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34118 Publications

Effect of heat exchanger internals on the main transition velocities in a bubble column

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

The application of bubble columns to industrial processes, such as Fischer-Tropsch synthesis and liquid-phase methanol synthesis, often involves a large amount of heat generation. That is why, heat exchangers are installed to remove the generated heat. However, the bubble dynamics in bubble columns with dense internals is still not well understood.
In this work, for the first time a flow regime identification in a bubble column with internals (dense vertical heat exchanger tubes) was performed. The bubble column had an inner diameter of 0.1 m and was equipped with a perforated plate distributor (55 holes, ø 0.5×10-3 m). The gas-liquid system consisted of air and deionized water. The clear liquid height Ho was set at 1.1 m. Superficial gas velocities Ug ranging from 0.01 up to 0.15 m/s were employed. The bubble column was equipped with 37 heat exchanger tubes having a square pitch with a diameter of 8×10-3 m and a clearance of 3×10-3 m. Gas holdup fluctuations were recorded by means of a conductivity wire-mesh sensor installed at an axial position of 0.715 m. The time series (60,000 points, sampling frequency (fs)=2000 Hz) were further treated based on the non-linear chaos theory (Schouten et al., 1994; Nedeltchev et al., 2014).
For comparison, the two main transition velocities Utrans in the empty bubble column (Ho=0.66 m) counterpart were also identified. The information entropies were extracted from X-ray data (29,000 points, fs=1000 Hz) recorded by the ultrafast tomographic facility. It was shown that in a bubble column with internals two main transition velocities Utrans can be identified by means of the Kolmogorov entropy (KE) profile. The flow regime boundaries are identifiable on the basis of the sudden change in the decreasing KE rate. It is interesting to note that well-pronounced local KE minima (Nedeltchev et al., 2014), known from empty bubble columns, are not observed in a bubble column with internals.
At Ug=0.05 m/s the bubbly flow (homogeneous) regime transforms itself into the transition regime. The rate of the KE decrease in both flow regimes is different. At Ug=0.11 m/s the heterogeneous regime (mixture of churn-turbulent and slug flow regimes) is formed. It is characterized with constant KE values. The existence of the slug flow regime in the column core is explainable with the relatively small diameter of the column at which, according to Wilkinson et al. (1992), the effect of the column wall is still present.
In an empty bubble column, two well-pronounced local minima of the information entropy values denote the two main Utrans values. The first transition velocity occurs earlier at Ug=0.04 m/s as compared to the column with internals, which means that the presence of internals stabilizes the bubbly flow regime. The second transition velocity (the onset of the heterogeneous flow regime) is unaffected by the internals.
In the full-length contribution, the time-dependent nature of the main transition velocities as well as the effect of the axial height on the Utrans values in bubble columns with and without internals will also be discussed in a comparable manner. A comparison between the transition velocities in the column core and annulus will also be shown.

Keywords: Bubble column with internals; Transition velocities; Kolmogorov entropy; Gas holdup fluctuations; Wire-mesh sensor; Ultrafast X-ray tomography

  • Lecture (Conference)
    Third International Symposium on Multiscale Multiphase Process Engineering, 08.-11.05.2017, Toyama City, Japan

Publ.-Id: 24457

Comparison Between the Boundaries of the Main Flow Regimes Identified by Ultrafast X-Ray Tomography in Different Parts from the Cross-Section of a Bubble Column

Nedeltchev, S.; Schubert, M.

Bubble columns are characterized by an effective phase contact, high heat and mass transfer coefficients, low maintenance and operating costs due to the absence of moving parts and low column pressure drop. Due to their numerous advantages bubble columns are used extensively in many applications (oxidation, chlorination, waste water treatment, etc.). Therefore, it is essential to have detailed knowledge about the hydrodynamic behavior of these gas-liquid contactors. The identification of the boundaries of the main hydrodynamic regimes is important for improvement of the design, operation and control of bubble columns. The main objective of our work is to apply a new identification method (based on the modified Shannon entropy) to x-ray tomography data for accurate determination of the boundaries of the main hydrodynamic regimes (homogeneous, transition and heterogeneous).
The time series (extracted from reconstructed raw images) were measured by means of ultrafast x-ray tomography (sampling frequency=1000 Hz) in a bubble column (0.1 m in ID) and they were subsequently treated by the modified Shannon entropy algorithm developed by Nedeltchev et al. (2016). The raw time series give very good information about the x-ray attenuation and they are measure for the density distribution and the fraction of gas phase in different regions from the column’s cross-section. The column was equipped with a perforated plate distributor (55 holes, Ø 0.5×10-3 m) and operated with an air-deionized water system at ambient conditions. The tomographic scans were performed at an axial height of 0.5 m.
The data were organized in groups of 100 points and their sums were calculated. These sums were needed for the calculation of the probabilities of appearance of a particular value in the time series and the local Shannon entropies. It was found that the maximum sum can be used as a flow regime identifier. It was shown that two well-pronounced minima can be distinguished in the maximum sum values extracted at different superficial gas velocities Ug in the central part of the column’s cross-section. The first local minimum occurs at Ug=0.03 m/s and identifies the end of the homogeneous regime. The onset of the heterogeneous regime occurs at Ug=0.07 m/s. It was illustrated that the information entropy extracted from the data in the entire cross-section is capable of identifying the two main transition velocities at 0.025 m/s and 0.085 m/s. So, it was concluded that the heterogeneous regime starts somewhat earlier in the center of the cross-section. The homogeneous regime in the center and the entire cross-section ends at practically the same Ug value (0.025-0.03 m/s). It is noteworthy that for air-water system the theoretical prediction (0.029 m/s) by the correlation of Reilly et al. (1994) is very close to our experimental results.
Such a comparison has been performed at 20 different segments of the column’s cross section. The approach enables the preparation of a radial profile of the transition velocities. Flow regime identification results based on the maximum sums, information amounts and Shannon entropies are compared and discussed.

Keywords: Bubble column; x-ray tomography; Shannon entropy; flow Regime identification

  • Lecture (Conference)
    ASME 2016 Heat Transfer, Fluids Engineering & Nanochannels, Microchannels and Minichannels Conference, 10.-14.07.2016, Washington DC, USA

Publ.-Id: 24456

LC-MS supported studies on the metabolism of the sigma-1 receptor ligand (–)-(S)-[18F]fluspidine

Ludwig, F.-A.; Fischer, S.; Houska, R.; Hoepping, A.; Patt, M.; Wünsch, B.; Sabri, O.; Steinbach, J.; Brust, P.

Objectives: In an ongoing clinical study (–)-(S)-[18F]fluspidine (1, 2) is being investigated for imaging of sigma-1 receptors in patients with major depression by PET. Beside estimation of the fraction of unchanged radiotracer in plasma and urine, radiometabolites formed should be detected and their structures elucidated.
Methods: (–)-(S)-[18F]Fluspidine or unlabelled reference were incubated with human liver microsomes (HLM) in presence of NADPH and/or activated glucuronic acid (UDPGA) at 37°C. Metabolites were detected by radio-HPLC or LC-MS and characterized by aid of reference compounds or structural elucidation using different MS methods (EPI, MS3). Plasma (10, 20, 30 min p.i) and urine (90 min p.i.) samples of human subjects receiving 268 (245-290) MBq (–)-(S)-[18F]fluspidine i.v. were investigated and compared to results from HLM incubations.
Results: By incubation with HLM mainly 3 hydroxylation products and one debenzylation product were formed. The product hydroxylated at the alkyl side chain was glucuronidated subsequently. Plasma samples (10, 20, 30 min p.i.) obtained from human showed 97.7%, 93.8%, and 88.6% (SD=2.6-7.9, n=6-8) of unchanged tracer. In urine (90 min p.i.) the fraction of tracer was 0–7.8% (average of 2.3%, n=10) and up to 3 main radiometabolites were detected (Figure 1). The one with the highest intensity, also found in plasma, matched the glucuronide formed in vitro. Debenzylation of the parent tracer was detected with a small proportion.
Conclusions: The results demonstrate an appropriate metabolic stability of (–)-(S)-[18F]fluspidine for the application as PET ligand. The structure of the major radiometabolite found in plasma and urine could be assigned by means of in vitro studies. Routes of metabolism are currently investigated in more detail. 302
[1] German Clinical Trial Register, DRKS-ID: DRKS00008321
[2] Fischer et al. Eur. J. Nucl. Med. Mol. Imaging 2011, 38, 540–551

  • Poster
    International Symposium On Radiopharmaceutical Sciences (ISRS), 14.-19.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)1, 385
    DOI: 10.1002/jlcr.3508

Publ.-Id: 24455

Non-linear quantum dynamics in strong and short electromagnetic fields

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

In our contribution we give a brief overview of two widely discussed quantum processes: electron-positron pairs production off a probe photon propagating through a polarized short-pulsed electromagnetic (e.m.) (e.g.\ laser) wave field or generalized Breit-Wheeler process and a single a photon emission off an electron interacting with the laser pules, so-called non-linear Compton scattering. We show that at small and moderate laser field intensities the shape and duration of the pulse are very important for the probability of considered processes. However, at high intensities the multi-photon interactions of the fermions with laser field are decisive and completely determined all aspects of subthreshold electron-positron pairs and photon production

Publ.-Id: 24452

The impact of the revised 17O(p,α)14N reaction rate on 17O stellar abundances and yields

Straniero, O.; Bruno, C. G.; Aliotta, M.; Best, A.; Boeltzig, A.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Cristallo, S.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Piersanti, L.; Prati, P.; Samorjai, E.; Strieder, F.; Szucs, T.; Takács, M. P.; Trezzi, D.

Context. Material processed by the CNO cycle in stellar interiors is enriched in 17O. When mixing processes from the stellar surface reach these layers, as occurs when stars become red giants and undergo the first dredge up, the abundance of 17O increases. Such an occurrence explains the drop of the 16O/17O observed in RGB stars with mass larger than 1.5 M_\solar. As a consequence, the interstellar medium is continuously polluted by the wind of evolved stars enriched in 17O . Aims. Recently, the Laboratory for Underground Nuclear Astrophysics (LUNA) collaboration released an improved rate of the 17O(p,alpha)14N reaction. In this paper we discuss the impact that the revised rate has on the 16O/17O ratio at the stellar surface and on 17O stellar yields. Methods. We computed stellar models of initial mass between 1 and 20 M_\solar and compared the results obtained by adopting the revised rate of the 17O(p,alpha)14N to those obtained using previous rates. Results. The post-first dredge up 16O/17O ratios are about 20% larger than previously obtained. Negligible variations are found in the case of the second and the third dredge up. In spite of the larger 17O(p,alpha)14N rate, we confirm previous claims that an extra-mixing process on the red giant branch, commonly invoked to explain the low carbon isotopic ratio observed in bright low-mass giant stars, marginally affects the 16O/17O ratio. Possible effects on AGB extra-mixing episodes are also discussed. As a whole, a substantial reduction of 17O stellar yields is found. In particular, the net yield of stars with mass ranging between 2 and 20 M_\solar is 15 to 40% smaller than previously estimated. Conclusions. The revision of the 17O(p,alpha)14N rate has a major impact on the interpretation of the 16O/17O observed in evolved giants, in stardust grains and on the 17O stellar yields.

Keywords: Nuclear Astrophysics


Publ.-Id: 24451

Active and passive electronics for smart implants

Makarov, D.

The portable consumer electronics necessitates functional elements to be lightweight, flexible, and wearable [1-4]. The unique possibility to adjust the shape of the devices offered by this alternative formulation of the electronics provides vast advantages over the conventional rigid devices particularly in medicine and consumer electronics. There is already a remarkable number of available flexible devices starting from interconnects, sensing elements towards complex platforms consisting of communication and diagnostic components.
We developed shapeable magnetoelectronics [5] – namely, flexible [6-8], printable [9,10], stretchable [11,12] and even imperceptible [13] magnetosensitive large area elements, which were completely missing in the family of flexible electronics, e.g. for smart skin applications. On the other hand, we realized self-assembled compact tubular microchannels based on strain engineering [14] with integrated passive sensory elements [15-17] and communication antenna devices [18] for on-chip and bio-medical applications, e.g. smart implants [19,20].
Combining these two research directions carried out at different length scales into a single truly interdisciplinary topic opens up the novel field of smart biomimetics [20]. In this respect, we demonstrated mechanically and electrically active compact biomimetic microelectronics, which can serve as a base for realization of novel regenerative neuronal cuff implants with unmatched functionalities. The biomimetic microelectronics can mechanically adapt to and impact the environment possessing the possibility to assess, adopt and communicate the environmental changes and even stimulate the environment electrically.
In my talk, these recent developments will be covered.

[1] M. G. Lagally, MRS Bull. 32, 57 (2007).
[2] J. A. Rogers et al., Nature 477, 45 (2011).
[3] S. Bauer et al., Adv. Mater. 26, 149 (2014).
[4] M. Kaltenbrunner et al., Nature 499, 458 (2013).
[5] D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
[6] G. Lin, D. Makarov et al., Lab Chip 14, 4050 (2014).
[7] M. Melzer, D. Makarov et al., Adv. Mater. 27, 1274 (2015).
[8] N. Münzenrieder, D. Makarov et al., Adv. Electron. Mater. (2016), 10.1002/aelm.201600188.
[9] D. Karnaushenko, D. Makarov et al., Adv. Mater. 27, 880 (2015).
[10] D. Karnaushenko, D. Makarov et al., Adv. Mater. 24, 4518 (2012).
[11] M. Melzer, D. Makarov et al., Adv. Mater. 27, 1333 (2015).
[12] M. Melzer, D. Makarov et al., Nano Lett. 11, 2522 (2011).
[13] M. Melzer, D. Makarov et al., Nat. Commun. 6, 6080 (2015).
[14] O. G. Schmidt et al., Nature 410, 168 (2001).
[15] I. Mönch, D. Makarov et al., ACS Nano 5, 7436 (2011).
[16] C. Müller, D. Makarov et al., Appl. Phys. Lett. 100, 022409 (2012).
[17] E. J. Smith, D. Makarov et al., Lab Chip 12, 1917 (2012).
[18] D. D. Karnaushenko, D. Makarov et al., NPG Asia Materials 7, e188 (2015).
[19] D. Karnaushenko, D. Makarov et al., Adv. Mater. 27, 6582 (2015).
[20] D. Karnaushenko, D. Makarov et al., Adv. Mater. 27, 6797 (2015).

Keywords: shapeable magnetoelectronics; magnetic field sensors

  • Invited lecture (Conferences)
    MRS Fall Meeting 2016, 27.11.-02.12.2016, Boston, USA

Publ.-Id: 24450

Observations on surface magnetic order in FeGe and FeSi

Makarov, D.; Streubel, R.; Perez Rodriguez, N.; Pierce, D. T.; Unguris, J.; Pofahl, S.; Schäfer, R.; Schmidt, M.; Baenitz, M.; Kronast, F.; Wilhelm, H.; Rößler, U. K.

The twisted magnetization textures in chiral magnets are inherently frustrated, similarly to the mesophases in chiral liquid-crystals. The twisted basic texture can become dramatically altered by the penetration of secondary twists over larger lengths and the formation of defects. Hence, a well-ordered and smooth texture like a simple spiral may be twisted or defected. In chiral liquid-crystal systems, the frustration results in the formation of defects like the disclination networks of blue phases or twisted-grain-boundary phases. Such states can easily be shaped and transformed under the influence of competing anisotropies, e.g., by applied fields in the bulk and by anchoring the molecules of a liquid crystal at surfaces.
We investigated surfaces of FeGe single crystals with the cubic B20 structure using various magnetic imaging techniques and found a ferromagnetic order above the magnetic ordering transition in the bulk. This ferromagnetic order is seen by magnetic optical Kerr effect (MOKE) microscopy as a simple ferromagnetic domain structure of an Ising-like magnet at room-temperature. Scanning electron microcopy with polarization analysis (SEMPA) and X-ray photoemission electron microscopy (XPEEM) allowed us to follow the evolution of a fine-structure in this ferromagnetic surface upon lowering the temperature, when the bulk of the FeGe crystal orders into the spiral ground-state.
We discover a static defect-ordered state with a network of line-defects emerges near the surface under the influence of a particular surface-magnetic ordering transition. These defects of the helical magnetic order are topologically necessary lines where the magnetic order becomes singular or passes through zero at elevated temperatures. This ferromagnetic skin has a strong uniaxial anisotropy and frustrates the helimagnetic texture by anchoring it to the surface. In the spiral below the Neel temperature at 279 K, conical modulations in the ferromagnetic surface layer are observed that prove the formation of a network of dislocations because the propagation direction of the surface-modulation deviates from the propagation direction in the bulk. Near magnetic ordering temperature a coexistence of bubble-like circular domains and stripes is observed in the surface layer. This illustrates the appearance of complex three-dimensional textures with defects, double-twists and spiral-like kinks near the surface and related to the particular surface-magnetic ordering. Hence, at the first-order transition between the precursor state and spiral order in zero magnetic field of FeGe, a co-existence of helical and skyrmionic textures is revealed. Ab initio calculations have been used to motivate the existence of enhanced spin-moments at the surfaces of FeGe and an increased effect of spin-orbit coupling. This explains the experimental observations of a surface-magnetic ordering in FeGe, which acts like a strongly uniaxial ferromagnetic film with an Ising-like character on the underlying spiral bulk state.
Similar experiments using MOKE and XPEEM on the isostructural compound FeSi give evidence of a fragile magnetic ordering at the surface of this anomalous paramagnetic semiconductor, too. This may mean that the FeSi surfaces may behave like strongly anisotropic ultrathin magnetic films, while no magnetic long-range ordering takes place in the bulk.

Keywords: FeGe; FeSi; skyrmions

  • Invited lecture (Conferences)
    MRS Fall meeting 2016, 27.11.-02.12.2016, Boston, USA

Publ.-Id: 24449

Argonne: Curved magnetic nanomembranes

Makarov, D.

While conventionally magnetic films and structures are fabricated on flat surfaces, the topology of curved surfaces has only recently started to be explored and leads to new fundamental physics as well as applied device ideas [1]. In particular, novel effects occur when the magnetization is modulated by curvature providing a new degree of freedom that leads to new magnetization configurations (see for instance [2,3]) and is predicted to have major implications on the spin dynamics due to topological constraints for instance in circular tubes and rolls [4].
Advances in this novel field solely rely on the understanding of the fundamentals behind the modifications of magnetic responses of 3D-curved magnetic thin films. The lack of an inversion symmetry and the emergence of a curvature induced effective anisotropy and Dzyaloshinskii-Moriya interaction are characteristic of curved surfaces [5-7], leading to curvature-driven magnetochiral effects [8-10] and topologically induced magnetization patterning [7, 11], including unlimited domain wall velocities in hollow tubes [4], chirality symmetry breaking [7-10] and Cherenkov-like effects for magnons [12]. In addition to these rich physics, the application potential of 3D-shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications [13], spin-wave filters [14], magneto-encephalography devices [15] and high-speed racetrack memory devices [4]. To this end, the initially fundamental topic of the magnetism in curved geometries strongly benefited from the input of the application-oriented community, which among others explores the shapeability aspect of the curved magnetic thin films. These activities resulted in the development of the family of shapeable magnetoelectronics [16], which already includes flexible [17], printable [18], stretchable [19] and even imperceptible [20] magnetic field sensorics.
These recent developments starting from the theoretical predictions to the fabrication and characterization of 3D-curved magnetic thin films and their application potential are in the focus of this talk.
[1] R. Streubel, DM et al., J. Phys. D: Appl. Phys. vol. 49, pp. 363001, 2016.
[4] M. Yan et al., Phys. Rev. Lett. vol. 104, pp. 057201, 2010.
[5] Y. Gaididei et al., Phys. Rev. Lett. vol. 112, pp. 257203, 2014.
[6] O. V. Pylypovskyi, DM et al., Phys. Rev. Lett. vol. 114, pp. 197204, 2015.
[7] O. V. Pylypovskyi, DM et al., Sci. Rep. vol. 6, pp. 23316, 2016.
[8] R. Hertel, SPIN vol. 03, pp. 1340009, 2013.
[9] M. Yan et al., Appl. Phys. Lett. vol. 100, pp. 252401, 2012.
[10] J. A. Otalora et al., Appl. Phys. Lett. vol. 100, pp. 072407, 2012.
[11] V. P. Kravchuk, DM et al., Phys. Rev. B vol. 85, pp. 144433, 2012.
[12] M. Yan et al., Phys. Rev. B vol. 88, pp. 220412, 2013.
[13] I. Mönch, DM et al., ACS Nano vol. 5, pp. 7436, 2011.
[14] F. Balhorn et al., Phys. Rev. Lett. vol. 104, pp. 037205, 2010.
[15] D. Karnaushenko, DM et al., Adv. Mater. vol. 27, pp. 6582, 2015.
[16] D. Makarov et al., Appl. Phys. Rev. vol. 3, pp. 011101, 2016.
[17] M. Melzer, DM et al., Adv. Mater. vol. 27, pp. 1274, 2015.
[18] D. Karnaushenko, DM et al., Adv. Mater. vol. 27, pp. 880, 2015.
[19] M. Melzer, DM et al., Nano Lett. vol. 11, pp. 2522, 2011.
[20] M. Melzer, DM et al., Nature Commun. vol. 6, pp. 6080, 2015.

Keywords: curved magnetic thin films; chiral interactions

  • Invited lecture (Conferences)
    Seminar at Argonne National Lab, 28.11.2016, Lemont, USA

Publ.-Id: 24448

New data for cosmogenic 53Mn and 60Fe in iron meteorites

Smith, T.; Leya, I.; Merchel, S.; Rugel, G.; Pavetich, S.; Fröhlich, M.; Wallner, A.; Fifield, K.; Tims, S.; Korschinek, G.; Faestermann, T.

Cosmogenic nuclides in meteorites can provide information on cosmic ray exposure (CRE) histories. In space, meteoroids are irradiated by galactic cosmic ray particles, inducing the production of cosmogenic nuclides (10Be, 26Al, 36Cl, 41Ca, 53Mn, 60Fe). Meteorites are routinely measured for 10Be, 26Al, and 36Cl. However the database for 53Mn and 60Fe is scarce due to the low availability of high-MV accelerators and the debate over the half-lives of 53Mn and 60Fe. We Report new 53Mn and 60Fe data for iron meteorites measured at Canberra (53Mn, 60Fe) and Munich (60Fe). Among these radionuclides, 53Mn has the longest half-life, thus is least influenced by terrestrial ages. The advantage of 53Mn and 60Fe isotopes is that only two (Fe, Ni) and one (Fe) target element(s), respectively, dominate production, overcoming the problem of inhomogeneous S and P distribution. Our new 60Fe data almost doubles that present in the literature. We measured 53Mn in seven subsamples of the iron meteorite Twannberg. The new 53Mn and 60Fe data, with 10Be, 26Al, 36Cl, 41Ca and the noble gases, will better constrain the CRE histories of meteorites and will also serve as benchmarks to validate and improve Monte-Carlo model calculations.

Keywords: AMS; meteorite; cosmogenic; exposure age; accelerator mass spectrometry

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 06.-10.03.2017, Mainz, Deutschland

Publ.-Id: 24447

Spin torque switching in nanopillars with antiferromagnetic reference layer

Arora, M.; Fowley, C.; Mckinnon, T.; Kowalska, E.; Sluka, V.; Deac, A. M.; Heinrich, B.; Girt, E.

Spin-transfer-torque induced switching is investigated in 200 nm diameter circularly shaped, perpendicular magnetized nanopillars. A synthetic antiferromagnet, consisting of two Co/Ni multilayers coupled anti-ferromagnetically across a Ru layer, is used as a reference layer to minimize the dipolar field on the free layer. The free layer is a single 4x[Co/Ni] multilayer. The use of Pt and Pd was avoided to lower the spin-orbit scattering in magnetic layers and intrinsic damping in the free layer, and therefore, reduce the critical current required for spin-transfer-torque switching. The intrinsic Gilbert damping of a continuous 4[Co/Ni] multilayer film was measured by ferromagnetic resonance to be alpha = 0.022, which is significantly lower than in Pt or Pd based magnetic multilayers. In zero magnetic field the critical current required to switch the free layer from the parallel to antiparallel alignment is 5.2 mA, and from antiparallel to parallel alignment is 4.9 mA. Given the volume of the free layer, V_FL = 1.011022 m3, the switching efficiency, I_c=(V_FL/µ0H_c), is 5.281020 A/Tm^3, twice as efficient as any previously reported device with a similar structure

Keywords: Spin transfer switching; perpendicular magnetic anisotropy; MRAM


Publ.-Id: 24446

Mass spectrometry and the evolution of the western Namibian drainage systems

Gärtner, A.; Linnemann, U.; Merchel, S.; Niedermann, S.; Gerdes, A.; Rugel, G.; Scharf, A.; Le Bras, L.; Hofmann, M.; Zieger, J.

Our multi-method MS study (AMS, noble gas MS, LA-(MC)-ICP-MS) aims to constrain the evolution of the western Namibian drainages since the last ca. 40 Ma. Therefore, fluvial sediments of several rivers and their precursors were sampled. In order to obtain precise Surface exposure ages of the various terrace levels, the routinely used cosmogenic nuclides 10Be, 21Ne, 26Al (quartz), and 36Cl (calcite) were applied either on surface samples or on depth-profiles consisting of 3 to 5 samples each. U-Pb small scale isochrone (SSI) ages of calcareous matrices were also used for terrace dating. Sedimentary provenances were revealed by detrital zircon (ZrSiO4) geochronology using U-Th-Pb and Lu-Hf isotope systematics. They indicate varying detrital zircon patterns through time. Our approach facilitates the recognition of changes in the fluvial sediment provenance at certain points in time. Such combined studies have a huge potential for revealing the palaeohydrological history, and to estimate amplitudes and processing Speeds of past events or changing sizes of catchment areas, which is of particular interest for modelling the palaeoclimate and palaeogeography.

Keywords: AMS; accelerator mass spectrometry; palaeoclimate; LA-ICP-MS

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 06.-10.03.2017, Mainz, Deutschland

Publ.-Id: 24445

Generic zinc corrosion studies at PWR LOCA conditions

Harm, U.; Kryk, H.; Wiezorek, M.; Hampel, U.

During the sump recirculation phase after loss-of-coolant accidents (LOCA) in pressurized water reactors (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps. The long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, supporting grids of sump strainers) may cause corrosion of the corresponding materials influencing the cooling water chemistry.
Generic investigations regarding such zinc corrosion processes, changes of the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden (TUD) and Zittau/Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD were focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting clogging effects [1-2].
Recent results of generic experiments in a lab-scale corrosion test facility led to further information regarding the main parameters determining the zinc corrosion rates and the whole corrosion process in such scenarios.
Main influences on the zinc corrosion rates were identified as the impact of the coolant jet onto the corroding surface and the particular flow conditions around submerged zinc surfaces.
In contrast, variations of the coolant temperature in the range between 25 °C and 70 °C as well as small changes in the boric acid concentration have no significant influence on the corrosion rates during the first stage of the corrosion process.
Further lab-scale experiments at realistic time-dependent LOCA parameters like calculated temperature courses in the sump and inside the reactor core are planned to evaluate, if zinc corrosion processes with subsequent zinc borate precipitations could lead to considerable clogging effects inside the reactor core.
The results obtained at lab-scale were complemented by corresponding experiments in semi-technical test facilities of the project partner HSZG.

[1] Seeliger, A.; Alt, S.; Kästner, W.; Renger, S.; Kryk, H., Harm, U. : Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - thermo- and fluid-dynamic effects. Nuclear Engineering and Design, 2016, 305, 489-502
[2] Hoffmann, W.; Kryk, H.; Seeliger, A.; Kästner, W.; Alt, S. & Renger, S.: Zinc corrosion after loss-of-coolant accidents in pressurized water reactors - physicochemical effects. Nuclear Engineering and Design, 2014, 280, 570-578

  • Contribution to proceedings
    48. Jahrestagung Kerntechnik (Annual Meeting on Nuclear Technology / AMNT 2017), 16.-17.05.2017, Berlin, Deutschland
    Generic Zinc Corrosion Studies At PWR LOCA Conditions, Berlin: INFORUM Verlags- und Verwaltungsgenossenschaft mbH, 978-3-926956-96-5
  • Lecture (Conference)
    48. Jahrestagung Kerntechnik (Annual Meeting on Nuclear Technology / AMNT 2017), 16.-17.05.2017, Berlin, Deutschland

Publ.-Id: 24444

Entwicklung und Überprüfung eines Photonenmodells für die Abstrahlung durch hochenergetische Elektronen

Burau, H.

This diploma thesis extends the open source particle-in-cell code PIConGPU by two new physics modules which incorporate effects of radiation emission and back reaction of highly relativistic electrons in strong electromagnetic background fields into the simulation. The first module involves the treatment of nonlinear Thomson- and Compton-scattering using the synchrotron approximation. It allows for the generation of X-ray and gamma photons in the classical regime as well as in the QED regime including self consistent radiation back reaction. Through simulations of collisions between laser pulses and electron bunches the impact of QED effects on experimental spectra is investigated. The second module covers the scattering of electrons on atomic nuclei including electron deflection and generation of Bremsstrahlung-photons. In a numerical case study it is shown that the analysis of Bremstrahlung can be used as experimental diagnostic for electron dynamics in overdense plasmas.

Keywords: PIConGPU; QED radiation reaction; nonlinear Comptonscattering; Bremsstrahlung

  • Diploma thesis
    TU Dresden, 2016
    Mentor: Prof. Ulrich Schramm, Prof. Tom Cowan, Dr. Michael Bussmann

Publ.-Id: 24443

Erste Tests für 44Ti-AMS an DREAMS

Scharf, A.; Bemmerer, D.; Ditrói, T.; Khojasteh, N.; Merchel, S.; Rugel, G.; Zuber, K.

Das Radionuklid 44Ti (T1/2 = 58,9 a) wird vor allem während Supernovaexplosionen gebildet und spielt eine wichtige Rolle für deren theoretische Modelle und die Nukleosynthese schwerer Elemente. In Supernovaüberresten kann 44Ti mittels &gamma-Astronomie nachgewiesen werden, allerdings befinden sich die Beobachtungen nicht im Einklang mit den theoretischen Modellen. Problematisch dabei ist, dass der Wirkungsquerschnitt der Reaktion 40Ca(&alpha,&gamma)44Ti bisher nur unzureichend bekannt ist [1].
Während bislang nur 44Ti-AMS-Messungen an großen Beschleunigern (ab 10 MV Terminalspannung) durchgeführt wurden [2], sollte es prinzipiell auch möglich sein, an 6-MV-Anlagen dieses Radionuklid zuverlässig zu messen. Wir präsentieren erste Tests an der AMS-Anlage DREAMS des HZDR, die zeigen, dass mithilfe einer Degrader-Folie eine zuverlässige Abtrennung des stabilen Isobars 44Ca und Messung des Radionuklids 44Ti auch bei Beschleunigungsspannungen von 6 MV möglich ist.
Diese ersten Tests dienen dazu, die Machbarkeit von AMS-basierten Messungen des Wirkungsquerschnitts der Reaktion 40Ca(&alpha,&gamma)44Ti an DREAMS auszuloten.
Das Projekt wurde unterstützt vom DAAD.

Ref.: [1] Schmidt et al., Phys. Rev. C 88, 025803 (2013)
[2] Nassar et al., Phys. Rev. Let. 96, 041102 (2006)

Keywords: AMS; DREAMS; 44Ti; Supernova; Nukleosynthese

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 06.-10.03.2017, Mainz, Deutschland, 06.-10.03.2017, Mainz, Deutschland

Publ.-Id: 24442

Experimental investigation on the influence of surfactant concentration on the bubble shape and mass transfer in a small channel

Haghnegahdar, M.; Boden, S.; Hampel, U.

In the work presented in this paper, the shape and absorption rate of an individual elongated Taylor bubble of CO2 through contaminated water was measured in millimeter-size channel. The influence of concentration of surfactant on dissolution rate of an individual elongated Taylor bubble of carbon dioxide in water was investigated using high resolution X-ray radiography technique in vertical channels. The bubbles were held stationary in the down-flowing liquid and the liquid-side mass transfer coefficient was determined from microfocus X-ray images.
The experiments cover a range of initial bubble equivalent diameter (deq: sphere-volume equivalent bubble diameter) varying from 6 to 10 mm. The pipe is a glass pipe with 6 mm inside diameter (D). The bubble is unceasingly monitored by holding the bubble stationary using downward flow of liquid. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles (Haghnegahdar et al., 2015). The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is milli-pore water contaminated by conventional surfactants and the gas phase is CO2.
The results confirmed the accumulation of surfactants on the tail of the bubbles. Furthermore, applying different concentrations of surfactant reveals that in our case, where surface coverage ratio of surfactant on the bubbles is high, increase of contamination does not have a noticeable influence on the mass transfer coefficient of bubbles.

Keywords: Surfactant concentration; Taylor bubble; Mass transfer coefficient

  • Poster
    14th Multiphase Flow Conference and Short Course:Simulation, Experiment and Application, 08.-10.11.2016, HZDR, Dresden, Germany

Publ.-Id: 24441

Investigation of surfactant effect on the bubble shape and mass transfer in a milli-channel

Haghnegahdar, M.; Boden, S.; Hampel, U.

In the work presented in this paper, the shape and absorption rate of an individual elongated Taylor bubble of CO2 through contaminated water was measured in millimeter-size channel. The influence of presence of trace amount of surfactant on dissolution rate of an individual elongated Taylor bubble of carbon dioxide in water was investigated using high resolution X-ray radiography technique in vertical channels. The bubbles were held stationary in the down-flowing liquid and the liquid-side mass transfer coefficient was determined from microfocus X-ray images.
The experiments cover a range of initial bubble equivalent diameter (deq: sphere-volume equivalent bubble diameter) varying from 6 to 10 mm. The pipe is a glass pipe with 6 mm inside diameter (D). The bubble is unceasingly monitored by holding the bubble stationary using downward flow of liquid. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles (Haghnegahdar et al., 2015). The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is milli-pore water contaminated by conventional surfactants and the gas phase is CO2.
The results confirmed the accumulation of surfactants on the tail of the bubbles. Furtheremore, it was shown that the presence of surfactants not only decrease the rate of mass transfer, but also change the bubble shape and liquid film thickness around the bubble.

Keywords: Surfactant; Taylor bubble; Carbon dioxide

  • Contribution to proceedings
    Dynamics of Evolving Fluid Interfaces - DEFI 2016, 12.-13.10.2016, Lyon, France
    Dynamics of Evolving Fluid Interfaces - DEFI 2016
  • Lecture (Conference)
    Dynamics of Evolving Fluid Interfaces - DEFI 2016, 12.-13.10.2016, Lyon, France

Publ.-Id: 24440

X-ray tomography studies of Taylor bubbles with mass transfer in small channels

Haghnegahdar, M.; Boden, S.; Hampel, U.

For milli- and micro-reactors the bubble shape and relative velocity between two phases are mainly governed by the cross-sectional shape of the channel. For channels with circular cross section (pipes) enormous attention has been paid in the last decades and many studies on hydrodynamics and mass transfer to be found in literature. However other channel cross sections such as square channels were a subject of only a few studies [1]. Concerning the role and importance of square channels in various existing and potential industrial applications such as micro-electromechanical systems, monolith froth reactors, there exist still some gaps particularly in related aspects of transport phenomena in these channels and there needs to be further experimental work to provide detailed heat and mass transfer data for model validation.
In the work presented in this paper, the dissolution rate of a single Taylor bubble of carbon dioxide in water was investigated using high resolution X-ray radiography and tomography technique in vertical channels. The liquid side mass transfer coefficient was calculated by measuring the changes in the size of the bubble at constant pressure. The experiments cover a large range of initial Taylor bubble length varying from 4 to 26 mm. The pipe is a glass pipe with 6 mm inside diameter and square cross section. The bubbles were held stationary using the technique of Schulze and Schluender [2]. The method which is used to measure the variation of the bubble size is X-ray tomography. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. Furthermore this technique allows tomography for square channels, while full 3D shape determination by optical techniques is difficult in square channels. The processed images which give volume (and also the interfacial area) of the bubble as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation.
The results for the long term dissolution of single CO2 bubbles show that the dissolution curves for bubbles with different initial size follow the same trend and have relatively constant slope. In addition, it is shown that the measured mass transfer coefficient increases as the equivalent diameter of the bubble (diameter of the sphere having the same volume) decreases. The trend for the change of liquid-side mass transfer coefficient as a function of bubble size is in accordance with the data predictivd by the penetration theory.

Keywords: Mass transfer coefficient; Taylor flow; CO2; small channel

  • Lecture (Conference)
    DFG Priority Programme SPP 1506: Transport Processes at Fluidic Interfaces Abschlusskolloquium, 09.-10.05.2016, RWTH Aachen, Germany

Publ.-Id: 24439

Enzymatic Decolorization of Dye-polluted Water Using Natural Cellular Carriers

Mohammed, I.; Schubert, M.; Hampel, U.

In the current years increasing efforts have been done to develop sustainable processes with smaller ecological footprint, which is. to decrease the industrial pollution and the environmental impact.
One serious pollutant that results from the textile industry etc. is the increasing usage of dyes. The treatment of dye-polluted water is still challenging since today's methods, such as absorption and membrane filtration, have their limitations.
The application of biocatalysts represents a sustainable solution as it results in nontoxic products at comparable eco-friendly treatment costs. In particular, oxidation enzymes, such as laccase, which can oxidize dye are in the scope. However, direct application of laccase enzyme is not favorable because it requires processes to recover the enzyme, while enzymes, immobilized on a carrier can be re-used as long as the activity is sufficiently high.
Loofa is a natural-grown material of the cucumber family, which provides attractive morphological properties. Moreover, loofa carrier can be decomposed after the process without additional treatment and is inexpensive.
In the contribution, the developed laccase immobilization methodology and the optimization of the immobilization using the Response Surface Methodology (RMS) will be discussed. Furthermore, the capability to degrade dye-polluted water will be evaluated and a novel bioreactor for the water treatment will be suggested

Keywords: Laccase; Enzymatic decolorization; Loofa sponge; Immobilization; Response surface methodology

  • Lecture (Conference)
    66th Canadian Chemical Engineering Conference(CSCh2016), 16.-19.10.2016, Quebec, Canada

Publ.-Id: 24438

In situ, steerable, hardware-independent and data-structure agnostic visualization with ISAAC

Matthes, A.; Hübl, A.; Widera, R.; Grottel, S.; Gumhold, S.; Bussmann, M.

The computation power of supercomputers grows faster than the bandwidth of their storage and network. Especially applications using hardware accelerators like Nvidia GPUs cannot save enough data to be analyzed in a later step. There is a high risk of loosing important scientific information. We introduce the in situ template library ISAAC which enables arbitrary applications like scientific simulations to live visualize their data without the need of deep copy operations or data transformation using the very same compute node and hardware accelerator the data is already residing on. Arbitrary meta data can be added to the renderings and user defined steering commands can be asynchronously sent back to the running application. Using an aggregating server, ISAAC streams the interactive visualization video and enables user to access their applications from everywhere.

Keywords: HPC; in situ; visualization; live rendering; petascale; particle-in-cell; C++11; CUDA; Alpaka; FOSS

Publ.-Id: 24437

Photon emissivity in the vicinity of a critical point - A case study within the quark meson model

Wunderlich, F.; Kämpfer, B.

The quark meson (linear sigma) model with linearized fluctuations displays at a critical end point the onset of a curve of first-order phase transitions (FOPTs) located at non-zero chemical potentials and temperatures below a certain cross-over temperature. The model qualifies well for an illustrative example to study the impact of the emerging FOPT, e.g. on photon emissivities. Such a case study unravels the tight interlocking of the phase structure with the emission rates, here calculated according to lowest-order tree level processes by kinetic theory expressions. It is the strong dependence of the rates on the effective masses of the involved degrees of freedom which distinctively vary over the phase diagram thus shaping the emissivity accordingly. At the same time, thermodynamic properties of the medium are linked decisively to these effective masses, i.e. a consistent evaluation of thermodynamics, governing for instance adiabatic expansion paths, and emission rates is maintained within such an approach.


Publ.-Id: 24436

Enzymatic Decolorization of Dye-polluted Water Using Natural Cellular Carriers 66th Canadian Chemical Engineering Conference/2016

Mohammed, I.; Schubert, M.; Hampel, U.

In the current years increasing efforts have been done to develop sustainable processes with smaller ecological footprint, which is. to decrease the industrial pollution and the environmental impact.
One serious pollutant that results from the textile industry etc. is the increasing usage of dyes. The treatment of dye-polluted water is still challenging since today's methods, such as absorption and membrane filtration, have their limitations.
The application of biocatalysts represents a sustainable solution as it results in nontoxic products at comparable eco-friendly treatment costs. In particular, oxidation enzymes, such as laccase, which can oxidize dye are in the scope. However, direct application of laccase enzyme is not favorable because it requires processes to recover the enzyme, while enzymes, immobilized on the carrier can be re-used as long as the activity is sufficiently high.
Loofa is a natural-grown material of the cucumber family, which provides attractive morphological properties. Moreover, loofa carrier can be decomposed after the process without additional treatment and is inexpensive.
In the contribution, the developed laccase immobilization methodology and the optimization of the immobilization using the Response Surface Methodology (RMS) will be discussed. Furthermore, the capability to degrade dye-polluted water will be evaluated and a novel bioreactor for the water treatment will be suggested

Keywords: Laccase; Enzymatic decolorization; Loofa sponge; Immobilization; Response surface methodology

  • Lecture (Conference)
    66th Canadian Chemical Engineering Conference, 16.-19.10.2016, Québec city, Quebec, Canada

Publ.-Id: 24435

Microbial reduction of uranium by anaerobic microorganisms isolated from a former uranium mine

Gerber, U.; Krawczyk-Bärsch, E.; Arnold, T.; Scheinost, A. C.

The former uranium mine Königstein (Germany) is currently in the process of a controlled flooding for remediation purposes. However, the flooding water still contains high concentrations of uranium and other heavy metals. For that reason the water has to be cleaned up by a conventional waste water treatment. The aim of this study was to investigate the interactions between anaerobic microorganisms and uranium for possible bioremediation approaches due to the fact, that microorganisms could be used as an alternative for the intensive and expensive waste water treatment.
Flooding water from the former uranium mine was directly sampled and gas-flushed with N2. 10 mM glycerol was added as carbon source. The approaches were incubated for six weeks at 30 °C. Samples were taken three times a week for measuring of the redox potential. Every week samples were taken to investigate the redox state of uranium by XANES (X-ray absorption near edge structure) measurements. During the incubation time the redox potential decreased from 660 mV to 300 mV. By Iterative Target-Factor Analysis (ITFA) it was determined that 100 % of uranium(VI) was reduced to uranium(IV) within six weeks of incubation. In addition, investigations of the supernatant with UV-vis resulted in the same findings. The results show that naturally occurring anaerobic microorganisms within the flooding water of the former uranium mine Königstein are able to reduce the soluble uranium(VI) into the less soluble uranium(IV). In conclusion, anaerobic microorganisms within the flooding water could be used as an alternative for bioremediation approaches.

Keywords: uranium reduction; bioremediation; sulphate-reducing bacteria

  • Lecture (Conference)
    BioRemid2017, 09.-10.03.2017, Granada, Espana

Publ.-Id: 24434

Dipolar Relaxation Dynamics at the Active Site of an ATPase Regulated by Membrane Lateral Pressure

Fischermeier, E.; Pospíšil, P.; Sayed, A.; Hof, M.; Solioz, M.; Fahmy, K.

The active transport of ions across biological membranes requires their hydration shell to interact with the interior of membrane proteins. However, the influence of the external lipid phase on internal dielectric dynamics is hard to access by experiment. Using the octahelical transmembrane architecture of the copper-transporting P1B-type ATPase from Legionella pneumophila as a model structure, we have established the site-specific labeling of internal cysteines with a polarity-sensitive fluorophore. This enabled dipolar relaxation studies in a solubilized form of the protein and in its lipid-embedded state in nanodiscs. Time-dependent fluorescence shifts revealed the site-specific hydration and dipole mobility around the conserved ion-binding motif. The spatial distribution of both features is shaped significantly and independently of each other by membrane lateral pressure.

Keywords: ATPase; fluorescence; time-resolved; nanodisc; membrane protein


Publ.-Id: 24433

Multiphase flow measurement

Hampel, U.

The lecture introduces and discusses principles of multiphase flow measurement. In detail it addresses fundamental issues of multiphase fluid dynamics, measureable parameters, hardware and software aspects of measurement techniques, as well as its relation to multiphase flow modelling and CFD code development.

Keywords: multiphase flow; flow measurement; local probes; PIV; tomography

  • Invited lecture (Conferences)
    Iraqi-German Partnership on Multiphase Flow Research and Training (IGP-Multiflow), Summer School, 03.-07.10.2016, Dresden, Germany

Publ.-Id: 24432

Curvature-Induced Asymmetric Spin-Wave Dispersion

Otálora, A. S.; Yan, M.; Schultheiss, H.; Hertel, R.; Kákay, A.

In magnonics, spin waves are conceived of as electron-charge-free information carriers. Their wave behavior has established them as the key elements to achieve low power consumption, fast operative rates, and good packaging in magnon-based computational technologies. Hence, knowing alternative ways that reveal certain properties of their undulatory motion is an important task. Here, we show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in thin films. The dispersion relation is asymmetric regarding the sign of the wave vector. It is a purely curvature-induced effect and its fundamental origin is identified to be the classical dipole-dipole interaction. The analytical expression of the dispersion relation has the same mathematical form as in thin films with the Dzyalonshiinsky-Moriya interaction. Therefore, this curvatureinduced effect can be seen as a “dipole-induced Dzyalonshiinsky-Moriya-like” effect.

Keywords: nanotubes; spin-wave dispersion; non-reciprocal


Publ.-Id: 24431

Avoiding pitfalls: Better performance of AMS at DREAMS

Rugel, G.; DREAMS-Users; Khojasteh, B. N.; Merchel, S.; Scharf, A.; Ziegenrücker, R.

Since autumn 2011, the DREsden AMS-facility (DREAMS), is performing routine AMS at the 6MV tandem accelerator of the ion beam centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf [1,2]. In routine operation are measurements of 10Be, 26Al, 36Cl, 41Ca, and 129I for a wide range of applications. Most of the samples are prepared at our own chemistry labs – or in close cooperation with the users – to allow best performance for diverse tasks [3]. Our performance to measure these routine isotopes improved considerably over the last years [2]. This successful approach needs a careful selection of measurement parameters like a propper measurement order, a specific tuning using low-level (traceable) standards and individual setting of detector parameters for each beam time. One example for an additional improvement is the low-background value of 26Al/27Al = 6 × 10−16 reached in blanks from commercial carriers. For 41Ca measurements we get 30% more transmission, while having ten times less background from 41K. Further promising developments include the upgrade to nonroutine
AMS-nuclides like 44Ti [4] and to actinides [5].
Ref.: [1] S. Akhmadaliev et al., NIMB 294 (2013) 5.
[2] G. Rugel et al., NIMB 370 (2016) 94.
[3] S. Merchel, this conference.
[4] A. Scharf, this conference.
[5] Nasrin B. Khojasteh, this conference.

Keywords: AMS; DREAMS; Be-10; Al-26; Cl-35; Ca-41; I-129

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Atome, Moleküle, Quantenoptik und Plasmen (SAMOP), 06.-10.03.2017, Mainz, Deutschland

Publ.-Id: 24430

Comparing field ionization models in simulations of laser-matter interaction

Garten, M.

Field ionization plays an important role in modeling the interaction of high-power, ultra-short lasers pulses with matter. Many field ionization models exist that have predictive capability at non-relativistic laser intensities and for laser pulse durations that much longer than the atomic time scales. Most existing models take a quasi-static approach to the laser field on atomic dimensions and time scales. Yet, with pulses as short as a few ~10 to ~100 as and intensities of 10 21 W/cm 2 the feasibility of these approximations becomes questionable. Still the exploration of plasma effects in relativistic laser matter interaction requires to test the boundaries of validity for these models. This thesis will take a step to point out the difficulties to be considered when existing ionization models are applied to such extreme cases.

Keywords: ionization; atomic physics; high-power; ultra-short; lasers

  • Bachelor thesis
    TU Dresden, 2013
    Mentor: Thomas Cowan, Ulrich Schramm
    0071 Seiten


Publ.-Id: 24429

Modelling Field Ionization in PIConGPU

Garten, M.; Huebl, A.; Widera, R.; Pausch, R.; Debus, A.; Burau, H.; Kluge, T.; Huang, L.; Bussmann, M.

It is vital to treat field ionization adequately and validate the different existing models critically in order to obtain trustworthy results from plasma simulations. This poster presents numerical methods for modelling field ionization in laser-plasma interactions. Based on results obtained in earlier Monte-Carlo simulations on CPU and later application to the fully-relativistic particle-in-cell code PIConGPU it is pointed out that different ionization models and the details of modelling field ionization can have a major influence on plasma dynamics.

Keywords: ionization; particle-in-cell; PIConGPU

  • Poster
    Summer School: Atoms and Plasmas in Super-Intense Laser Fields, 12.-22.07.2015, Erice, Italia

Publ.-Id: 24428

Short Wavelength Magnons in Magnetic Vortex Structures

Dieterle, G.; Förster, J.; Gangwar, A.; Wintz, S.

In recent years magnonics has become one of the prime topics in magnetics research. The prospect of possible technological applications has played a major part in this development. The reliable generation of spin waves with short wavelengths is an ongoing challenge in this eld, as it is di cult by means of a patterned stripline antenna. Here we report on the imaging of spiral shaped short wavelength spin waves emitted by a magnetic vortex core in a permalloy disc. We take advantage of the magnetic perturbation generated by the small moving core, 10-20nm in diameter, to generate spin waves of sub-100nm wavelength. Imaging of these waves has been done using Time-Resolved Scanning Transmission X-Ray Microscopy at the MAXYMUS endstation of the BESSY II synchrotron facility. The experimentally derived dispersion relations match with analytical expressions for hybridized modes between Damon-Eshbach and exchange dominated magnons in in nite ferromagnetic lms. This holds as well for our micromagnetic simulations in these vortex structures.

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion kondensierte Materie, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 24427

Ultra-fast thermal processing of TCO and other thin films

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

Thermal processing in the ms 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. The presentation focuses on the FLA of transparent conducting oxides.

Keywords: flash lamp annealing; thin film applications; transparent conducting oxide

  • Invited lecture (Conferences)
    6. Workshop Transparente leitfähige Materialien, 22.-23.11.2016, Erfurt, Deutschland

Publ.-Id: 24426

Practical demonstration of Eulerian & Lagrangian MPF simulation

Esch, T.; Krepper, E.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of a rectangular bubble colum and of a spray. Modeling advices and datasets are given.

Keywords: Bubble column; ANSYS-CFX; ANSYS-FLUENT

  • Lecture (Conference)
    14th Multiphase Flow Conference and Short Course: Simulation, Experiment and Application, 08.-10.11.2016, Dresden, Germany

Publ.-Id: 24425

Control of the magnetization dynamics through the Magneto- Elastic coupling effect

Finizio, S.; Wintz, S.; Kirk, E.; Suszka-Gorzny, A.; Gilga, S.; Raabe, J.

The magneto-elastic (ME) coupling has recently become of inter- est thanks to its numerous applications, e.g. in the fabrication of magneto-electric multiferroics. This effect has been recently studied quasi-statically on micro- and nanostructured magnetostrictive materials strained using piezoelectric substrates. However, due to limitations in the RF properties of piezoelectric materials, the influence of the ME coupling on the magneto-dynamical processes has not yet been investigated in depth. Here, thanks to a newly-developed approach that allows the in-situ straining of magnetostrictive materials whilst preserving good RF properties of the substrate, we present a first study of the influence of the ME coupling on the gyration dynamics of magnetic vortices in microstructured magnetostrictive elements using time-resolved x-ray magnetic microscopy. In particular, we observe that the application of a strain to the magnetostrictive material leads to a reduction of the gyration eigenfrequency, and to a modification of the orbit of the vortex core, both of which can be controlled by changing the magnitude of the applied strain.

  • Poster
    DPG Frühjahrstagung der Sektion kondensierte Materie, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 24424

Optical double fiber probe for online measurements in multiphase reactors

Meitzner, C.; Schäfer, T.; Hampel, U.; Lange, R.

A variety of measurement techniques already exist to characterize multiphase flows in large scale as well as in mini scale systems. But when looking at smaller dimensions than millimeters and higher flow velocities the amount of available techniques diminishes drastically. Another problem is the capability of existing solutions to be applicable for online measurements even in non-transparent systems. On this account the current work presents a measurement technique based on optical fibers which is comparable to other commonly applied techniques, but additionally works in a running chemical reaction process. The current work deals with the validation of the double fiber system and a detailed comparison to several widely accepted conventional and modern measurement techniques. These are high speed camera, gravimetric analysis and ultrafast X-ray tomography. The experimental work has been performed in a cold flow loop operating setup with a gas-liquid flow. The final aim has been to characterize the multiphase flow in a mini channel system of a monolith. The investigated monoliths have a cell density of 39 cpsi and 400 cpsi and are made of Cordierite, an opaque ceramic material. By using the developed optical fiber system and the mentioned reference techniques parameters like bubble velocity, flow regime, hold-up or phase distribution have been assessed to compare the common techniques with the newly developed fiber system. The presented fiber optic measurement technique allows reliable, reproducible measurements of local phase characteristics. The mounting space of maximum 250 μm realizes a high local resolution even at small scales. In comparison to other techniques high level of agreement has been proven.

Keywords: optical double fiber probe; multiphase reactors; multiphase flow; monolith

  • Lecture (Conference)
    ProcessNet Jahrestreffen der Fachgruppe Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland
  • Contribution to proceedings
    ProcessNet Jahrestreffen der Fachgruppe Reaktionstechnik 2017, 22.-24.05.2017, Würzburg, Deutschland

Publ.-Id: 24423

Towards a fully atomistic modelling of laser-plasma interaction in PIConGPU.

Garten, M.; Huebl, A.; Burau, H.; Grund, A.; Widera, R.; Zacharias, M.; Kluge, T.; Bussmann, M.

In laser-generated plasmas the free electron density is a crucial parameter for plasma dynamics. Therefore, to model its spatial and temporal evolution the adequate treatment of ionization is vital. This poster presents the work in progress on numerical field ionization methods implemented in the world's fastest 3D3V electromagnetic particle-in-cell code PIConGPU. Thus, computing a value for the systematic error via repeating simulations with varying ionization schemes is in reach. With high performance computing we can give a range of validity for predictions of pump-probe experiments with high power lasers and X-ray free electron lasers.

Keywords: ionization; particle-in-cell; PIConGPU; XFEL

  • Poster
    Annual HZDR PhD Seminar 2016, 17.-19.10.2016, Ahorn Hotel Oberwiesenthal, Deutschland

Publ.-Id: 24422

Just-in-time Dosimetry using Positron Emission Tomography

Zacharias, M.; Bussmann, M.; Schöne, S.; Widera, R.; Eckert, C.; Zenker, E.

Outline of data acquisition requirements of in-beam dosimetry using Positron Emission Tomography and presentation of the developed GPU code "raptr".

Keywords: raptr PET dosimetry GPU

  • Lecture (Conference)
    Topical Workshop on Parallel Computing for Data Acquisition and Online Monitoring, 07.-08.03.2016, Karlsruher Institut für Technologie, Deutschland
  • Lecture (Conference)
    CSCS-USI Summer School 2016, 17.-28.07.2016, Hotel Serpiano, Schweiz

Publ.-Id: 24421

Enhancing field ionization modeling in PIConGPU towards a fully atomistic description of laser-matter interaction

Garten, M.; Huebl, A.; Burau, H.; Grund, A.; Widera, R.; Zacharias, M.; Kluge, T.; Bussmann, M.

In laser-generated plasmas the free electron density is a crucial parameter for plasma dynamics. Therefore, to model its spatial and temporal evolution the adequate treatment of ionization is vital. This poster presents the work in progress on numerical field ionization methods implemented in the world's fastest 3D3V electromagnetic particle-in-cell code PIConGPU. Thus, computing a value for the systematic error via repeating simulations with varying ionization schemes is in reach. With high performance computing we can give a range of validity for predictions of pump-probe experiments with high power lasers and X-ray free electron lasers.

Keywords: ionization; particle-in-cell; PIConGPU; XFEL

  • Poster
    EUCALL Annual Workshop 2016, 31.08.2016, HZDR, Deutschland

Publ.-Id: 24420

Analysis and applications of a multi-field approach for plunging jet configurations

Krepper, E.; Lucas, D.; Zidouni, F.

A generalized approach developed for the simulation of two-phase flow problems with multi-scale interfacial structures is applied for the simulation of a plunging jet. The GEneralized TwO Phase flow (GENTOP) modeling approach considers different scales in term of interfacial structure. The explicit statistical simulation of the interface between continuous gas and fluid is combined with the Euler/Euler simulation of dispersed gas. For the dispersed gas the Multiple Size Group (MUSIG) approach simulates different bubble sizes. The mass transfer between the bubble sizes is considered by bubble breakup and coalescence models. The gas entrainment during the plunging jet is described by the transition between continuous gas and dispersed gas. Therefor a special sub grid model is applied.
This set of models is applied for the simulation of plunging jet experiments performed by Chanson et al. (2004). In the tests different geometric scales of plunging jet were investigated and here analyzed. The paper shows the capabilities of this approach and identifies weak points which need further development.

Keywords: CFD; two phase flow; Euler/Euler approach; interfacial area; plunging jet

  • Contribution to proceedings
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 13.-15.09.2016, Cambridge, USA
  • Lecture (Conference)
    Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 13.-15.09.2016, Cambridge, USA

Publ.-Id: 24419

Gamma-ray computed tomography for investigations on centrifugal pumps under gas entrainment conditions

Schäfer, T.

The lecture gives an introduction to high-resolution gamma-ray computed tomography and its application for quantitative measurements and visualization of two-phase flow in industrial and scientific applications. Exemplarily, recent results from investigations on an industrial centrifugal pump under several gas entrainment conditions will be presented.

Keywords: gamma-ray computed tomography; two-phase flow; centrifugal pump

  • Lecture (others)
    Iraqi-German Partnership on Multiphase Flow Research and Training (IGP-Multiflow), Summer School 2016, 02.-09.10.2016, Dresden, Deutschland

Publ.-Id: 24417

Simulation of an MSLB scenario using the 3D neutron kinetic core model Dyn3D coupled with the CFD software Trio U

Grahn, A.; Gommlich, A.; Kliem, S.; Bilodid, Y.; Kozmenkov, Y.

In the framework of the European project NURESAFE, the reactor dynamics code DYN3D, developed at HZDR, was coupled with the CFD solver Trio_U, developed at CEA France, in order to replace DYN3D’s one-dimensional hydraulic part with a full three-dimensional description of the coolant flow in the reactor core at higher spatial resolution. The present document gives an introduction into the coupling method and shows results of its application to the simulation of an MSLB accident of a PWR.

Keywords: reactor safety; code coupling; thermal hydraulics; computational fluid dynamics; reactor dynamics


Publ.-Id: 24416

Unsteady single phase natural circulation flow mixing prediction using 3D thermal-hydraulic system and CFD codes

Bousbia Salah, A.; Ceuca, S. C.; Puragliesi, R.; Mukin, R.; Grahn, A.; Kliem, S.; Vlassenbroeck, J.; Austregesilo, H.

Advanced 3D computational tools are increasingly used to simulate complex phenomena occurring during scenario involving operational transients and accidents in nuclear power plants. Among these scenarios, one can mention the asymmetric coolant mixing under natural circulation flow regimes. This issue motivated some detailed experimental investigations carried out within the OECD/NEA PKL projects. The aim of these investigations was, besides the assessment of the mixing phenomenon in the reactor pressure vessel, to provide experimental data for computer code validations. In the current study, the ROCOM/PKL-3 T2.3 experimental test is assessed using on one hand thermal-hydraulic system codes with 3D capabilities, and on the other hand a CFD computational tool. The results emphasize the capabilities and the differences between the considered computational tools as well as their suitability for such purposes.


Publ.-Id: 24415

Editorial for special issue on process tomography in flow measurement and instrumentation

Hampel, U.

Analysis and control of industrial processes is inseparably interlinked with appropriate process measurement techniques. Among such distributed sensing, imaging and tomography are emerging technologies, which gain more and more attention, as they have the capability to measure field quantities. Research and application in the field of process tomography is continuously intense and recently many innovative concepts and ideas have been born and demonstrated. Exchange of knowledge within the process tomography community and transfer of knowledge to research and industry are supported by the International Society for Industrial Process Tomography on the basis of regular expert meetings. This special issue is a compilation of the 21 most important contributions from the 7th International Symposium on Industrial Process Tomography ISPT7, held in Dresden, Germany, Sept. 1-4, 2015. It covers a broad range of process tomography technologies but also a broad range of technology readiness levels from very fundamental aspects, such as raw data processing or new methods of analysis of tomographic images, new modalities, such as microwave tomography, up to important industrial applications, such as cyclone separators, bubble column reactors and waste water abatement.

Keywords: process tomography; flow measurement


Publ.-Id: 24414

Tackling challenges in AMS sample preparation

Merchel, S.; Le Bras, L.; Gurlit, S.; Rugel, G.; Scharf, A.; Opel, T.; Wetterich, S.

Since 2009 the DREAMS (DREsden Accelerator Mass Spectrometry) facility offers users to do their own sample preparation for AMS targets. A large number of samples from interdisciplinary research Topics such as astronomy, climate, cosmochemistry and geology could be transformed into BeO, Al2O3, AgCl and CaF2 showing reasonable to excellent performance [Rugel et al., this DPG.]. However, besides our constant approach to become a little better every day, sometimes very new challenges can arise due to the low availability of the sample material, low radionuclide concentration or a possible contamination of the sample with disturbing elements and nuclides. Two examples:
Ice samples are always in our focus. As we were facing Problems with 10Be contamination in "dirty" ground ice, we measured 36Cl and natCl by isotope dilution in permafrost ice wedge samples as heavy as 1.6 kg. The chemical yield of AgCl was only 20-35% (and is a function of total natCl), which might be improved by preconcentration steps.
For the determination of in-situ or atmospheric 26Al in marine and terrestrial sediments [e.g. Gärtner et al., this DPG.], we had sometimes unaccountable low chemical yields, which seems to be partially due to
redissolving aluminium hydroxide in the last washings.
Thanks to A. Gärtner, P. Ludwig, D. Rodrigues and several students for providing/processing samples.

Keywords: AMS; accelerator mass spectrometry

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 06.-10.03.2017, Mainz, Deutschland

Publ.-Id: 24413

Methoden der Zustandsüberwachung von Transport- und Lagerbehältern für abgebrannte Brennelemente und wärmeentwickelnde hochradioaktive Abfälle bei verlängerter Zwischenlagerung

Hampel, U.

Der Vortrag stellt das vom BMWi geförderte gleichnamige Vorhaben vor. In diesem werden nichtinvasive Prüf- und Überwachunsgmethoden zur Erkennung von Veränderungen des Inventars von Transport- und Lagerbehältern (Typ CASTOR) auf ihre Machbarkeit untersucht. Hintergund ist die in Deutschland absehbare verlängerte Zwischenlagerung abgebrannter Brennelemente in Trockenlägern an den heutigen Kernkraftwerksstandorten. Für Zwischenlagerungszeiträume von mehreren Jahrzehnten ist heue keine verlässliche Aussage über etwaige Zustandsveränderungen an den Brennelementen möglich. Daher kommt nichtinvasiven Monitoringverfahren für den Behälterinhalt ein große Bedeutung zu. Untersucht werden Verfahren auf Basis von Gamma-, Neutronen- und Myonenstrahlung, akustische und schwingungsspektroskopische Verfahren sowie Thermographieverfahren.

Keywords: Nukleare Sicherheit; verlängerte Zwischenlagerung; Brennelemente; Trockenlager; Transport- und Lagerbehälter; CASTOR; Monitoring

  • Invited lecture (Conferences)
    12. Projektstatusgespräch zu BMWi-geförderten FuE-Projekten zur Entsorgung radioaktiver Abfälle, 09.-10.11.2016, Karslruhe, BRD

Publ.-Id: 24412

Multiphase flow measurement via tomography : fundamentals, challenges and needs

Hampel, U.

The invited lecture discussed and demonstrates the application of tomographic imaging in multiphase flow measurement. Thereby the discussion is guided along prototypical application examples in the fields of oil and gas production, chemical engineering and nuclear engineering. Emphasize is given to open quesions and future needs to improve applicability and significance of tomographic imaging techniques in fundmental and engineering research.

Keywords: multiphase flow; flow measurement; tomograpy; chemical engineering; nuclear engineering; oil and gas production

  • Invited lecture (Conferences)
    8th World Congress On Industrial Process Tomography, 26.-29.09.2016, Iguassu Falls, Brasilien

Publ.-Id: 24411

Analysis of self-assembled monolayer coating and the influence on dropwise condensation

Unger, S.; Sarker, D.; Hampel, U.

Das Phänomen der Tropfenkondensation, sowie der damit verbundene hohe Wärmeübertragungskoeffizient, haben ein großes Potential für die Optimierung industrieller Kondensationsprozesse. Ein wesentlicher Parameter der Kondensationsoberfläche bei der Tropfenkondensation ist der Kontaktwinkel eines Flüssigkeitstropfens auf einer Oberfläche. Insbesondere bei Arbeitsmedien mit geringen Oberflächenspannungen, sind niedrige Oberflächenenergien notwendig, um Tropfenkondensation zu realisieren. Selbst-aggregierende Monoschichten (SAM) auf der Basis von Phosphonsäure stellen eine Möglichkeit zur Herstellung von hydrophoben Oberflächen dar, welche auch bei Instandhaltung nachträglich aufgebracht oder erneuert werden können. Der Einfluss derartiger Beschichtungen auf das Verhalten von Kondensationssystemen wird untersucht.
Ein hoher Kontaktwinkel kennzeichnet die hydrophobe Eigenschaft einer Oberfläche, welche mit Hilfe von SAM durch ein auf Phosphonsäure basierendes nass¬chemisches Verfahren erzeugt wurde. Durch eine Kombination von künstlich eingestellter Rauigkeit und SAM-Beschichtung ist es möglich Kontaktwinkel in einem weiten Spektrum gezielt einzustellen. Dies eröffnet die Möglichkeit, individuell auf den Kondensationsprozess und Dampfgehalt angepasste Funktionsflächen zu fertigen.
Besonders hohe Kontaktwinkel wurden auf Proben mit hoher Rauigkeit und bei SAM mit langen Kohlenstoffketten gemessen. Aufgrund des nasschemischen Beschichtungsverfahrens können beliebige Geometrien, wie beispielsweise innen-berippte Rohre und Hohlstrukturen, behandelt werden. Dies ermöglicht die gezielte Beeinflussung der Wärmeübertragungseigenschaften und des Kondensat-Ablaufes in einer Struktur. In einem integralen Versuchsstand wird der Einsatz dieser neuartigen Wärmeübertragerflächen mit hoher Auflösung untersucht.

Keywords: dropwise condensation; condensation; heat transfer

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

Publ.-Id: 24410

Bioremediation of uranium contaminated sites by Acidovorax facilis - a microscopic and spectroscopic study

Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.

For remediation of uranium contaminated environments from activities such as uranium mining and uranium processing, microorganisms could be important due to their ability to immobilize radionuclides and heavy metals. To improve bioremediation strategies based on a better understanding of binding mechanisms on the molecular level, we applied uranium interaction experiments with Acidovorax facilis, an aerobic, Gram-negative Betaproteobacteria, which is commonly found in soils. Experiments were performed in batch cultures under aerobic conditions at 25 °C using nutrient broth. The cells were grown to an optical density (OD600) of around 1.5. For sorption experiments UO2(NO3)2 was added to the culture to achieve an initial uranium concentration of 0.05 and 0.1 M, respectively, at a neutral pH range. Energy-filtered transmission electron microscopy (EF-TEM) coupled with electron energy-loss spectroscopy (EELS) and time-resolved laser fluorescence spectroscopy (TRLFS) were applied. The results provide spectroscopically and microscopically evidence of uranium sorbed at the outer membrane of Acidovorax f. cells by showing high electron density and uranium ionization intensity peaks. In addition, uranium was detected in the small polyphosphate granules of the cells, indicating the formation of a uranyl-phosphate complex as a result of an intracellular bioaccumulation process. The results support the TRLFS measurements, concluding that uranium is bound on carboxylic functionality groups, e.g., peptidoglycan (R−COO−UO2) and either on phosphoryl groups, e.g., uranyl-lipopolysaccharide-complexes R-O-PO3-UO2 and [R-O-PO3]2-UO22- of the outer membrane [1].
[1] Barkleit, A. et al. (2008). Dalton Transaction 2879-2886.

Keywords: uranium; bioremediation; Acidovorax f; EF-TEM; TRLFS

  • Lecture (Conference)
    BioRemid2017, 09.-10.03.2017, Granada, Espana

Publ.-Id: 24409

Structure of interfaces in GaN/AlN and Ge/Si multilayered heterosystems by XAFS spectroscopy

Erenburg, S. B.; Trubina, S. V.; Zhuravlev, K. S.; Malin, T. V.; Zinovyev, V. A.; Dvurechenskii, A. V.; Kuchinskaya, P. A.; Kvashnina, K. O.

III-nitride heterostructures in the form of multilayered quantum wells (MQWs) or quantum dots (QDs) and interacting Ge QDs (“quantum molecules”) are promising candidates for high-speed intersubband (ISB) optical devices relying on the quantum confinement of electrons. Microstructural parameters (interatomic distances, coordination numbers, and Debye–Waller factors) were determined by means of EXAFS spectroscopy based on the Synchrotron Radiation, and the relationship between the variations in these parameters and the morphology of superlattices and symmetric assembles of QDs were established. The EXAFS technique has been used to study the local structure of thin hexagonal GaN/AlN MQWs grown by ammonia MBE at different temperatures. It is shown that the heterointerface intermixing leads to a decrease in the Ga-Al interatomic distance and the Ga–Ga coordination number in MQWs. The degree of intermixing in the boundary layers rises from 30% to 40% with increase of the growth temperature from 795 to 895◦ C. It was found that in the first phase of quantum molecules growth Ge atoms concentration is 25%. With further growth (deposition of the base layers) Ge concentration increases up to 35–45%, depending on the temperature (from 610 to 550◦C) of deposition

  • Open Access Logo Contribution to proceedings
    XXXI International Conference on Equations of State for Matter (ELBRUS2016), 01.03.-06.11.2016, Elbrus, Kabardino-Balkaria, Russia
    Journal of Physics: Conference Series 774(2016), 012128
    DOI: 10.1088/1742-6596/774/1/012128

Publ.-Id: 24407

Shape change of biogenic elemental selenium nanomaterials decreases their colloidal stability

Jain, R.; Jordan, N.; Tsushima, S.; Hübner, R.; Weiss, S.; Lens, P.

Selenium is an important element for technology and dietary supplements but it is toxic at slightly higher concentration. Thus, its removal from the wastewaters is important. Microbial reduction of selenium oxyanions in thermophilic bioreactor (55 oC) removed higher selenium when compared to the control mesophilic bioreactor (30 oC). This study demonstrated that the better performance of the thermophilic bioreactor was due to the better settling properties of biogenic elemental selenium nanorods (BioSe-Nanorods) produced in thermophilic conditions compared to biogenic elemental selenium nanospheres (BioSe-Nanospheres) produced in mesophilic conditions. The BioSe-Nanorods were less colloidally stable than the extracellular polymeric substances (EPS) capped BioSe-Nanospheres as demonstrated by the former's lesser negative zeta potential values when exposed to elevated concentrations of NaCl and CaCl2 as well as better settling in different lake waters. The lower colloidal stability was due to a lesser negative surface charge density of BioSe-Nanorods compared to BioSe-Nanospheres. This study also argued that the EPS were the corona of BioSe-Nanorods as well. Further, this study observed that the formation of BioSe-Nanorods proceeds via BioSe-Nanospheres. This study demonstrates the importance of the shape of nanoparticles in determining their bioremediation effectiveness and the fate in the environment.

Keywords: Surface charge density; ζ-potential; microbial reduction; selenium nanorods; DFT


Publ.-Id: 24406

Interatomic potential to study the formation of NiCr clusters in high Cr ferritic steels

Bonny, G.; Bakaev, A.; Olsson, P.; Domain, C.; Zhurkin, E. E.; Posselt, M.

Under irradiation NiSiPCr clusters are formed in high-Cr ferritic martensitic steels as well as in FeCr model alloys. In the literature little is known about the origin and contribution to the hardening of these clusters. In this work we performed density functional theory (DFT) calculations to study the stability of small substitutional NiCr-vacancy clusters and interstitial configurations in bcc Fe. Based on DFT data and experimental considerations a ternary potential for the ferritic FeNiCr system was developed. The potential was applied to study the thermodynamic stability of NiCr clusters by means of Metropolis Monte Carlo (MMC) simulations. The results of our simulations show that Cr and Ni precipitate as separate fractions and suggest only a limited synergetic effect between Ni and Cr. Therefore our results suggest that the NiCrSiP clusters observed in experiments must be the result of other mechanisms than the synergy of Cr and Ni at thermal equilibrium.

Keywords: interatomic potential; Fe-Cr-Ni alloys; precipitates; clusters

Publ.-Id: 24405

Terahertz free-electron laser spectroscopy of excitons in III-V semiconductor quantum wells and single quantum dots

Schneider, H.; Stephan, D. R.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Eßer, F.; Helm, M.

Using intense, spectrally narrow terahertz pulses from the free-electron laser facility FELBE in Dresden, Germany, we have investigated exciton population dynamics in III-V QWs and single quantum dots. To this end, carriers are optically injected by picosecond near-infrared pulses to populate the lowest excitonic level. Using narrowband terahertz pulses, excitons are resonantly excited into higher levels. Time-dependent photoluminescence measurements based on a streak camera system and on time-correlated photon counting, respectively, then allow us to study the transient population of dipole-allowed higher exciton levels and to access the relaxation dynamics.

Keywords: excitons; GaAs; quantum well; quantum dot; terahertz; free-electron laser; time-resolved photoluminescence

  • Invited lecture (Conferences)
    SPIE Photonics Asia, Symposium on "Infrared, Millimeter Wave, and Terahertz Technologies", 12.-14.10.2016, Beijing, China

Publ.-Id: 24404

Terahertz free-electron laser spectroscopy of semiconductor nanostructures

Schneider, H.

This talk reviews recent spectroscopic studies on semiconductor nanostructures using the THz free-electron laser FELBE. Its intense, quasi-continuous, nearly transform-limited ps pulses provide unique research opportunities to advance THz science.

Keywords: spectroscopy; terahertz; free-electron laser

  • Invited lecture (Conferences)
    The 8th International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPTW 2016), 10.-12.10.2016, Chongqing, China

Publ.-Id: 24403

MHD sloshing instability in liquid metal batteries

Horstmann, G. M.; Weber, N.; Weier, T.

Liquid metal batteries (LMBs) are discussed today as a cheap grid scale energy storage, as required for the deployment of fluctuating renewable energies. LMBs incorporate stratified three-layer fluid systems consisting of two liquid metal electrodes separated by a thin molten salt electrolyte. Due to the high electrical conductivities of the liquid metals, LMBs are highly susceptible for becoming unstable by MHD interactions of magnetic fields induced by internal and external currents. Besides the Tayler instability and the electrovortex instability, the so-called sloshing instability, also known as the metal pad roll instability in aluminum reduction cells, was identified as a key instability mechanism capable to cause short-circuits. Dimensionless stability parameters derived from inviscid two-layer systems can predict the onsets for sloshing and short-circuits with some success for a limited parameter range, but the two-layer description is far from perfect. To quantify the two-layer limitations, a three-layer dispersion relation was derived and deviations from the two-layer system were discussed. On this basis it is planned to extract three-layer stability criteria additionally including viscous damping to predict instability onsets in direct dependence of the geometrical parameters and material properties of LMBs. Further to this, three-layer experiments are under development aiming to measure the interaction and stability of interfacial waves using Doppler Ultrasound Velocimetry (DOP) and Magnetic Field Tomography (MFT) for checking the validity of different stability criteria.

Keywords: MHD; Sloshing; Liquid Metal Battery

  • Poster
    MHD Days 2016, 30.11.-02.12.2016, Göttingen, Deutschland

Publ.-Id: 24402

Long-range interactions in the effective low energy Hamiltonian of Sr2IrO4: a core level resonant inelastic x-ray scattering study

Agrestini, S.; Kuo, C.-Y.; Moretti Sala, M.; Hu, Z.; Kasinathan, D.; Ko, K.-T.; Glatzel, P.; Rossi, M.; Cafun, J.-D.; Kvashnina, K. O.; Matsumoto, A.; Takayama, T.; Takagi, H.; Tjeng, L. H.; Haverkort, M. W.

We have investigated the electronic structure of Sr2IrO4 using core level resonant inelastic x-ray scattering. The experimental spectra can be well reproduced using ab initio density functional theory based multiplet ligand field theory calculations, thereby validating these calculations. We found that the low-energy, effective Ir t2g orbitals are practically degenerate in energy. We uncovered that covalency in Sr2IrO4, and generally in iridates, is very large with substantial oxygen ligand hole character in the Ir t2g Wannier orbitals. This has far reaching consequences, not only are onsite crystal-field energies determined by the long range crystal-structure, more significantly, magnetic exchange interactions will have long range distance dependent anisotropies in the spin direction. These findings set constraints and show pathways for the design of d5 materials that can host compass like magnetic interactions.

Publ.-Id: 24401

Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Ablyazimov, T.; Abuhoza, A.; Adak, R. P.; Adamczyk, M.; Agarwal, K.; Aggarwal, M. M.; Ahammed, Z.; Ahmad, F.; Ahmad, N.; Ahmad, S.; Akindinov, A.; Akishin, P.; Akishina, E.; Akishina, T.; Akishina, V.; Akram, A.; Al-Turany, M.; Alekseev, I.; Alexandrov, E.; Alexandrov, I.; Amar-Youcef, S.; Anđelić, M.; Andreeva, O.; Andrei, C.; Andronic, A.; Anisimov, Y.; Appelshäuser, H.; Argintaru, D.; Atkin, E.; Avdeev, S.; Averbeck, R.; Azmi, M. D.; Baban, V.; Bach, M.; Badura, E.; Bähr, S.; Balog, T.; Balzer, M.; Bao, E.; Baranova, N.; Barczyk, T.; Bartoş, D.; Bashir, S.; Baszczyk, M.; Batenkov, O.; Baublis, V.; Baznat, M.; Becker, J.; Becker, K.-H.; Belogurov, S.; Belyakov, D.; Bendarouach, J.; Berceanu, I.; Bercuci, A.; Berdnikov, A.; Berdnikov, Y.; Berendes, R.; Berezin, G.; Bergmann, C.; Bertini, D.; Bertini, O.; Beşliu, C.; Bezshyyko, O.; Bhaduri, P. P.; Bhasin, A.; Bhati, A. K.; Bhattacharjee, B.; Bhattacharyya, A.; Bhattacharyya, T. K.; Biswas, S.; Blank, T.; Blau, D.; Blinov, V.; Blume, C.; Bocharov, Y.; Book, J.; Breitner, T.; Brüning, U.; Brzychczyk, J.; Bubak, A.; Büsching, H.; Bus, T.; Butuzov, V.; Bychkov, A.; Byszuk, A.; Cai, X.; Cálin, M.; Cao, P.; Caragheorgheopol, G.; Carević, I.; Cătănescu, V.; Chakrabarti, A.; Chattopadhyay, S.; Chaus, A.; Chen, H.; Chen, L.; Chen, J.; Chepurnov, V.; Cherif, H.; Chernogorov, A.; Ciobanu, M. I.; Claus, G.; Constantin, F.; Csanád, M.; D'Ascenzo, N.; Das, S.; Das, S.; de Cuveland, J.; Debnath, B.; Dementiev, D.; Deng, W.; Deng, C.; Deppe, H.; Deppner, I.; Derenovskaya, O.; Deveaux, C. A.; Deveaux, M.; Dey, K.; Dey, M.; Dillenseger, P.; Dobyrn, V.; Doering, D.; Dong, S.; Dorokhov, A.; Dreschmann, M.; Drozd, A.; Dubey, A. K.; Dubnichka, S.; Dubnichkova, Z.; Dürr, M.; Dutka, L.; Dželalija, M.; Elsha, V. V.; Emschermann, D.; Engel, H.; Eremin, V.; Eşanu, T.; Eschke, J.; Eschweiler, D.; Fan, H.; Fan, X.; Farooq, M.; Fateev, O.; Feng, S.; Figuli, S. P. D.; Filozova, I.; Finogeev, D.; Fischer, P.; Flemming, H.; Förtsch, J.; Frankenfeld, U.; Friese, V.; Friske, E.; Fröhlich, I.; Frühauf, J.; Gajda, J.; Galatyuk, T.; Gangopadhyay, G.; García Chávez, C.; Gebelein, J.; Ghosh, P.; Ghosh, S. K.; Gläßel, S.; Goffe, M.; Golinka-Bezshyyko, L.; Golovatyuk, V.; Golovnya, S.; Golovtsov, V.; Golubeva, M.; Golubkov, D.; Gómez Ramírez, A.; Gorbunov, S.; Gorokhov, S.; Gottschalk, D.; Gryboś, P.; Grzeszczuk, A.; Guber, F.; Gudima, K.; Gumiński, M.; Gupta, A.; Gusakov, Y.; Han, D.; Hartmann, H.; He, S.; Hehner, J.; Heine, N.; Herghelegiu, A.; Herrmann, N.; Heß, B.; Heuser, J. M.; Himmi, A.; Höhne, C.; Holzmann, R.; Hu, D.; Huang, G.; Huang, X.; Hutter, D.; Ierusalimov, A.; Ilgenfritz, E.-M.; Irfan, M.; Ivanischev, D.; Ivanov, M.; Ivanov, P.; Ivanov, V.; Ivanov, V.; Ivanov, V.; Ivashkin, A.; Jaaskelainen, K.; Jahan, H.; Jain, V.; Jakovlev, V.; Janson, T.; Jiang, D.; Jipa, A.; Kadenko, I.; Kähler, P.; Kämpfer, B.; Kalinin, V.; Kallunkathariyil, J.; Kampert, K.-H.; Kaptur, E.; Karabowicz, R.; Karavichev, O.; Karavicheva, T.; Karmanov, D.; Karnaukhov, V.; Karpechev, E.; Kasiński, K.; Kasprowicz, G.; Kaur, M.; Kazantsev, A.; Kebschull, U.; Kekelidze, G.; Khan, M. M.; Khan, S. A.; Khanzadeev, A.; Khasanov, F.; Khvorostukhin, A.; Kirakosyan, V.; Kirejczyk, M.; Kiryakov, A.; Kiš, M.; Kisel, I.; Kisel, P.; Kiselev, S.; Kiss, T.; Klaus, P.; Kłeczek, R.; Klein-Bösing, C.; Kleipa, V.; Klochkov, V.; Kmon, P.; Koch, K.; Kochenda, L.; Koczoń, P.; Koenig, W.; Kohn, M.; Kolb, B. W.; Kolosova, A.; Komkov, B.; Korolev, M.; Korolko, I.; Kotte, R.; Kovalchuk, A.; Kowalski, S.; Koziel, M.; Kozlov, G.; Kozlov, V.; Kramarenko, V.; Kravtsov, P.; Krebs, E.; Kreidl, C.; Kres, I.; Kresan, D.; Kretschmar, G.; Krieger, M.; Kryanev, A. V.; Kryshen, E.; Kuc, M.; Kucewicz, W.; Kucher, V.; Kudin, L.; Kugler, A.; Kumar, A.; Kumar, A.; Kumar, L.; Kunkel, J.; Kurepin, A.; Kurepin, N.; Kurilkin, A.; Kurilkin, P.; Kushpil, V.; Kuznetsov, S.; Kyva, V.; Ladygin, V.; Lara, C.; Larionov, P.; Laso García, A.; Lavrik, E.; Lazanu, I.; Lebedev, A.; Lebedev, S.; Lebedeva, E.; Lehnert, J.; Lehrbach, J.; Leifels, Y.; Lemke, F.; Li, C.; Li, Q.; Li, X.; Li, Y.; Lindenstruth, V.; Linnik, B.; Liu, F.; Lobanov, I.; Lobanova, E.; Löchner, S.; Loizeau, P.-A.; Lone, S. A.; Lucio Martínez, J. A.; Luo, X.; Lymanets, A.; Lyu, P.; Maevskaya, A.; Mahajan, S.; Mahapatra, D. P.; Mahmoud, T.; Maj, P.; Majka, Z.; Malakhov, A.; Malankin, E.; Malkevich, D.; Malyatina, O.; Malygina, H.; Mandal, M. M.; Mandal, S.; Manko, V.; Manz, S.; Marin Garcia, A. M.; Markert, J.; Masciocchi, S.; Matulewicz, T.; Meder, L.; Merkin, M.; Mialkovski, V.; Michel, J.; Miftakhov, N.; Mik, L.; Mikhailov, K.; Mikhaylov, V.; Milanović, B.; Militsija, V.; Miskowiec, D.; Momot, I.; Morhardt, T.; Morozov, S.; Müller, W. F. J.; Müntz, C.; Mukherjee, S.; Muńoz Castillo, C. E.; Murin, Y.; Najman, R.; Nandi, C.; Nandy, E.; Naumann, L.; Nayak, T.; Nedosekin, A.; Negi, V. S.; Niebur, W.; Nikulin, V.; Normanov, D.; Oancea, A.; Oh, K.; Onishchuk, Y.; Ososkov, G.; Otfinowski, P.; Ovcharenko, E.; Pal, S.; Panasenko, I.; Panda, N. R.; Parzhitskiy, S.; Patel, V.; Pauly, C.; Penschuck, M.; Peshekhonov, D.; Peshekhonov, V.; Petráček, V.; Petri, M.; Petriş, M.; Petrovici, A.; Petrovici, M.; Petrovskiy, A.; Petukhov, O.; Pfeifer, D.; Piasecki, K.; Pieper, J.; Pietraszko, J.; Płaneta, R.; Plotnikov, V.; Plujko, V.; Pluta, J.; Pop, A.; Pospisil, V.; Poźniak, K.; Prakash, A.; Prasad, S. K.; Prokudin, M.; Pshenichnov, I.; Pugach, M.; Pugatch, V.; Querchfeld, S.; Rabtsun, S.; Radulescu, L.; Raha, S.; Rami, F.; Raniwala, R.; Raniwala, S.; Raportirenko, A.; Rautenberg, J.; Rauza, J.; Ray, R.; Razin, S.; Reichelt, P.; Reinecke, S.; Reinefeld, A.; Reshetin, A.; Ristea, C.; Ristea, O.; Rodriguez Rodriguez, A.; Roether, F.; Romaniuk, R.; Rost, A.; Rostchin, E.; Rostovtseva, I.; Roy, A.; Roy, A.; Rożynek, J.; Ryabov, Y.; Sadovsky, A.; Sahoo, R.; Sahu, P. K.; Sahu, S. K.; Saini, J.; Samanta, S.; Sambyal, S. S.; Samsonov, V.; Sánchez Rosado, J.; Sander, O.; Sarangi, S.; Satława, T.; Sau, S.; Saveliev, V.; Schatral, S.; Schiaua, C.; Schintke, F.; Schmidt, C. J.; Schmidt, H. R.; Schmidt, K.; Scholten, J.; Schweda, K.; Seck, F.; Seddiki, S.; Selyuzhenkov, I.; Semennikov, A.; Senger, A.; Senger, P.; Shabanov, A.; Shabunov, A.; Shao, M.; Sheremetiev, A. D.; Shi, S.; Shumeiko, N.; Shumikhin, V.; Sibiryak, I.; Sikora, B.; Simakov, A.; Simon, C.; Simons, C.; Singaraju, R. N.; Singh, A. K.; Singh, B. K.; Singh, C. P.; Singhal, V.; Singla, M.; Sitzmann, P.; Siwek-Wilczyńska, K.; Skwira-Chalot, I.; Som, I.; Song, G.; Song, J.; Sosin, Z.; Soyk, D.; Staszel, P.; Strikhanov, M.; Strohauer, S.; Stroth, J.; Sturm, C.; Sultanov, R.; Sun, Y.; Svirida, D.; Svoboda, O.; Szabó, A.; Szczygieł, R.; Talukdar, R.; Tang, Z.; Tanha, M.; Tarasiuk, J.; Tarassenkova, O.; Târzilă, M.-G.; Teklishyn, M.; Tischler, T.; Tlustý, P.; Tölyhi, T.; Toia, A.; Topil'Skaya, N.; Träger, M.; Tripathy, S.; Tsakov, I.; Tsyupa, Y.; Turowiecki, A.; Tuturas, N. G.; Uhlig, F.; Usenko, E.; Valin, I.; Varga, D.; Vassiliev, I.; Vasylyev, O.; Verbitskaya, E.; Verhoeven, W.; Veshikov, A.; Visinka, R.; Viyogi, Y. P.; Volkov, S.; Volochniuk, A.; Vorobiev, A.; Voronin, A.; Voronin, A.; Vovchenko, V.; Vznuzdaev, M.; Wang, D.; Wang, X.-W.; Wang, Y.; Wang, Y.; Weber, M.; Wendisch, C.; Wessels, J. P.; Wiebusch, M.; Wiechula, J.; Wielanek, D.; Wieloch, A.; Wilms, A.; Winckler, N.; Winter, M.; Wiśniewski, K.; Wolf, G.; Won, S.; Wu, K.-J.; Wüstenfeld, J.; Xiang, C.; Xu, N.; Yang, J.; Yang, R.; Yin, Z.; Yoo, I.-K.; Yuldashev, B.; Yushmanov, I.; Zabołotny, W.; Zaitsev, Y.; Zamiatin, N. I.; Zanevsky, Y.; Zhalov, M.; Zhang, Y.; Zhang, Y.; Zhao, L.; Zheng, J.; Zheng, S.; Zhou, D.; Zhou, J.; Zhu, X.; Zinchenko, A.; Zipper, W.; Zrelov, M.; Zryuev, V.; Zumbruch, P.; Zyzak, M.

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.

Publ.-Id: 24400

Nukleare Transmutation: Moderne Alchemie oder Chance für die Kernenergie?

Kögler, T.

Mit Beschluss des Bundestages vom 30. Juni 2011 wird Deutschland bis 2022 seine Kernkraftwerke schrittweise stilllegen. Mit der Energiewende soll bis 2050 ein Großteil der benötigten Energie aus regenerativen Trägern bereitgestellt werden. Bis dahin ist es ein langer und schwieriger Weg, auf welchem noch zahlreiche technologische Probleme gelöst werden müssen.
Im Gegensatz zur Bundesrepublik setzen viele Länder (z.B.: China) weiterhin auf die Kernenergie. Ein Grund dafür: neuartige Reaktorkonzepte (Gen IV) machen diese sicherer und effizienter, vor allem stellen sie Lösungen zur Beseitigung des nuklearen Abfalls vor.
Dieser Vortrag beschäftigt sich mit ausgewählten Aspekten der Energiewende, erläutert die physikalischen Prozesse die zur Erzeugung oder Vernichtung des hochradioaktiven Kernabfalls führen und gibt einen Überblick über zukünftige Reaktortechnologien und Transmutationsanlagen.

Keywords: Nukleare Transmutation; Generation IV Reaktoren; Energiewende; Beschleunigergetriebene Systeme

  • Lecture (others)
    Energie, Resourcen, Umwelt, 06.03.2017, Löbau, Deutschland
  • Lecture (others)
    Löbauer Umweltforum, 18.02.2017, Löbau, Deutschland

Publ.-Id: 24399

Terahertz spectroscopy of semiconductor nanostructures with a free-electron laser

Schneider, H.

In this talk I will present recent experimental investigations on carrier dynamics in graphene studied via pump-probe spectroscopy, on time-resolved photoluminescence dynamics of single InAs/GaAs quantum dots under pulsed inter-sublevel excitation, and on sub-diffraction limited terahertz imaging by a GaAs-based superlens studied by scattering near-field optical microscopy. The experiments have been carried out using the mid-infrared/terahertz free-electron laser facility FELBE in Dresden, Germany.

Keywords: free-electron laser; terahertz; semiconductor nanostructures

  • Lecture (others)
    Seminar, Ecole Normale Superieure, Laboratoire Pierre Aigrain, 23.09.2016, Paris, France
  • Lecture (others)
    Seminar, Chinese Academy of Engineering Physics, 18.10.2016, Chengdu, China

Publ.-Id: 24398

Terahertz-induced inter-sublevel dynamics of single InAs/GaAs quantum dots studied by micro-photoluminescence

Stephan, D.; Bhattacharyya, J.; Huo, Y. H.; Schmidt, O. G.; Rastelli, A.; Helm, M.; Schneider, H.

We explore the transient response of single self-assembled InAs/GaAs quantum dots (QD) to narrow-band terahertz (THz) pulses produced by the free-electron laser FELBE at HZDR. The THz excitation is tuned to the electron inter-sublevel s-to-p transition. For the QDs under study, this transition occurs in the range 13-20 meV because of in-situ intermixing. The THz pulse is applied at a time delay of about 0.7 ns after interband excitation. The dynamics of electron excitation and relaxation between QD sublevels is revealed by time-resolved micro-photoluminescence (PL) measurements performed on individual QDs.

Keywords: quantum dot; photoluminescence; terahertz; free-electron laser

  • Lecture (Conference)
    33rd International Conference on the Physics of Semiconductors (ICPS 2016), 31.07.-05.08.2016, Beijing, China

Publ.-Id: 24397

Terahertz pump-terahertz probe system at Novosibirsk free electron laser: commissioning and results of first experiments

Choporova, Y. Y.; Gerasimov, V. V.; Hübers, H.-W.; Knyazev, B. A.; Kulipanov, G. N.; Ovchar, V. K.; Pavelyev, V. S.; Zhukavin, R. K.; Schneider, H.; Vinokurov, N. A.; Volodkin, B. O.; Shastin, V. N.

A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser facility. Monochromatic laser radiation with a bandwidth of about 1% can be tuned within the spectral ranges of 90 - 240 and 30 - 90 μm. The laser emits radiation as a continuous stream of 100-ps pulses with a repetition rate of 5.6 MHz. The average radiation power can reach 100 W. The temperature of samples located in a helium cryostat can be varied from 2 up to 325 K. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in a germanium crystal will be presented.

Keywords: free-electron laser; pump-probe

  • Lecture (Conference)
    41st International Conference on Infrared, Millimeter and Terahertz Waves, 25.-30.09.2016, Kopenhagen, Denmark
  • Contribution to proceedings
    41st International Conference on Infrared, Millimeter and Terahertz Waves, 25.-30.09.2016, Kopenhagen, Denmark, 1-2
    DOI: 10.1109/IRMMW-THz.2016.7758465

Publ.-Id: 24396

First terahertz-range experiments on pump-probe setup at Novosibirsk free electron laser

Choporova, Y. Y.; Gerasimov, V. V.; Knyazev, B. A.; Sergeev, S. M.; Shevchenko, O. A.; Zhukavin, R. K.; Abrosimov, N. V.; Kovalevsky, K. A.; Ovchar, V. K.; Hübers, H.-W.; Kulipanov, G. N.; Shastin, V. N.; Schneider, H.; Vinokurov, N. A.

A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser. The laser emits a tunable monochromatic terahertz radiation. To prove the proper system operation, we investigated the time-resolved absorption of a sample of n-type germanium doped with antimony, which was previously investigated at the FELBE facility, in the temperature range from 5 to 50 K. The measured relaxation time amounted to about 1.7 ns, which agreed with the results obtained at FELBE. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in a germanium crystal at cryogenic temperatures are presented for wavelengths of 105, 146 and 150 μm.

Keywords: free-electron laser; pump-probe

  • Lecture (Conference)
    2016 International Conference "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia
  • Open Access Logo Contribution to proceedings
    2016 International Conference "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia
    Physics Procedia, Volume 84, Pages 1-434 (2016) Proceedings of the Int. Conf. "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016) Edited by N. A. Vinokurov and B. A. Knyazev: Elsevier, 1875-3892, 152
    DOI: 10.1016/j.phpro.2016.11.027

Publ.-Id: 24395

A light-weight compact proton gantry design with a novel dose delivery system for broad-energetic laser-accelerated beams

Masood, U.; Cowan, T. E.; Enghardt, W.; Hofmann, K. M.; Karsch, L.; Kroll, F.; Schramm, U.; Wilkens, J. J.; Pawelke, J.

Proton beams provide superior dose-conformity in radiation therapy. However, the large sizes and costs limit the widespread use of proton therapy (PT). The recent progress in proton acceleration via high-power laser systems has made it a compelling alternative to conventional accelerators, as it could potentially reduce the overall size and cost of the PT facilities. However, the laser-accelerated beams exhibit different characteristics than conventionally accelerated beams, i.e. very intense proton bunches with large divergences and broad-energy spectra. For the application of laser-driven beams in PT, new solutions for beam transport, such as beam capture, integrated energy selection, beam shaping and delivery system are required due to due to the specific beam parameters. The generation of these beams are limited by the low repetition rate of high-power lasers and this limitation would require alternative solutions for tumour irradiation which can efficiently utilize the available high proton fluence and broad-energy spectra per proton bunch to keep treatment times short. This demands new dose delivery system and irradiation field formation schemes. In this paper, we present a multi-functional light-weight and compact proton gantry design based on ironless pulsed high-field magnets for laser-driven sources. This achromatic design includes an improved beam capturing and energy selection system, with a novel beam shaping and dose delivery system, so-called ELPIS. ELPIS system utilizes magnetic fields, instead of physical scatterers, for broadening the spot-size of broadenergetic beams while capable of simultaneously scanning them in lateral directions. To investigate the clinical feasibility of this gantry design, we conducted a treatment planning study with a 3D treatment planning system augmented for the pulsed beams with optimizable broad-energetic widths and selectable beam spot sizes. High quality treatment plans could be achieved with such unconventional beam parameters, deliverable via the presented gantry and ELPIS dose delivery system. The conventional PT gantries are huge and require large space for the gantry to rotate the beam around the patient, which could be reduced up to 4 times with the presented pulse powered gantry system. With the development of next generation high-power laser systems, with petawatt laser power, necessary to reach proton energies required for therapy application, it could be possible to reduce the footprint of the PT facilities, without compromising on clinical standards.


Publ.-Id: 24394

Characterization of anisotropically shaped silver nanoparticle arrays via spectroscopic ellipsometry supported by numerical optical modeling

Gkogkou, D.; Shaykhutdinov, T.; Oates, T. W. H.; Gernert, U.; Schreiber, B.; Facsko, S.; Hildebrandt, P.; Weidinger, I. M.; Esser, N.; Hinrichs, K.

The present investigation aims to study the optical response of anisotropic Ag nanoparticle arrays deposited on rippled silicon substrates by performing a qualitative comparison between experimental and theoretical results. Spectroscopic ellipsometry was used along with numerical calculations using finite-difference time-domain (FDTD) method and rigorous coupled wave analysis (RCWA) to reveal trends in the optical and geometrical properties of the nanoparticle array. Ellipsometric data show two resonances, in the orthogonal x and y directions, that originate from localized plasmon resonances as demonstrated by the calculated near-fields from FDTD calculations. The far-field calculations by RCWA point to decoupled resonances in x direction and possible coupling effects in y direction, corresponding to the short and long axis of the anisotropic nanoparticles, respectively.

Keywords: Anisotropy; FDTD; Nanostructure characterization; Optical modeling; RCWA; Spectroscopic ellipsometry

Publ.-Id: 24393

Retention of selenium by calcium aluminate hydrate (AFm) phases under strongly reducing radioactive waste repository conditions

Rojo, H.; Scheinost, A. C.; Lothenbach, B.; Laube, A.; Wieland, E.; Tits, J.

Safety assessment studies of future nuclear waste repositories carried out in many countries predict selenium-79 to be a critical radionuclide due to its presence in the anionic form resulting in weak retardation by most common rock minerals. This assumption, however, ignores its potential uptake by AFm phases, positively charged anion exchangers which are present in significant quantities in the cementitious materials used in artificial barriers. Here we report for the first time wet chemistry and spectroscopic data on the interaction of the most reduced selenium anion species, i.e. HSe-, with two AFm phases commonly found in cement, monocarbonate (AFm-CO3) and hemicarbonate (AFm-OHCO3). Batch sorption experiments show that Se(-II) is retained much more strongly (Rd = 100±50 L kg-1) by the hemicarbonate than by the monocarbonate (Rd = 4±2 L kg-1). The cause of this different sorption behavior was elucidated by extended X-ray absorption fine-structure (EXAFS) spectroscopy, showing that Se(-II) is mainly intercalated in the larger and hence more accessible interlayer of the hemicarbonate (d-spacing = 0.82 nm), whereas most Se(-II) is sorbed by the anion exchange sites on the outer surfaces of the AFm platelets in the case of monocarbonate, where the interlayer space is less accessible due to the smaller d-spacing of 0.75 nm. EXAFS spectra of oxidation experiments further show that Se(-II) in the interlayers is better protected from oxidation than Se(-II) sorbed to the outer surfaces. The quantitative sorption data along with the molecular-scale processes obtained from this study provide crucial insight into the Se mobility in the cementitious near-field of a radioactive waste repository under reducing conditions.

Keywords: AFm phases; layered double hydroxides; selenide sorption; reducing conditions; x-ray absorption spectroscopy


Publ.-Id: 24392

A new convenient route to radiofluorinated or radioiodinated aromatic amino acid analogues

Serre, A.; Chezal, J.-M.; Canitrot, D.; Witkowski, T.; Degoul, F.; Debiton, E.; Miot-Noirault, E.; Wenzel, B.; Maisonial-Besset, A.

Aim: Amino acid transporters (AATs) are proteins that supply cells with amino acids (AAs). Cancer cells, compared to normal ones, often present a rapid growth and a high proliferation rate, supported by increased expression and/or activity of AATs. Radiolabeled AAs that intensively accumulate in tumour cells can provide high contrast SPECT or PET imaging of primary lesions and distant metastases. One of the most upregulated AAT in cancers is the LAT1 system which transports large neutral AAs as branched and aromatic ones. Therefore, a lot of radiolabelled tyrosine analogues have been developed (i.e. O-2-[18F]fluoroethyl-L-tyrosine, [18F]DOPA, [123I]ITIC(OH)). While radioiodinated derivatives of some of these electron-rich arenes are easily available, fluoroaryl analogues are particularly complicated to access by classical nucleophilic substitution with [18F]F-. Based on the ITIC(OH) scaffold, we developed a new synthetic pathway to easily produce radioiodinated or radiofluorinated tyrosine analogues.
Material and methods: A convergent synthetic pathway (Fig. 1) was designed to produce the radioiodinated tracers, reference fluorinated derivatives, and radiofluorinated compounds from common organotin intermediates. The latter were synthesized from iodinated analogues and labelled with [125I]iodide using electrophilic demetallation reaction or converted into iodonium salts for 18F-labelling. The reference fluorinated derivatives were obtained by treatment of the organotin compounds by F-TEDA-PF6. The enantiomeric excess of all produced compounds was assessed by chiral analytic HPLC analyses. For comparison, the corresponding derivatives from the series D were also synthesized.
Results: Our synthetic approach allowed the successful production of non-radioactive iodinated or fluorinated derivatives with high ee (>99%) and with a controlled position of halogenation. While, corresponding radioiodinated structures were easily synthesized using classical electrophilic substitution from organotin intermediates, the access to iodonium salt precursors and radiofluorinated derivatives warranted a lot of investigations to achieve acceptable (radio)chemical yields. Chiral analytical HPLC analyses revealed that no racemisation occurred during radiolabelling with [125I]iodide or [18F]fluoride.
Conclusion: We developed an efficient method to access to radioiodinated or radiofluorinated cyclic tyrosine analogues via organotin and iodonium salt intermediates. This strategy could be extended to a broad range of electron-rich aromatic derivatives.

Fig. 1. Convergent synthetic approach to access to radioiodinated and radiofluorinated cyclic tyrosine analogues via organotin intermediates

  • Poster
    ISRS2017 - 22nd International Symposium on Radiopharmaceutical Sciences, 14.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, 184
    DOI: 10.1002/jlcr.3508

Publ.-Id: 24391

Understanding the temperature-dependent evolution of solution processed metal oxide transistor characteristics based on molecular precursor derived amorphous indium zinc oxide

Sanctis, S.; Hoffmann, R. C.; Precht, R.; Anwand, W.; Schneider, J. J.

Amorphous indium zinc oxide (IZO) thin films are accessible by solution-deposition of mixtures of molecular single-source precursors with dimethyl 2-hydroxyimino- and 2-nitromalonato ligands (dmm-NOH and Hdmm-NO2, respectively). Thermal combustion of the precursor molecules In3O3(dmm-NO2)3.(toluene) and [Zn4O(dmm-NO)6] leads to a highly exothermic decomposition reaction yielding amorphous indium zinc oxide (IZO) even at a temperature of 150 °C. The main aim of the present investigation is to correlate the electronic performance in such solution processed field-effect transistors (FET) with the presence of surface groups and bulk defects depending on the processing temperatures of the resulting IZO films (250 to 400 °C). In depth electronic characterization using X-Ray- and Photoelectron Emission Spectroscopy (XPS and UPS) reveals major electronic changes during thin film formation in the temperature range between 275 and 300 °C. These findings are confirmed by Positron Annihilation Spectroscopy (PAS) which allows the monitoring of defects in a picometer range in the resulting functional IZO thin films. Resulting transistor mobilities (m) of the semiconducting IZO films are in the range of those of amorphous silicon even at a processing temperature of 250 °C and increase up to 6 and 9.5 cm2 (V s)-1 at 350 and 400 °C with on/off ratios of 105 up to 107, respectively.

Keywords: indium zinc oxide; XPS; UPS; PAS; electronic properties

Publ.-Id: 24390

Bi(III) immobilization inside MIL-101: enhanced photocatalytic performance

Kovalenko, K. A.; Ruban, N. V.; Adonin, S. A.; Korneev, D. V.; Erenburg, S. B.; Trubina, S. V.; Kvashnina, K.; Sokolov, M. N.; Fedin, V. P.

A novel hybrid material Bi(III)@MIL-101 (Bi(III) = Bi-containing oxoclusters, MIL-101 = chromium(III) oxoterephthalate) has been obtained by the intra-pore hydrolysis of guest bismuth(III) chloride in ammonia solution. The compound was fully characterized by chemical analysis, PXRD, nitrogen sorption and TEM techniques. According to characterization techniques all Bi species are only inside matrix and elemental analysis reveals ca. 1 Bi atom per mesocage. The chemical structure of Bi(III)-containing clusters inside MIL-101 matrix has been suggested according to EXAFS study. The catalytic activity of Bi(III)@MIL-101 has been tested in photodegradation of methyl red (MR). An introduction of Bi(III)-species inside MIL-101 has significantly increased the photocatalytic performance in comparison with layered BiOCl which has been obtained in the same synthetic conditions without MIL-101.


Publ.-Id: 24389

The State of Platinum in Pyrite Studied by X-Ray Absorption Spectroscopy of Synthetic Crystals

Filimonova, O. N.; Nickolsky, M. S.; Trigub, A. L.; Chareev, P. V.; Kvashnina, K. O.; Kovalchuk, E. V.; Vikentyev, I. V.; Tagirov, B. R.

Pyrite (FeS2) is a typical container of Pt in ores of magmatic and hydrothermal origin and in some carbonrich ores of sedimentary-diagenetic origin. Knowledge of the state of Pt disseminated in the matrix of pyrite, including local atomic environment (type of atoms in the nearest and distant coordination shells, coordination numbers, interatomic distances) and oxidation state, is necessary for physical-chemical modeling of platinum group element mineralization and for the improvement of Pt ore extraction and processing technologies. Here we report results of an investigation of local atomic structure of synthetic Pt-bearing pyrites by means of X-ray absorption spectroscopy (XAS). Synthesis experiments, performed at 580° and 590°C in a Pt-saturated system by means of salt-flux method, yielded crystals of pyrite with concentrations of Pt up to 4 wt %. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the distribution of Pt within the pyrite grains is of zonal character, but within the distinct zones Pt is distributed homogeneously. Negative correlation between the concentrations of Pt and Fe was observed in the synthesized pyrite grains. The slope of the correlation line corresponds to the formation of the solid solution in the Pt-Fe-S system and/or to the formation of PtS2. The XAS experiments revealed the existence of two forms of Pt in pyrite. The main form is the solid solution Pt(IV), which isomorphically substitutes for Fe. The Pt-S distance in pyrite is ~0.1 Å longer than that of Fe-S in pure pyrite. The distortion of the pyrite crystal structure disappears at R >2.5 Å. The second Ptrich form was identified by means of high-resolution transmission electron microscopy (HRTEM) as nanosized inclusions of PtS2. Heating experiments with in situ registration of X-ray absorption spectra resulted in partial decomposition (dissolution) of PtS2 nanosized inclusions with the formation of the solid solution (Fe1–xPtx)S2. Therefore, the PtS2 nanosized particles can be considered as a quench product. Our data demonstrate that both Pt solid solution and PtS2 nanosized inclusions (at high Pt content) can exist in natural Pt-bearing pyrites.


  • Secondary publication expected from 15.11.2020

Publ.-Id: 24388

Impact of Synthetic Route on Structural and Physical Properties of Butyl-1,4-Diammonium Lead Iodide Semiconductors

Safdari, M.; Phuyal, D.; Philippe, B.; Svensson, P. H.; Butorin, S. M.; Kvashnina, K. O.; Rensmo, H.; Gardner, L. K. J. M.

We report on the significant role of the synthetic route and importance of solvent for synthesis of organic-inorganic lead iodide materials. Through one route, intercalation of dimethylformamide in the crystal structure was observed leading to one dimensional (1D) [NH3(CH2)4NH3]Pb2I6 structure of the product. This product was compared with the two dimensional (2D) [NH3(CH2)4NH3]PbI4 recovered from aqueous solvent based synthesis with the same precursors. UV-visible absorption spectroscopy showed a red-shift of 0.1 eV for the band gap of the 1D network in relation to the 2D system. This shift primarily originates from a shift in the valence band edge as determined from photoelectron- and X-ray spectroscopy results. These findings also suggest iodide 5p orbital as the principle component in the density of states in the valence band edge. Single crystal data shows change in the local coordination around iodide, while in both materials, lead atoms are surrounded by iodide atoms in octahedral units. The conductivity of the one dimensional material ([NH3(CH2)4NH3]Pb2I6) was 50% of the two dimensional material ([NH3(CH2)4NH3]PbI4). The fabricated solar cells reflect these changes in the chemical and electronic structure of both materials, although the total light conversion efficiency of solar cells based on both products were similar.

Publ.-Id: 24387

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

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

The Ribbon Growth on Substrate (RGS) technology is a promising technology that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. In order to optimize this process, insights from modelling the
liquid metal flow are very desirable. The RGS process is dominated by a time-dependent, three-dimensional free-surface flow of the processed melt under the influence of electromagnetic forces. Thereby, main flow structures and possible instabilities strongly depend
on the melt shape. We have developed a new numerical multiphysics-software within the OpenFOAM (extensions) framework, which allows us to efficiently simulate hydrodynamic and electrodynamic effects and their interaction.

Keywords: RGS; Multiphysics; Free-surface; Eddy-currents; OpenFOAM

  • Contribution to proceedings
    10th PAMIR International Conference - Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference Fundamental and Applied MHD, Cagliari: Arti Grafiche Pisano, 978-88-90551-93-2, 257-261
  • Lecture (Conference)
    10th PAMIR International Conference - Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy, 20.-24.06.2016, Cagliari, Italy

Publ.-Id: 24386

Observations on bubble shapes in bubble columns under different flow conditions

Ziegenhein, T.; Lucas, D.

The bubble shape is fundamental for every aspect of modelling bubbly flows. The interface is usually highly deformable so that the bubble shape is in general dependent on the surrounding flow field. Since recent work on this topic addressed almost entirely single-bubbles rising in quiescent flow, the extent of such flow field dependencies is rather unknown. This study examines the effect on the bubble shape when flow properties, i.e. the gas flow rate, sparger setup, and column geometry, are changed by evaluating six different bubble column experiments. The results of this integral approach reveal that the bubble shape of small bubbles is distinctly influenced whereas the shape of large bubbles is unchanged. Averaged over all flow rates, we find that the size-dependent bubble shapes are quite similar for all six experiments.
Further studies focusing on single local effects like the shear rate or wake effects are highly desirable to obtain a deeper understanding of the underlying processes; for this purpose, the given results can help to assess the most important effect and in which extend it should be studied.

Keywords: Bubble shape; Bubbly flows; Bubble column; Turbulent flow; Swarm effects


Publ.-Id: 24384

Airlift Reactor – Experiment and CFD Simulation

Ziegenhein, T.

It is more and more possible to design bubbly flow reactors with methods of the computational fluid dynamics (CFD). Measurements that can be used for model validation, however, are often missing, especially for complex setups like airlift reactors. Such measurements include locally resolved information about the dispersed and continuous phase, particularly the information about the flow field and interface structures are important. In the present work Reynolds stresses, liquid velocity and gas void fraction profiles as well as bubble size distributions are provided at several positions in the riser and the downcomer in a rectangular airlift reactor for this purpose. In addition, the hydrodynamics inside this airlift reactor are described in detail by the measured values.

Keywords: dispersed gas-liquid multiphase flow; airlift reactor; model validation; particle tracking velocimetry; turbulence; videography

  • Poster
    14th Multiphase Flow Conference & Short Course, 08.-10.11.2016, Dresden, Deutschland

Publ.-Id: 24383

Lattice vibrations and electrical transport in (Bi1-xInx)2Se3 films

Zhu, J.; Liu, F.; Zhou, S.; Franke, C.; Wimmer, S.; Volobuev, V. V.; Springholz, G.; Pashkin, A.; Schneider, H.; Helm, M.

We present Raman, terahertz transmission, and transport measurements on (BiIn)2Se3 films to study the evolution of phonon modes and resistivity with an increasing indium content across the metal-insulator phase transition. The frequencies of two Raman-active modes E2g and A21g as well as an infrared-active mode Eu increase with an increasing indium content due to the smaller atomic weight of indium compared to bismuth. Terahertz data are fitted by a Drude Lorentz model. Drude scattering rates increase from 47 to 75 cm -1 with an increasing indium content from 0% to 16% due to stronger impurity scattering. The carrier concentration drops significantly for x=24%. The temperature dependence of the resistivity switches from metallic at x=16% to insulating at x =24%, indicating a metal-insulator transition in between.

Keywords: lattice vibrations; Raman spectra; topological insulators; electrical transport; Bi2Se3

Publ.-Id: 24382

Experimental investigations on the lift force for turbulent flows with low Morton number

Ziegenhein, T.; Lucas, D.

The lateral lift force has an important influence on the gas distribution in bubbly flows. For this reason reliable closure models reflecting this force are required for CFD-simulations of bubbly flows. In Direct Numerical Simulations as well in experimental investigation it was shown that the lift force strongly depends on the bubble size and even changes its sign depending on the bubble size. Tomiyama et al. (2002) obtained a correlation from experiments with single bubbles in a linear laminar shear flow for high Morton number systems, which is frequently used in CFD-simulations. In this work the lift force is determined experimentally in low Morton number systems with a turbulent background flow. Single bubbles move through a linear shear field generated in a flat column by asymmetric aerating. An averaged bubble trajectory is obtained from a long-term averaged gas volume fraction field along which the force balance including buoyancy, drag, virtual mass and lift is solved to determine the lift force coefficient. The additional parameters required, as relative velocity are obtained from the experiments. The dependency of the lift force coefficient on the horizontal bubble diameter is in good agreement with the data obtained by Tomiyama et al., however the Wellek correlation for the aspect ratio seems to be not valid for the pure system considered.

Keywords: Lift Force; Bubbly flows; Turbulence

  • Lecture (Conference)
    ICMF 2016 International Conference on Multiphase Flow, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 24381

Computational Fluid-Dynamic modeling of the pseudo-homogeneous flow regime in large-scale bubble columns

Besagni, G.; Inzolia, F.; Ziegenhein, T.; Lucas, D.

An understanding of the fluid dynamics and the transport phenomena in bubble columns (in the homogeneous and heterogeneous flow regimes) is of fundamental importance to support the design and scale-up methods. In this respect, multiphase Computational Fluid-Dynamics (CFD) simulations in the Eulerian multi-fluid framework are particularly useful to study the fluid dynamics in large-scale reactors; in particular, this study concerns the modeling of the fluid dynamics in bubble columns within the boundaries of the homogeneous flow regime. Reliable predictions of the homogeneous flow regime with this approach are, however, limited up to now. One important drawback is that usually the needed closure models for the interphase forces, turbulence and coalescence and break-up are selected case-by-case, which hinder improvement of the predictive value. A set of closure relations has been collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been extended to the pseudo-homogeneous flow regime—characterized by a wide spectrum of bubble sizes and typically associated with the large sparger openings used in industrial applications—in large-scale bubble columns, thus establishing a first step towards the simulation of industrial-scale reactors. To this end, the benchmark considered is a comprehensive dataset obtained for a large-scale bubble column, which has been built accordingly with the well-known scale up criteria (large-diameter, high aspect ratio and large sparger openings). The numerical approach has been tested in its fixed-poly-dispersed formulation (considering the two- and four-classes approaches to represent the dispersed phase) and considering the coalescence and break-up closures. The results suggest that the correct simulation of the fluid dynamics in the bubble column requires the definition of coalescence and break-up closures. The results have been critically analyzed and the reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as basis for future studies.

Keywords: CFD; Bubble column; Large-scale; Bubble size distribution; Coalescence and break-up; Validation


  • Secondary publication expected

Publ.-Id: 24380

Synthesis of coordination polymers of tetravalent actinides (U and Np) with phthalate or mellitate ligand in aqueous medium

Martin, N. P.; März, J.; Volkringer, C.; Henry, N.; Hennig, C.; Ikeda-Ohno, A.; Loiseau, T.

Four coordination polymers bearing uranium or neptunium have been hydrothermally synthesized at 130°C, from a tetravalent actinide chloride (AnCl4) source in association with phthalic (noted 1,2-H2bdc hereafter) or mellitic (noted H6mel hereafter) acid in aqueous mediua. With the phthalate ligand, two analogous assemblies ([An2O2(H2O)2(1,2-bdc)2]·H2O ; An = U4+ (1) or Np4+ (2)) have been isolated and are built up from the connection of square anti-prismatic polyhedra (AnO8) linked to each other via μ3-oxo groups (edge-sharing mode) in order to construct infinite zig-zag ribbons. The phthalate molecules connect adjacent chains to each other to generate a 2D network. Water molecules are bonded to the actinide center or found intercalated between the layers. With the mellitate ligand, two distinct structures have been identified. The uranium-based compound (U2(OH)2(H2O)2(mel) (3)) exhibits a 3D structure composed of dinuclear units of UO8 polyhedra (square anti-prism) linked via common edge (μ2-hydroxo). The 3D framework consists of the connection of the mellitate linker with the dinuclear brick with its six carboxylate arms. The structure of the neptunium mellitate ([(NpO2)10(H2O)14(Hmel)2]·12H2O (4)) reveals the oxidation of the initial Np(IV) toward Np(V) in our synthetic hydrothermal conditions, and this generates typical neptunyl entities with pentagonal bipyramidal environment (NpO7 unit). The resulting network is a layered assembly, composed of sheets of NpO7 linked in a square net, with cation-cation interactions between neptunyl bond (Np=O) and Np-O bonds from the pentagonal plane. The cohesion of the 3D structure is ensured by the mellitate molecules acting as bridging linkers between the NpO7 sub-network. For the mellitate, only four carboxylate groups are engaged with the connection of the NpO7-based layer.

Keywords: actinides; uranium; neptunium; coordination; polymers; carboxylate; complexation


Publ.-Id: 24379

Dissociation between brown adipose tissue 18F-FDG uptake and thermogenesis in uncoupling protein deficient mice

Hankir, M. K.; Kranz, M.; Keipert, S.; Andreasen, S.; Kern, M.; Patt, M.; Klöting, N.; Hesse, S.; Brust, P.; Jastroch, M.; Fenske, W. K.

18F-FDG PET imaging is routinely used to assess recruitment of BAT thermogenesis which requires mitochondrial uncoupling protein 1 (UCP1). It remains unsettled whether 18F-FDG uptake by BAT is altered in the absence of UCP1-mediated heat production.
METHODS: UCP1 knockout (UCP1 KO) and wild-type (WT) mice received single intraperitoneal injections of the selective β3 adrenergic receptor agonist CL 316, 243 (1mg/kg) and underwent metabolic cage, infrared thermal imaging and static 18F-FDG PET/MRI experiments. Bioenergetics of isolated brown adipocytes were examined by extracellular flux analysis.
RESULTS: In response to CL 316, 243 treatment, oxygen consumption and BAT thermogenesis were diminished in UCP1 KO mice; however the stimulation of 18F-FDG uptake by BAT was fully retained. Brown adipocytes derived from UCP1 KO mice exhibited defective induction of uncoupled respiration when glycolytic flux appeared normal.
CONCLUSION: Increased glucose metabolism in BAT can occur independently of UCP1-mediated thermogenesis.

Keywords: PET; thermogenesis

Publ.-Id: 24378

Sorption competition of trivalent metals on corundum (α-Al2O3) studied on the macro- and microscopic scale

Virtanen, S.; Eibl, M.; Meriläinen, S.; Rossberg, A.; Lehto, J.; Rabung, T.; Huittinen, N.

Sorption of trivalent actinides and lanthanides onto the surface of geological materials relevant for nuclear waste disposal is a topic that has been widely studied in recent years. However, the sorption properties of metals are often investigated by studying the sorption behaviour of a single metal at a time, thus, these experiments do not account for potential effects of sorption competition in the presence of multiple dissolved elements or compounds. Bradbury and Baeyens (2005) performed extensive investigations of the sorption competition between various metal cations on the clay mineral montmorillonite. By investigating the competition of metals with similar and dissimilar chemical behaviour (e.g. tendency to hydrolysis and valence state), the authors concluded that metal cations with dissimilar chemical properties do not affect the uptake of one another by the clay mineral, whereas metals with similar chemistries do. Thus, if the data obtained in single metal sorption experiments are used in the safety assessment of nuclear disposal, careful considerations of the chemical environment in the near- or far-field of nuclear waste repository is needed to avoid the possible overestimation of radionuclide sorption.
In this study, we have combined batch sorption and spectroscopic experiments that were performed with Eu(III), Cm(III) and Am(III) in in the absence and presence of Y(III) as competing cation. The objective was to investigate how the sorption behaviour of trivalent actinides and lanthanides is affected by the presence of another trivalent metal. Following the findings of Bradbury and Baeyens (2005) our hypothesis is that the addition of higher concentrations of trivalent Y(III) together with a chemically similar trivalent metal, Eu(III), Cm(III) or Am(III), would affect the sorption behaviour of that metal.
Batch sorption experiments were performed with Eu(III) at different pH (pH-edges) and concentrations (isotherms). The competing metal Y(III) was added before Eu(III) to the mineral suspension in concentrations ranging from 1×10-6 M to 1×10-4 M. In the Eu(III) pH-edge experiments, the sorption of 1×10-5 M Eu(III) was investigated on 0.5 g/l corundum at varying pH, with and without Y(III). In the Eu(III) isotherm experiments, the initial Eu(III) concentration was varied between 1×10-9 M – 1×10-4 M and Y(III) was used in the competing isotherm samples at a constant pH of 7. Batch experiments showed that the addition of Y(III) did decrease the sorption of Eu(III) (Figure 1) on a macroscopic scale. However, as the main emphasis of this study was the possible changes happening at the molecular level as a results of sorption competition, spectroscopic methods were also employed. Time-resolved laser fluorescence spectroscopy (TRLFS) enables the investigations of Cm(III) sorption speciation directly on the mineral surface. We investigated the changes in the speciation of 1×10-7 M Cm(III) in 0.5 g/l corundum suspensions at varying pH under non-competing and competing conditions using 1×10-4 M Y(III). The results indicate changes in the Cm(III) sorption species distribution, thus, confirming our findings in the batch sorption experiments showing that 1×10-4 M Y(III) suppresses Cm sorption complex formation on the mineral surface depending on the solution pH (Figure 2). Cm(III) luminescence spectra of only Cm(III) and of Cm(III) together with Y(III), show that the fraction of aqueous Cm species is substantially greater with high concentrations of Y(III) present. Only when the pH is increased above 7, the first Cm sorption species appears, resulting in a shift of the observed emission peak maximum. X-ray absorption spectroscopy (XAS) was applied to identify the formed trivalent actinide sorption complexes. We investigated the sorption of 6×10-6 M or 2×10-5 M Am(III) on the corundum surface at pH 8.5 in the absence and presence of 2×10-5 or 2×10-4 M Y(III). The treatment of the XAS-data is still ongoing and results will be discussed more closely in the conference presentation.

  • Lecture (Conference)
    Ninth international conference on nuclear and radiochemistry (NRC9), 29.08.-02.09.2016, Helsinki, Finland

Publ.-Id: 24377

Molecular interactions of two fungi with uranium and europium

Wollenberg, A.; Günther, A.; Merroun, M. L.; Raff, J.; Stumpf, T.

If radionuclides are released in the environment their mobility and behavior is influenced by interactions with abiotic and biotic matter. As fungi are ubiquitous in nature they have to be taken into consideration in particular. For example, fungi can bind radionuclides in different ways, with the result that the radionuclides are immobilized and preventing further migration through the soil. The aim of this study was to investigate the binding of uranium and europium, the latter as surrogate for trivalent actinides, by fungi Schizophyllum commune and Leucoagaricus naucinus.
First batch experiments showed the binding of U(VI) and Eu(III) by fungi depends on the initial conditions. Both fungi showed increasing sorption capacities with higher initial metal concentrations and lower initial biomass. In contrast, the fungi showed different metal binding behavior in dependence on pH. Scanning transmission electron microscopy in combination with high angle annular dark-field analysis (HAADF-STEM) revealed location of U(VI) on the surface and inside of cells of Schizophyllum commune.
Furthermore the U(VI)-binding of the fungi was investigate with time-resolved laser-induced fluorescence spectroscopy (TRLFS) depending on metal concentration. The results showed the speciation of U(VI) is changed in the initial solution during binding process. In addition, it was demonstrated that mainly phosphate groups are responsible for the binding on the surface of the biomass.

Keywords: fungi; uranium; europium

  • Poster
    15. Symposium on Remediation, 13.-14.10.2016, Jena, BRD

Publ.-Id: 24376

Studies of activation monitors at the HZDR medical cyclotron: Simulation and Experiment

Konheiser, J.; Müller, S. E.

The neutron source terms for a proton beam hitting an O-18 enriched water target were calculated with MCNP6 and FLUKA. First comparisons of simulation and experiments for activation studies at the IBA CYCLONE 18/9 cyclotron.

  • Lecture (others)
    16. AAA Workshop, 05.12.2016, Garching, Germany

Publ.-Id: 24375

22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,γ)23Na

Slemer, A.; Marigo, P.; Piatti, D.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Bressan, A.; Broggini, C.; Bruno, C.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F.; Prati, P.; Straniero, O.; Szücs, T.; Takács, M. P.; Trezzi, D.

We investigate the impact of the new LUNA rate for the nuclear reaction 22Ne(p,γ)23Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally- pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre- main sequence up to the termination of the TP-AGB phase, for a few sets of stellar models with initial masses in the range 3.0 M⊙ − 6.0 M⊙ and three values of metallicity, Zi = 0.0005, Zi = 0.006, and Zi = 0.014. We compare the results of the Ne-Na nucleosynthesis obtained with the new LUNA rate and others available in the literature. We find that the improvement in the astrophysical S-factor obtained with LUNA has remarkably reduced the corresponding nuclear uncertainties in the 22Ne and 23Na AGB yields, which drop from factors of ≃ 10 to just a few for the lowest metallicity models. The uncertainties that still affect the 22Ne and 23Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, dredge-up events, convection). With the new LUNA data AGB stars with hot-bottom burning produce amounts of 23Na that are in between those predicted with NACRE and Iliadis et al. rates. Finally, we discuss how the LUNA results impact on the hypothesis that invokes primordial massive AGB and super-AGB stars as the main agents of the observed O-Na anticorrelation in Galactic globular clusters. In this context, we derive quantitative constraints on the efficiencies that should characterize other key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anticorrelation and the observational constraints on the CNO abundance. While best-fitting AGB models can be actually singled out, yet they cannot be taken as a theoretical piece in full support to the AGB hypothesis, as various issues still remain.

Keywords: stars: evolution; stars: AGB and post-AGB; stars: carbon; stars: abundances; stars: mass loss; Physical Data and Processes: nuclear reactions, nucleosynthesis, abundances


Publ.-Id: 24374

FENABIUM: Research at HZDR

März, J.; Schöne, S.; Radoske, T.; Kaden, P.

Vortrag zum Kick-off Meeting des FENABIUM Verbundprojekts (BMBF) mit der TU Dresden und Universität Leipzig.
Die Ergebnisse zeigen die Synthese und Charakterisierung vierwertiger Actinidkomplexe mit Amidinen und Schiffschen Basen unter Schutzgasbedingungen, die in der Gruppe "Chemie der f-Elemente" des Instituts für Ressourcenökologie durchgeführt wurden.

Keywords: Actinide complex; Chemistry of the f-elements

  • Lecture (Conference)
    FENABIUM Kick-off Meeting, 14.11.2016, Dresden, Deutschland

Publ.-Id: 24373

Bentonite-geotechnical barrier and source for microbial life

Matschiavelli, N.; Steglich, J.; Kluge, S.; Cherkouk, A.

The storage of highly radioactive waste is a challenging task for many scientists. For a deep geological deposition of the waste a multi-barrier concept is favoured, which combines a technical barrier (canister including the highly radioactive waste), a geotechnical barrier (e.g. Bentonite) and the geological barrier (host rock). Due to their properties, namely a high swelling capacity and a low hydraulic conductivity, Bentonites fulfil in this system a sealing and buffering function. Depending on the mineral composition Bentonites contain many suitable electron-donors and –acceptors, enabling potential microbial life. For the potential repository of nuclear waste the microbial mediated transformation of Bentonite could influence its properties as a barrier material. To elucidate the microbial potential within selected Bentonites, microcosms were set up containing a certain amount of Bentonite (20 g) and 40 ml anaerobic synthetic Opalinus-clay-pore water solution under an N2/CO2-gas-atmosphere. Substrates like acetate and lactate were supplemented to stimulate potential microbial activity. Microcosms were incubated in the dark, without shaking at 30°C. Within an indefinite time scale samples were taken at different time-points of incubation and were analysed regarding geochemical parameters like pH, O2-concentration, redox potential, iron-concentration and sulphate-concentration as well as biological parameters like the consumption and formation of metabolites. First results show that bentonites represent a source for microbial life, demonstrated by the consumption of lactate and the formation of pyruvate. Furthermore, microbial iron-reduction was determined. The results reveal the importance of the selection of the best suitable Bentonite in order to avoid transformation by indigenous microbes.

  • Poster
    Microbiology and Infection 2017 - 5th Joint Conference of the DGHM & VAAM, 05.-08.03.2017, Würzburg, Deutschland

Publ.-Id: 24372

The upper critical field and its anisotropy in (Li1−xFex)OHFe1−ySe

Wang, Z.; Yuan, J.; Wosnitza, J.; Zhou, H.; Huang, Y.; Jin, K.; Zhou, F.; Dong, X.; Zhao, Z.

The temperature dependence of the upper critical field (Hc2) in a (Li1−xFex)OHFe1−ySe single crystal (Tc ≈ 40 K) has been determined by means of magnetotransport measurements down to 1.4 K both for inter-plane (H‖c, H‖cc2) and in-plane (H‖ab, H‖abc2) field directions in static magnetic fields up to 14 T and pulsed magnetic fields up to 70 T. H‖cc2 exhibits a quasilinear increase with decreasing temperature below the superconducting transition and can be described well by an effective two-band model with unbalanced diffusivity, while H‖abc2 shows a flattening below 35 K and follows the Werthamer–Helfand–Hohenberg (WHH) model incorporating orbital pair-breaking and spin-paramagnetic effects, yielding zero-temperature critical fields of H‖cc2(0) ≈ 67 T and H‖abc2(0) ≈ 98 T. The anisotropy of the upper critical fields, γ(T)= H‖abc2/ H‖cc2 monotonically decreases with decreasing temperature from about 7 near Tc to 1.5 at 0 K. This reduced anisotropy, observed in most Fe-based superconductors, is caused by the Pauli limitation of H‖abc2.

Publ.-Id: 24371

Afterglow of the dynamical Schwinger process: soft photons amass

Otto, A.; Kämpfer, B.

We consider the conversion of an electric field into photons as a secondary probe of the dynamical Schwinger process. In spatially homogeneous electric fields, quantum fluctuations of electron-positron (e+e−) pairs are lifted on the mass shell leaving asymptotically a small finite pair density. The e+e− dynamics in turn couples to the quantized photon field and drives its on-shell mode occupation. The spectral properties of the emerging asymptotic photons accompanying the Schwinger process are calculated in lowest-order perturbation theory. Soft photons in the optical range are produced amass in the sub critical region, thus providing a promising discovery avenue, e.g.\ for laser parameters of the Extreme Light Initiative (ELI-NP) to be put in operation soon.


Publ.-Id: 24370

Extended soft-wall model for the QCD phase diagram

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

The soft-wall model, emerging as bottom-up holographic scenario anchored in the AdS/CFT correspondence, displays the disappearance of normalisable modes referring to vector mesons at a temperature $T_{\dis}$ depending on the chemical potential μ, $T_{\dis}(\mu)$. We explore options for making $T_{\dis}(\mu)$ consistent with the freeze-out curve Tf.o.(μ) from relativistic heavy-ion collisions and the cross-over curve Tc(μ) from QCD at small values of μ.

Publ.-Id: 24369

Study of magnetic, structural and magnetocaloric properties of La0.6Pr0.4Mn2Si2 under high pressures and magnetic field

Kastil, J.; Arnold, Z.; Isnard, O.; Skourski, Y.; Kamarad, J.; Itié, J. P.

The structural, magnetic and magnetocaloric properties of La0.6Pr0.4Mn2Si2 compound were measured in wide range of temperature, magnetic field and hydrostatic pressure. The structural study up to 10 GPa confirmed the existence of critical Mn-Mn distance 0.2883 nm for the ferromagnetic to antiferromagnetic transition at room temperature. The results demonstrated the crucial role of the volume in the suppression of the ferromagnetic phase above the transition temperature T1 = 168 K under pressure. The huge pressure shift of the transition temperature T1, dT1 /dp = 230 K/GPa, was observed. Based on our magnetization measurement the low temperature transition at T2 = 30 K is connected with reorientation of Mn moment and the rare-earth sublattice is not ordered in this case. The direct magnetocaloric measurement showed moderate values of the adiabatic temperature change connected with the magnetic transition at Tc and T1 and confirmed the first order character of the transition at T1 and second order character of the transition at Tc.

Publ.-Id: 24368

Uranium(VI) retention by Ca-bentonite under (hyper)alkaline conditions

Philipp, T.; Schmeide, K.

The presentation summerizes the results of batch experiments on the uranium(VI) sorption on Ca-bentonite under (hyper)alkaline conditions combined with Time-resolved laser-induced fluorescence spectroscopy (TRLFS).

Keywords: sorption; clay; Ca-bentonite; uranium(VI); hyperalkaline; high ionic strengths; TRLFS

  • Lecture (others)
    3. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, Heidelberg, 25.-26.10.2016, Heidelberg, Deutschland

Publ.-Id: 24367

New possibilities of plasma immersion ion implantation (PIII) and deposition (PIII&D) in industrial components using metal tube fixtures

Ueda, M.; Silva, A. R.; Pillaca, E. J. D. M.; Mariano, S. F. M.; Rossi, J. O.; Oliveira, R. M.; Pichon, L.; Reuther, H.

New possibilities of Plasma Immersion Ion Implantation (PIII) and deposition (PIII&D) for treating industrial components in the batch mode have been explored. A metal tubular fixture is used to allocate the components inside around and along the tube, exposing to the plasma only the parts of each component that will be implanted. Hollow cathode- like plasma is generated only inside the tube filled with the desired gas, by applying high negative voltage pulses to the hollow cylindrical metal fixture which is insulated from the vacuum chamber walls. The metal tube (Me-tube) loaded with workpieces can be set-up inside the vacuum chamber in the standing-up, upside down or lying down arrangements. PIII tests were also run with and without metal sheet lids on the tube as well as with and without the components. Sputtering deposition and carbonitriding are also possible in this scheme by placing carbon tapes inside the tube and running the process with nitrogen PIII. Relatively clean DLC (Diamond Like Carbon) PIII&D deposition is possible by this method also since the plasma occupies mainly the Me-tube interior and not the whole chamber. Furthermore, operating high density PIII and PIII&D systems without additional plasma source, using only the high voltage pulser, is now possible to treat three dimensional parts. These methods are very convenient for batch processing of industrial parts by ion implantation and by ion implantation and deposition, in which a large number of small to medium size components can be treated by PIII and PIII&D, very quickly, efficiently and also at low cost.

Publ.-Id: 24366

Visualizing concentration distributions in macroscopic samples in the course of geochemical processes

Kulenkampff, J.; Karimzadeh, L.; Schymura, S.; Barthen, R.; Gründig, M.; Lippold, H.; Lippman-Pipke, J.

Geochemical processes, although generally well characterized on the molecular scale, are complicated by structural effects and process-inherent pattern formation. These effects cause variable scaling behaviour of the processes. This can be investigated through a significant process variable, the concentration of a geochemical species. As experimental method, therefore, we established positron emission tomography (PET) for high-resolving, sensitive, and quantitative tomographic imaging of tracer distributions in representative samples on the scale of drill cores (Kulenkampff et al. 2016). In contrast to other groups, we utilize a high-resolution PET-scanner and specially designed reconstruction software („GeoPET“) with about four times higher spatial resolution (about 1 mm) than standard medical PET scanners. This resolution is adequate for drill core sizes, and enables to visualize and analyze preferential pathway effects and local accumulations of tracers in detail, with an integration volume just above the typical pore scale. Thus, the method is ideally suited for parameterizing and verifying reactive transport simulations on the relevant macro-scale.
We applied the method on a variety of reactive transport processes, including leaching of copper minerals, injection of water glass for barrier improvement, transport of plant protectants in the soil, and transport of nano-particles in soils, rocks and technical devices.
Generally, both with conservative and reactive tracers, we observe strong localization of the transport pathways. This formation of preferential transport pathways implies that simulation models should consider a decrease of the effective volume and effective internal surface area, as well as high concentration gradients and non-uniform concentration distributions. PET is the potential method for parameterizing such models without prior flow simulations based on tomographic modalities for structural imaging, like µCT.

Kulenkampff, J., Gründig, M., Zakhnini, A., and Lippmann-Pipke, J.: Geoscientific process monitoring with positron emission tomography (GeoPET), Solid Earth, 7, 1217-1231, 2016.

Keywords: process tomography; PET; leaching; reactive transport

  • Lecture (Conference)
    9th International Conference on Porous Media & Annual Meeting, 08.-11.05.2017, Rotterdam, Niederlande

Publ.-Id: 24365

Non-destructive tomographic monitoring of transport processes in barrier material (Opalinus clay) with PET

Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.

Parameterizing transport in barrier materials is a challenge, because the processes are extremely slow, limited to smallest quantities, and frequently strongly localized, e.g. to fractures. These processes are generally well characterized on the molecular scale, but strongly affected by structural effects on the larger scales. Due to the intricate derivation of experimentally substantiated parameters, the impact of these scaling effects is often unduly neglected in process simulations for safety assessment.
As most sensitive tomographical modality, which is capable to monitor traces with molecular concentrations on macroscopic samples, we apply positron-emission-tomography (PET) with a high-resolution scanner („GeoPET“) for parameterizing transport in barrier materials (Kulenkampff et al. 2016a).
We focus here on diffusion in Opalinus clay as potential barrier rock for nuclear waste deposits (Kulenkampff et al. 2016b, 2016c). Our method is complementary to diffusion experiments in small diffusion cells and additionally provides information on heterogeneity and anisotropy of the process.
We derived anisotropic diffusion coefficients from the measured spatiotemporal tracer distribution which are in accordance with results from diffusion cells (Lippmann-Pipke et al., 2016). The spatial characteristic of the tracer distribution suggests that this anisotropy is caused by preferential transport along fine layers on the millimetre to centimetre scale. This finding should be considered in process simulations, because it means a reduction of the volume that effectively is affected by the process and thus faster progress of the tracer and a reduction of the reactive internal surface area, when adsorption is considered.
Other examples, where we take advantage from the favourable features of the GeoPET-method, are advective fluid transport in fractured salt and crystalline rocks, as well as reactive injection of water glass into salt rock.
In all these cases we monitor tracer concentrations and thus the key parameter for reactive transport modelling. We recommend GeoPET as unique experimental method to verify transport simulations on the macroscopic scale of drill cores.

Kulenkampff, J., Gründig, M., Zakhnini, A., and Lippmann-Pipke, J.: Geoscientific process monitoring with positron emission tomography (GeoPET), Solid Earth, 7, 1217-1231, 2016a.
Kulenkampff, J., Zakhnini, A., Gründig, M., and Lippmann-Pipke, J.: Quantitative experimental monitoring of molecular diffusion in clay with positron emission tomography, Solid Earth, 7, 1207-1215, 2016b.
Kulenkampff, J., Gründig, M., Zakhnini, A., Lippmann-Pipke, J.: Observation of 22Na+ - Diffusion in Opalinus Clay using Positron Emission Tomography (GeoPET) (mpeg-movie),, 2016c.
Lippmann-Pipke, J., Gerasch, R., Schikora, J., and Kulenkampff, J.: Benchmarking PET for geoscientific applications: 3D quantitative diffusion coefficient estimation in clay rock, Comput. Geosci., in review, 2016.

Keywords: diffusion; clay; anisotropy; heterogeneity; tomography; PET

  • Lecture (Conference)
    9th International Conference on Porous Media & Annual Meeting, 08.-11.05.2017, Rotterdam, Niederlande

Publ.-Id: 24364

New insights into the pretargeting approach to image and treat tumours

Patra, M.; Zarschler, K.; Pietzsch, H.-J.; Stephan, H.; Gasser, G.

Tumour pretargeting is a promising strategy for cancer diagnosis and therapy allowing for the rational use of long circulating, highly specific monoclonal antibodies (mAbs) for both non-invasive cancer radioimmunodetection (RID) and radioimmunotherapy (RIT). In contrast to conventional RID/RIT where the radionuclides and oncotropic vector molecules are delivered as presynthesised radioimmunoconjugates, the pretargeting approach is a multistep procedure that temporarily separates targeting of certain tumour-associated antigens from delivery of diagnostic or therapeutic radionuclides. In principle, unlabelled, highly tumour antigen specific mAb conjugates are, in a first step, administered into a patient. After injection, sufficient time is allowed for blood circulation, accumulation at the tumour site and subsequent elimination of excess mAb conjugates from the body. The small fast-clearing radiolabelled effector molecules with a complementary functionality directed to the prelocalised mAb conjugates are then administered in a second step. Due to its fast pharmacokinetics, the small effector molecules reach the malignant tissue quickly and bind the local mAb conjugates. Thereby, corresponding radioimmunoconjugates are formed in vivo and, consequently, radiation doses are deposited mainly locally. This procedure results in a much higher tumour/non-tumour (T/NT) ratio and is favourable for cancer diagnosis and therapy as it substantially minimises the radiation damage to non-tumour cells of healthy tissues. The pretargeting approach utilises specific noncovalent interactions (e.g. strept(avidin)/biotin) or covalent bond formations (e.g. inverse electron demand Diels–Alder reaction) between the tumour bound antibody and radiolabelled small molecules. This tutorial review descriptively presents this complex strategy, addresses the historical as well as recent preclinical and clinical advances and discusses the advantages and disadvantages of different available variations.

Publ.-Id: 24362

Erste Untersuchungen zur Uranrückhaltung an C-S-H-Phasen und Ca-Bentonit

Philipp, T.; Wolter, J.-M.

Im Rahmen des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“ wird unter Anderem die Radionuklidrückhaltung an Tongestein und Tonmineralen unter hyperalkalinen Bedingungen und bei hohen Ionenstärken untersucht. Der Vortrag fasst die ersten Ergebnisse zur Sorption von Uran(VI) an Ca-Bentonit unter Variation verschiedener Umgebungsparameter (S/L-Verhältnis, U(VI)-Konzentration, pH, An-/Abwesenheit von CO2) zusammen.

Keywords: Ca-Bentonit; Ton; Montmorillonit; Uran(VI); Sorption; hyperalkalin; hohe Ionenstärke

  • Lecture (others)
    2. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 22.03.-23.11.2016, München, Deutschland

Publ.-Id: 24361

Leaching of uranium(VI) doped CSH phases in high saline water

Wolter, J.-M.

Leaching experiments of uranium(VI) doped calcium-silicate-hydrate (CSH) phases were carried out in a 2.5 M sodium chloride solution and different additions like sodium bicarbonate or sodium sulfate to determine the CSH stability in high saline water. The results were backed up with several spectroscopic techniques like time resolved laser fluorescence spectroscopy (TRLFS), infrared spectroscopy (IR) and powder x-ray diffraction (PXRD) to structural changes of the CSH phases through the leaching.

Keywords: Uranium; CSH; TRLFS; IR; PXRD; sodium chloride; sodium sulfate; sodium carbonate

  • Lecture (others)
    3. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 24.10.2016, Heidelberg, Deutschland

Publ.-Id: 24360

Radioactive particles as concentrated sources related to uptake and dose in mammals

Johansen, M. P.; Child, D.; Ikeda-Ohno, A.; Payne, T. E.; Howell, N.; Caffrey, E.; Collins, R. N.

The radiological residues at the former weapons testing sites in Australia, at Maralinga, Emu and the Monte Bello Islands, often occur in particulate form (“hot particles”). Large numbers of these particles were emitted from nuclear test detonations and non-nuclear tests. For example, more than 3000 readily identifiable particles can occur in the soil of a single square meter, in a plume that extends for tens of kilometres at the Taranaki site (Maralinga). The physical and chemical characteristics of these particles affect their mobility and availability for uptake into living organisms. These particles, which are weathering slowly, may contain long-lived radionuclides (e.g. 239Pu) and thus will provide persistent sources of smaller, more readily respirable hot-particles, as well as ionic forms of radionuclides, for many thousands of years. From these Australian sites, we have gathered a series of particles that have weathered and interacted with the environment for 50+ years since their initial formation and release events. The particles are being evaluated using a range of methods including gamma spectrometry, PSL autoradiography, Accelerator Mass Spectrometry analysis (AMS), leaching studies, and X-ray fluorescence microscopy (XFM) at the Australian Synchrotron. Significant findings include the clustering of 137Cs on the exterior of a glassy fission fragment, with 90Sr occurring in the nearby interior, suggesting the 137Cs may be more available for weathering processes, and the beta emissions from the 90Sr may be largely self-shielded within the particle. In contrast, a different particle from a nearby site lacked any fission products, but contained Pu(IV) oxyhydroxides, consistent with weathering in a semi-arid environment. The 239Pu would impart significant dose to nearby tissue. However, XFM data, including X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) indicate particles with a “core-shell” structure, with most Pu(IV) oxyhydroxide clustered in the core surrounded by an external layer containing Ca, Fe, and U. Detailed dose modelling suggests most of the alpha emissions from particles > 5μm are self-shielded within the particles themselves, and therefore impart lower dose than the equivalent dissolved Pu. However, when Pu exists on exterior surfaces, a hot particle that has been internalised (e.g. lodged in a mammalian lung) may produce relatively intense dose rates to adjacent tissues.

Keywords: actinides; plutonium; mammal; uptake; particulates; bioavailability; radio ecology

  • Poster
    Australian Synchrotron User Meeting 2016, 24.-25.11.2016, National Centre for Synchrotron Science, AS, Australia

Publ.-Id: 24359

A laser-based hadrontherapy facility: current status at HZDR

Kraft, S.

Laser based ion acceleration has the potential to serve as a more flexible solution as compared to conventional ion beam therapies. In order to explore these potentials, several groups from physics, biology and medicine have joint forces in Dresden.
This talk will give an overview over the activities focusing especially on the proton source and the beam transport. The Ti:Sapph laser system was upgraded to 500TW in order to produce higher energies and starts operation this summer. Additionally, new target types such as solid hydrogen and liquid crystals where tested. For beam transport novel techniques with pulsed power magnets producing field of up to 20 Tesla are implemented.

  • Invited lecture (Conferences)
    3rd ELImed workshop, 07.-09.09.2016, Catania, Italien

Publ.-Id: 24358

Methodological accuracy of image-based electron-density assessment using dual-energy computed tomography

Möhler, C.; Wohlfahrt, P.; Richter, C.; Greilich, S.

Purpose: Electron density is the most important tissue property influencing photon and ion dose distributions in radiotherapy patients. Dual-energy computed tomography (DECT) enables the determination of electron density by combining the information on photon attenuation obtained at two different effective x-ray energy spectra. Most algorithms suggested so far use the CT numbers provided after image reconstruction as input parameters, i.e. are imaged-based. To explore the accuracy that can be achieved with these approaches, we quantify the intrinsic methodological and calibration uncertainty of the seemingly simplest approach.
Methods: In the studied approach, electron density is calculated with a one-parametric linear superposition (‘alpha blending’) of the two DECT images, which is shown to be equivalent to an affine relation between the photon attenuation cross sections of the two x-ray energy spectra. We propose to use the latter relation for empirical calibration of the spectrum-dependent blending parameter. For a conclusive assessment of the electron-density uncertainty, we chose to isolate the purely methodological uncertainty component from CT-related effects such as noise and beam hardening.
Results: Analyzing calculated spectrally weighted attenuation coefficients, we find universal applicability of the investigated approach to arbitrary mixtures of human tissue with an upper limit of the methodological uncertainty component of 0.2%, excluding high-Z elements such as iodine. The proposed calibration procedure is bias-free and straightforward to perform using standard equipment. Testing the calibration on five published data sets, we obtain very small differences in the calibration result in spite of different experimental setups and CT protocols used. Employing a general calibration per scanner type and voltage combination is thus conceivable.
Conclusion: Given the high suitability for clinical application of the alpha-blending approach in combination with a very small methodological uncertainty, we conclude that further refinement of image-based DECT-algorithms for electron-density assessment is not advisable.

Keywords: proton and ion beam therapy; electron density; effective atomic number; range uncertainty; treatment planning

Publ.-Id: 24357

The prospect of laser plasma accelerators for ion beam therapy of cancer

Schramm, U.

Talk and podium discussion on prospect of laser accelerated ions for therapy applications

Keywords: ion beam cancer therapy

  • Invited lecture (Conferences)
    International Symposium on Ultrafast Intene Laser Science ISUILS, 02.-05.10.2016, Cassis, Frankreich

Publ.-Id: 24356

ELI related activities, potential partners and status in Germany

Schramm, U.; Schramm, B.; Sauerbrey, R.

Presentation of the German position to ELI DC and ELI ERIC

Keywords: ELI

  • Invited lecture (Conferences)
    ELI DC 2nd partners meeting, 16.-17.11.2016, Bukarest, Rumänien

Publ.-Id: 24355

Development of the first fluorine-18 labelled radioligand for imaging of the adenosine A2B receptor

Lindemann, M.; Wenzel, B.; Hinz, S.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Teodoro, R.; Juhl, C.; Müller, C.; Brust, P.; Steinbach, J.

The G protein-coupled A2B receptor differs from other adenosine receptor subtypes (A1, A2A, A3) by its low affinity towards the endogenous ligand adenosine. It is suggested to be involved in various pathological processes accompanied by increased levels of adenosine, e.g. inflammation, hypoxia, and cancer. To enable the investigation of the function and expression of A2B-receptor in living organisms, we developed a fluorine-18 labelled radioligand with the particular aim of imaging of neurooncological and neuroinflammatory processes by PET.
Based on the pyrazine compound 1 [1] (Fig. A) several novel fluorine-containing derivatives were synthesized in four steps and their affinities and selectivities toward all four adenosine receptor subtypes were determined. The most promising candidate PA51 was radiolabelled by using the corresponding nitro precursor in DMSO with thermal as well as microwave heating (Fig. B). To study the in vivo metabolism of [18F]PA51 plasma and brain samples obtained from mouse at 30 min p.i. were investigated by using (a) conventional extraction procedures and (b) a micellar HPLC approach.
[18F]PA51 (binding affinities in Fig. B) was successfully synthesized with radiochemical yields of 36.1±4.6% (dec. corr., formulated product), molar activities of 10-30 GBq/µmol, and radiochemical purities of =99% (determined by analytical HPLC by UV absorption at ? = 254 nm). In vivo studies in mice revealed high initial brain uptake (5 min p.i.). Fast metabolism was found with formation of a single major radiometabolite able to cross the blood-brain barrier.
[18F]PA51 is unsuitable for imaging of A2B receptors in brain in vivo due to the presence of a radiometabolite. However, the initially high uptake of activity in the brain encourages further structural modifications to improve the selectivity and the metabolic stability.
[1] P. Eastwood, et al. ACS Med. Chem. Lett. 2011, 2, 213-218.

Keywords: A2B receptor; fluorine-18; PET

  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences, 14.-19.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, 411
    DOI: 10.1002/jlcr.3508

Publ.-Id: 24354

Entwicklung des ersten F-18-markierten Radioliganden zur molekularen Bildgebung des Adenosinrezeptors A2B im Gehirn

Lindemann, M.; Wenzel, B.; Hinz, S.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Teodoro, R.; Juhl, C.; Müller, C.; Brust, P.; Steinbach, J.

Ziel: Der G-Protein-gekoppelte A2B-Rezeptor wird, im Gegensatz zu den anderen drei Rezeptorsubtypen (A1, A2A, A3) nur bei hohen Adenosinkonzentrationen aktiviert (Entzündungen, Hypoxie, Tumore). Bisher gibt es noch keinen hochaffinen und selektiven PET-Radioliganden für diesen Rezeptor. Daher wollen wir einen F-18-markierten Radioliganden für den A2B-Rezeptor zur Darstellung von neuroonkologischen und neuroinflammatorischen Prozessen mittels PET entwickeln.

Methodik: Basierend auf einer Pyrazinstruktur [1] wurden neuartige fluorierte Derivate synthetisiert und deren Affinität und Selektivität gegenüber den Rezeptorsubtypen bestimmt. Ausgehend von einem Nitropräkursor wurde die geeignetste Verbindung, PA51, in DMSO bei 150°C mit F-18 markiert. Nach Isolierung mittels semipräparativer HPLC wurde [18F]PA51 in Mäuse injiziert, um Hirnaufnahme (5 und 30 min p.i.) und Metabolismus (30 min p.i.) zu untersuchen. Die Radiometabolite wurden in Plasma- und Hirnproben mit mizellarer HPLC bestimmt.

Ergebnisse: Die Radiomarkierung von [18F]PA51 (A2B Ki=4.24±0.04 nM; A1 Ki=20.9±5.22 nM; A2A Ki=55.0±6.10 nM; A3 Ki=796 nM) konnte mit einer radiochemischen Ausbeute von 36.1±4.6% (zerfallskorrigiert), molaren Aktivitäten im Bereich von 10-30 GBq/µmol und einer radiochemischen Reinheit von = 99% durchgeführt werden. Die Mausstudien zeigten eine initial hohe Aktivitätsanreicherung im Gehirn (SUV5 min p.i. = 4). Allerdings wurde 30 min p.i. eine schnelle Metabolisierung im Plasma beobachtet und im Gehirn ein Radiometabolit mit 30% der Gesamtaktivität nachgewiesen.

Schlussfolgerungen: [18F]PA51 ist für einen Einsatz als PET-Radioligand zur molekularen Bildgebung des A2B-Rezeptors im Gehirn nicht geeignet. Deshalb sind weitere strukturelle Modifikationen geplant, um die metabolische Stabilität und die Selektivität der Verbindung zu erhöhen.


[1] Eastwood et al. ACS Med. Chem. Lett. 2011, 2, 213.

Keywords: A2B Rezeptor; F-18

  • Lecture (Conference)
    Nuklearmedizin 2017, 26.-29.04.2017, Dresden, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 56(2017)2, A45

Publ.-Id: 24353

Spatial variability of source composition and petrogenesis in rift and rift flank alkaline lavas from the Eger Rift, Central Europe

Haase, K. M.; Beier, C.; Regelous, M.; Rapprich, V.; Renno, A. D.

Geochemical data on Oligocene melilititic and nephelinitic rocks from the northern Eger Rift flank in Central Europe reveal significant differences to nephelinites and basanites of volcanic complexes in the rift axis. The mafic rift flank lavas are more enriched in TiO2, P2O5 and CaO but have lower SiO2 compared to the alkaline volcanic rocks in the Eger Rift. The differences inmajor element compositions imply (1) lower degrees of partial melting beneath the rift flank than beneath the rift axis evident fromlower SiO2 and higher (Ce/Yb)N ratios in the off-axis basalts and (2) different assemblages of fractional crystallization. The mafic rift flankmagmas experienced crystal fractionation of olivine followed by clinopyroxene fractionation in contrast to early simultaneous olivine and clinopyroxene fractionation in the magmas below the rift basin. In addition, assimilation of continental crustal rocks is associated with crystal fractionation and changes the composition of the lavas. The rift axis lavas are enriched in Nb and Ba relative to La and have higher Sr and lower Nd isotope ratios than the rift flank magmas indicating differentmantle sources. The melting zones beneath the rift axis and the rift flank region are separated although they are only some 20 km apart and no melt exchange between the magma systems is observed. All magmas probably experienced mixing between a deep carbonatitic and a shallower low-degree silicate melt.

Keywords: Continental rifting; Intraplate volcanism; Magma formation; Fractional crystallization; Crustal assimilation

Publ.-Id: 24352

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