh sensor only provided single-plane measurements.
In this contribution, continued two-phase flow studies will be described using the ultrafast electron beam X-ray scanner ROFEX to additionally measure hydrodynamic parameters of the flow field around new designed obstacles contactless.

  • Contribution to proceedings
    47th Annular Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
  • Lecture (Conference)
    47th Annular Meeting on Nuclear Technology, 12.05.2016, Hamburg, Deutschland

Publ.-Id: 23525

A pilot study to use the 36Cl bomb peak as a tracer for groundwater flow velocities in the Western Dead Sea catchment

Wilske, C.; Suckow, A.; Roediger, T.; Geyer, S.; Weise, S. M.; Merchel, S.; Rugel, G.; Pavetich, S.; Merkel, B. J.; Siebert, C.

The aquifer system of the western Dead Sea catchment is stressed by semi-arid to arid climate conditions, limited groundwater recharge rates and increasing water abstractions for human water needs. The groundwater flow system is dominated by two main Cretaceous limestone aquifers with karst characteristics and discharging in springs in the Lower Jordan Valley and Dead Sea region. The karst properties give reason to assume parts of the flow system having high transmissivities and groundwater flow velocities, respectively. For estimating recharge rates and rain water infiltration time periods, 36Cl and 3H were used, with the anthropogenic bomb peaks as input functions.
The chloride content in groundwater of the limestone aquifers enriches after contact with the saline Quaternary sediments and groundwater in the Lower Jordan Valley. The 36Cl/Cl ratios in groundwater were found to be up to 1E-12 in the recharge area and decrease to 1E-14 in the discharge area. Groundwaters in the recharge area show partly 36Cl/Cl ratios comparable to those in recent precipitation. The wide range of 36Cl/Cl in the recharge area indicates different stages of chlorine isotope and elemental mixing within the recharge area or aquifer system. This may be due to varying Cl input (dependent on altitude and coastal proximity), varying 36Cl input (regional variation in fallout) or both. Together with 3H analyses it is possible to evaluate the recent rain water component in the springs emerging from the uppermost part of the Cretaceous aquifers.
Our results show that a combination of the 36Cl/Cl and 3H measurements in groundwater and a correlation to the atmospheric input curves of 36Cl/Cl and 3H allow estimating the admixture of post-bomb recharge in groundwater.

Keywords: 36Cl/Cl; tritium; groundwater age dating; Western Dead Sea catchment; AMS

  • Lecture (Conference)
    43rd IAH International Congress “Groundwater and society: 60 years of IAH”, 25.-29.09.2016, le Corum , Montpellier, France


Publ.-Id: 23523

Bestimmung langlebiger Radionuklide mittels Beschleunigermassenspektrometrie (AMS): Applikationen und metrologische Aspekte

Merchel, S.

Die Bestimmung langlebiger Radionuklide (t1/2 = ~ka bis Ma) profitierte maßgeblich in den letzten Jahrzehnten von den technischen Entwicklungen auf dem Gebiet der hochsensitiven Beschleunigermassenspektrometrie (accelerator mass spectrometry, AMS). Die AMS besitzt gegenüber der konventionellen Massenspektrometrie den Vorteil, dass sie Störsignale, hervorgerufen von Molekülionen oder Isobaren, effektiver unterdrücken kann. Typische Nachweisgrenzen liegen im Bereich von 10-15 (Radionuklid/stabiles Nuklid) bzw. 105 Radionuklidatome oder 10-9 Bq.
Die Anwendungsfelder der Methode haben sich stark ausgeweitet: Die anfänglich bevorzugt untersuchten Proben aus der Kosmochemie, der Astrophysik und den Kernreaktionsdaten, werden zunehmend von Proben aus den Bereichen Strahlenschutz, Nuklearsicherheit, Nuklearentsorgung, Radioökologie, Phytologie, Ernährungswissenschaften, Toxikologie und Pharmakologie verdrängt. Die größte Bedeutung der angewandten AMS-Forschung liegt allerdings in den Geo- und Umweltwissenschaften. So können mit den kosmogen „in-situ“ produzierten Nukliden 10Be, 26Al und 36Cl relativ plötzlich auftretende prähistorische Ereignisse wie Vulkanausbrüche, Bergstürze, Tsunamis, Meteoriteneinschläge, Erdbeben und Gletscherbewegungen datiert werden. Anhand dieser Gletscherbewegungen und Untersuchungen an Eisbohrkernen können zudem Klimaveränderungen rekonstruiert werden.
Die Qualitätssicherung in der AMS (mit Ausnahme von 14C/12C) ist ein wichtiger, aber bisher leider vernachlässigter Aspekt. Wenige Ringversuche mit desaströsen Ergebnissen und das fast komplette Fehlen primärer Referenzmaterialien (mit Ausnahme von 41Ca/Ca) zeigen, dass die AMS zwar extrem nachweisempfindlich und oft auch präzise ist, aber momentan leider keine rückführbaren Daten liefert. Der Einsatz metrologisch rückgeführter Referenzmaterialien wäre allerdings für fast alle AMS-Applikationen wünschenswert und für wenige zwingend erforderlich.

Keywords: AMS; metrology; standard; reference material; radionuclide

  • Invited lecture (Conferences)
    Abteilungskolloquium der Abteilung 6 „Ionisierende Strahlung“ der Physikalisch-Technischen Bundesanstalt, 31.05.2016, Braunschweig, Deutschland

Publ.-Id: 23522

Novel Biotechnological Approaches for the Recovery of Metals from Primary and Secondary Resources

Pollmann, K.; Kutschke, S.; Matys, M.; Kostudis, S.; Hopfe, S.; Raff, J.

Microorganisms have developed various mechanisms to deal with metals, thus providing numerous tools that can be used in biohydrometallurgical processes. “Biomining” processes, that includes bioleaching and biooxidation processes, facilitate the degradation of minerals accompanied by a release of metals. These processes are especially attractive for low-grade ores and are used on industrial scale mainly for sulfidic ores. In biosorption processes, biomass or certain biomolecules are used to bind and concentrate selected ions or other molecules from aqueous solutions. Biosorptive materials can be an environmentally friendly and efficient alternative to conventional methods such as ion exchange resins. Other interesting mechanisms are bioaccumulation, bioflotation, bioprecipitation, and biomineralisation. Although these processes are well known and have been studied in detail during the last decades, the recent strong progress of biotechnologies such as genetic enginnering and molecule design as well as their combination with novel developments of material sciences such as nanotechnologies facilitate new strategies for the application of biotechnologies in mineral processing. The article gives a summary of current activities in this field that are performed in our group.

Keywords: biomining; biohydrometallurgy; bioleaching; biosorption; nanomaterials

Publ.-Id: 23521

Role of Transient Reflection in Graphene Nonlinear Infrared Optics

Suess, R. J.; Winnerl, S.; Schneider, H.; Helm, M.; Berger, C.; de Heer, W. A.; Murphy, T. E.; Mittendorff, M.

Understanding the optical response of graphene at terahertz frequencies is of critical importance for designing graphene-based devices that operate in this frequency range. Here we present a terahertz pump-probe measurement that simultaneously measures both the transmitted and reflected probe radiation from multilayer epitaxial graphene, allowing for an unambiguous determination of the pump-induced absorption change in the graphene layers. The photon energy in the experiment (30 meV) is on the order of the doping level in the graphene which enables the exploration of the transition from interband to intraband processes, depending on the amount of pump-induced heating. Our findings establish the presence of a large, photoinduced reflection that contributes to the change in sign of the relative transmitted terahertz radiation, which can be purely positive or predominantly negative depending on the pump fluence, while the change in absorption is found negative at all fluences. We develop a hot carrier model that confirms the sign-reversible nature of the relative transmitted terahertz radiation through the graphene multilayer and determine that this behavior originates from either an absorption-bleached or reflection-dominated regime. The theoretical results are incorporated into a model utilizing an energy balance equation that reproduces the measured pump-probe data. These findings, which extend to mid- and far infrared frequencies, show the importance of considering reflection in graphene-light interactions and have implications for the design of future terahertz photonic components.

Keywords: Ultrafast dynamics; graphene; infrared spectroscopy; terahertz


Publ.-Id: 23520

Surface modified ultrasmall nanoparticles as dual labelled imaging agents

Singh, G.; Licciardello, N.; Hunoldt, S.; Bergmann, R.; Faramus, A.; de Cola, L.; Stephan, H.

The development of multimodal imaging agents for biomedical applications is a growing field of research. The idea behind the use of nuclear and optical dual labelled imaging probes is the possibility to synergistically exploit the advantages of positron emission tomography (PET) and optical imaging. The use of dual imaging probes enhances sensitivity, spatial and temporal resolution, tissue penetrability and allows the simultaneous acquisition of complementary information which can improve diagnosis and treatment of diseases.
The utilization of nanomaterials in medicine holds a promising potential in emerging applications of diagnostic imaging as well as the prospect of new capabilities for delivering targeted therapies tailored for specific diseases. Due to their biocompatibility, luminescence properties and the possibility to covalently functionalize their surface, water-soluble ultrasmall (<5 nm) silicon nanoparticles (SiNPs) are excellent candidates in this perspective.(1,2)
Amine-terminated ultrasmall silicon nanoparticles were prepared according to a reported method with slight modifications.(3) Here we report the functionalization of amine-terminated SiNPs with the sulfo-cyanine 5 dye (sCy5) to obtain an optical imaging probe and with biomolecules, such as single-domain antibodies (sdAb) for active targeting of a cancer biomarker. SiNPs are also modified with radiolabel such as 64Cu, coordinated to bispidines(4), to obtain a dual, nuclear and optical, probe.
The functionalization of SiNPs with dyes, radiotracers and targeting molecules will open the path for targeted dual imaging of cancer, possibly allowing diagnosis and therapy in in vivo systems.

1) M. Rosso-Vasic et al., J. Mater. Chem. 2009, 19, 5926.
2) C. -H. Lai et al., Nano Lett. 2016, 16, 807−811.
3) Y. Zhong et al., J. Am. Chem. Soc. 2013, 135, 8350.
4) H. Stephan et al., Chem. Eur. J. 2014, 20, 17011.

Keywords: Silicon nanoparticles; Biomedical applications; Radiolabeling; Positron emission tomography; Optical imaging

  • Poster
    European Chemistry Congress, 11.-15.09.2016, Seville, Spain

Publ.-Id: 23519

Modellierung und Validierung von Feldionisation in parallelen Particle-in-Cell-Codes

Garten, M.

Die Modellierung von Feldionisation in Particle-in-Cell(PIC)-Codes ist eine wichtige Voraussetzung zur Untersuchung der Wechselwirkung hochintensiver, ultrakurzer Laserpulse mit Materie. Es existieren bereits zahlreiche Modelle, die akkurate Vorhersagen im Bereich nicht-relativistischer Intensitäten und oberhalb atomarer Zeitskalen treffen können. Weiterhin existieren auch zahlreiche PIC-Codes, die für den Einsatz auf CPUs konzipiert wurden und Feldionisation berücksichtigen. Das Ziel dieser Arbeit ist die Modellierung von Feldionisation auf neuen, hochparallelen GPU-Architekturen. Diese werden in den letzten Jahren verstärkt für wissenschaftliche Simulationen eingesetzt und bieten einen deutlichen Geschwindigkeitsvorteil gegenüber CPUs. Die Modellierung von Feldionisation auf GPGPUs birgt einige Herausforderungen und es ist das erweiterte Ziel dieser Arbeit, die Implementierung auch zu verifizieren. Dabei wird ein Einblick in die Schwierigkeiten gegeben, die bei der Anwendung existierender Ionisationsmodelle durch Einschränkungen der Modelle selbst, des PIC-Schemas sowie der Plasmadynamik zu beachten sind. In Folge dieser Arbeit wurde PIConGPU, der derzeit schnellste, vollständig relativistische Particle-in-Cell-Code der Welt, um ein allgemeines Werkzeug zur Modellierung von Ionisation erweitert. Dieses ermöglicht die Simulation neuer und spannender physikalischer Anwendungsfälle im Bereich der Laser-Plasmaphysik.

Keywords: Particle-In-Cell; field ionization; GPGPU; PIConGPU; ADK; BSI

  • Master thesis
    HZDR, TU Dresden, 2015
    Mentor: Prof. Dr. Thomas Cowan, Prof. Dr. Ulrich Schramm, Dr. Michael Bussmann
    0097 Seiten

Publ.-Id: 23518

Instrumentation for experiments on a fuel element mock-up for the study of thermal hydraulics for loss of cooling or coolant scenarios in spent fuel pools

Arlit, M.; Partmann, C.; Schleicher, E.; Schuster, C.; Hurtado, A.; Hampel, U.

After the Fukushima accident the focus in nuclear safety research has been extended to the spent fuel pool. In the consequence of a longer persisting station black out or loss of integrity of the pool, the cooling of the fuel elements can potentially not be guaranteed. Thus, the investigation of the thermal hydraulics of potential accident scenarios is of great scientific interest. The German national joint project SINABEL (SIcherheit NAsslager BrennElement-Lagerbecken) deals with the experimental investigation and the modelling of thermal hydraulics during the dry-out of a spent fuel pool in the consequence of a loss of cooling scenario. For this purpose a fuel element mock-up with electrically heated rods is constructed. During a dry-out scenario the water in the fuel element mock-up heats up to boiling temperature and evaporates. The water level decreases due to the continuing heating and the rods will be exposed to steam atmosphere. Parameters that have to be measured are the surface temperature of the rods, the height of the water level and the temperature as well as the velocity of the steam in the subchannels of the rod bundle.
The fuel element mock-up is designed according to the original dimensions of a BWR fuel element with pitch-to-diameter ratio- P/D = 1.24 and rod diameter D = 10 mm in a 10 x 10 square array. The housing consists of several metal boxes. To avoid heat sinks (adiabatic situation with no radial heat flow) the components are produced without flanges and are surrounded by a compact thermal insulation. The accessibility for instrumentation and other installations is reduced to the top side. The surface temperatures of the rods are measured by thermocouples and the water level by pressure transducers and electrical needle probes respectively.
For measuring both the temperature and the velocity of the steam in the small sub-channels no standard instrumentation is available. The applicability of established measurement techniques, such as Particle Imaging Velocimetry or Pitot tube, is not given due to constructional aspects of the test facility and the given flow properties (high temperatures, low velocities). Therefore, in this study a newly developed measurement system will be used. The experimental operating conditions are temperatures up to ϑ = 500 °C and very low local steam velocities down to v = 0.01 m/ s. Furthermore, the flow is expected to be laminar. The requirement for spatial resolution is to have one measurement point per subchannel in all subchannels of one rod bundle quadrant.
The presented solution is a thermal anemometry grid sensor TAGS, that is grid-type arrangement of special temperature-sensor elements measuring both, the temperature and the velocity nearly simultaneously. The sensitive elements are mounted on a ceramic grid-like structured substrate and connected to each other in a matrix arrangement. This sensor is connected to a special excitation and data acquisition electronics, applying the measurement technique of resistance thermometry for temperature measurement and thermal anemometry for velocity measurement. Within the paper a detailed description of the instrumentation of the fuel element mock-up in general and more specifically the TAGS are presented together with first results.

Keywords: Spent fuel pool; temperature measurement; thermal anemometry; grid sensor

  • Contribution to proceedings
    SWINTH-2016 (Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH-2016
  • Lecture (Conference)
    SWINTH-2016 (Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics), 15.-17.06.2016, Livorno, Italia

Publ.-Id: 23517

Thermal anemometry grid sensor for flow velocity measurement in the subchannels of a fuel element mock-up during dry-out

Arlit, M.; Schleicher, E.; Hampel, U.

For the determination of steam velocities in the subchannels of a fuel element mock-up during dry-out no suitable measurement techniques are available under the given boundary conditions of high temperatures and restricted accessibility. The newly developed thermal anemometry grid sensor closes this gap. Within the paper applied methods, technological aspects as well as a special calibration procedure for the measurement in superheated steam are presented.

Keywords: Thermal Anemometry; Grid Sensor; Temperature grid sensor

  • Contribution to proceedings
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
    Proceedings of the 47th Annual Meeting on Nuclear Technology
  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland

Publ.-Id: 23516

Investigation of the Radial Effect On the Transition Velocities in a Bubble Column Based On the Modified Shannon Entropy

Nedeltchev, S.; Hampel, U.; Schubert, M.

A new method for flow regime identification in a bubble column (0.15 m in ID) based on a modification of the Shannon entropy (SE) algorithm was developed. The bubble column was equipped with a perforated plate distributor (14 holes, Ø 4×10-3 m) and operated with an air-deionized water system at ambient conditions. The newly introduced dimensionless ratio of minimum SE to maximum SE was capable of identifying the main transition velocities at three different dimensionless radial positions (r/R): 0.0 (core), 0.63 (inversion point) and 0.88 (annulus).
In the core of the column the new parameter identified successfully three transition velocities Utrans at 0.034, 0.089 and 0.134 m/s. They mark the end of the gas maldistribution regime, the onset and the end of the churn-turbulent flow regime, respectively. Three Utrans values (at 0.045, 0.089 and 0.124 m/s) were also identified in the annulus of the column. However, the second transition velocity identified the boundary between the first and second transition sub-regimes. The third transition velocity distinguished the onset of the churn-turbulent flow regime. It was found that in the core of the column both the transition and churn-turbulent flow regimes start earlier, which is due to the earlier onset of the bubble coalescence caused by higher gas fraction in the column center.
At the inversion point of the axial liquid velocity the end of the gas maldistribution regime is shifted to a somewhat higher Utrans value (0.067 m/s). The second transition sub-regime begins at 0.101 m/s, whereas the onset of the churn-turbulent regime is identified at 0.124 m/s.
The SE algorithm was also applied to both the first and second half of the time series and the ratio of both SEs was successfully used as a flow regime identifier.

Keywords: Bubble column; Gas holdup fluctuations; Wire-mesh sensor; Transition velocities; Modified Shannon entropy

Publ.-Id: 23515

Application of X-ray absorption spectroscopy to actinide research

Scheinost, A. C.

An overview will be given on the applications of x-ray absorption spectroscopy to actinide research, including topics in nuclear waste management and development of fourth generation nuclear fuel

Keywords: XAFS; Nuclear fuel; nuclear waste disposal

  • Invited lecture (Conferences)
    11th School on the Physics and Chemistry of the Actinides, 13.-16.03.2016, Grenoble, France

Publ.-Id: 23514

Distillation Tray Efficiency Modeling: A Forgotten Chapter

Vishwakarma, V.; Schubert, M.; Hampel, U.

Cross-flow trays are highly reputed among vapour-liquid contacting devices due to their versatility. They have been into existence for two centuries; still the estimation of their mass transfer efficiency relies mostly on experience. There have been numerous attempts in the past to understand the nature of liquid mixing and flow patterns on trays. However, very few have managed to relate their findings with tray efficiency.
The present work aims at reviewing mathematical models developed for predicting distillation tray efficiency. These models were developed by considering simplified assumptions namely plug flow, uniform vapour composition, constant froth height etc. It is needless to mention the requirement of an improved mathematical model accounting real flow scenarios. This work also attempts to encourage the fraternity of fluid separation technology to revive the efficacy of tray modeling.

Keywords: Distillation Trays; Murphree Tray Efficiency; Eddy Diffusion Model; Residence Time Distribution

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrenstechnik, 16.-17.03.2016, Garmisch-Partenkirchen, Germany

Publ.-Id: 23512

A gas cell for stopping, storing and polarizing radioactive particles

Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Nuñez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Willmann, L.; Wilschut, H. W.

A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The stopped particles are polarized by optical pumping. The degree of polarization that can be achieved is studied. A maximum polarization of 50% was found. The dynamic processes in the cell are described with a phenomenological model.

Keywords: β decay; Gas catcher; Polarization in buffer gas; Plasma

Publ.-Id: 23511

Controlled polar asymmetry of few-cycle and intense mid-infrared pulses

Schmidt, C.; Bühler, J.; Mayer, B.; Pashkin, A.; Leitenstorfer, A.; Seletskiy, D.

We demonstrate synthesis of ultrabroadband and phase-locked two-color transients in the multi-terahertz frequency range with amplitudes exceeding 13 MV cm−1. Subcycle polar asymmetry of the electric field is adjusted by changing the relative phase between superposed fundamental and second harmonic components. The resultant broken symmetry of the field profile is directly resolved via electro-optic sampling. Access to such waveforms provides a direct route for control of low-energy degrees of freedom in condensed matter as well as non-perturbative light–matter interactions under highest non-resonant electric bias.

Keywords: polar asymmetry; THz; harmonic synthesis; quantum control; mid-infrared; high field; non-perturbative light–matter interaction

Publ.-Id: 23510

Magnetically patterned rolled-up exchange bias tubes: A paternoster for superparamagnetic beads

Ueltzhöffer, T.; Streubel, R.; Koch, I.; Holzinger, D.; Makarov, D.; Schmidt, O. G.; Ehresmann, A.

We realized a deterministic transport system for superparamagnetic beads in a paternoster-like manner with position-dependent trajectories and velocities by rolling up exchange bias layer systems with engineered parallel stripe magnetic domains to tubular architectures possessing distinct azimuthally aligned magnetic domain patterns. By applying periodic pulse sequences of very weak external magnetic fields and taking advantage of the magnetic stray field emerging from the tubular structures, we demonstrate the transport for different superparamagnetic beads either in or above the rolled-up tubes acting as channels. This transport mechanism features high step velocities and remote control of not only the direction and trajectory but also the velocity of the transport without the need of fuel or catalytic material. Therefore, this approach paves the way towards novel 3D-applications in biotechnology, including particle transport related phenomena in lab-on-a chip and lab-in-a-tube devices.

Keywords: Rolled-up tube; exchange bias; ion bombardment induced magnetic patterning; particle transport; superparamagnetic beads; lab-in-a-tube; lab-on-a-chip

Publ.-Id: 23509

Magnetic Suspension Arrays Technology: Controlled Synthesis and Screening in Microfluidic Networks

Lin, G.; Karnaushenko, D. D.; Canon Bermudez, G. S.; Schmidt, O. G.; Makarov, D.

Information tagging and processing are vital in information-intensive applications, e.g. telecommunication and high-throughput drug screening. Magnetic suspension arrays technology may offer intrinsic advantages to screening applications by enabling high distinguishability, the ease of code generation and the feasibility of fast code readout, though the practical applicability of magnetic suspension arrays technology remains hampered by the lack of quality administration of encoded microcarriers. Here we realize a logic-controlled microfluidic system enabling controlled synthesis of magnetic suspension arrays in multiphase flow networks. The smart and compact system offers a practical solution for the quality administration and screening of encoded magnetic microcarriers and addresses the universal need of process control for synthesis in microfluidic networks, i.e. on-demand creation of droplet templates for high information capacity. The demonstration of magnetic suspension arrays technology enabled by magnetic in-flow cytometry opens the avenue toward point-of-care multiplexed bead-based assays, clinical diagnostics and drug discovery.

Keywords: suspension arrays technology; magnetic flow cytometry; magnetic sorting; droplet microfluidics; controlled synthesis

Publ.-Id: 23508

Magnetism in curved geometries

Streubel, R.; Fischer, P.; Kronast, F.; Kravchuk, V. P.; Sheka, D. D.; Gaididei, Y.; Schmidt, O. G.; Makarov, D.

Extending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, curvilinear geometry brings about two exchangedriven interactions, namely effective anisotropy and antisymmetric vector exchange, i.e. effective Dzyaloshinskii-Moriya interaction. As a consequence, the family of novel curvature-driven effects emerges, which includes magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. The broad range of altered physical properties makes these curved architectures appealing in view of fundamental research on e.g. skyrmionic systems, magnonic crystals or exotic spin configurations. In addition to these rich physics, the application potential of three-dimensionally shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications, spin-wave filters, advanced magneto-encephalography devices for diagnosis of epilepsy or for energy-efficient racetrack memory devices. These recent developments starting from the theoretical predictions to the fabrication of three-dimensionally curved magnetic thin films, hollow cylinders or wires and their characterization using integral means as well as the development of advanced tomography approaches are in the focus of this review.

Publ.-Id: 23506

Polycrystalline ZnTe thin film on silicon synthesized by pulsed laser deposition and subsequent pulsed laser melting

Xu, M.; Gao, K.; Wu, J.; Cai, H.; Yuan, Y.; Prucnal, S.; Hübner, R.; Skorupa, W.; Helm, M.; Zhou, S.

ZnTe thin films on Si substrates have been prepared by pulsed laser deposition and subsequent pulsed laser melting (PLM) treatment. The crystallization during PLM is confirmed by Raman scattering, x-ray diffraction and room temperature photoluminescence (PL) measurements. The PL results show a broad peak at 574 nm (2.16 eV), which can be assigned to the transitions from the conduction band to the acceptor level located at 0.145 eV above the valence band induced by zinc-vacancy ionization. Our work provides an applicable approach to low temperature preparation of crystalline ZnTe thin films.

Keywords: ZnTe; Pulsed laser melting


Publ.-Id: 23505

Crystalline Electric Field and Kondo Effect in SmOs4Sb12

Mombetsu, S.; Yanagisawa, T.; Hidaka, H.; Amitsuka, H.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Ho, P.-C.; Maple, M. B.

Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs4Sb12 has the Γ67 quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the Γ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic Response below ≈20 T cannot be explained using the localized 4f-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures.

Publ.-Id: 23504

Prediction of flow patterns of rotating inclined reactors using a modified permeability approach

Subramanian, K.; Winkler, M.; Härting, H. U.; Schubert, M.

A new inclined rotating tubular fixed bed reactor was recently suggested for process intensification of heterogeneous catalytic multiphase reactions. With that concept, favorable operating conditions can be adjusted operating the reactor in a wetting intermittency mode via periodic catalyst immersion in a stratified gas-liquid flow. This flow pattern adjustment, which requires a careful selection of reactor inclination and rotation, was found to eventually enhance the reaction rate.
In this work an attempt has also been made to predict the flow patterns using computational fluid dynamics. A three-dimensional model based on the relative permeability approach was developed, where gas and liquid phases flow co-currently downwards through the inclined rotating tubular fixed bed reactor. The simulation results are validated against experimental data. The model can clearly predict the four evolving pattern, i.e. stratified, sickle, annular and dispersed flow depending on the operating conditions. In particular, the effect of gas and liquid superficial velocity on liquid saturation and pressure drop for the stratified flow, the most beneficial one with regard to process intensification, was studied in detail, which revealed model predictions within the error range of 15%. It was further verified that the model is capable of correctly predicting the hydrodynamics for aqueous liquid mixtures with varying viscosity and surface tension.

Keywords: Rotating fixed bed; reactor inclination; multiphase flow pattern; computational fluid dynamics; relative permeability concept

Publ.-Id: 23503

Process intensification of gas-liquid downflow and upflow packed beds by a new low-shear rotating reactor concept

Dashliborun, A. M.; Härting, H.-U.; Schubert, M.; Larachi, F.

In the present work, a new low-shear rotating reactor concept was introduced for process intensification of heterogeneous catalytic reactions in cocurrent gas-liquid downflow and upflow packed-bed reactors. In order to properly assess potential advantages of this new reactor concept, exhaustive hydrodynamic experiments were carried out using embedded low-intrusive wire mesh sensors. The effect of rotational velocities on liquid flow patterns in the bed cross-section, liquid saturation, pressure drop, and regime transition was investigated. Furthermore, liquid residence time and Péclet number estimated by a stimulus-response technique and a macro-mixing model were presented and discussed with respect to the prevailing flow patterns. The results revealed that the column rotation induces different flow patterns in the cross-section of packed bed operating in a concurrent downflow or upflow mode. Moreover, the new reactor concept exhibits a more flexible adjustment of pressure drop, liquid saturation, liquid residence time and back-mixing at constant flow rates.

Keywords: Process intensification; low-shear rotating fixed bed; hydrodynamics; upflow and downflow; flow pattern

  • Open Access Logo AIChE Journal 63(2017)1, 283-294
    Online First (2016) DOI: 10.1002/aic.15549
  • Lecture (Conference)
    International Symposia on Chemical Reaction Engineering - ISCRE24, 12.-15.06.2016, Minneapolis, USA

Publ.-Id: 23502

Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis

Hannaske, R.

Zwischen 10 und 1000 s nach dem Urknall bildeten sich während der Big Bang Nukleosynthese (BBN) die ersten leichten Elemente aus Protonen und Neutronen. Die primordialen Häufigkeiten dieser Elemente hingen von denWirkungsquerschnitten der beteiligten Kernreaktionen ab. Vergleiche zwischen den Ergebnissen nuklearer Netzwerkrechnungen mit astronomischen Beobachtungen bieten eine einzigartige Möglichkeit, etwas über das Universum zu dieser Zeit zu erfahren.
Da es für die p(n,g)d-Reaktion, die eine Schlüsselreaktion der BBN ist, kaum Messungen im relevanten Energiebereich gibt, beruht deren Reaktionsrate in Netzwerkrechnungen auf theoretischen Berechnungen. Darin fließen auch experimentelle Daten der Nukleon-Nukleon-Streuung, des Einfangquerschnitts für thermische Neutronen sowie (nach Anwendung des Prinzips des detaillierten Gleichgewichts) der d(g,n)p-Reaktion mit ein. Diese Reaktion, die Photodissoziation des Deuterons, ist bei BBN-Energien (Tcm = 20–200 keV) ebenfalls kaum vermessen. Die großen experimentelle Unsicherheiten machen Vergleiche mit den präzisen theoretischen Berechnungen schwierig. In den letzten Jahren wurde die d(g,n)p-Reaktion und insbesondere der M1-Anteil des Wirkungsquerschnitts mit quasi-monoenergetischen g-Strahlen aus Laser-Compton-Streuung oder durch Elektrodesintegration untersucht. Üblicherweise verwendete man für Messungen des d(g,n)p-Wirkungsquerschnitts entweder die auf wenige diskrete Energien beschränkte Strahlung des g-Zerfalls oder Bremsstrahlung, für die aber eine genaue Photonenflussbestimmung sowie der Nachweis von einem der Reaktionsprodukte und dessen Energie nötig ist. Da diese Energie im Bereich der BBN relativ gering ist, gab es bisher noch keine absoluten Messung des d(g,n)p-Wirkungsquerschnitts bei Tcm < 5 MeV mit Bremsstrahlung.
Das Ziel dieser Dissertation ist eine solche Messung mit einer Unsicherheit von 5 % im für die BBN relevanten Energiebereich und darüber hinaus bis Tcm ~ 2,5 MeV unter Verwendung gepulster Bremsstrahlung an der Strahlungsquelle ELBE. Dieser supraleitende Elektronenbeschleuniger befindet sich am Helmholtz-Zentrum Dresden-Rossendorf und stellte einen Elektronenstrahl hoher Intensität bereit. Die kinetische Elektronenenergie von 5 MeV wurde mit einem Browne-Buechner-Spektrometer präzise gemessen. Die Energieverteilung der in einer Niob-Folie erzeugten Bremsstrahlungsphotonen wurde berechnet. Die Photonenflussbestimmung nutzte die Kernresonanzstreuung an 27Al, das sich mit deuteriertem Polyethylen in einem mehrschichtigen Target befand. Die 27Al-Abregungen wurden mit abgeschirmten, hochreinen Germanium-Detektoren nachgewiesen, deren Effektivität mit GEANT4 simuliert und durch Quellmessungen normiert wurde. Die Messung der Energie der Neutronen aus der d(g,n)p-Reaktion erfolgte mittels deren Flugzeit in Plastikszintillatoren, die an zwei Seiten von Photoelektronenvervielfachern mit hoher Verstärkung ausgelesen wurden. Die Nachweiseffektivität dieser Detektoren wurde in einem eigenen Experiment in den Referenz-Neutronenfeldern der PTB Braunschweig kalibriert. Die Nachweisschwelle lag bei etwa 10 keV kinetischer Neutronenenergie.Wegen der guten Zeitauflösung der Neutronendetektoren und des ELBE-Beschleunigers genügte eine Flugstrecke von nur 1 m. Die Energieauflösung betrug im d(g,n)p-Experiment 1–2 %. Leider gingen viele Neutronen bereits durch Streuung in dem großen Target verloren oder sie wurden erst durch Teile des kompakten Experimentaufbaus in die Detektoren gestreut. Beide Effekte wurden mit Hilfe von FLUKA simuliert um einen Korrekturfaktor zu bestimmen, der aber bei niedrigen Energien relativ groß war.
Der d(g,n)p-Wirkungsquerschnitts wurde daher nur im Bereich 0.7 MeV < Tcm < 2.5 MeV bestimmt. Die Ergebnisse stimmen mit anderen Messungen, Daten-Evaluierungen sowie theoretischen Rechnungen überein. Die Gesamtunsicherheit beträgt circa 6.5 % und kommt zu fast gleichen Teilen von den statistischen und systematischen Unsicherheiten. Die statistische Unsicherheit könnte durch eine längere FLUKA Simulation noch von 3–5 % auf 1 % verringert werden. Die systematische Unsicherheit von 4.5 % ist vorrangig auf die Photonenflussbestimmung, die Neutronen-Nachweiseffektivität und die Target-Zusammensetzung zurückzuführen.

Keywords: Big Bang nucleosynthesis; bremsstrahlung; gamma-ray spectroscopy; neutron time-of-flight; nuclear astrophysics; photon scattering; neutron detector; efficiency; FLUKA

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-071 2016
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 23501

Investigation of Pressure Hammer with Wire Mesh Sensor and High Speed Imaging Techniques

Traudt, T.; Bombardieri, C.; Schleicher, E.; Manfletti, C.

Previous water hammer tests have revealed pressure spikes in the cavitation area. With the aim of explaining the phenomena and enhancing the understanding of the pressure hammer phenomenon in general, a high speed imaging (HSI) setup was installed at the test bench. To complement the high speed imaging a wire mesh sensor was used. The wire mesh sensor (WMS) allowed the measurement of the cross-sectional void fracture distribution in the pipe while the flow was cavitating. The results of the measurements will be presented and discussed.

  • Contribution to proceedings
    Space Propulsion 2016, 02.-06.05.2016, Rom, Italien
    Proceedings of SP2016
  • Lecture (Conference)
    Space Propulsion Conference, 02.-06.05.2016, Rom, Italien

Publ.-Id: 23500

Single-shot betatron source size measurement from a laser-wakefield accelerator

Köhler, A.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Irman, A.; Schramm, U.

Betatron radiation emitted by accelerated electrons in laser-wakefield accelerators can be used as a diagnostic tool to investigate electron dynamics during the acceleration process. We analyse the spectral characteristics of the emitted betatron pattern utilizing a 2D x-ray imaging spectroscopy technique. Together with simultaneously recorded electron spectra and x-ray images, the betatron source size, thus the electron beam radius, can be deduced at every shot.

Keywords: Betatron radiation; Laser wakefield acceleration; x-rays

  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23499

Quantum oscillations and the Fermi surface topology of the Weyl semimetal NbP

Klotz, J.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Schmidt, M.; Nicklas, M.; Baenitz, M.; Uhlarz, M.; Wosnitza, J.; Felser, C.; Yan, B.

The Weyl semimetal NbP was found to exhibit topological Fermi arcs and exotic magnetotransport properties. Here, we report on magnetic quantum-oscillation measurements on NbP and construct the three-dimensional Fermi surface with the help of band-structure calculations. We reveal a pair of spin-orbit-split electron pockets at the Fermi energy and a similar pair of hole pockets, all of which are strongly anisotropic. The Weyl points that are located in the kz ≈ π/c plane are found to exist 5 meV above the Fermi energy. Therefore, we predict that the chiral anomaly effect can be realized in NbP by electron doping to drive the Fermi energy to the Weyl points.

Publ.-Id: 23498

Exotic Ground State and Elastic Softening under Pulsed Magnetic Fields in PrTr2Zn20 (Tr = Rh, Ir)

Ishii, I.; Goto, H.; Kamikawa, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Onimaru, T.; Matsumoto, K. T.; Takabatake, T.; Suzuki, T.

To investigate a field-induced level crossing of the ground-state doublet in PrTr2Zn20 (Tr = Rh, Ir), we performed ultrasonic measurements in pulsed magnetic fields applied along the [110] and [001] directions and analyzed the results in the framework of the strain-susceptibility approach. Above 40 T for H ∣∣ [110], we observed an elastic softening of the transverse modulus (C11 − C12)/2 corresponding to the ground-state doublet. In both compounds the softening is followed by a minimum at about 47 T at low temperatures. We predict the presence of a new field-induced phase boundary in PrTr2Zn20 at this field with two possible cases. The magnetic field of the minimum cannot be explained by only the quadrupole interaction.

Publ.-Id: 23497

Magnetic phase diagram of the helimagnetic spinel compound ZnCr2Se4 revisited by small-angle neutron scattering

Cameron, A. S.; Tymoshenko, Y. V.; Portnichenko, P. Y.; Gavilano, J.; Tsurkan, V.; Felea, V.; Loidl, A.; Zherlitsyn, S.; Wosnitza, J.; Inosov, D. S.

We performed small-angle neutron scattering (SANS) measurements on the helimagnetic spinel compound ZnCr2Se4. The ground state of this material is a multi-domain spin-spiral phase, which undergoes domain selection in a magnetic field and reportedly exhibits a transition to a proposed spin-nematic phase at higher fields. We observed a continuous change in the magnetic structure as a function of field and temperature, as well as a weak discontinuous jump in the spiral pitch across the domain-selection transition upon increasing field. From our SANS results we have established the absence of any long-range magnetic order in the high-field (spin-nematic) phase. We also found that all the observed phase transitions are surprisingly isotropic with respect to the field direction.

Publ.-Id: 23496

Kinetic Monte Carlo simulation of irradiation-induced nanostructure evolution in Oxide Dispersion Strengthened Fe alloys

Liedke, B.; Posselt, M.; Murali, D.; Claisse, A.; Olsson, P.

Rigid-lattice Kinetic Monte Carlo simulations are performed in order to investigate the modification of Y-Ti-O nanoclusters during irradiation, at selected temperatures, doses and dose rates. The simulations use input parameters for the atomic interactions and the migration barriers obtained by DFT calculations as well as data on representative examples of the cascade debris determined by Molecular Dynamics. Before irradiation the nanostructure is prepared by performing thermal relaxation of a system with randomly distributed Y, Ti, O atoms, and vacancies. The concentration of Y, Ti, and O is chosen according to the common 14 YWT ODS alloy and both low and high vacancy contents are considered. The nanostructures obtained in the preparation step were used subsequently in KMC simulations of irradiation. The results demonstrate the competition between ballistic effects leading to the dissolution and the growth of the clusters. While the former effect dominates at high doses and low temperatures the latter prevails at low doses and high temperatures. On the other hand, the nanoclusters formed in the preparation step show a very high stability under irradiation within the temperature and dose range relevant for the application of ODS alloys in advanced nuclear reactors. The findings of this work are consistent with the results of experimental studies of ion and neutron irradiation of ODS alloys.

Keywords: Oxide Dispersion Strengthened Fe-Cr alloys; Kinetic Monte-Carlo; radiation damage; nanoclusters

  • Lecture (Conference)
    3rd International Workshop on ODS Materials, 21.-22.04.2016, HZDR, Germany

Publ.-Id: 23495

Self-assembly of [2+2] Co(II) metallomacrocycles and Ni(II) metallogels with novel bis(pyridylimine) ligands

Kelly, N.; Gloe, K.; Doert, T.; Hennersdorf, F.; Heine, A.; März, J.; Schwarzenbolz, U.; Weigand, J. J.; Gloe, K.

Two novel 46-membered Co(II) metallomacrocycles, [Co2Cl4(L1)2]∙CH2Cl2 and [Co2(NO3)2(L1)2(H2O)2](NO3)2∙4H2O, with 1,4-bis[4-(2-pyridylmethylideneamino)phenyloxy]benzene (L1) have been synthesized and characterized. Both Co(II) centers in these dinuclear complexes possess an octahedral coordination environment formed by a N4 donor set of two L1 ligands and two chloride anions or one monodentate nitrate and one water molecule, respectively. Whereas in the first case disordered solvent molecules are present in the macrocycle’s cavity in the second one a nitrate anion is embedded in the macrocycle. Furthermore, the molecular structures of L1, L3 and L4 were determined and solution studies of the complex formation of these ligands with Co(II), Ni(II) and Cu(II) in dichloromethane/methanol (v/v = 1:1) using UV/Vis and ESI-MS spectroscopic measurements were performed. In contrast to the self-assembling behavior of the bis(2-pyridylimine) ligand L1 the bis(3-pyridylimine) ligand L4 was also demonstrated to form metallogels when reacted with NiCl2∙6H2O in tetrahydrofuran under defined conditions.

Keywords: Bispyridylimine ligands; Cobalt(II); Nickel(II); Metallomacrocycles; Metallogel; Self-assembly; Supramolecular chemistry

Publ.-Id: 23493

Bestimmung langlebiger Radionuklide mittels Beschleunigermassenspektrometrie (AMS) für archäometrische Fragestellungen

Merchel, S.; DREAMS-Team; DREAMS-Users

Die Radiokarbondatierung (C-14) ist insbesondere durch die hochsensitive Beschleunigermassenspektrometrie (accelerator mass spectrometry = AMS) seit Jahrzehnten ein Standardverfahren in der Archäometrie. Das Potential anderer Radionuklide wie Ca-41, Cl-36 und Be-10 mit längeren Halbwertszeiten (0.1-1.4 Ma) ist jedoch noch weitestgehend unausgeschöpft. Dies liegt u. a. an den technologischen, physikalischen und geo- und umweltwissenschaftlichen Einschränkungen und Schwierigkeiten, die zwingend berücksichtigt werden müssen, um eine akkurate Datierung zu ermöglichen.
So ist die indirekte Datierung von in Sedimenten abgelagerten Artefakten bis hin zu einigen Millionen Jahren durch die AMS-Bestimmung des in der Atmosphäre gebildeten Be-10 nur möglich, wenn der lokale Startwert des Be-10/Be-9-Verhältnisses bekannt ist.
Die direkte Altersbestimmung von Knochen über das „in-situ“ gebildete Ca-41 und Aufnahme entlang der Nahrungskette scheint aufgrund der extrem niedrigen Ca-41/Ca-Verhältnisse methodisch noch schwierig zu sein. Technologische Weiterentwicklungen auf dem Gebiet der AMS-Ionenquellen scheinen aber vielversprechend, die Methode in den nächsten Jahren zur Anwendung zu bringen.
Die Datierung von historischen Bauwerken aus kalziumhaltigen Baumaterialien (z.B. Kalkstein) mittels „in-situ“-produzierten Cl-36 ist wegen der Vorbestrahlung der Materialien vor der menschlichen Verwendung bis hin zu Tiefen von 30 m nur eingeschränkt möglich. Sie führt in der Regel zu überschätzten Altern. Gleiches gilt für Einritzungen und Zeichnungen an Oberflächengesteinen.

Keywords: archaeometry; AMS; dating; age; cosmogenic nuclide

  • Poster
    Tagung „Archäometrie und Denkmalpflege 2016“, 27.09.-01.10.2016, Göttingen, Deutschland
  • Metalla (2016)8, 30-33

Publ.-Id: 23492

Retrospective assessment of delivered proton dose in prostate cancer patients based on daily in-room CT imaging

Stützer, K.; Päßler, T.; Valentini, C.; Exner, F.; Thiele, J.; Hölscher, T.; Krause, M.; Richter, C.

Retrospective calculation of the delivered proton dose in prostate cancer patients based on a unique dataset of daily CT images.
Inter-fractional motion in prostate cancer patients treated at our proton facility is counteracted by water-filled endorectal ballon and bladder filling protocol. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double-scattered proton beams covering the respective iCTV. Stability of fiducial markers and anatomy were checked in 12 patients by daily scheduled in-room control CT (cCT) after immobilization and positioning according to bony anatomy utilizing orthogonal X-ray. In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98%>95%, D2% <107%), bladder (V75Gy <15%, V70Gy <25%, V65Gy <30%), rectum (V70Gy <10%, V50Gy <40%) and femoral heads (V50Gy <5%) are compared to those in the treatment plan. Intra-therapy variation is represented in DVH bands.
No alarming differences were observed between planned and retrospectively accumulated dose: iCTV constraints were met, except for one patient (D98%=94.6% in non-boosted iCTV). Considered bladder and femoral head values were below the limits. Rectum V70Gy was slightly exceeded (<11.3%) in two patients.
First intra-therapy variability analysis in 4 patients showed no time-dependent parameter drift, revealed strongest variability for bladder dose. In some fractions, iCTV coverage (D98%) and rectum V70Gy was missed.
Double scattered proton plans are accurately delivered to prostate cancer patients due to fractionation effects and the applied precise positioning and immobilization protocols. As a result of rare interventions after daily 3D imaging of the first 12 patients, in-room CT frequency for prostate cancer patients was reduced. The presented study supports this decision.

Keywords: in-room CT; proton therapy; prostate cancer

  • Lecture (Conference)
    AAPM 58th Annual Meeting and Exhibition, 31.07.-04.08.2016, Washington D.C., United States of America
  • Abstract in refereed journal
    Medical Physics 43(2016)6, 3455
    DOI: 10.1118/1.4956111

Publ.-Id: 23491

Retrospective analysis of daily accumulated proton dose in prostate cancer patients

Stützer, K.; Päßler, T.; Valentini, C.; Exner, F.; Thiele, J.; Agolli, L.; Hölscher, T.; Krause, M.; Richter, C.

The study presents the first series of daily in-room CT images acquired from the first 12 prostate cancer patients after proton-specific immobilization and positioning procedures and followed by actual proton radiotherapy at the University Proton Therapy Dresden. Based on this unique dataset, the actually delivered proton dose is calculated retrospectively for each fraction, analyzed for inter-fractional variability and accumulated to a total dose for comparison with the treatment plan.

Introduction: The steep dose gradients and small number of treatment fields require reproducible anatomical geometry and positioning in proton therapy to secure an accurate dose delivery. Prostate cancer is known to be subjected to inter-fractional variation due to day-to-day variation in bowel, rectum and bladder filling. Adequate positioning and treatment protocols were investigated prior the start of proton therapy to prostate cancer patients in our institute [1]. The presented study analyzes the suitability of these protocols by means of a retrospective evaluation of actually delivered proton dose in comparison to the treatment plan.

Material and Methods: Inter-fractional motion in prostate cancer patients treated at the University Proton Therapy Dresden is counteracted by water-filled endorectal ballon and bladder filling protocol. Patient positioning is based on bony anatomy match utilizing orthogonal X-Ray imaging. Stability of implanted fiducial markers and anatomy were checked in the first 12 patients by daily scheduled in-room control CT (cCT) after immobilization and positioning. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double-scattered proton beams covering the respective internal clinical target volume (iCTV). In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98% > 95%, D2% < 107%), bladder (V75Gy < 15%, V70Gy < 25%, V65Gy < 30%), rectum (V70Gy < 10%, V50Gy < 40%) and femoral heads (V50Gy < 5%) are compared to those in the treatment plan. Intra-therapy variation is represented in DVH bands.

Result: Due to CT maintenance, physician’s decision and initial workflow optimization, the median number of actually acquired cCTs within 37 fractions was 32 (range: 27-37). Seven patients received the sequential boost series prior the nominal series due to concerns that anatomy might change noticeably during six weeks of therapy and then margin concepts might be insufficient. One patient received a nominal plan of 37 fractions to an iCTV excluding seminal vesicles.
First intra-therapy variability analysis in 5 patients showed no time-dependent parameter drift and revealed strongest variability for bladder dose. In some fractions, iCTV coverage (D98%) and rectum V70Gy was missed. An illustration of the dosimetric evaluation is shown for an exemplary patient in Figure 1.
No alarming differences (cp. Table 1) were observed between planned and retrospectively accumulated dose for all 12 patients: iCTV constraints were met, except for one patient (D98% = 94.4% in non-boosted iCTV). Considered bladder and femoral head dosimetric values were below the limits. Rectum V70Gy was slightly exceeded (<11%) in two patients.

Conclusion: Double scattered proton plans are accurately delivered to prostate cancer patients due to fractionation effects and the applied precise positioning and immobilization protocols. As a result of rare interventions after daily 3D imaging of the first 12 patients, in-room CT frequency for prostate cancer patients was reduced. The presented study supports this decision.

[1] M. Schneidt et al. (2015) Prospective evaluation of patient positioning for interfractional variation in proton therapy of prostate cancer. 3rd ESTRO Forum, Barcelona

Keywords: in-room CT; prostate cancer; proton therapy; dose accumulation

  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V. 19. Jahrestagung der Deutschen Sektion der International Society for Magnetic Resonance in Medicine (ISMRM) e. V., 07.-10.09.2016, Würzburg, Deutschland

Publ.-Id: 23489

Clinical use of dual-energy CT for proton treatment planning to reduce CT-based range uncertainties

Wohlfahrt, P.; Möhler, C.; Jakobi, A.; Baumann, M.; Enghardt, W.; Krause, M.; Greilich, S.; Richter, C.

To improve CT-based particle treatment planning the additional tissue information provided by dual-energy CT (DECT) compared to single-energy CT (SECT) can be clinically used to reduce CT-based range uncertainties and to analyze intra- and interpatient tissue variations. First, a DECT scan protocol was optimized and clinically introduced. Second, in a first analysis patient DECT scans were evaluated concerning CT number variability.

Material and Methods:
After an experimental analysis of several CT scan settings concerning beam hardening, image quality and planned dose distribution using tissue surrogates, head and body phantoms and real tissues, an optimized and standardized DECT protocol (voltages: 80/140 kVp, kernel: D34) is clinically applied for patients treated with protons. 45 planning and 360 control DECT scans of overall 70 patients were acquired with a single-source DECT scanner (Siemens SOMATOM Definition AS) until October 2015. Contouring and treatment planning are performed on pseudo-monoenergetic CT scans (MonoCT) derived by a weighted sum of both CT datasets. 25 patients with different tumor sites (head, head & neck, prostate, pelvis) and overall 200 DECT scans were initially investigated to evaluate intra- and interpatient tissue variabilities. Based on the frequency distribution of voxelwise 80/140kVp CT number pairs, a linear correlation of low-density, soft and bony tissues can be determined, respectively.

A DECT-based MonoCT of 79 keV is found optimal for proton treatment planning. Assuming identical CT dose to a SECT scan, the MonoCT shows a signal-to-noise ratio increased by 8% and a CT number constancy raised by 23% on average and up to 69% for bones. Consequently, the current uncertainties of a heuristic conversion of CT numbers into stopping power ratios (SPR) using a look-up table are reduced.
Evaluation of patient variability revealed that 80/140kVp CT number pairs of human tissues are on average well described by linear correlations with a slope (± σ) of (1.023 ± 0.006) for low-density, (0.825 ± 0.008) for soft and (0.696 ± 0.006) for bony tissues. The slope variation between different patients, independent from tumor site and patient size, is comparable to the variability between different control DECT scans of one patient (σ of about 1-3%). However, a band of CT number pairs deviating from the mean linear correlation, e.g. caused by image noise and partial volume effects, reveals potential insuperable uncertainties of a voxel-based heuristic CT number-to-SPR conversion.

The clinical application of DECT-based MonoCT can contribute to a more precise range prediction. Further improvements are expected from a direct, non-heuristic SPR calculation, which is not yet clinically available. The further growing DECT patient database enables not only a detailed analysis of intra- and interpatient variations, but also a robustness analysis for different direct SPR prediction approaches.

Keywords: dual-energy CT; proton therapy

  • Lecture (Conference)
    ESTRO 35 - annual meeting, 29.04.-03.05.2016, Turin, Italy
  • Abstract in refereed journal
    Radiotherapy and Oncology 119(2016)Suppl.1, S70-S71

Publ.-Id: 23488

Non-equilibrium dynamics of magnetically anisotropic particles under oscillating fields

Steinbach, G.; Gemming, S.; Erbe, A.

In this article, we demonstrate how colloidal self-assembly and non-equilibrium dynamic processes can be enhanced by anisotropic particles. As an example, we study spherical particles with radially off-centered net magnetic moment in an oscillating field. Based on complementary data from a numerical simulation of spheres with shifted dipole and experimental observations from particles with hemispherical ferromagnetic coating, it is explained how this magnetic asymmetry gives rise to dynamic structural and orientational phenomena on a two-particle basis. We further present the behavior of ensembles of coated particles. It illustrates the potential for controlled reconfiguration based on the presented two-particle dynamics.

Keywords: Rotational dynamics; Few- and many-body systems; Colloids


Publ.-Id: 23487

Performance and Application Status of the Superconducting Photoinjector at ELBE

Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.

A new SRF gun has been commissioned at the ELBE linac. The gun has an improved 3.5-cell cavity and a superconducting solenoid is integrated. Beam parameter measurements have been carried out with a Cu photocathode.

Keywords: photoinjector; superconducting cavity; electron source; photocathode

  • Invited lecture (Conferences)
    OSA High-Brightness Sources and Light-Driven Interaction Congress, 20.-22.03.2016, Long Beach, USA

Publ.-Id: 23486

Fabrication of Sub-Micron Surface Structures on Copper, Stainless Steel and Titanium using Picosecond Laser Interference Patterning

Bieda, M.; Siebold, M.; Lasagni, A. F.

Picosecond direct laser interference patterning is investigated theoretically and experimentally for the bulk metals copper, stainless steel and titanium. In the past, results on thermal modelling for nanosecond irradiation were reported for pitches in the range of several micrometers. When nanosecond pulses are utilized, the smallest possible pitch on metals is limited by the thermal diffusion length. In this case, the laser patterning process is predominantly determined by heat conduction mechanisms, and pitches less than 1 μm are not feasible. Picosecond laser pulses allow values below 1 μm pitch size on metallic surfaces. The modelling and simulation of DLIP is based on the two-temperature-model and was carried out for a pulse duration of 35 ps at 515 nm wavelength and a laser fluence of 0.1 J cm-2. The subsurface temperature distribution of both electrons and phonons was computed for periodic structures with a pitch of 0.8 μm. The increase in temperature rises for a lower absorption coefficient and a higher thermal conductivity (larger absorption depth) . The distance, at which the maximum subsurface temperature occurs, increases for a small absorption coefficient. High absorption and low thermal conductivity minimizes internal heating and give rise to a pronounced surface micro topography with pitches smaller than 1 μm. Periodic line-like surface structures were produced using two interfering beams on copper, stainless steel and titanium surfaces with a pitch of 0.7 μm using a Yb:YAG-Laser with 515 nm wavelength and a pulse duration of 35 ps.

Publ.-Id: 23485

Stakeholder integration in new product development – A systematic analysis of drivers and firm capabilities

Martin, M. V.; Reinhardt, R.; Gurtner, S.

In this article, we develop a conceptual model of stakeholder integration in new product development (NPD) that (i) explains the drivers of the process and (ii) proposes a framework of capabilities that firms need for successful stakeholder integration. The focus lies on external stakeholders that directly influence the adoption of new products. We conduct a systematic literature review and content analyze a sample of 96 peer-reviewed journal articles. The study is restricted to the medical device industry to enable the use of specific search terms and the consistent categorization of information. We dedicate a section to showing how the framework applies to other settings. The drivers of stakeholder integration are classified into push factors (i.e., expected benefits for the focal firm) and pull factors (i.e., expected benefits for the stakeholders). This study provides an initial model of how stakeholder integration works based on its drivers. In addition, three related stakeholder integration capabilities emerge: stakeholder identification capability, stakeholder interaction capability and stakeholder input integration capability. The paper proposes a description of these capabilities for stakeholder integration in NPD and, thus, contributes to stakeholder theory and research on the management of NPD. The results open new paths for empirical testing and offer practical guidance on how to successfully integrate stakeholders in NPD processes.

Keywords: Stakeholder; New Product Development; Innovation

Publ.-Id: 23484

Smart Kd‑concept for realistic description of sorption processes

Stockmann, M.; Becker, D.; Flügge, J.; Schikora, J.; Noseck, U.; Brendler, V.

Sorption on mineral surfaces is an important retardation process to be considered in safety assessments of both chemotoxic and radioactive waste repositories. Most often conventional conservative concepts with temporally and spatially constant distribution coefficients (Kd‑values) are applied in reactive transport simulations.
This work describes, for the first time, a new methodology, where temporally and spatially variable distribution coefficients, so‑called smart Kd‑values were calculated for a more realistic description of sorption processes. This concept is based on a Bottom-Up approach (Davis 1998) of a competitive mineral-specific sorption of dissolved species on surfaces, combining surface complexation models with ion exchange and precipitation in a quasi-thermodynamic manner. The respective multi-dimensional matrices are computed a-priori to any run of the reactive transport codes (here: r³t, Fein 2004). During the run of such transport codes respective calls to the Kd–matrix with an appropriate averaging deliver parameter-specific Kd–values.
Three computer codes were coupled to form one tool: PHREEQC, UCODE and SIMLAB. This strategy has various benefits: (1) One can calculate smart Kd‑values for a reasonable number of environmental parameter combinations; (2) It is possible to perform uncertainty and sensitivity analysis based on such smart Kd‑matrices; (3) The approach is highly flexible with respect to chemical reactions and environmental conditions; (4) The overall methodology is much more efficient in computing time than a direct coupling of the geochemical speciation code with reactive transport codes.
The capability of this new methodology is demonstrated for the sorption of radioactive waste repository-relevant elements such as U, Am, or Np on a natural sandy aquifer. This served as a proof-of-concept for the new methodology to describe the sorption behavior in dependence of changing geochemical conditions. Results were compared to conservative Kd–values from literature used so far.

Fig 1: Kd histogramm for Am(III) in the upper aquifer of the Gorleben cap rock
Sensitivity and uncertainty analysis for the nuclides revealed the importance of ternary interaction effects, the non-concervatism of some generic distribution coefficients used so far, and the effects of input parameter correlation. Moreover, a ranking of the sensitivity of the environmental parameters nearly always put pH value, dissolved inorganic carbon and the content of matrix cations in the first places. Consequently, the mechanistic processes involving them (and their error distribution functions) should deserve higher attention in future research schemes.
Davis, J. A., Coston, J. A., Kent, D. B., Fuller, C. C. (1998): Application of the surface complexation concept to complex mineral assemblages. Environ. Sci. Technol. 32, 2820-2828.
Fein, E. (2004): Software Package r³t. Model for Transport and Retention in Porous Media. Report GRS-192, Braunschweig.

Keywords: nuclear waste disposal; safety assessment; modelling; thermodynamics; sorption; uncertainty; sensitivity; radionuclides

  • Lecture (Conference)
    DAEF 2016 - 2nd Conference on Key Topics in Deep Geological Disposal – Challenges of a Site Selection Process: Society – Procedures – Safety, 26.-28.09.2016, Köln, Deutschland

Publ.-Id: 23483

Vacancy Defect Complexes in Silicon: Charge and Spin Order

Liu, Y.; Pan, R.; Zhang, X.; Han, J.; Yuan, Q.; Tian, Y.; Yuan, Y.; Liu, F.; Wang, Y.; N'Diaye, A. T.; Arenholz, E.; Chen, X.; Sun, Y.; Song, B.; Zhou, S.

We investigate the interaction between charges and spin order of the defect complex V6 in silicon. The first-principles calculations predict spin resolved band splitting incurred by a neutral V6 yet with no net spin. Therefore, any shift of Fermi level can trigger the spin polarization. Both s and p states contribute local moments in the positively charged V6. The ferromagnetic coupling is only obtained between a positively charged V6 and a neutral one. In silicon after neutron irradiation, magnetism is achieved even at room temperature. The 3s∗3p∗ hybrid states of V6 are probably responsible for the observed long-range magnetic order. Our results unravel the role of charged V6 in inducing magnetism and will be useful in understanding and further manipulating the intrinsic properties of defect complexes in silicon and other semiconductors.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors; defect complex; charge state


Publ.-Id: 23482

Late Quaternary paleoenvironmental records from the Chatanika River valley near Fairbanks (Alaska)

Schirrmeister, L.; Meyer, H.; Andreev, A.; Wetterich, S.; Kienast, F.; Bobrove, A.; Fuchs, M.; Sierralta, M.; Herzschuh, U.

Perennially-frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine, deep marine, and glacier records because of the long-term and good preservation of fossil records under stable permafrost conditions. A permafrost tunnel in the Vault Creek Valley (Chatanika River Valley, near Fairbanks) exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late Quaternary environmental history of Interior Alaska. The multi-proxy approach includes different dating techniques (radiocarbon-accelerator mass spectrometry [AMS 14C], optically stimulated luminescence [OSL], thorium/uranium radioisotope disequilibria [230Th/U]), as well as methods of sedimentology, paleoecology, hydrochemistry, and stable isotope geochemistry of ground ice.

The studied sequence consists of 36-m-thick late Quaternary deposits above schistose bedrock. Main portions of the sequence accumulated during the early and middle Wisconsin periods. The lowermost unit A consists of about 9-m-thick ice-bonded fluvial gravels with sand and peat lenses. A late Sangamon (MIS 5a) age of unit A is assumed. Spruce forest with birch, larch, and some shrubby alder dominated the vegetation. High presence of Sphagnum spores and Cyperaceae pollen points to mires in the Vault Creek Valley. The overlying unit B consists of 10-m-thick alternating fluvial gravels, loess-like silt, and sand layers, penetrated by small ice wedges. OSL dates support a stadial early Wisconsin (MIS 4) age of unit B. Pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site. The following unit C is composed of 15-m-thick ice-rich loess-like and organic-rich silt with fossil bones and large ice wedges. Unit C formed during the interstadial mid-Wisconsin (MIS 3) and stadial late Wisconsin (MIS 2) as indicated by radiocarbon ages. Post-depositional slope processes significantly deformed both, ground ice and sediments of unit C. Pollen data show that spruce forests and wetlands dominated the area. The macrofossil remains of Picea, Larix, and Alnus incana ssp. tenuifolia also prove the existence of boreal coniferous forests during the mid-Wisconsin interstadial, which were replaced by treeless tundra-steppe vegetation during the late Wisconsin stadial. Unit C is discordantly overlain by the 2-m-thick late Holocene deposits of unit D. The pollen record of unit D indicates boreal forest vegetation similar to the modern one.

The permafrost record from the Vault Creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation, and formation of ice-wedge polygons and post-depositional deformation by slope processes. The record represents a typical Wisconsin valley-bottom facies in Central Alaska.

Keywords: Permafrost; Interior Alaska; Loess; Cryolithology; Geochronology; Paleoecology; Landscape dynamics


Publ.-Id: 23481

Synthesis and characterization of modified ultrasmall nanoparticles as multimodal imaging agents

Singh, G.; Hunoldt, S.; Licciardello, N.; Stephan, H.; Faramus, A.; de Cola, L.

The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications.[1] The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles[2] (Si NPs) of size <5 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cyanine 5[3] dye was attached selectively to the amine terminated Si NPs. The single domain antibody is also conjugated with the particles for specific targeting of the cancerous tumors via a molecular handle such as PEG-Maleimide, which facilitates the targeting as well as maintains the hydrophilicity of the particles at the same time. Bispidines[4] are to be used as a copper chelator for radiolabeling the particles by 64Cu and could be used for the in vitro and in vivo studies by Positron emission tomography.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

[1] G. J. Cheon, Y. Chang, J. Yoo, J. Cheon, Angew. Chem. 2008, 120, 6355 –6358.
[2] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S. Lee, Y. He, J. Am. Chem. Soc. 2013, 135, 8350−8356.
[3] K. Viehweger, L. Barbaro, K. P. García, T. Joshi, G. Geipel, J. Steinbach, H. Stephan, L. Spiccia, B. Graham, Bioconjugate Chem. 2014, 25, 1011−1022.
[4] H. Stephan, M. Walther, S. Fähnemann, P. Ceroni, J. Molloy, G. Bergamini, F. Heisig, C. E. Müller, W. Kraus, P. Comba, Chem. Eur. J. 2014, 20, 17011-17018.

  • Poster
    Analytica Conference 2016, 10.-12.05.2016, Munich, Germany

Publ.-Id: 23480

Intrinsic diamagnetism in the Weyl semimetal TaAs

Liu, Y.; Li, Z.; Guo, L.; Chen, X.; Yuan, Y.; Liu, F.; Prucnal, S.; Helm, M.; Zhou, S.

We investigate the magnetic properties of TaAs, a prototype Weyl semimetal. TaAs crystals show diamagnetism with magnetic susceptibility of about −7×10−7 emu/(g Oe) at 5 K. A general feature is the appearance of a minimum at around 185 K in magnetization measurements as a function of temperature, which resembles that of graphite. No phase transition is observed in the temperature range between 5 K and 400 K.

Keywords: Diamagnetism; Weyl semimetal; TaAs; Magnetic susceptibility

  • Journal of Magnetism and Magnetic Materials 408(2016), 73-76
    DOI: 10.1016/j.jmmm.2016.01.100
  • Poster
    33rd International Conference on the Physics of Semiconductors, 31.07.-05.08.2016, Beijing, China

Publ.-Id: 23479

In-beam PET at clinical proton beams with pile-up rejection

Helmbrecht, S.; Enghardt, W.; Fiedler, F.; Iltzsche, M.; Pausch, G.; Tintori, C.; Kormoll, T.

Positron emission tomography (PET) is a means of imaging the β+-activity produced by the radiation field in ion beam therapy and therefore for treatment verification. Prompt Γ-rays that are emitted during beam application challenge the detectors and electronics of PET systems, since those are designed for low and medium count rates. Typical PET detectors operated according a modified Anger principle suffer from multiple events at high rates. Therefore, in-beam PET systems using such detectors rely on a synchronization of beam status and measurement to reject deteriorated data.

In this work, a method for pile-up rejection is applied to conventional Anger logic block detectors. It allows for an in-beam data acquisition without further synchronization.

Though cyclotrons produce a continuous wave beam, the radiation field shaping technique introduces breaks in the application.
Time regimes mimicking synchrotrons as well as cyclotron based ones using double-scattering or pencil beam scanning field shaping at dose rates of 0.5, 1.0 and 2.0 Gy/min were investigated. Two types of inhomogeneous phantoms were imaged. The first one simulates cavity structures, the other one mimics a static lung irradiation.

It could be shown that, depending on the dose rate and the beam time structure, in-beam measurement including a few seconds decay time only, yield images which revealed all inhomogeneities in the phantoms. This technique can be the basis for the development of an in-beam PET system with traditional detectors and off-the-shelf electronics.

Keywords: Positron emission tomography; in-beam PET; Pile up; Proton therapy; Ion beam therapy

Publ.-Id: 23478

Influence of uranium(VI) on the metabolism of plant cells

Sachs, S.; Geipel, G.; Fahmy, K.; Obeid, M. H.; Bok, F.

Detailed knowledge of the radionuclide transfer in the environment including the food chain represents the basis for the reliable assessment of the resulting risk potential for human and wildlife. In order to improve the knowledge of the underlying processes, interaction processes of plants with actinides are studied (e.g., [1-3]). Due to the interaction with heavy metal ions, plants segregate metal chelates into the rhizosphere, store metal chelates in vacuoles or synthesize protective metabolites that can bind metal ions and consequently reduce their availability in the cytoplasm [4].

In the present work we study the interaction of uranium(VI) with canola cell suspensions (Brassica napus) as a function of the uranium(VI) concentration. The influence of uranium(VI) on the cell metabolism is studied by microcalo-rimetry. Our results show that in the presence of uranium(VI) concentrations >100 µM the heat flow generated by the cells is decreased, which indicates a lower metabolic activity of the cells compared to control samples cultivated in the absence of uranium(VI). These results agree to cell viability data measured applying the MTT test [5]. Furthermore, we study the release of plant cell metabolites in consequence of the cell contact with uranium(VI). Focusing on flavonoids, flavonoid glycosides, and phenolic acids, a solid phase extraction method coupled with high-performance liquid chromatography is developed. This method allows the separation and enrichment of cell metabolites from the nutrient medium as well as their fractionation as basis for their further identification. Knowledge of an element’s speciation is crucial for understanding its biochemical and biological behavior. Therefore, the uranium(VI) speciation in the nutrient medium is determined by time-resolved laser-induced fluorescence spectroscopy and calculated by thermodynamic modeling. The objective is to correlate the influence of uranium(VI) on the metabolic activity of the cells with the uranium(VI) speciation in the nutrient medium.

The authors thank J. Seibt, S. Heller, J. Philipp, and S. Gurlit for their technical support.

[1] Günther, A. et al. (2003) Radiochim. Acta 91, 319-328.
[2] Laurette, J. et al. (2012) Environ. Exp. Bot. 77, 96-107.
[3] Geipel, G. et al. (2015) Biometals 28, 529-539.
[4] Weiler, E., Nover, L. (2008) Allgemeine und molekulare Botanik, Thieme, Stuttgart.
[5] Mosmann, T. (1983) J. Immunol. Meth. 65, 55-63.

Keywords: Plants; plant cells; metabolism; interaction; actinides; uranium; microcalorimetry; solid phase extraction; HPLC; speciation; TRLFS

  • Poster
    10th International Biometals Symposium (Biometals 2016), 10.-15.07.2016, Dresden, Germany

Publ.-Id: 23477

Untersuchung zum Einfluss lokaler Strömungszustände auf das Auftreten der Siedekrise

Geißler, T.; Franz, R.; Hampel, U.

Die Effizienz von Verdampfungssystemen hängt maßgeblich von der übertragbaren Wärmestromdichte ab. Eine Leistungssteigerung ist durch das Auftreten der Siedekrise limitiert. Dabei kommt es durch ein abruptes Abfallen des Wärmeübergangskoeffizienten in leistungsbestimmten Systemen zu einem starken Temperaturanstieg der Heizfläche, welcher zu einem Versagen der Strukturelemente führen kann. Sicherheitsmargen sorgen in industriellen Anwendungen für einen ausreichenden Schutz vor diesem kritischen Zustand. Mit einer verlässlichen Vorhersage der Siedekrise können diese Margen allerdings reduziert werden. Durch Experimente mit hochaufgelöster Messung der Wandtemperatur und Bestimmung der Phasenverteilung während des Siedens werden Verdampfungsprozesse besser verstanden und CFD-Modell-Entwicklung unterstützt.

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Wärme- und Stoffübertragung, 01.-02.03.2016, Kassel, Deutschland

Publ.-Id: 23475

On the influence of local flow structure on the boiling crisis

Geißler, T.; Franz, R.; Hampel, U.

Nucleate boiling is one of the main heat transfer mechanism in safety analysis of nucleate power plants. Thereby the decision if the boiling crisis is occurs is on central aspect and main purpose of this study. The MORENA experiment is designed to make a contribution towards the understanding of the influence of local two-phase flow structures on the boiling crisis by the help of fast electron beam X-ray tomography (ROFEX) and infrared thermography.

Keywords: heat transfer; boiling crisis; x-ray tomography; MORENA; infrared thermography; CHF

  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
  • Contribution to proceedings
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
    Proceedings of the 47th Annual Meeting on Nuclear Technology

Publ.-Id: 23474

Mechanism of attenuation of uranyl toxicity by glutathione in Lactococcus lactis

Obeid, M. H.; Oertel, J.; Solioz, M.; Fahmy, K.

Both prokaryotic and eukaryotic organisms possess mechanisms for the detoxification of heavy metals, which are found among distantly related species. We investigated the role of intracellular glutathione (GSH), which in a large number of taxa plays a role in the protection against the toxicity of common heavy metals. Anaerobically grown Lactococcus lactis containing an inducible GSH synthesis pathway was used as a model organism. Its physiological condition allowed study of putative GSH-dependent uranyl detoxification mechanisms without interference from additional reactive oxygen species. By microcalorimetric measurements of the metabolic heat during cultivation, it was shown that intracellular GSH attenuates the toxicity of uranium at a concentration in the range of 10-150 µM. In this concentration range, no effect was observed with copper which was used as a reference for redox-metal toxicity. At higher copper concentrations, GSH aggravated metal toxicity. Isothermal titration calorimetry revealed the endothermic binding of U(VI) to the carboxyl group(s) of GSH, rather than to the reducing thiol group involved in copper interactions. The data indicate that the primary detoxifying mechanism is the intracellular sequestration of carboxyl-coordinated U(VI) into an insoluble complex with GSH. The opposite effects on uranyl and on copper toxicity can be related to the difference in coordination chemistry of the respective metal-GSH complexes, which cause distinct growth phase-specific effects on enzyme metal interactions.

Keywords: calorimetry; radiotoxicity; growth model; metabolic monitoring; toxicology

Publ.-Id: 23473

Electron Dynamics in Silicon−Germanium Terahertz Quantum Fountain Structures

Sabbagh, D.; Schmidt, J.; Winnerl, S.; Helm, M.; Di Gaspare, L.; de Seta, M.; Virgilio, M.; Ortolani, M.

Asymmetric quantum well systems are excellent candidates to realize semiconductor light emitters at far-infrared wavelengths not covered by other gain media. Group-IV semiconductor heterostructures can be grown on silicon substrates, and their dipole-active intersubband transitions could be used to generate light from devices integrated with silicon electronic circuits. Here, we have realized an optically pumped emitter structure based on a three-level Ge/Si0.18Ge0.82 asymmetric coupled quantum well design. Optical pumping was performed with a tunable free-electron laser emitting at photon energies of 25 and 41 meV, corresponding to the energies of the first two intersubband transitions 0 → 1 and 0 → 2 as measured by Fourier-transform spectroscopy. We have studied with a synchronized terahertz timedomain spectroscopy probe the relaxation dynamics after pumping, and we have interpreted the resulting relaxation times (in the range 60 to 110 ps) in the framework of an out-of-equilibrium model of the intersubband electron−phonon dynamics. The spectral changes in the probe pulse transmitted at pump−probe coincidence were monitored in the range 0.7−2.9 THz for different samples and pump intensity and showed indication of both free carrier absorption increase and bleaching of the 1 → 2 transition. The quantification from data and models of the free carrier losses and of the bleaching efficiency allowed us to predict the conditions for population inversion and to determine a threshold pump power density for lasing around 500 kW/cm2 in our device. The ensemble of our results shows that optical pumping of germanium quantum wells is a promising route toward siliconintegrated far-infrared emitters.

Keywords: silicon photonics; quantum wells; chemical vapor deposition; terahertz spectroscopy; pump−probe spectroscopy; germanium

Publ.-Id: 23472

Growth and characterization of multi-crystalline silicon ingots

Schmid, E.; Funke, C.; Behm, T.; Würzner, S.; Pätzold, O.; Galindo, V.; Stelter, M.; Möller, H.-J.

This paper summarizes studies in the field of growth and characterization of multi-crystalline (mc) silicon ingots performed within the Cluster of Excellence "Structure Design of Novel High-Performance Materials via Atomic Design and Defect Engineering (ADDE)". Experimental results on the interaction between impurities, inclusions, dislocations and grain boundaries in multi-crystalline (mc) silicon ingots grown from well-mixed and poorly mixed melts in graphite-containing and graphite free configurations are presented. The ingots were grown in a high-vacuum induction furnace by the vertical Bridgman (VB) method and the degree of impurity mixing within the melt was modified by changing the growth configuration and the growth rate. Vertical and horizontal slices were prepared from the ingots and analyzed by Fourier transform IR spectroscopy, as well as reflected-light and IR transmission microscopy to measure the axial carbon concentration and the distribution of dislocations or inclusions, respectively. The correlation between individual inclusions and dislocations has been investigated by correlative reflected-light/IR transmission and scanning electron microscopy in both setups. The influence of the melt mixing on the segregation of carbon is demonstrated and discussed with respect to the consequences for the formation of inclusions and dislocation clusters in multi-crystalline silicon. Additionally the alignment of dislocations in samples from VB-grown ingots and wafers from edge-defined film-fed (EFG) growth are investigated. Crystallographic orientations of single grains and dislocation structures are analyzed by electron backscatter diffraction and by the "traces on two parallel surfaces" method. The influence of the growth and cooling conditions on the final alignment of dislocations in mc-Si is discussed and explained.

Keywords: multi-crystalline (mc) silicon ingots

  • Contribution to external collection
    Rafaja, David: Functional structure design of new high-performance materials via atomic design and defect engineering (ADDE), Freiberg: Saxonia, 2016, 978-3-934409-68-2, 26-41

Publ.-Id: 23471

Terahertz Near-Field Investigation of a Plasmonic GaAs Superlens

Fehrenbacher, M.

This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration.
For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-070 2016
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 23470

Design Study of a Traveling-Wave Thomson-Scattering Experiment for the Realization of Optical Free Electron Lasers

Steiniger, K.; Albach, D.; Debus, A.; Loeser, M.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.

We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric fi eld of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator fi eld. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses.
An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. In the talk we show how diff raction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser fi eld along the electron trajectory. Furthermore we give tolerance limits on alignment errors to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the scheme.

Keywords: traveling-wave; thomson-scattering; FEL; x-ray; pulse-front tilt; out-of-focus

  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23469

Design Study for an Optical Free-Electron Laser Realized by Traveling-Wave Thomson-Scattering

Steiniger, K.; Albach, D.; Bussmann, M.; Irman, A.; Jochmann, A.; Loeser, M.; Pausch, R.; Röser, F.; Schramm, U.; Debus, A.

We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric field of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator field. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses. An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. The poster shows how diffraction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser field along the electron trajectory. Furthermore we give limits on alignment tolerances to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the design.

Keywords: traveling-wave; Thomson scattering; FEL; x-ray; tilted laser pulse; out-of-focus

  • Lecture (Conference)
    Student Retreat@2. Annual MT Meeting, 07.-08.03.2016, Karlsruhe, Deutschland
  • Poster
    2. Annual MT Meeting, 08.-11.03.2016, Karlsruhe, Deutschland

Publ.-Id: 23468

First evidence of a water soluble Pu(IV) - [Pu6(OH)4O4]12+ - hexanuclear cluster.

Tamain, C.; Dumas, T.; Guillaumont, D.; Hennig, C.; Guilbaud, P.

A singular Pu(IV) hexanuclear cluster [Pu6(OH)4O4]12+ stabilized by DOTA ligands has been structurally characterized for the first time both in the solid state and in water solution using X-ray diffraction, Vis-NIR and X-ray absorption spectroscopies. The cluster solubility in water and its high stability in a relatively large pH range are of the upmost importance for plutonium environmental speciation.

Keywords: Pu(IV); DOTA; SCXRD; EXAFS; UV-Vis

Publ.-Id: 23467

Free - Surface Modelling in the Ribbon Growth on Substrate (RGS)process

Beckstein, P.; Galindo, V.; Gerbeth, G.

The cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. In contrast to other crystallization methods, like e.g. melt spinning or even directional solidification, the RGS process allows high volume manufacturing, better crystallization control and a high material yield due to a substrate driven process. To optimize the application of RGS further, insights from modelling the liquid metal flow are very desirable. We have already conducted extensive numerical investigations in order to study the involved AC magnetic fields. For the RGS technology, these magnetic fields play an essential role in realizing inductive heating and an additional magnetic retention effect.
New simulation results demonstrate the effect of the applied AC magnetic fields on the melt flow of liquid silicon. The focus is thereby devoted to the simulation of the melt surface deformation based on a multi-physical modelling approach in OpenFOAM (foam-extend). Our developed numerical tool allows us to model hydrodynamic and magnetodynamic effects and their interaction. Studies of the time-dependent free-surface flow under the influence of magnetic forces are the key for improving the RGS process as main flow structures and possible instabilities strongly depend on the melt shape.

Keywords: RGS process; OpenFOAM extend; Free-Surface Modelling

  • Poster
    1st German Czechoslovak Conference on Crystal Growth, GCCCG-1 / DKT2016, 16.-18.03.2016, Dresden, Germany

Publ.-Id: 23466

Clinical application of a prompt gamma based in-vivo proton range verification using a knife-edge slit camera

Nenoff, L.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Baumann, M.; Pausch, G.; Richter, C.

To improve the precision and reduce the margins for particle therapy, in-vivo range verification is desirable. In this study, a range verification based on prompt gamma imaging (PGI) was applied to patients and compared with in-room CT data.

  • Poster
    55th Annual Conference PTCOG 55, 22.-28.05.2016, Prague, Czech Republic

Publ.-Id: 23465

First experience from the clinical application of a prompt gamma based proton range verification system in passive scattering mode and sensitivity evaluation compared to active scanning

Nenoff, L.; Priegnitz, M.; Barczyk, S.; Trezza, A.; Golnik, C.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Hotoiu, L.; Prieels, D.; Baumann, M.; Pausch, G.; Richter, C.

After a first clinical application of a prompt gamma knife-edge slit-camera in double scattering (DS) mode, systematic measurements and quantitative analysis of patient data have been started. To investigate the detection sensitivity of the slit camera for range deviations in DS compared to pencil beam scanning (PBS), phantom measurements in both treatment modes with clinically relevant treatment plans have been performed.

  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 07.-10.09.2016, Würzburg, Deutschland

Publ.-Id: 23464

Multistage bioassociation of uranium to a halophilic archaeon under highly saline conditions

Bader, M.; Müller, K.; Foerstendorf, H.; Drobot, B.; Schmidt, M.; Musat, N.; Swanson, J. S.; Reed, D. T.; Stumpf, T.; Cherkouk, A.

For the final disposal of radioactive waste in a deep geological repository, salt rock is considered as a potential host rock formation. A lot of research has been conducted regarding the physical and geochemical properties and retention suitability of this potential host rock. However, information about the indigenous microorganisms and their impact on the migration behavior of radionuclides in a worst-case scenario – the release of radionuclides – are widely missing in particular. In this work, we studied the interactions between the radionuclide uranium and the extreme halophilic archaeon Halobacterium (Hbt.) noricense. Extensive investigations were performed with an isolate originating from an Austrian salt mine, Hbt. noricense DSM-15987 [1]. Surprisingly, the obtained kinetics of the sorption experiments showed that bioassociation is not only a sorption process; i.e. fast sorption within the first hours until reaching a stable equilibrium state. The obtained kinetics showed a multistage process with a fast sorption phase during the first two hours of exposure. For the next hours an increasing amount of uranium was detectable (ICP-MS) in the supernatant, implying that the sorbed uranium was released from the cells. Subsequently, the amount of bioassociated uranium was found to increase very slowly until a maximum sorption of 80% was reached after 48 h. For more molecular information of these, hitherto unknown, bioassociation processes on archaeal cells, several spectroscopic and microscopic methods were applied. In situ Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) spectroscopy provided evidence that uranium simultaneously binds to carboxylic and to phosphate groups within the initial sorption process of uranium to cells of Hbt. noricense DSM-15987. Despite of the high chloride concentration (3 M) required for the experiments and of the resulting quenching effect of chloride on uranium luminescence, we were able to detect weak signals by Laser-induced Fluorescence spectroscopy. The obtained results support the bioassociation kinetics where a higher amount of sorbed uranium was found after 2 hours of exposure time than after 5 hours. From parallel factor analysis, a preference for uranium to carboxylic groups could be verified. Furthermore, the impact of uranium on archaeal cells over time was monitored microscopically, and the viability was proven using the LIVE/DEAD® Bac LightTM Bacterial Viability Kit from Molecular probes. Moreover, it was shown that with increasing uranium concentration the cells tend to form biofilm-like agglomerates. We assume that this effect might reflect a stress reaction to protect the cells from environmental challenges like the presence of uranium. The heavy metal ions could be localized on the cell surface of the halophilic archaeon within the first sorption phase and later on in the biofilm-like agglomerates by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy.
Due to the fact that Hbt. noricense is an archaeon commonly found in salt rock, the kinetics of uranium bioassociation was investigated as well with the Hbt. noricense WIPP strain isolated from the Waste Isolation Pilot Plant (WIPP), NM, USA. The obtained kinetic curve showed the same shape as the one from the Hbt. noricense DSM-15987 strain. Additionally, Hbt. noricense WIPP formed similar but smaller biofilm-like structures. In summary, independent of the origin of both strains, both halophilic archaea obviously interact with dissolved uranium within a unique bioassociation process. This process, including the subsequent biofilm formation, will be investigated in more detail in the near future.
[1] Gruber, C. et al. (2004) Extremophiles, Vol. 8, 431-439.

Keywords: Halophilic archaeon; uranium bioassociation; Halobacterium noricense

  • Lecture (Conference)
    Halophiles (11th International Meeting), 22.-26.05.2016, San Juan, Puerto Rico

Publ.-Id: 23463

Insights into the use of specific metal binding of self-assembling S-layer proteins

Vogel, M.; Drobot, B.; Günther, T.; Lehmann, F.; Weinert, U.; Pollmann, K.; Raff, J.

Most bacteria and all archaea possess as outermost cell envelope surface-layer (S-layer) proteins. These self-assembling proteins form nanostructured lattices with different symmetries, provide regular arranged pores with defined size and possess different kinds of regular arranged functional groups. The formation of stable and functional S-layer lattices via self-assembly on the cell surface, on different technical surfaces as well as interfaces is a dynamic and complex process. Despite the fact that S-layer proteins have been investigated for over 30 years, the full reaction cascade of self-assembly, which includes the role of different bivalent cations such as Ca2+ and Mg2+, are still not fully understood.
Furthermore, S-layers have a number of important intrinsic properties, e.g. they provide cellular wall protection, mediate selective exchange of molecules and therefore function as molecular sieves. Interestingly, S-layers from bacterial isolates recovered from heavy metal contaminated environments have outstanding metal binding properties and are highly stable. They show potential for selective binding of several metals some of them with high affinity. Therefore, three aspects of the metal-interactions with S-layer proteins must be taken into account.
First, S-layers possess different functionalities, e.g. carboxyl-, phosphoryl, hydroxyl groups, binding toxic metals and metalloids, like U and As, unspecifically and by this hinder them to enter the interior of prokaryotic cells. This interaction process is strongly driven by pH-value as the functionalities need to be deprotonated. Second, precious metals like Au and Pd are likewise bound unspecifically to functional groups, but presumably covalently making the binding irreversible unless the S-layer protein is destroyed completely.
Third, some metals are needed for native protein folding of the S-layer protein monomer, self-assembly, and the formation of highly-ordered lattices. These particular metals are bivalent cations such as Ca2+. As known from titration experiments, certain S-layer proteins bind Ca2+ specifically, thereby forming very stable complexes. There are at least two different binding sites for these bivalent cations showing different binding affinities. Important is that these binding sites not only allow selective binding of calcium, but also of chemical-equal elements including the trivalent lanthanides (Eu3+, Tb3+), possessing comparable ionic radii. This was proven by titration and laser fluorescence spectroscopic experiments.
This study shows that the intrinsic properties and physiological functions of the S-layer proteins build the base for its selective metal binding behavior and its potential for fabrication of biohybrid materials. So by combining S-layers with a layer-by-layer technique different materials can be furnished with coatings. The produced biohybrid materials can be directly used as selective metal filter material for the removal or recovery of strategic relevant metals using pH-value as regulating parameter for selective metal binding and also conceivably release.

Keywords: S-layer; metal binding; coatings; biohybrid; lanthanides

  • Lecture (Conference)
    Materials Science and Engineering - MSE 2016 Congress, 27.-29.09.2016, Darmstadt, Deutschland

Publ.-Id: 23462

Nanoparticle guests in lyotropic liquid crystals

Dölle, S.; Park, J. H.; Schymura, S.; Scalia, G.; Lagerwall, J. P. F.

In this chapter we discuss the benefits, peculiarities and main challenges related to nanoparticle templating in lyotropic liquid crystals. We first give a brief bird’s-eye view of the field, discussing di↵erent nanoparticles as well as di↵erent lyotropic hosts that have been explored, but then quickly focus on the dispersion of carbon nanotubes in surfactant-based lyotropic nematic phases. We discuss in some detail how the trans- fer of orientational order from liquid crystal host to nanoparticle guest can be verified and which degree of ordering can be expected, as well as the importance of choosing the right surfactant and its concentra- tion for the stability of the nanoparticle suspension. We introduce a method for dispersing nanoparticles with an absolute minimum of stabi- lizing surfactant, based on dispersion below the Kra↵t temperature, and we discuss the peculiar phenomenon of filament formation in lyotropic nematic phases with a su cient concentration of well-dispersed carbon nanotubes. Finally, we describe how the total surfactant concentration in micellar nematics can be greatly reduced by combining cat- and an- ionic surfactants, and we discuss how nanotubes can help in inducing the liquid crystal phase close to the isotropic–nematic boundary.

Keywords: Nanopartikel; nanoparticles; lyotrope; Flüssigkristalle; lyotropic liquid crystals; Kohlenstoffnanoröhrchen; carbon nanotubes

  • Book chapter
    Lagerwall, Jan P.F., Scalia, Giusy: Liquid Crystals with Nano and Microparticles, London: World Scientific, 2016, 695-722
    DOI: 10.1142/9789814619264_0020

Publ.-Id: 23460

Free-surface dynamics in the Ribbon Growth on Substrate (RGS) process

Beckstein, P.; Galindo, V.; Gerbeth, G.; Schönecker, A.

he cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. Compared to other crystallization methods, such as melt spinning, the RGS process allows better crystallization control, high volume manufacturing and high material yield due to the substrate driven process. In order to optimize RGS further, insights from modelling the liquid metal in the casting frame under electromagnetic fields are very desirable. We performed numerical investigations in order to study the involved AC magnetic fields, which are an essential part of the RGS process to realize a magnetic retention effect. Our simulation results demonstrate the effect of the applied AC magnetic fields on the silicon melt flow. The main focus is thereby devoted to the simulation of the melt surface deformation based on a complex modelling approach. This time-dependent free-surface flow under the influence of magnetic forces is the key for optimizing the RGS process.

Keywords: Ribbon Growth on Substrate; Semi-conductor processing; AC magnetic fields; Magnetic retention; OpenFOAM extensions; COMSOL Multiphysics; Moving mesh; Surface-tracking; Free-surface; Dome-shaping

  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials, 12.-16.10.2015, Cannes sur Mer, France
    EPM 2015 8th International Conference on Electromagnetic Processing of Materials, St. Martin d'Héres: SIMAPLaboratory, 978-2-9553861-0-1, 167-170
  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials, 12.-16.10.2016, Cannes sur Mer, France

Publ.-Id: 23459

Translation of a prompt gamma based proton range verification system to first clinical application

Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Golnik, G.; Bombelli, L.; Enghardt, W.; Fiedler, F.; Fiorini, C.; Hotoiu, L.; Janssens, G.; Keitz, I.; Mein, S.; Perali, I.; Prieels, D.; Smeets, J.; Thiele, J.; Vander Stappen, F.; Werner, T.; Baumann, M.

To improve precision of particle therapy, in vivo range verification is highly desirable to reduce range uncertainties and thereby increase the advantage of proton therapy. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically, although proposed 12 years ago. We report on the translational implementation as well as the worldwide first clinical application of prompt gamma imaging (PGI) based range verification. A prototype of a PGI camera was used to measure the prompt gamma depth distribution during proton treatment of a head and neck tumor. Inter-fractional variations of the prompt gamma profile were evaluated and anatomical changes were independently verified.

  • Lecture (Conference)
    ESTRO 35, European society for radiotherapy and oncology, 29.04.-03.05.2016, Turin, Italy

Publ.-Id: 23458

First clinical application of a prompt gamma based in vivo proton range verification using a knife-edge slit camera

Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Bombelli, L.; Fiorini, C.; Hotoiu, L.; Perali, I.; Prieels, D.; Enghardt, W.; Baumann, M.

To improve precision of particle therapy, in vivo range verification is highly desirable. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically. Here we report on the worldwide first clinical application of prompt gamma imaging (PGI) based range verification.

  • Lecture (Conference)
    ICTR-PHE 2016, International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)Suppl. 1, S89-S90
    DOI: 10.1016/S0167-8140(16)30184-0

Publ.-Id: 23457

Comparison of SIMS and RBS for depth profiling of silica glasses implanted with metal ions

Lorinčík, J.; Veselá, D.; Vytykáčová, S.; Švecová, B.; Nekvindová, P.; Macková, A.; Mikšová, R.; Malinský, P.; Böttger, R.

Ion implantation of metal ions, followed by annealing, can be used for the formation of buried layers of metal nanoparticles in glasses. Thus, photonic structures with nonlinear optical properties can be formed. In this study, three samples of silicaglasses were implanted with Cu+, Ag+, or Au+ ions under the same conditions (energy 330 keV and fluence 1 × 1016 ions/cm2), and compared to three identical silicaglass samples that were subsequently coimplanted with oxygen at the same depth. All the implantedglasses were annealed at 600 °C for 1 h, which leads to the formation of metal nanoparticles. The depth profiles of Cu,Ag, and Au were measured by Rutherford backscattering and by secondary ion mass spectrometry and the results are compared and discussed.

Keywords: Rutherford backscattering; Secondary ion mass spectroscopy; Gold; Silver; Amorphous metals

Publ.-Id: 23456

A strategy for the qualification of multi-fluid approaches for nuclear reactor safety

Lucas, D.; Rzehak, R.; Krepper, E.; Ziegenhein, T.; Liao, Y.; Kriebitzsch, S.; Apanasevich, P.

CFD-simulations for two-phase flows applying the multi-fluid approach are not yet qualified to provide reliable predictions for unknown flows. Among others, one important reason is the missing agreement within the community on closure models to be used. Considering specific phenomena or not, using different models and adjustable constants, most papers presenting a model validation end up with a good agreement with experimental data. However a case by case selection of models and constants does not help to improve the predictive capabilities of such models. For this reason the definition of baseline models considering all known phenomena that could be important is proposed. In such baseline models all parameter have to be defined, i.e., there are no tuning parameters by definition. Therefore these baseline models have to be applied to many experiments with different complexity. Shortcomings of the models and our physical understanding of the complex flow phenomena have to be identified by detailed analyses on the deviations between experimental data and simulation results. A modification of the baseline model will only be done if it bases on physical considerations and improves the overall performance of the model. This requires a huge effort, but seems to be the only way to improve the situation. In particular more complete experimental data are required. Joint activities on the development of such baseline models are desirable. The paper illustrates this strategy by a baseline model for polydisperse bubbly flows which is presently developed at HZDR.

Keywords: CFD; two-phase flow; multi-fluid; bubbly flow; validation

Publ.-Id: 23455

Terahertz spectroscopy of individual donors in silicon by low-temperature s-SNOM

Lang, D.; Winnerl, S.; Schneider, H.; Li, J.; Clowes, S.; Murdin, B.; Döring, J.; Kehr, S. C.; Eng, L. M.; Helm, M.

Isolated atoms or ions, typically confined in traps, are ideal systems for studying fascinating coherent quantum effects such as photon echoes. Likewise, isolated donor impurity atoms in semiconductors like silicon show a hydrogen-like spectrum, shifted to the far infrared due to the small effective mass and high dielectric constant [1]. Excited Rydberg states are of particular interest for quantum information, because they allow one to prepare long-living microscopic polarization states.

In contrast to previous far-field spectroscopic studies which probed ensembles of many impurities, we aim here at studying individual impurity centers. To this end, low-temperature scattering-type scanning near-field optical microscopy (s-SNOM) is employed and a free-electron laser is used as a precisely tunable terahertz source [2]. Our silicon samples contain different donors (P, Bi) with different defect densities, respectively, and are pre-characterized by conventional Fourier transform infrared spectroscopy.

[1] Greenland et al., Nature 465, 1057 (2010).
[2] Döring et al., Appl. Phys. Lett. 105, 053109 (2014).

Keywords: terahertz; silicon; nanoscopy; s-SNOM; spectroscopy; low-temperature; impurities; free-electron laser

  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
  • Poster
    Silicon Quantum Information Processing 2016: Towards hybrid quantum circuits, 08.09.2016, Cambridge, United Kingdom

Publ.-Id: 23454

Overview of methodology for spatial homogenization in the Serpent 2 Monte Carlo code

Leppanen, J.; Pusa, M.; Fridman, E.

This paper describes the methods used in the Serpent 2 Monte Carlo code for producing homogenized group constants for nodal diffusion and other deterministic reactor simulator calculations. The methodology covers few-group reaction cross sections, scattering matrices, diffusion coefficients and poison cross sections homogenized in infinite and B1 leakage-corrected critical spectra, as well the calculation of assembly discontinuity factors, pin-power form factors, delayed neutron parameters and total and partial albedos. Also included is a description of an automated burnup sequence, which was recently implemented for the handling of restart calculations with branch variations. This capability enables covering the full range of local operating conditions required for the parameterization of group constants within a single run. The purpose of this paper is to bring the methodological description provided in earlier publications up to date, and provide insight into the developed methods and capabilities, including their limitations and known flaws.

Keywords: Serpent; Monte Carlo; spatial homogenization; group constants; automated burnup sequence


Publ.-Id: 23453

Bipolar resistive switching of p-YMnO3/n-SrTiO3:Nb junctions

Bogusz, A.; Blaschke, D.; Abendroth, B.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.

Resistive switching (RS) phenomena of oxides in metal-insulatormetal structures have been widely investigated due to promising applications as a non-volatile memory and in neuromorphic circuits. In our previous works, we have demonstrated unipolar RS of YMnO3-based structures [1]. This work investigates the non-volatile RS switching in Au/YMnO3-/Nb:SrTiO3-/Al structures with (p-YMnO3-)-(n-Nb:SrTiO3-) junctions. The YMnO3- films are deposited by pulsed laser deposition on the (100)-SrTiO3- doped with 0.5 wt.% of Nb substrates and exhibit bipolar RS. Observed RS behavior is assigned to the coupled electronic and ionic processes which depend on the depletion layer extension in the p-n junction. Exploitation of RS in p-n junctions offers additional functionalities of memristive devices, e.g. related to their optical properties.
[1] A. Bogusz et al., AIP Advances 4 (2014), A. Bogusz et al., Adv. Mater. Res. 1101 (2015).

  • Lecture (Conference)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 23452

Nonlinear Terahertz Absorption of Graphene Plasmons

Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.

Subwavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at the resonant frequency is predicted to significantly enhance the light-graphene interaction, which could enable nonlinear optics at low intensity in atomically thin, subwavelength devices. To date, the nonlinear response of graphene plasmons and their energy loss dynamics have not been experimentally studied. We measure and theoretically model the terahertz nonlinear response and energy relaxation dynamics of plasmons in graphene nanoribbons. We employ a terahertz pump − terahertz probe technique at the plasmon frequency and observe a strong saturation of plasmon absorption followed by a 10 ps relaxation time. The observed nonlinearity is enhanced by 2 orders of magnitude compared to unpatterned graphene with no plasmon resonance. We further present a thermal model for the nonlinear plasmonic absorption that supports the experimental results. The model shows that the observed strong linearity is caused by an unexpected red shift of plasmon resonance together with a broadening and weakening of the resonance caused by the transient increase in electron temperature. The model further predicts that even greater resonant enhancement of the nonlinear response can be expected in high-mobility graphene, suggesting that nonlinear graphene plasmonic devices could be promising candidates for nonlinear optical processing.

Keywords: Graphene; plasmons; nonlinear; pump−probe; terahertz

Publ.-Id: 23451

The twofold nature of Coulomb scattering in graphene

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

Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial non-equilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88meV to suppress efficiently the optical phonon scattering as the photon energy is below the optical phonon energy (~200meV). In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process (see Fig. 1). This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling in which the carrier injection and relaxation dynamics is calculated by solving graphene Bloch equations including orientational phase and energy relaxation in Born-Markov approximation.

[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

  • Poster
    Graphene Week 2016, 13.-17.06.2016, Warszawa, Polska

Publ.-Id: 23450

Slow noncollinear Coulomb scattering in the vicinity of the Dirac point in graphene

König-Otto, J.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k-directions pointing radially away from the Dirac point. Our study reveals, however, that in almost intrinsic graphene full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps timescale. This effect is very promising for infrared and THz devices based on hot carrier effects.

Publ.-Id: 23448

Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.

Keywords: Detector; graphene; fast detctor; broadband detector

  • Lecture (Conference)
    7th international workshop on terahertz technology and applications, 15.-16.03.2016, Kaiserslautern, Deutschland

Publ.-Id: 23447

Graphene-based fast hot-electron bolometer with bandwidth from THz to VIS

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. S.; Murphy, T. E.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

We present a fast detector (rise time 40 ps) operating at room temperature that is capable to detect radiation from the THz to visible spectral range (demonstrated wavelengths 500 µm – 780 nm) [1]. The detector consists of a CVD-grown graphene flake contacted by a broadband logarithmic periodic antenna. SiC acts as a substrate material that does not interfere with the detection mechanism in the desired frequency range, even within the Reststrahlen band of SiC (6 – 12 µm). The detector is ideal for timing purposes. Near infrared (mid- and far infrared) pulse energies of the order of 10 pJ (1 nJ) are sufficient to obtain good signal-to-noise ratios. We suggest that the bandwidth is limited by the antenna dimensions (typically several mm) on the long wavelength side and by the bandgap of SiC (380 nm) on the short wavelength side.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: detector; graphene; fast detector; broadband detector

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23446

Noncollinear Coulomb scattering in graphene

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

Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial nonequilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88 meV to suppress efficiently the optical phonon scattering. In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process. This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling.
[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

Keywords: graphene; ultrafast dynamics; anisotropy

  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23445

Unusual Coulomb Effects in Graphene

Winnerl, S.

After a brief overview on the ultrafast carrier dynamics in graphene we focus on two Coulomb-mediated effects. The first one is related to the very different scattering times for collinear versus non-collinear scattering. Collinear Coulomb scattering, due to many possibilities to fulfill energy and momentum conservation requirements, is extremely fast (sub-100 fs timescale). Non-collinear scattering, on the other hand, can be surprisingly slow, namely on the scale of a few ps. This observation is in contrast to the common belief that a non-equilibrium carrier distribution in graphene fully thermalizes on a sub-100 fs timescale. We show that polarization resolved pump-probe experiments at low photon energies, i.e. below the optical phonon energy of ~200 meV, allow one to trace the non-collinear Coulomb scattering and to control its efficiency by varying the pump fluence. The second surprising Coulomb effect is the direct observation of strong Auger scattering in Landau quantized graphene. The Auger scattering in this case can efficiently deplete an energy level while that level is optically pumped at the same time. Finally the potential of graphene for photonic and fast optoelectronic devices such as THz sources and detectors will be discussed.

Keywords: graphene; ultrafast dynamics

  • Lecture (others)
    Seminarvortrag im Rahmen des Graduiertenkollegs Electronic Properties of Carbon Based Nanostructures, 22.01.2016, Regensburg, Deutschland

Publ.-Id: 23444

Emittance compensation schemes for a superconducting rf injector

Vennekate, H.; Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Xiang, R.

Contemporary particle injector technologies provide different advantages depending on the chosen design. In the case of copper rf injectors these is primarily the high accelerating field, enabling the generation of high charge bunches with very low emittance. However, the cost of that is a comparably low repetition rate. DC guns, on the other hand, can provide higher repetition rates and consequently increased beam currents at lower beam quality, i.e., increased emittance. The concept of a superconducting rf injector offers the opportunity to combine the advantages of both these concepts. However, it demands special concepts for emittance compensation, as the common approach with overlapping magnetic fields during the rf acceleration interferes with the limitations of superconductivity. The ELBE SRF Gun project is one of the most advanced in this field. Gun II, the second SRF injector at the Electron Linear accelerator with high Brilliance and low Emittance (ELBE), introduces new features for emittance compensation which were studied in detail over the last years. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method uses rf focusing by retracting the photocathode’s tip from the last cell of the resonator. This paper discusses both of these schemes by briefly outlining their setups, discussing results of numerical simulations of their impact, and presenting results of initial experimental beam measurements with Gun II.

Keywords: SRF Gun; Solenoid; RF Focusing; Emittance Compensation; Transverse Emittance

Publ.-Id: 23443

Plasmonic efficiency enhancement at the anode of strip line photoconductive terahertz emitters

Singh, A.; Winnerl, S.; König-Otto, J. C.; Stephan, D. R.; Helm, M.; Schneider, H.

We investigate strip line photoconductive terahertz (THz) emitters in a regime where both the direct emission of accelerated carriers in the semiconductor and the antenna-mediated emission from the strip line play a significant role. In particular, asymmetric strip line structures are studied. The widths of the two electrodes have been varied from 2 µm to 50 µm. The THz emission efficiency is observed to increase linearly with the width of the anode, which acts here as a plasmonic antenna giving rise to enhanced THz emission. In contrast, the cathode width does not play any significant role on THz emission efficiency. This is a consequence of the emission being caused by photoexcited electrons while the effect of photoexcited holes is negligible.

Keywords: Terahertz emitters; photoconductivity; plasmonic antenna

Publ.-Id: 23441

A review of thermal processing in the subsecond range: semiconductors and beyond

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

Thermal processing in the subsecond range comprises modern, non-equilibrium annealing techniques which allow various material modifications at the surface without affecting the bulk. Flash lamp annealing (FLA) is one of the most diverse methods of short time annealing with applications ranging from the classical field of semiconductor doping to the treatment of polymers and flexible substrates. It still continues to extend to other material classes and applications, and becomes of interest for an increasing number of users.
In this review we present a short, but comprehensive and consistent picture about the current state of the art of FLA, sometimes also called pulsed light sintering. In the first part we take a closer look to the physical and technological background, namely to the electrical and optical specifications of flash lamps, the resulting temperature profiles and the corresponding implications on process-relevant parameters like reproducibility and homogeneity. The second part briefly considers the various applications of FLA starting with the classical task of defect minimization and ultra-shallow junction formation in Si, followed by further applications in Si technology, namely in the fields of hyperdoping, crystallization of thin amorphous films and photovoltaics. Subsequent chapters cover the topics of doping and crystallization in Ge and silicon carbide, doping of III-V semiconductors, diluted magnetic semiconductors, III-V nanocluster synthesis in Si, annealing of transparent conducting oxides and high-k materials, nanoclusters in dielectric matrices and the use of FLA for flexible substrates.

Keywords: flash lamp annealing; pulsed light sintering; semiconductors

Publ.-Id: 23440

Arguing on entropic and enthalpic first-order phase transitions in strongly interacting matter

Wunderlich, F.; Yaresko, R.; Kämpfer, B.

The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement–deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t. ”incoming” or ”outgoing” serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions.

Publ.-Id: 23439

Laser assisted Breit-Wheeler and Schwinger processes

Nousch, T.; Otto, A.; Seipt, D.; Kämpfer, B.; Titov, A. I.; Blaschke, D.; Panferov, A. D.; Smolyansky, S. A.

The assistance of an intense optical laser on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ signifcantly from transiently achieved mode occupations.

Publ.-Id: 23438

Electromagnetic probes of a pure-glue initial state in nucleus-nucleus collisions at energies available at the CERN Large Hadron Collider

Vovchenko, V.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stöcker, H.

Partonic matter produced at the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, but quarks and antiquarks are produced at later times.
The dynamical evolution of this chemically nonequilibrium system is described by the ideal (2+1)–dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state is taken as a linear interpolation of the lattice data for the pure gluonic matter and the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy. The results are obtained assuming different equilibration times, including the case when the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the invariant mass spectra of dileptons, but a rather modest suppression of the pT -distributions of direct photons. It is demonstrated that a noticeable enhancements of photon and dilepton elliptic flows might be a good signature of the pure glue initial state.


Publ.-Id: 23437

Spectral caustics in laser-assisted x-ray Compton scattering

Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.

We study the process of laser-assisted Compton scattering: The Compton scattering of x-rays from an XFEL off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons [1]. We observe sharp peak structures in the plateau region. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element, relating the caustic peak positions to the laser-driven electron motion [2].

  • Contribution to external collection
    in: Jahresbericht 2015 Helmholtz-Institut Jena (HIJ):, Jena: HIJ, 2016


Publ.-Id: 23436

Bonding structure and morphology of chromium oxide films grown by pulsed-DC reactive magnetron sputter deposition

Gago, R.; Vinnichenko, M.; Hübner, R.; Redondo-Cubero, A.

Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (f) and for substrate temperatures, Ts, up to 450 ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES). On unheated substrates, by increasing f the growth rate is higher and the O/Cr ratio (x) rises from ~2 up to ~2.5. Inversely, by increasing Ts the atomic incorporation rate drops and x falls to ~1.8 . XRD shows that samples grown on unheated substrates are amorphous and that nanocrystalline Cr2O3 (x = 1.5) is formed by increasing Ts. In amorphous CrOx , XANES reveals the presence of multiple Cr environments that indicate the growth of mixed-valence oxides, with progressive promotion of hexavalent states with f. XANES data also confirms the formation of single-phase nanocrystalline Cr2O3 at elevated Ts. These structural changes also reflect on the optical and morphological properties of the films.

Keywords: oxide materials; vapour deposition; atomic scale structure; NEXAFS/XANES

Publ.-Id: 23435

Attachment of hydrophobic particles to the surface of an immersed gas bubble

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

The transport of colloidal particles at the fluidic interface of a binary fluid is of significant importance to the flotation process. Flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The fine attaching particles have so far been modelled as point particles, thereby neglecting the deformation of the fluidic interface. Here the combination of the smooth profile method with an in-house binary fluid model is suggested to directly simulate the attachment of a single particle to an immersed bubble under various capillary numbers.

Keywords: Froth flotation; Three-phase system; Particle attachment

  • Contribution to proceedings
    81st Annual meeting of the Society of Chemical Engineers Japan, 13.-15.03.2016, Kansai University, Senriyama Campus, Japan
    Proceedings of the 81st Annual meeting of the Society of Chemical Engineers Japan

Publ.-Id: 23434

Proton Beams for Physics Experiments at OncoRay

Helmbrecht, S.; Fiedler, F.; Meyer, M.; Kaever, P.; Kormoll, T.

Purpose: At the OncoRay center in Dresden at proton therapy facility is in operation. The first patient was treated in December 2014. The system is driven by an IBA (IBA Proton Therapy, Louvain-la-Neuve, Belgium) Cyclone 230 isochronous cyclotron with a maximum proton energy of 230 MeV. Patients are treated in one room equipped with a 360° rotating gantry. Besides patient treatment a strong focus is on research. A dedicated experimental room is part of the facility. In the current state of expansion this room is equipped with a fixed beam line. Beam energies between 70 and 230 MeV and currents up to about 120 nA at 230 MeV can be provided.
Materials and Methods: An in house developed control system (figure 1) allows for a parallel operation of the treatment and the experimental beamline. Absolute priority for the treatment room is ensured by the control software.
The beam current is controlled by a dedicated hardware directly. Continuous wave beams as well as pulsed beams with repetition rates up to 333 Hz with variable duty cycles are available. The beam is monitored by means of a segmented ionization chamber. The beam can be activated manually, for a defined time or until a certain charge has been reached at the beam exit. A direct continuance after a beam switch to the treatment room is possible.
Results: The proton therapy system itself is operated by an IBA team, that ensures excellent beam stability and availability. Since only one treatment room is present, experiments can be performed conveniently during the day shifts. Requests from the treatment room cause interruptions of 1-2 min duration in intervals of about 20 min.
Conclusions: In summary, the OncoRay center is equipped with an experimental beamline that combines the reliability and beam quality of a commercial clinical proton therapy system with the flexibility of an in house developed control system whose design parameters are governed by the needs of physical and translational research.

  • Poster
    ICTR-PHE 2016 - International Conference on Translational Research in Radio-Oncology - Physics for Health in Europe, 15.05.2016, Genf, Schweiz
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)S1, S60-S61
    DOI: 10.1016/S0167-8140(16)30124-4

Publ.-Id: 23433

Comparison of a Separated Flow Response to Localized and Global-type Disturbances

Monnier, B.; Williams, D. R.; Weier, T.; Albrecht, T.

The flow structure and lift response of a separated flow over an airfoil that is subjected to an impulsive type of pitching motion is compared to the response produced by a localized pulse disturbance at the leading edge of an airfoil. Time-resolved PIV data is used to obtain the velocity field on the suction surface of the airfoil. POD analysis shows that the majority of energy is contained within the first four modes. Strong similarities in the shapes of the POD basis functions are found, irrespective of the type of actuation (global or local). The time-varying coefficient of the second POD mode tracks the negative of the lift coefficient in each case. Basis functions from the localized actuation data were projected on the velocity field of the globally actuated flow to obtain a hybrid set of coefficients. The hybrid coefficients matched reasonably well with the coefficients obtained from the original POD analysis for the globally excited flow. Both types of actuation were found to generate very similar Lagrangian flow structures. The results suggest a certain degree of universality in the POD modes/flow structures for the separated flow over an airfoil, irrespective of the type of excitation.


Publ.-Id: 23432

Simulation of liquid metal batteries

Weber, N.; Beckstein, P.; Galindo, V.; Herreman, W.; Landgraf, S.; Nore, C.; Stefani, F.; Weier, T.

The increasing deployment of highly fluctuating renewable energy sources, as e.g. wind and solar power plants, demands for stationary energy storage. Pumped storage hydro power, which is the only technology widely used today, can not be applied in all places; new technologies are therefore required. A promising alternative is the liquid metal battery (LMB). Easy scale-up, low priced raw materials, a simple set-up, long life-time and extremely high current densities make it a promising candidate for grid-scale energy storage. Liquid metal batteries are built as a stable density stratification of two liquid metals, separated by a likewise liquid salt. During discharge, the upper metal will lose electrons; the ion will diffuse through the electrolyte layer and alloy there with the cathode metal. In order to build such batteries cheap, they have to be large; however, this implies currents in the order of kilo-amperes. The battery current and its interaction with magnetic fields may be the source of different instabilities, leading to a fluid flow in the liquid metal battery. Stirring the cathode may be advantageous by mixing or removing reaction products from the salt-cathode interface. However, very strong fluid flow may even wipe away the electrolyte layer and lead to a short-cirucit. This must be avoided.

We present a numerical model implemented in OpenFOAM, coupling the Navier-Stokes equation with Maxwell’s equations. The electric potential is determined by solving a Poisson equation; the current by Ohm’s law and the
magnetic field by Biot-Savart’s law. This model is used to simulate the Tayler instability in the batterie’s anode. A multi-region model, similar to chtMultiRegionFoam, is used to model electro-vortex flow. Finally, a multiphase model, based on multiphaseInterFoam, allows to simulate deformation of the electrolyte layer as well as metal pad rolling, known from aluminium reduction cells.

  • Lecture (Conference)
    11th OpenFOAM Workshop, 26.-30.06.2016, Guimarães, Portugal

Publ.-Id: 23431

Interaction of Eu(III) and Cm(III) with mucin – a key component of the human mucosa

Wilke, C.; Raff, J.; Barkleit, A.; Ikeda-Ohno, A.; Stumpf, T.

Lanthanides (Ln) and actinides (An) could potentially be chemo- and radiotoxic when they are incorporated into the food chain after accidental releases to the environment. This spectroscopic study focuses on the interaction of Ln(III) and An(III) with mucin, one of the essential components of human mucosa, for better understanding of their behaviour in human gastrointestinal tract in case of oral ingestion. The first spectroscopic screening with TRLFS (Time-Resolved Laser-Induced Fluorescence Spectroscopy) revealed mucin as a fundamental binding partner of Eu(III) as well as of Cm(III) in the human gastrointestinal tract. Mucin is an important glycoprotein of the mucosa, working as an important protective barrier on the digestive system and functions. Mucin can interact with metal ions via a variety of their saccharides. This contribution is dedicated to the identification of dominant binding groups of Mucin with Ln(III) and An(III) by spectroscopy (TRLFS, IR, NMR) and thermodynamic calculations

Keywords: lanthanides; actinides; Eu(III); Cm(III); TRLFS; spectroscopy; mucin

  • Contribution to proceedings
    Goldschmidt, 26.06.-01.07.2016, Yokohama, Japan
  • Lecture (Conference)
    Goldschmidt, 26.06.-01.07.2016, Yokohama, Japan

Publ.-Id: 23430

Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion

Oertel, J.; Keller, A.; Prinz, J.; Schreiber, B.; Hübner, R.; Kerbusch, J.; Bald, I.; Fahmy, K.

Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the “outer shape” of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~ 10 nm diameter containing a lipid bilayer ~ 5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials.

Keywords: metallization; biotemplate; infrared; FTIR; Raman; SERS; gold nanoparticle

Publ.-Id: 23429

Development of antioxidant COX-2 inhibitors as radioprotective agents for radiation therapy – a hypothesis-driven review

Laube, M.; Kniess, T.; Pietzsch, J.

Radiation therapy (RT) evolved to be a primary treatment modality for cancer patients. Unfortunately, the cure or relief of symptoms is still accompanied by radiation-induced side effects with severe acute and late pathophysiological consequences. Inhibitors of cyclooxygenase-2 (COX-2) are potentially useful in this regard because radioprotection of normal tissue and/or radiosensitizing effects on tumor tissue have been described for several compounds of this structurally diverse class. This review aims to substantiate the hypothesis that antioxidant COX-2 inhibitors are promising radioprotectants because of intercepting radiation-induced oxidative stress and inflammation in normal tissue, especially the vascular system. For this, literature reporting on COX inhibitors exerting radioprotective and/or radiosensitizing action as well as on antioxidant COX inhibitors will be reviewed comprehensively with the aim to find cross-points of both and, by that, stimulate further research in the field of radioprotective agents.

Keywords: Coxibs; Cyclooxygenases; Normal tissue; NSAIDS; Oxidative stress; Radiation-induced vascular dysfunction; Radioprotection; Radiosensitization; Reactive oxygen/nitrogen species; Tumor models

Publ.-Id: 23428

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