Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

31860 Publications
Transitions between electromagnetic flow states in liquid metal batteries
Kelley, D. H.; Ashour, R. F.; Weber, N.; Salas, A.; Weier, T.;
High temperature batteries for stationary energy storage typically involve large electrical currents running through liquid electrodes and/or electrolytes. Those currents, in combination with Earth's magnetic field or the magnetic fields produced by the currents themselves, impose forces on the liquid layers that can drive flow and change battery performance. We report on experiments and simulations studying flow driven by electromagnetic forces in the molten electrodes of liquid metal batteries, with and without thermal convection. Our measurements and simulations reveal transitions between azimuthal and poloidal circulation. The implications of both types of flow for battery performance will be discussed.
Keywords: liquid metal battery, electro-vortex flows
  • Lecture (Conference)
    High Temperature Batteries for Stationary Energy Storage Workshop, 19.-20.09.2017, Trondheim, Norwegen

Publ.-Id: 25905 - Permalink


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.; Faßbender, J.ORC
Nanostructured Ferritic Alloys (NFA) are considered as promising candidates for the structural materials of future fusion and fission reactors [1]. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer size yttria-based oxide particles. In this research project (started in November 2016) the nature of nanometer-size yttria-based oxide clusters in a bcc Fe matrix shall be investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the nanoclusters. The investigations shall clarify the conditions for the formation of nonstoichiometric clusters that are coherent with the bcc lattice and for the formation of oxide phases (in particular Y2O3 and Y2Ti2O7). The energetics of the different structures shall be determined and compared. Furthermore, the interaction of the nanoparticles with intrinsic point defects and He atoms shall be studied. Preliminary studies and their results on structure and energetics of certain Y-Ti-O nanoclusters will be presented on the poster. Two models are considered: (i) clusters consisting of Y, Ti, and O atoms on substitutional or defect sites of the bcc lattice [2-4], and (ii) cluster consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe [5].
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403, 113 (2010)
[3] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[4] M. Posselt, D. Murali, B. K. Panigrahi, Model. Simul. Mater. Sc. 22, 085003 (2014)
[5] L. Barnard, G. R. Odette, I. Szlufarska, D. Morgan. Acta Mater. 60 (2012) 935 (2012)
Keywords: oxide nanoclusters, bcc Fe, nanoferritic alloy, DFT
  • Poster
    NSF/CECAM School on Computational Materials Science: From Basics to Applications, 17.-27.07.2017, Lausanne, Switzerland

Publ.-Id: 25904 - Permalink


Influence of foreign atoms on the diffusion of oxygen in bcc Fe
Wang, X.; Posselt, M.; Faßbender, J.ORC
In this research project (started in September 2016) the diffusion of foreign atoms in bcc Fe shall be investigated by first-principle methods and kinetic Monte Carlo simulations. The focus of the present work is on the diffusion of oxygen under the influence of other foreign atoms such as Al, Cr, Si, Ti, and Y. Oxygen plays e.g. an important role in the formation and evolution of nanoclusters in nanostructured ferritic Fe-Cr alloys which are considered as promising candidates for structural materials of future fusion and fission reactors [1]. In bcc Fe the most stable site of oxygen is the octahedral interstitial position and the tetrahedral interstitial position is the saddle point for the migration [2-5]. The presence of foreign atoms and intrinsic point defects modifies the migration path [5-7]. Using DFT calculations the binding energy between oxygen and a foreign atom is determined for different neighbor distances. Then the modified migration barriers are calculated, i.e. for the O jump between the first and the second neighbor of a foreign atom, etc. The results shall be used in kinetic Monte Carlo simulations of the whole diffusion process and for the determination of the corresponding diffusion coefficient in dependence on the concentration of foreign atoms. Finally, the calculated diffusion coefficient shall be compared with the few existing experimental data on oxygen diffusion in dilute iron alloys.
[1] G. R. Odette, JOM-J. Min. Met. Mat. S. 66, 2427 (2014)
[2] C.L. Fu, M. Krcmar, G.S. Painter, X.-Q. Chen, Phys. Rev. Lett. 99, 225502 (2007)
[3] D. Murali, B.K. Panigrahi, M.C. Valsakumar, S. Chandra, C.S. Sundar, B. Raj, J. Nucl. Mater. 403, 113 (2010)
[4] A. Claisse, P. Olsson, Nucl. Instr. Meth. B 303, 18 (2013)
[5] S.L. Shang, H.Z. Fang, J. Wang, C.P. Guo, Y. Wang, P.D. Jablonski, Y. Du, Z.K. Liu, Corrosion Sci. 83, 94 (2014)
[6] P. Liu, W. Xing, X. Cheng, D. Li, Y. Li, X.-Q. Chen, Phys. Rev. B 90, 024103 (2014)
[7] C. Barouh, T. Schuler, C.-C. Fu, T. Jourdan, Phys. Rev. B 92, 104102 (2015)
Keywords: diffusion, oxygen, bcc Fe, DFT, foreign atoms
  • Poster
    NSF/CECAM School on Computational Materials Science: From Basics to Applications, 17.-27.07.2017, Lausanne, Switzerland

Publ.-Id: 25903 - Permalink


Balanced 20 kA DC Distributor for Magnetized Taylor Couette Systems Utilizing Thermostatic Controlled Water Valves with CO2 Adsorption Charge Sensors as Current Controller
Seilmayer, M.; Krauter, N.;
A quasi coaxial system consisting of a central current carrying copper rod and five symmetric return paths takes up to 20 kA and provides a homogeneous magnetic field B[phi] to a Taylor-Couette flow. One challenging part of the system is the design of the current distributor, which is supposed to divide the return current into several equally weighted lines. The individual components like the copper rods as well as all electrical contacts provide a characteristic resistance, each in the same magnitude of several micro Ohm. By initial installation this will support an imbalance in the current distribution affecting the symmetry of the magnetic field. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. Controlling the outflow temperature of the required water cooling offers an indirect access to set the current by thermostatically operated valves with CO2 adsorption charge in conjunction with the temperature dependent branch resistance. A numerical investigation proves that a stable current distribution can be achieved by a couple of paralleled thermal controlled heater valves with proportional characteristics. Finally, recent ironless Hall-effect current sensors help to calibrate the system so that the current homogeneity differs less than 1% from optimal state in a wide range of currents.
Keywords: Magnetic Fields, High Current, Magnetized Taylor Couette, PROMISE, MRI, AMRI, HMRI

Downloads:

Publ.-Id: 25902 - Permalink


Characterization of U(VI) sequestration by Acidovorax facilis - a spectroscopic and microscopic approach
Krawczyk-Bärsch, E.; Gerber, U.; Müller, K.; Moll, H.; Rossberg, A.; Steudtner, R.; Merroun, M. L.;
To improve bioremediation strategies based on a better understanding of binding mechanisms on the molecular level, we applied U(VI) interaction experiments with Acidovorax facilis. This is a facultative aerobic, chemoorganotrophic gram-negative betaproteobacterium, ubiquitously distributed in the nature including uranium-contaminated sites. Our study combines a variety of microscopic and spectroscopic techniques in order to elucidate the interaction process of U(VI) with A. facilis. Kinetic U(VI) sorption experiments were performed under aerobic conditions at 30°C by adjusting an initial U(VI) concentration to 0.1 mM at a pH of 5 by adding UO2(NO3)2 to the batch culture.
The results showed that different cell compartments play a major role in the sequestration of U(VI). Our findings clearly point out that the local coordination of U(VI) on functional groups of the cell membrane components of A. facilis depends upon time incubation. U(VI) biosorption by outer membrane lipopolysaccharide (LPS) containing phosphoryl residues was observed by TRLFS within the first hours of contact between the cells and U(VI). By increasing the incubation time up to 24 h the implication of carboxyl groups within the cell wall peptidoglycan (PGN) was proved in addition to phosphoryl groups. These results support those obtained by EXAFS, where a relative short average U-Oeq bond length of 2.35 Å was observed, indicating a binding of the U(VI) via organic phosphate groups (from LPS) in a monodentate fashion. The strong interaction of U(VI) with phosphorylic and carboxylic groups was reinforced by ATR FT-IR spectroscopic studies due to the presence of characteristic phosphoryl vibrations. Most of the bound U(VI) presumably remained on the cells, more precisely on the phosphorylic functionalities at the cell membrane. In addition to these functional groups located at the cell surfaces, U is coordinated also, but with low degree, to phosphoryl groups of the intracellular polyphosphate granules as was indicated by STEM analysis.

U. Gerber et al., Journal of Hazardous Materials 317(2016), 127-134.
E. Krawczyk-Bärsch, U. Gerber et al., Journal of Hazardous Materials (2017), under review.
Keywords: Uranium, Bioremediation, STEM, TRLFS, EXAFS, ATR FT-IR
  • Invited lecture (Conferences)
    16. Remediation Colloquium, 05.-06.10.2017, Jena, Deutschland

Publ.-Id: 25901 - Permalink


Digitalizing the Circular Economy
Reuter, M. A.;
The background of the talk is presented in the recent paper “Digitalizing the Circular Economy”: http://link.springer.com/article/10.1007/s11663-016-0735-5. While this paper provides the overall picture, the focus of the talk will be to show with various brief example how FACT Sage was used during the design and optimization of Outotec-Ausmelt's Top Submerged Lance (TSL) smelting technology (see paper for details), for both primary and secondary materials covering Cu, Pb, Ni, Sn, Zn-residues (jarosite/Goethite for In/Ge/Ag etc. recovery), copper scrap & ewaste, PGMs etc. processing. The talk will thus give a brief overview of the technology, its position in the bigger system of industrial applications and then how for example metal recovery and slag chemistry where optimized using FACT. The talk will end also showing how the FACT knowledge flows into work described in the following blog the presenter was involved in: https://www.fairphone.com/en/2017/02/27/recyclable-fairphone-2/ .
  • Invited lecture (Conferences)
    GTT Annual Workshop 2017 / GTT Users' Meeting 2017, 28.-30.06.2017, Herzogenrath, Deutschland

Publ.-Id: 25900 - Permalink


GPU-Accelerated Kinetic Lattice Monte Carlo for Experimental-Scale Studies
Kelling, J.; Heinig, K. H.; Weigel, M.; Gemming, S.;
Micro- and nano-structured materials, including composites, are crucial for future energy technologies. Key processes during production and life-time are governed by self-organization in phase separation processes at the micro and nano scale.
Examples include nano-structured Silicon thin film absorber layers in solar cells providing tailored band-gaps [1] on top of reduced production cost. In the case of micro-patterned electrolyte-matrices, used in a range of fuel cell technologies, both production and aging are governed by phase separation and affect the efficiency and lifetime of large industrial installations.

Simulations of these out-of-equilibrium, inhomogeneous real world systems provide important insights, finding reaction pathways for self-organization and self-alignment of nanostructures. To this end, 3D kinetic Metropolis lattice Monte Carlo simulations can be used to model physical systems at experimental scales in an atomistic way, thereby side-stepping many caveats connected with the alternative phase-field simulations.

These same long-time and large-scale simulations also provide important insights into more fundamental physical problems. The question of super-universality, that is if and how different types of quenched disorder affect universal properties, is still under investigation even for fundamental models like Ising [2], realization of which can be found in important complex magnetic systems, apart from binary mixtures.

We propose massively parallel simulation techniques using the architecture of modern graphics processing units (GPUs) to address these problems, ranging from the kinetic Metropolis Monte Carlo to any Potts models with quenched disorder.
While pioneering work in this area [3] focused on efficient but correlated stochastic cellular automaton implementations, our simulations can be virtually correlation-free [4].

Here, we present two implementations for large-scale simulations on GPUs: One is optimized to offer fast time-to-solution on experimental-scale simulations [5], the other provides highly efficient parameter studies or large sample sizes for large-scale simulations [6]. Harnessing the compute power of modern (multi-)GPU installations leads to increased energy efficiency as well as reduced time-to-solution.

[1] Apl. Phys. Lett. 103, 133106 (2013); Appl. Phys. Lett. 103, 203103 (2013); Nanolett. 16, 1942 (2016)
[2] e.g. EPL 117, 10012 (2017); Phys. Rev. B 88 042129 (2013); Phys. Rev. B 78 224419 (2012); J. Phys. A 24 L1087 (1991)
[3] J. Comp. Phys. 228, 4469 (2009); Phys. Proc. 15 92 (2001)
[4] http://arxiv.org/abs/1705.01022 ; https://arxiv.org/abs/1701.03638
[5] EPJST 210, 175 (2012)
[6] Phys. Rev. E 94 022107 (2016)
Keywords: Kinetic Lattice Monte-Carlo, GPU, Non-equilibrium, Selforganization
  • Lecture (others)
    TYC@Imperial, 16.10.2017, London, England
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, USA

Publ.-Id: 25899 - Permalink


Decoupling the two roles of liquid Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates
Tauchnitz, T.; Nurmamytov, T.; Hübner, R.; Engler, M.; Facsko, S.; Schneider, H.; Helm, M.; Dimakis, E.;
Liquid Ga droplets play a double role in the self-catalyzed growth of GaAs nanowires on Si(111) substrates covered with a native SiOx layer: they induce the formation of nano-sized holes in SiOx and drive the nanowire growth directly onto the underlying Si. The independent control of the two mechanisms is a prerequisite for mastering the growth of nanowires, but it is challenging in a conventional growth procedure where they both take place under the same droplets. As a result, serious growth implications occur, i.e. an uncontrolled number density/yield of vertical nanowires, a broad nanowire length distribution, and growth reproducibility issues.
To resolve those issues, we have developed a three-step in-situ surface modification procedure (SMP) of the SiOx/Si(111) substrates, which decouples the droplet-assisted hole formation in SiOx from the droplet-assisted growth of GaAs nanowires. Step-1 concerns the first thermal annealing of the substrate, during which extremely small pinholes are created in the SiOx layer. Ga deposition and droplet formation takes place at a lower substrate temperature in step-2. Depending on the substrate temperatures in both steps 1 and 2, the number density of Ga droplets can be varied deliberately from 107 to 1010 cm-2. Step-3 concerns the second thermal annealing of the substrate, during which all Ga droplets are evaporated completely from the substrate surface and an identical number of nano-sized holes of controlled size develop at their place. After the SMP, GaAs nanowires are always grown under identical conditions (Tgr=615°C, V/III=11) without pre-deposition of Ga. We found that different types of GaAs structures (vertical nanowires, inclined nanowires, or faceted islands) can nucleate inside the SMP-induced SiOx holes depending on the size of the latter (e.g. the nucleation of vertical nanowires is favored in 8 nm wide holes).
After careful selection of the SMP parameters (substrate temperatures and annealing durations), it is possible (i) to precisely control of the number density of vertical GaAs nanowires from 106 cm-2 to 109 cm-2 without changing the growth temperature or beam fluxes, (ii) to control the size of the SiOx holes in favor of high yields of vertical nanowires (up to 80 % of the total GaAs structures), (iii) to reproduce the wide range of nanowire number densities as well as the high yield values also on substrates from different batches, (iv) to obtain exceptionally narrow nanowire length distributions (below 1 % for 3 µm long nanowires), and (v) to control the nanowire diameter independent of the nanowire length and number density by changing only the V/III ratio.
  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

Publ.-Id: 25898 - Permalink


Ga droplets on SiOx/Si(111) substrates: nucleation and etching
Tauchnitz, T.; Nurmamytov, T.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.;
Liquid Ga droplets have been widely used in molecular beam epitaxy to induce the nucleation of nanostructures as well as to remove surface oxides from the substrate prior to epitaxial growth. In this work, we have employed Ga droplets to etch nanoholes into the native surface oxide of Si(111) substrates for the subsequent growth of III-V nanostructures. To that end, we studied the nucleation kinetics of Ga droplets on SiOx and the interaction between Ga adatoms/droplets and SiOx.
For given Ga flux and deposition time, we found that the number density of Ga droplets depends not only on the substrate temperature during deposition, but also on the annealing history of the substrate. This is attributed to the dependence of Ga adatom diffusivity on the surface morphology and/or the composition of the native oxide layer, both of which can be modified during the annealing. With an appropriate selection of substrate temperatures for the annealing and the Ga deposition steps, it was possible to vary deliberately the number density of Ga droplets within four orders of magnitude, i.e. 107-1010 cm-2. Interestingly, the droplet size and contact angle were found to be independent of the number density. This finding implies that low number densities of droplets are accompanied by an extensive loss of Ga atoms from the substrate surface. We discuss various explanations, such as desorption of Ga adatoms from the SiOx surface or reaction of Ga adatoms with SiOx and formation of volatile Ga2O.
All Ga droplets induce local modifications in the SiOx surface that evolve into nanoholes during a subsequent thermal annealing (which also results in complete evaporation of the Ga droplets). Depending on their size (which is a function of annealing temperature and duration), nanoholes can accommodate the nucleation of nanostructures on the underlying Si surface. As an example, we demonstrate the epitaxial growth of GaAs nanowires in the self-catalyzed mode. The number density of nanowires was controlled precisely and reproducibly within the range of 107-109 cm-2, whereas their length distribution was exceptionally narrow.
  • Poster
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

Publ.-Id: 25897 - Permalink


Aqueous Gold Overgrowth of Silver Nanoparticles: Merging the Plasmonic Properties of Silver with the Functionality of Gold
Mayer, M.; Steiner, A. M.; Röder, F.; Formanek, P.; König, T. A. F.; Fery, A.;
To date, it has not been possible to combine the high optical quality of silver particles with good chemical stability and synthetic convenience in a fully aqueous system, while simultaneously allowing chemical surface functionalization. We present a synthetic pathway for future developments in information, energy and medical technology where strong optical/electronic properties are crucial. Therefore, the advantages inherent to gold are fused with the plasmonic properties of silver in a fully aqueous Au/Ag/Au core-shell-shell system. These nanoparticles inherit low dispersity from their masked gold cores, yet simultaneously exhibit the strong plasmonic properties of silver. Protecting the silver surface with a sub-skin depth gold layer enables oxidant stability and functionality without altering the Ag-controlled optical properties. This combines both worlds - optical quality and chemical stability - and furthermore it is not limited to a specific particle shape.

Publ.-Id: 25896 - Permalink


Radiotracer Application at Dresden University and Fraunhofer Institute for Nondestructive Material Testing (Dresden)
Zeuner, A.; Krueger, P.; Jentsch, T.;
In 1957, the Faculty of Nuclear Technology was founded at the Dresden University of Technology. One of the aims of this faculty was to develop methods of radio tracer usage and to apply these methods at technical scale. The group "Technical Isotope Application" performed a lot of measurements in industrial plants. This group worked under different names up to 2005. Since about 2000, some capabilities have been transferred to the Fraunhofer Institute of Non-Destructive Testing, Dresden branch. In the following, an overview is given on working fields or investigated equipments, resp.
1. Application and development of radionuclide generators
Radiotracer investigations are done preferably by using short-lived radionuclides. As in nuclear medicine, the application of radionuclide generators (Mo-99/Tc-99m and Snl13/ Inl13m) has advantages also in technological applications, especially the long usability of the generator system. For dedicated purposes, namely the investigation of high temperature processes, a new generator system (Ba-140/La-140) was developed and applied.
2. Work on further development of radio tracer
- In many papers, the momentum method was explored. This method has the advantage, that a residence time distribution is interpreted without any model assumptions. The mean residence time and other parameters are calculated only from statistical moments and applied to
material transport processes.
- Activity estimation is an important part prior an investigation will be accepted by the radiation protection authorities. A computer program is developed based on the plant values and on the expected worst residence time distribution.
- During radiotracer measurements, the residual pulse density sometimes does not decrease to the original background. With the assumption, that the residual pulse density is caused by deposition of radioactive material near the detector, correction procedures were developed and used.
3. Working fields
Open radionuclides:
Residence time measurements in
- Water, waste water, filtration
- Gas exchange and reactions in gas phase; fluid beds
- Conveyers, dryers, rotary kilns, mills
- Plants for chemical fibres, polymers; in extruders and others
- Estimation of oil consumption of cumbustion engines
- Particle tracking in a screw conveyer by activated glass balls
- Investigation of mixing processes Application of sealed sources
- Estimation of ash content and heat value of brown coal
- Estimation of sedimentation in a smoke channel of a thermal cracker
- Steam estimation in streaming hot water
  • Poster
    The 6th International Conference on Tracers and Tracing Methods, TRACER 6, 06.-08.06.2011, Oslo, Norge

Publ.-Id: 25895 - Permalink


What Ga droplets can and cannot do in the growth of GaAs nanowires on Si
Tauchnitz, T.; Balaghi, L.; Hübner, R.; Bischoff, L.; Schneider, H.; Helm, M.; Dimakis, E.;
The central role of liquid Ga droplets in the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates will be overviewed, including our recent findings. Initially, Ga droplets interact with the surface oxide layer that typically covers a Si substrate and create nanoholes. The nucleation of GaAs nanowires takes place there, in direct contact with the underlying Si. Using a sequence of Ga deposition and substrate annealing steps, the number density of nanowires can be controlled from 107 to 109 cm-2 without the need for pre-patterned substrates. During the growth of nanowires, the Ga droplet on their apex captures Ga adatoms and As4 molecules efficiently and, thus, enhances the local growth rate in favor of the axial elongation of the nanowires. The contact angle of the droplet with the underlying nanowire determines the phase of the growing crystal. Long segments of pure zinc blende phase are possible, whereas wurtzite has been demonstrated only for short segments. On the other hand, Ga-catalyzed growth has certain inherent limitations. Those concern the axial growth of ternary alloys, the abruptness of axial hetero-interfaces and the ability for defect-free interruptions of the axial growth. Most of those limitations are related to the solubility properties of other elements (i.e. In, Al, As) in Ga droplets. As a method of probing and controlling the growth processes inside the droplets, the droplet-confined alternate pulsed epitaxy is introduced.
  • Invited lecture (Conferences)
    19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia

Publ.-Id: 25894 - Permalink


Selective mass enhancement close to the quantum critical point in BaFe2(As1−xPx)2
Grinenko, V.; Iida, K.; Kurth, F.; Efremov, D. V.; Drechsler, S.-L.; Cherniavskii, I.; Morozov, I.; Hänisch, J.; Förster, T.; Tarantini, C.; Jaroszynski, J.; Maiorov, B.; Jaime, M.; Yamamoto, A.; Nakamura, I.; Fujimoto, R.; Hatano, T.; Ikuta, H.; Hühne, R.;
A quantum critical point (QCP) is currently being conjectured for the BaFe2(As1−xPx)2 system at the critical value xc ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field Hc2. Here we report Hc2 data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that Hc2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe2(As1−xPx)2. The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

Publ.-Id: 25893 - Permalink


Interactions of natural occurring microorganisms with uranium(VI)
Gerber, U.; Schäfer, S.; Krawczyk-Bärsch, E.;
The uranium waste mine Königstein (Saxony, Germany) is heavily polluted with heavy metals, especially with uranium. Despite the high concentrations of heavy metals, the mine is a reservoir for many different microorganisms that have evolved special strategies to survive in these extreme environments. Their ubiquitous occurrence is of fundamental interest to understand the migration behavior of radionuclides within the biosphere.
Furthermore, microorganisms could be used to clean-up contaminated soils, sediments, and waters by removing uranium and other radionuclides, due to bioremediation processes.
Keywords: Bioremediation, Uranium(VI), microorganisms
  • Lecture (others)
    Im Rahmen einer Vorlesung der Universidad Tenica Federico Santa Maria, 27.07.2017, Valparaiso, Chile

Publ.-Id: 25892 - Permalink


Evaporation-assisted magnetic separation of rare earth ions in aqueous solutions
Lei, Z.; Fritzsche, B.; Eckert, K.ORC
This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient despite the presence of a counteracting Brownian motion. For that purpose, we study a rare earth chloride (DyCl3) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure. The temporal evolution of the refractive index field of this solution, as a result of heat and mass transfer, is measured by means of a Mach-Zehnder interferometer. We develop a numerical algorithm which splits the refractive index field into two parts, one space-dependent and conservative and the other time-dependent and transient. By using this algorithm in conjunction with a numerical simulation of the temperature and concentration field, we are able to show that 90\% of the refractive index in the evaporation-driven boundary layer is caused by an increase in the concentration of Dy(III) ions. A simplified analysis of the gravitational and magnetic forces, entering the Rayleigh number, leads to a diagram of the system's instability. Accordingly, the enrichment layer of elevated Dy(III) concentration is placed in a spatial zone dominated by a field gradient force. This leads to the unconditional stability of this layer in the present configuration. The underlying mechanism is the levitation and reshaping of the evaporation-driven boundary layer by the magnetic field gradient.
Keywords: magnetic separation, rare earth salt; paramagnetism; interferometer; field gradient force

Downloads:

Publ.-Id: 25891 - Permalink


General Evolution Equation for the Specific Interfacial Area of Dendrites During Alloy Solidification
Neumann-Heyme, H.; Eckert, K.ORC; Beckermann, C.
The specific area of the solid-liquid interface of an assembly of dendrites is an important integral measure of the morphology of the microstructure forming during alloy solidification. It represents the inverse of a characteristic length scale and is needed for the prediction of solidification defects and material properties. In the present study, the evolution of the interfacial area of dendrites is analysed using 3D phase-field simulations. A general evolution equation is developed for the specific interfacial area as a function of time and solid volume fraction that accounts for the effects of growth, curvature-driven coarsening and interface coalescence. The relation is validated using data from previously performed synchrotron X-ray tomography and isothermal coarsening experiments. It is found to be valid for arbitrary and even varying cooling rates and for a wide range of binary alloys. The rate constant in the evolution equation is successfully related to alloy properties.
Keywords: Dendritic solidification; Interfacial area; Phase-field simulation; Synchrotron X-ray tomography experiments

Downloads:

Publ.-Id: 25890 - Permalink


A new degree of freedom for electron holography
Röder, F.; Lubk, A.; Houdellier, F.; Denneulin, T.; Snoeck, E.; Hÿtch, M. J.;
Off-Axis Electron Holography permits the direct reconstruction of amplitude and phase of electron waves elastically scattered by an object (see, e.g., [1]). The technique employs the Möllenstedt biprism to mutually incline an object modulat-ed wave and a plane reference wave to form an interference pattern at the detec-tor plane. Limited coherence of the electron beam in presence of aberrations at-tenuates high spatial frequencies of the object exit wave spectrum, which is de-scribed by the sideband envelope function. We explore an extension of the con-ventional electron holography set-up given by deliberately tilting the reference wave independent from the object wave. This allows the transfer of spatial fre-quencies beyond the conventional sideband information limit as predicted by a generalized transfer theory for Off-Axis Electron Holography [2]. This is based on the idea that a reference wave tilted by q0 compensates the wave aberration for the spatial frequency q0 of the object wave spectrum. Thus, an off-axis hologram series with varying reference wave tilt allows in principle a linear synthesis of an effective coherent aperture with a radius reaching out beyond the conventional information limit. Furthermore, an object-independent measurement of aberra-tions as well as strain measurements by dark-field electron holography can be realized using this setup. The experimental realization of an arbitrarily tilted refer-ence wave is challenging and could be realized for the first time at the Hitachi HF3300C I2TEM at CEMES Toulouse for one direction [3]. We used an additional biprism placed in the illumination system. Three condenser lenses were adjusted to provide a demagnified image of the condenser biprism at the sample plane under parallel illumination. The pre-specimen deflectors were adapted to maintain the incident wave vector of the object wave and to realize a tilt of the reference wave as a function of the condenser biprism voltage. Finally, we have experimen-tally shown that dark-field holography can be conducted with an object-independent reference alleviating the need for a uniform area of known structure.

[1] H. Lichte, M. Lehmann, Rep. Prog. Phys. 71 (2008) 016102.
[2] F. Röder, A. Lubk, Ultramicoscopy 152 (2015) 63-74.
[3] F. Röder, F. Houdellier,T. Denneulin, E. Snoeck, M.J. Hÿtch, Ultramicoscopy 161 (2016) 23–40.
Keywords: electron holography, tilted reference wave, aperture systhesis, dark-field
  • Invited lecture (Conferences)
    PICO 2017 - Forth Conference on Frontiers of Aberration Corrected Electron Microscopy, 30.04.-04.05.2017, Kasteel Valsbroek, The Netherlands

Publ.-Id: 25889 - Permalink


Micro-flow magnetic separation of rare earth metals ions in aqueous solutions
Kolczyk, K.; Wojnicki, M.; Yang, X.; Mutschke, G.; Kutyla, D.; Kowalik, R.; Zabinski, P.;
Due to application in many modern technologies, rare earth elements (REE) nowadays attract higher and higher interest. These metals are produced both from primary and secondary sources in hydrometallurgical processes which are often complicated and costly. The most problematic step of production is the separation of ions. Due to these reasons it is desirable to improve the current processes.
Here, High Magnetic Gradient Separation (HGMS) appears to be attractive. It utilizes the different magnetic properties of rare earth metal ions to achieve separation by attraction or repulsion in an inhomogeneous magnetic field [1][2].
The present work investigates the separation of REE ions in aqueous solutions based on their magnetic properties. The experiments were carried out in micro-flow cells produced by a 3D printing technology (Fig. 1). The cells consist of a spiral channel next to which a spiral of an iron wire is arranged. The inhomogeneous magnetic field in the cross section of channel is created by the placement of the cell in a laboratory electromagnet. During the flow of the solution the metal ions experience a force from the gradient magnetic field. At the outflow, the near-wire and the far-wire half of the solution are collected and analyzed. Different solutions consisting of a single species and of mixtures of metals ions were investigated at different flow rates, and the concentrations were analyzed by UV/VIS spectrometry.
The results will be presented in detail at the conference. The conducted experiments state a preliminary determination of the influence of a gradient magnetic field on the transport of ions in aqueous solutions in the flow state.

[1] K. Kołczyk, M. Wojnicki, D. Kutyła, R. Kowalik, P. Żabiński, A. Cristofolini, Archives of Metallurgy and Materials, 61 (2016) 1919–1924.
[2] K. Kolczyk, D. Kutyla, M. Wojnicki, A. Cristofolini, R. Kowalik, P. Zabinski, MAGNETOHYDRODYNAMICS 52 (2016) 541-547.
Keywords: magnetic separation, rare earth metals, aqueous solution, microfluidics UV/VIS spectrometry
  • Lecture (Conference)
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

Publ.-Id: 25888 - Permalink


Contactless manipulation of fluids and measurement of concentration changes in microfluidic systems by imposed magnetic fields
Uhlemann, M.; Hähnel, V.; Kahn, F.; Mutschke, G.; König, J.; Fritsch, I.;
New technologies based on transport, actuation and manipulation of fluids and objects in the micro- and nanometer scale are rapidly developing. The enormous scientific and technological interest focuses on lab-on-a-chip approaches which are applicable in analytics and monitoring in medicine, in biology and in the environmental sector. Avoiding mechanical forces, alternative pumping concepts gain in importance.
Contactless external driving forces such magnetic fields and field gradients for fluid manipulation and electrochemical and analytical approaches are of interest.
Several microfluidic approaches were employed to prove the concept of fluid manipulation by overlaying magnetohydrodynamic (MHD) effects generated by the Lorentzforce (FL) and the magnetic field gradient force (FB) [1]. For this purpose suitable microstructures were designed and applicable materials were chosen to generate high magnetic field gradients in the immediate vicinity of the surface of the microfluidic chip. These are generated by magnetic field gradient templates consisting of μm-thin CoFe stripes which are saturated by a permanent NdFeB magnet. They were employed to manipulate liquids with paramagnetic ions (e.g. Mn2+). Potential time transients as a measure for concentration changes between the electrodes with and without superimposed magnetic field gradients are recorded and the enrichment [2] is detected by fluorescence microscopy supported by magnetic field gradient simulation.
For driving fluid flow the redox system K3Fe(CN)6/K4Fe(CN)6 which is commonly used for redox-MHD [3] was used and superimposed by high magnetic field gradients generated by the same method. Then, a fluid flow can be controlled by on-off-switching of the cell current originating from the electrodes which is generating a Lorentz force. In combination with the magnetic field gradient template a desired change of velocity and flow direction is realized as well as localized enrichment of ions. To clarify the impact of the magnetic field gradient, the template can be positioned in different orientation and distances in between the electrodes facing each other to reduce or enhance the fluid flow. Video microscopy and particle velocity measurements illustrate and quantify the effects further supported by numerical simulations.
Keywords: Redox-reaction, microfluidics, magnetic fields, Lorentz force, Kelvin force, PIV, numerical simulation
  • Lecture (Conference)
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

Publ.-Id: 25887 - Permalink


Numerical simulation of mass transfer and convection near a hydrogen bubble during water electrolysis in magnetic fields
Mutschke, G.; Bazcyzmalski, D.; Karnbach, F.; Uhlemann, M.; Yang, X.; Eckert, K.; Fröhlich, J.; Cierpka, C.;
Hydrogen produced from wind or solar power could be used easily for storing energy also at large scale, thus allowing to bridge the gap between supply and demand of renewable energy with respect to time and place. When splitting water by electrolysis, a deeper look at local phenomena near single bubbles at the electrode might be helpful to improve our understanding of the process. In the recent literature, magnetic fields are discussed with respect to the bubble departure, thereby possibly influencing the efficiency of the process [1-7].
The contribution will present numerical simulations resolving in detail local phenomena near a single hydrogen bubble at the cathode during the electrolysis of water in external magnetic fields. The modeling is supported by data of recent experiments on hydrogen single bubbles evolving at a platinum micro-electrode [7-9]. The results will provide insight into the local and temporal behavior of electrolyte convection, species concentration and mass transfer during electrolysis. Furthermore, the influence of the Lorentz force caused by vertical and horizontal magnetic fields on the departure will be discussed in detail (see Figs. 1 and 2).

[1] X. Yang et al., Langmuir 31 (2015) 8184-8193.
[2] D. Fernandez et al., Langmuir 30 (2014) 13065-13074.
[3] H. Liu et al., J. Electroanal. Chem. 754 (2015) 22-29.
[4] H. Liu et al., Can. J. Chem. Eng. 9999 (2015) 1-8.
[5] D. Baczyzmalski et al., Exp. Fluids 56 (2015) 162ff.
[6] J. Koza et al., Electrochem. Comm. 10 (2009) 425-429.
[7] F. Karnbach et al., J. Phys. Chem. C 120 (2016) 15137-15146.
[8] D. Baczyzmalski et al., J. Electrochem. Soc. 163 (2016) E248-E257.
[9] G. Mutschke et al., Magnetohydrodynamics 53 (2017) 193-198.
[10] D. Baczyzmalski et al., submitted to Phys. Rev. Fluids (2017).
Keywords: electrolysis, hydrogen evolution, magnetic field, Lorentz force, mass transfer, convection, numerical simulation
  • Poster
    International Conference on Magneto-Science 2017, 23.-27.10.2017, Reims, Frankreich

Publ.-Id: 25886 - Permalink


Growth and detachment of single hydrogen bubbles in a magnetohydrodynamic shear flow
Baczyzmalski, D.; Karnbach, F.; Mutschke, G.; Yang, X.; Eckert, K.; Uhlemann, M.; Cierpka, C.;
This study investigates the effect of a magnetohydrodynamic (MHD) shear flow on the growth and detachment of single sub-millimeter-sized hydrogen gas bubbles. These bubbles were electrolytically generated at a horizontal Pt microelectrode (100 μm in diameter) in an acidic environment (1 M H2SO4). The inherent electric field was superimposed by a homogeneous electrode-parallel magnetic field of up to 700 mT to generate Lorentz forces in the electrolyte, which drive the MHD flow. The growth and motion of the hydrogen bubble was analyzed by microscopic high-speed imaging and measurements of the electric current, while particle tracking velocimetry (μPTV) and particle image velocimetry (μPIV) were applied to measure the surrounding electrolyte flow. In addition, numerical flow simulations were performed based on the experimental conditions. The results show a significant reduction of the bubble growth time and detachment diameter with increasing magnetic induction, which is known to improve the efficiency of water electrolysis. In order to gain further insight into the bubble detachment mechanism, an analysis of the forces acting on the bubble was performed. The strong MHD-induced drag force causes the bubble to slowly slide away from the center of the microelectrode before its detachment.
This motion increases the active electrode area and enhances the bubble growth rate. The results further indicate that at large current densities the coalescence of tiny bubbles formed at the foot of the main bubble might play an important role for the bubble detachment.
Moreover, the occurrence of Marangoni stresses at the gas-liquid interface is discussed.
Keywords: electrolysis, hydrogen evolution, magnetic field, Lorentz force, PIV, numerical simulation

Publ.-Id: 25885 - Permalink


Probing the Impact of the Initiator Layer on Grafted-from Polymer Brushes: A Positron Annihilation Spectroscopy Study
Panzarasa, G.; Aghion, S.; Marra, G.; Wagner, A.; Liedke, M. O.; Elsayed, M.; Krause-Rehberg, R.; Ferragut, R.; Consolati, G.;
Grafting-from is the technique of choice to obtain polymer brushes. It is based on the growth of polymer chains directly from an initiator-functionalized surface, and its development gained momentum thanks to recent advances in controlled polymerization techniques. However, despite the great amount of work that has been performed on this subject, the influence exerted by the initiator layer on the characteristics of the resulting brushes has been almost completely overlooked. Our group has already demonstrated that positron annihilation spectroscopy (PAS) is a valuable analytical tool for the study of polymer brushes. Here, we applied this technique to show that differences in the organization of the initiator layer dramatically reflect on the characteristics of polymer brushes. Brushes made by surface-initiated atom transfer radical polymerization (ATRP) of a pH-responsive polymer, poly(dimethylaminoethyl methacrylate) (PDMAEMA), were investigated also in terms of the effects of protonation and of the incorporation of silver nanoparticles inside the brushes, shining a new light on the internal structure of such complex, fascinating systems.
Keywords: Grafting-from polymer brushes positron annihilation spectroscopy surface-initiated atom transfer radical polymerization (ATRP)

Publ.-Id: 25884 - Permalink


Modeling in vivo relative biological effectiveness in particle therapy for clinically relevant endpoints
Lühr, A.; von Neubeck, C.; Helmbrecht, S.; Baumann, M.; Enghardt, W.; Krause, M.;
Background
The relative biological effectiveness (RBE) of particle therapy compared to photon radiotherapy is known to be variable but the exact dependencies are still subject to debate. In vitro data suggested that the RBE is to a large extend independent of ion type if parametrized by the beam quality Q. This study analyzed the RBE dependence of pre-clinical data on late toxicity with an emphasis on the beam quality.
Material and Methods
Published pre-clinical RBE dose-response data of the spinal cord following one and two fractions of photon and carbon ion irradiation were compiled. The beam quality for each treatment condition was obtained from Monte Carlo simulations. The αp and βp parameters of the linear-quadratic (LQ) model for particle irradiation were determined from the pre-clinical data and provided as a function of Q. An introduced model proposed αp to increase linearly with Q and βp to remain constant. RBE values predicted by the model were compared to the published data.
Results
The αp parameter was highly correlated with Q (R2 = 0.96) with a linear slope of 0.019 Gy-1. No significant variation of βp with Q was found. RBE and Q were also highly correlated (R2 = 0.98) for one and two fractions. The (extrapolated) RBE at Q = 0 (theoretical photon limit) for one and two fractions was 1.22 and significantly larger than 1 (p = 0.004). The model reproduced the dependence of RBE on fractionation well.
Conclusion
Fraction dose and beam quality Q were sufficient to describe the RBE variability for a late toxicity model within a carbon ion treatment field. Assuming the independence of the identified RBE parameters on the ion type might suggest the translation of variable (pre-) clinical RBE data from carbon ion to proton therapy.

Downloads:

Publ.-Id: 25883 - Permalink


Towards Reconfigurable Field Effect Transistors: Controlled Nickel Silicidation using Flash Lamp Annealing
Khan, M. B.; Deb, D.; Georgiev, Y. M.; Prucnal, S.; Voelskow, M.; Erbe, A.;
Classical scaling down of CMOS technology is reaching its end in the next few years. To facilitate further the enhancement in the complexity and performance of electronic circuits without increasing the chip area, devices with new materials, new architectures, enhanced functionality and new computation principles have gained importance. Our work focuses on fabricating devices with new architectures and enhanced functionality i.e. devices which can be reconfigured as a p- or n-channel field effect transistor (FET). These reconfigurable FETs are based on Silicon (Si) nanowires (NWs), which are silicided at both ends to form Si-NiSi2-Si Schottky junctions. Formation of NiSi2 is a pre-requisite for proper functioning of these devices since fermi level of NiSi2 aligns itself near the mid-bandgap of Si, thereby enabling tuning of band by application of electrostatic potential for its function as a p/n FET [1]. Moreover, control over silicide length is also important to scale the Si channel and to have symmetric contacts on both sides of the nanowire [2]. These issues are the focus of our recent work.
In this paper, we report on comparison between silicidation of undoped Si NWs using rapid thermal annealing (RTA) and flash lamp annealing (FLA). The nanowires are fabricated on silicon on insulator (SOI) substrates by a top down process based on electron beam lithography (EBL) and subsequent inductively coupled plasma (ICP) etching. Hydrogen silsesquioxane (HSQ), a negative tone EBL resist, is used to provide high quality sub-15nm lithographic nanowire patterns, which are transferred into SOI by optimised ICP etching based on C4F8/SF6/O2 mixed gas chemistry. Subsequently, nickel (Ni) is sputtered at lithographically defined areas followed by RTA, which yields atomically sharp NiSi2-Si Schottky junctions. However, the main drawback of this silicidation process is the poor control over Ni silicide phase formation and the progression length of the silicidation along the Si NWs (Fig. 1). These effects lead to an inhomogeneous silicidation process, which prevents symmetric Si channel formation and downscaling.
To provide better control over the silicidation process, a ms-range FLA is investigated as a potential replacement of RTA. Initially, the FLA was performed for 3, 6 and 20 ms on bulk silicon by either flashing the front (f-FLA) or rear (r-FLA) side of the samples. Formation of NiSi and the composition was investigated by micro-Raman (Fig. 2) and Rutherford Backscattering Spectrometry (RBS) (Fig. 3). It is shown that after 6 and 20 ms annealing 50 nm Ni is fully converted to stoichiometric NiSi with atomically sharp interface between NiSi and Si. Cubic NiSi displays Raman active phonon modes at 193 and 217 cm-1, which suggests that the fabricated layer is tensile strained. These preliminary results on bulk Si suggest that the FLA promises to provide better control over silicidation process of the nanowires, thereby enhancing the performance of reconfigurable FETs. Results on silicidation of nanowires will be presented at the conference.
Keywords: Silicon nanowire; silicidation; reconfigurable transistor; Schottky junction
  • Poster
    Micro and nanoengineering, 18.-22.09.2017, Braga, Portugal

Publ.-Id: 25882 - Permalink


Electrical Characterization of sub-20 nm Silicon Nanowires Fabricated using Electron Beam Lithography and Inductively Coupled Plasma Etching
Khan, M. B.; Deb, D.; Georgiev, Y. M.; Fuchs, F.; Schuster, J.; Erbe, A.;
Scaling down of CMOS faces strong challenges due to which new materials, enhanced functionality and new device concepts have gained importance. These concepts include undoped silicon nanowire based reconfigurable devices which can be programmed as p-FET or n-FET by controlling the electrostatic potential applied across gate. In this work, electrical characterization of undoped sub-20 silicon nanowires (SiNWs) is reported. SiNWs are fabricated on intrinsic SOI substrates in <110> and <100> crystal directions by a top down approach. Hydrogen silsesquioxane (HSQ), a negative tone electron beam resist is used for nano- patterning as well as hard mask for etching. Nanowire etching process is optimized using an inductively coupled plasma (ICP) source and C4F8/SF6/O2 mixed gas recipe at 18 oC. These NWs are oxidized to form a SiO2 shell and subsequently silicidized. For silicidation the SiO2 shell is wet etched at pre-defined positions followed by Nickel(Ni) sputtering and diffusion which yield silicide-silicon(Schottky) junctions. Ni is used for silicidation to selectively control the charge carriers injection at the junctions. Different transport and silicidation progress was observed in <110> and <100> crystal directions.
Keywords: Silicon nanowire; etching; lithography; schottky barrier devices
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft, 19.-24.03.2017, Dresden, Germany

Publ.-Id: 25881 - Permalink


Electromagnetically excited flows and instabilities in liquid metal batteries
Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Salas, A.; Starace, M.; Stefani, F.; Weber, N.;
We will provide an overview of the liquid metal battery (LMB) related activities at the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) with a focus on magnetohydrodynamic aspects of future large scale LMBs. High current densities together with a large cross section will result in substantial currents accompanied by considerable magnetic fields. Thus electromagnetically driven flows and instabilities should be taken into account for large enough installations. While beneficial effects of mild electromagnetically driven flows are to be expected for the cathodes, the thin electrolyte layers have to be protected against violent motion.

The Tayler instability (TI) can be understood as a generic case of a current driven instability under perfectly uniform current, i.e., ideal conditions. In this sense it constitutes sort of an upper bound for a current bearing fluid to remain at rest. Modifying the magnetic field distribution in the cell is an effective means to suppress the TI.
Different field configurations to achieve TI suppression and their relative merits will be discussed and related to TI saturation mechanisms.
Non-uniform current distributions are more typical for real settings. They give rise to rotational Lorentz force distributions and will thereby also generate electro-vortex flows (EVFs). In terms of LMBs the concrete shape of the current collectors plays a crucial role in whether EVFs exist and how they might interact with the TI. We will conclude with electromagnetically exited interface instabilities and discuss similarities to and differences from sloshing modes known from aluminium reduction cells.
Keywords: liquid metal batteries, Tayler instability, electro-vortex flows, interfacial instabilities
  • Lecture (Conference)
    High Temperature Batteries for Stationary Energy Storage Workshop, 19.-20.09.2017, Trondheim, Norwegen

Publ.-Id: 25880 - Permalink


Arrival time and Intensity Binning at high quasi-cw repetition rates: the big data challenge
Green, B.; Kovalev, S.; Deinert, J.; Wang, Z.; Awari, N.; Chen, M.; Germanskiy, S.; Gensch, M.;
  • Lecture (Conference)
    ARD-ST3 annual meeting, 19.-21.07.2017, Zeuten, DESY, Germany

Publ.-Id: 25879 - Permalink


Experimental investigation of pilot scale bubble column reactor with various internals using fine wire-mesh sensors
Lavetty, C.;
In this master thesis the hydrodynmamic behavior of a bubble column reactor with various dense heat exchanging tube patterns and tube sizes has been investigated using fine wire-mesh sensors. With the special design of the wire-mesh sensors it was possible to manufacture one set of sensors while using different inlets to mimic the specific tube pattern. A three level wire-mesh sensor with a 64x64x64 grid was used in order to asses the local and global hydrodynamics, such as, bubbles size distribution, gas velocity profile, phase holdup and its distribution. For the first time, with this technique it is possible to gain insights in the flow behaviour within complex geometries, e.g. sub-channels of the tube bundle. Therfore, regime maps were generated covering all hydrodynamic flow regimes, namely, bubbly, transition and churn-turbulent flow regime. Du to the insertion of the tube bundle within the reactor, the radial holdup profile changes drastically compared to the empty counterpart. It reveals zones of liquid up flow within the sub-channel and liquid downflow within the viscinity of the tube due to additional wall brought into the system. Furthermore, a correlation has been developed in order to describe the overall holdup in dependence on tube size and pattern for the current investigations as well as for past investigations.
  • Master thesis
    University of Edinbourgh, 2018
    Mentor: Möller, Felix
    108 Seiten

Publ.-Id: 25878 - Permalink


Numerical Optimization of Finned Heat Exchanger Using Ansys CFX
Ayob, A. A.; Unger, S.;
his report investigates the effect of tube geometry and different fin parameters towards heat transfer and flow properties in a heat exchanger using Ansys CFX for a single phase system. The purpose of this study was focused on improving heat transfer efficiency around a single tube within a heat exchanger. Stainless steel was used as the construction material for the tube and the flowing medium is air at ambient conditions. Tube length was kept constant at 212 mm. The temperature of the tube wall was kept constant at 330.15 K and inlet air temperature at 300.15 K. Inlet air velocity was varied from 0.5 m/s to 5 m/s to observe how the structure performed at different Reynolds number. The main results that were observed were “goodness” factor (ratio of Colburn number to friction factor), pressure drop (∆P), increase in air temperature (∆T), efficiency, and average heat transfer coefficient (HTC).
An initial simulation was modelled and compared to literature. This was done to ensure that it was performing as intended. The accuracy of Ansys CFX was studied to ensure that changing the software properties such as mesh, residual target and turbulence model would not have much impact on the results. It was decided that manipulating software properties changed the results by less than 5% would suffice. The effect of tube geometry was studied by changing the shape from annular to oval shaped and by changing the outer diameter of oval tubes from 27mm to 16 mm. From the results, it was concluded that an oval tube with 16 mm outer diameter was the best design as it gave the lowest pressure drop (0.05 – 1.9 Pa) and highest “goodness” factor (0.4), even though it had the lowest value for heat transfer coefficient. The 16 mm oval tube was used for the simulation of different fin parameters The fin parameters varied were fin thickness, fin height, and fin pitch. Only one parameter was manipulated while other parameters were maintained at a constant value. The fin height was manipulated from 6mm to 46mm. It was observed that a smaller fin height would give efficiencies up to 96%, lower pressure drop but the lowest “goodness” factor. At low air velocities, a 6 mm fin height had a lower value for ∆T compared to 46 mm tall fin by 58%. The difference decreases to 0.016% when air velocity reaches 5 m/s. Next, f in thickness was changed from 0.25 mm to 4mm. The results showed that increasing the fin thickness increases the average heat transfer coefficient and ∆T but resulted in higher ∆P. When air velocity is low, the difference in ∆T was 53%. This decreased with increasing velocity. Lastly, fin pitch was manipulated from 0.25 mm to 6 mm. It was found that a fin pitch value of 0.25-1 mm reduced the amount of air able to flow between the fins. At low velocities of around 0.5 m/s, increasing the fin pitch beyond 4 mm had a negative effect on HTC and ∆T. This value changes when air velocity exceeds 3 m/s, where a fin pitch larger than 2 mm had lower values for average heat transfer coefficient and ∆T.
  • Master thesis
    The University of Edinburgh, 2017
    Mentor: Sebastian Unger

Publ.-Id: 25877 - Permalink


Transformation of biomass components to high-value products: reductive amination of ethyl levulinate with amines
Shumilov, V. V.; Salmi, T.; Murzin, D.; Hupa, L.; Eränen, K.; Kumar, N.; Sulman, E.; Schubert, M.; Boden, S.; Hampel, U.;
Transformation of biomass components to high-value products used in industry over structured catalysts is the idea behind this project. Synthesis of 5-Methyl-1-Hydroxyethyl-2-Pyrrolidone by reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine in the presence of hydrogen was performed. Reactor which uses porous ceramic monolith as a catalytic carrier was studied.

For the development of a new catalytic system, alumina was chosen as a carrier material and sponge replica technique was used for its production. Porous ceramics with different pore types and sizes are widely applied in chemical industry. The unique properties of porous materials allow to carry out a spectrum of well-established and recent applications, such as molten metal filtration, catalysis, refractory and thermal insulation, hot gas filtration. Porous form is perfect for heterogeneous catalysis because of high surface area, which enables liquid (or gas) to contact the catalyst intensively.

Alpha-Alumina is a strong material the surface area of which is low and so to enlarge surface area covering of the foam with a layer of gamma-alumina which has a much bigger surface area was performed.

Two methods of gamma-alumina coating were performed. One of them is covering alpha-alumina frame with gamma-alumina slurry. This method is limited by the pore size, as the smallest pores will be blocked after slurry adding. The second method is a hot water solution deposition where sedimentation of gamma-alumina from its salt takes place.

Pt and Ru in the form of nanoparticles were successfully deposited on the surface of the porous structure. Catalysts were characterized by nitrogen desorption, SEM, EDXA, TEM and other methods. Reactor represents a tube with a diameter about 20 mm and length about 350 mm into which porous catalyst is placed.

Reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine which was performed. Ethyl levulinate is a product of levulinic acid transformation. Levulinic acid is a well-known precursor for pharmaceuticals, plasticizers and other additives. It is a building block or starting material for a wide range of compounds.
  • Lecture (Conference)
    10th World Congress of Chemical Engineering, 01.-05.10.2017, Barcelona, Spain

Publ.-Id: 25876 - Permalink


Development of structured reactors for transformation of biomass components to high-value products - green process industry
Salmi, T.; Shumilov, V. V.; Eränen, K.; Kumar, N.; Hupa, L.; Murzin, D.; Boden, S.; Schubert, M.; Hampel, U.; Sulman, E.;
Transformation of biomass components to high-value products used in industry over structured catalysts is the idea behind this project. Synthesis of 5-Methyl-1-Hydroxyethyl-2-Pyrrolidone by reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine in the presence of hydrogen was performed. Reactor which uses porous ceramic monolith as a catalytic carrier was studied.

For the development of a new catalytic system, alumina was chosen as a carrier material and sponge replica technique was used for its production. Porous ceramics with different pore types and sizes are widely applied in chemical industry. The unique properties of porous materials allow to carry out a spectrum of well-established and recent applications, such as molten metal filtration, catalysis, refractory and thermal insulation, hot gas filtration. Porous form is perfect for heterogeneous catalysis because of high surface area, which enables liquid (or gas) to contact the catalyst intensively.

Alpha-Alumina is a strong material the surface area of which is low and so to enlarge surface area covering of the foam with a layer of gamma-alumina which has a much bigger surface area was performed.

Two methods of gamma-alumina coating were performed. One of them is covering alpha-alumina frame with gamma-alumina slurry. This method is limited by the pore size, as the smallest pores will be blocked after slurry adding. The second method is a hot water solution deposition where sedimentation of gamma-alumina from its salt takes place.

Pt and Ru in the form of nanoparticles were successfully deposited on the surface of the porous structure. Catalysts were characterized by nitrogen desorption, SEM, EDXA, TEM and other methods. Reactor represents a tube with a diameter about 20 mm and length about 350 mm into which porous catalyst is placed.

Reductive amination of ethyl levulinate using 3-aminopropanol as the alkyl amine which was performed. Ethyl levulinate is a product of levulinic acid transformation. Levulinic acid is a well-known precursor for pharmaceuticals, plasticizers and other additives. It is a building block or starting material for a wide range of compounds.
  • Poster
    10th International Symposium on Catalysis in Multiphase Reactors and Multifunctional Reactors, 07.-10.07.2017, Qingdao, China

Publ.-Id: 25875 - Permalink


Quasi-two-dimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor-Couette flow
Mamatsashvili, G.; Stefani, F.; Guseva, A.; Avila, M.;
Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite a lot of theoretical, numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors of protoplanetary disks, liquid cores of planets and liquid metals in laboratory.
We investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI), a relative of standard magnetorotational instability with only axial magnetic field, in magnetized Taylor-Couette flow using direct numerical simulations. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter plays a special role for its dynamics and determines the growth rate. We show that this parameter is also important in the present nonlinear problem. With increasing its value, a sudden transition (bifurcation) from weakly nonlinear, where the system is slightly above the linear stability threshold, to turbulent regime occurs. The energy spectra corresponding to these two regimes, also differ qualitatively. Remarkably, the nonlinear states in these cases remain mostly axisymmetric and in fact represents a type of sustained two-dimensional magnetohydrodynamic turbulence driven by HMRI. Although the contribution of non-axisymmetric modes increases with the Elsasser number, their total energy still remains more than order of magnitude smaller than that of the axisymmetric ones.
Keywords: MHD, helical magnetorotational instability, turbulence, Taylor-Couette flow, numerical simulations

Publ.-Id: 25874 - Permalink


Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
Gogichaishvili, D.; Mamatsashvili, G.; Horton, W.; Chagelishvili, G.; Bodo, G.;
We investigate magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI) in Keplerian disks with a nonzero net azimuthal magnetic field using shearing box simulations.
As distinct from most previous studies, we analyze turbulence dynamics in Fourier (${\bf k}$-) space to understand its sustenance.
The linear growth of MRI with azimuthal field has a transient character and is anisotropic in Fourier space, leading to anisotropy of nonlinear processes in Fourier space. As a result, the main nonlinear process appears to be a new type of angular redistribution of modes in Fourier space -- the \emph{nonlinear transverse cascade} -- rather than usual direct/inverse cascade. We demonstrate that the turbulence is sustained by interplay of the linear transient growth of MRI (which is the only energy supply for the turbulence) and the transverse cascade. These two processes operate at large length scales, comparable to box size and the corresponding small wavenumber area, called \emph{vital area} in Fourier space is crucial for the sustenance, while outside the vital area direct cascade dominates. The interplay of the linear and nonlinear processes in Fourier space is generally too intertwined for a vivid schematization. Nevertheless, we reveal the \emph{basic subcycle} of the sustenance that clearly shows synergy of these processes in the self-organization of the magnetized flow system. This synergy is quite robust and persists for the considered different aspect ratios of the simulation boxes. The spectral characteristics of the dynamical processes in these boxes are qualitatively similar, indicating the universality of the sustenance mechanism of the MRI-turbulence.
Keywords: Magnetorotational instability, turbulence, nonmodal growth, accretion disks

Publ.-Id: 25873 - Permalink


THz timing tool: status report
Gensch, M.;
  • Lecture (Conference)
    EUCALL annual meeting, 07.-09.06.2017, Grenoble, France

Publ.-Id: 25872 - Permalink


Big Data Challenge @ TELBE
Gensch, M.;
  • Lecture (Conference)
    LEAPS-IT Meeting, 26.-29.06.2017, Grenoble, France

Publ.-Id: 25871 - Permalink


Follow up on THz Radiation Sources
Gensch, M.;
  • Invited lecture (Conferences)
    ARD-ST3 annual meeting, 19.-21.07.2017, Zeuthen, Deutschland

Publ.-Id: 25870 - Permalink


High-field High-repetition-rate superradiant compact THz sources for the coherent control of matter
Gensch, M.;
...........................................................................................................................
  • Invited lecture (Conferences)
    THz source @ TRIUMF workshop, 05.-07.07.2017, Vancouver, Canada

Publ.-Id: 25869 - Permalink


High-field Repetition-Rate THz Sources for the selective coherent control of Matter
Gensch, M.;
The past 10 years have seen a growing number of THz sources coming into operation worldwide that are based on superradiant emission from ultra-short highly charged electron bunches [1]. The superradiant principle allows generating carrier-envelope stable THz pulses with high pulse energy and a large variety of different THz waveforms. If superconducting radiofrequency accelerator technology is used then the THz pulses can be generated with a unique combination of high-THz fields and high repetition-rates. The challenges and scientific opportunities of superradiant THz sources for the coherent THz control of Matter are discussed based on the experiences from two pilot facilities: TELBE [2], the worldwide first THz user facility based on superradiant THz emission from a compact quasi-cw SRF driven linear accelerator and THz-FLASH [3,4] the worldwide first facility that operates as a afterburner of the SRF accelerator-driven FLASH XUV SASE FEL. Based on example benchmark experiments the meanwhile achievable time resolution and dynamic range of multicolor ultra-fast experiments is presented. As will be shown novel pulse-resolved detection schemes opera-ting at high repetition rates in the few 100 kHz regime allow to achieve time-resolution of better than 30 fs and a dynamic range of better than 106 [5]. Limits in pulse energy and frequency range inflicted by the specific accelerator designs are discussed.

[1] M. Gensch, SUPER-RADIANT LINAC-BASED THz SOURCES IN 2013, Proceedings of FEL13, New York, (2013), WEIBNO01.
[2] B. Green et al, High-field High-repetition-rate Sources for the coherent THz control of Matter, Sci. Rep. 6 (2016), 22256.
[3] M. Gensch et al, New infrared undulator beamline at FLASH, Infrared Phys. Technol.51 (2008) ,428.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few femtosecond timing at 4th Generation X-ray Lightsources, Nat. Photon.5 (2011), 162.
[5] S. Kovalev et al, Probing ultrafast dynamics an 4th generation lightsources with high dynamic range, Struct. Dyn. 4 (2017), 10159.
  • Invited lecture (Conferences)
    TRIUMF colloquium, 07.07.2017, Vancouver, Canada

Publ.-Id: 25868 - Permalink


Influence of the specificities of ion irradiation on the nanostructural evolution in Fe alloys: an object kinetic Monte Carlo study
Chiapetto, M.; Malerba, L.; Castin, N.; Heintze, C.; Becquart, C. S.;
This work investigates the nanostructural evolution under ion irradiation in both a binary Fe-C alloy and an Fe-9%Cr-C alloy at 300°C, using an object kinetic Monte Carlo model originally developed to simulate neutron irradiation in Fe-(Cr)-C alloys. We studied the effect of specificities of ion irradiation that are expected to have an impact on the evolution of radiation-induced defect clusters as compared to neutron irradiation. The most relevant impact is due to the difference in dose-rate between neutron and ion irradiation. Moreover, the effect of two different ion irradiation regimes (continuous versus pulsed) on the nanostructure evolution material was also investigated: the presence of Cr was seen to lead to a different response over accumulated dose, the reason having been identified in the defect cluster recombination mechanism.
Keywords: kinetic Monte Carlo, Fe-Cr alloys, ion irradiation, continuous irradiation, pulsed irradiation
  • Contribution to proceedings
    NEA International Workshop on Structural Materials for Innovative Nuclear Systems (SMINS-4), 11.-14.07.2016, Manchester, UK

Publ.-Id: 25867 - Permalink


[18F]Fluorid- und [18F]FDG-PET/CT zur Beurteilung der Biomaterial-unterstützten Geweberegeneration bei einem kritischen Knochendefektmodell der Ratte
Neuber, C.; Förster, Z.; Hofheinz, F.; Rammelt, S.; Pietzsch, J.;
Ziel/Aim:
Kritische Knochendefekte nach Trauma oder Tumorresektion sind eine klinische Herausforderung. Aktuelle Ansätze zur gezielten Unterstützung der Knochenregeneration schlagen den Einsatz von Biomaterialien vor, die mit einer artifiziellen extrazellulären Matrix (aEZM) aus Kollagen und Glykosaminoglykan-Derivaten beschichtet sind. Ziel dieses Pilotversuches war es, den Einfluss derartiger aEZM im Tiermodell zu charakterisieren.
Methodik/Methods:
In einen kritischen Knochendefekt im Femur adulter Ratten wurden Polycaprolacton-co-Laktid-Scaffolds implantiert, die mit Kollagen (Coll), Coll+Chondroitinsulfat (Coll/CS) oder Coll+hochsulfatierter Hyaluronsäure (Coll/s3HA) beschichtet waren. Als Negativkontrolle diente der Leerdefekt. Die Knochenneubildung und Wundheilung wurde nach 4 und 8 Wochen mittels Na[18F]F- und [18F]FDG-PET/CT beurteilt. Mittels CT wurde ein dem Defektbereich entsprechendes volume of interest definiert und der entsprechende SUVmean ermittelt. Darüber hinaus wurden die Femura ex vivo mittels µCT und histologischer Methoden charakterisiert.
Ergebnisse/Results:
Im Vergleich zum Leerdefekt führten die Scaffolds nach 4 Wochen zu einer erhöhten Na[18F]F-Anreicherung, was auf eine verstärkte initiale Knochenmineralisation schließen lässt. Unterschiede zwischen den verschiedenen aEZM wurden nicht beobachtet. Die im Vergleich zum Leerdefekt erhöhte [18F]FDG-Anreicherung nach 4 und 8 Wochen bei den Scaffolds weist auf eine vermehrte Zellaktivierung bzw. -proliferation in der Scaffold-Umgebung hin. Die Beschichtung mit Coll/CS resultierte nach 4 Wochen im größten SUVmean.
Schlussfolgerungen/Conclusions:
Die Kombination von Na[18F]F- und [18F]FDG-PET/CT gestattet die Charakterisierung der Biomaterial-unterstützten Geweberegeneration bei einem kritischen Knochendefektmodell der Ratte. Die Beschichtung mit einer aEZM aus Kollagen und Glykosaminoglykanen fördert die Knochenregeneration.
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Publ.-Id: 25866 - Permalink


Active targeting and in vivo multimodal imaging of renally excretable polymer nanoparticles
Pant, K.; Zarschler, K.; Neuber, C.; Pufe, J.; Pietzsch, J.; Steinbach, J.; Stephan, H.; Haag, R.;
Multimodal imaging represents a strategy to integrate multiple modalities on a single carrier molecule so as to increase the detection sensitivity and to obviate the need to administer compounds with different pharmacokinetics. In this regard, dendritic polyglycerols are highly biocompatible nanoscale scaffolds with multiple attachment sites, anti-fouling properties and small size (2-20 nm).1 The great versatility of the dendritic polyglycerols allows to fine tune physicochemical parameters such as the size, water solubility, surface charge that are relevant for the successful preparation of theranostic systems. Previous experiments showed that the dendritic polyglycerols (>10kDa) show a fast renal clearance with negligible uptake in the mononuclear phagocytic system (MPS) organs such as the liver and spleen.2-3 The purpose of this work to design a PET/OI dual modal construct based on dendritic polyglycerols for epidermal growth factor receptor (EGFR) targeting. In this regard, a one-pot strategy was employed for simultaneous attachment of fluorescent labels for optical imaging (cy3/cy7) and macrocyclic chelators based on a 1,4,7-triazacyclononane system for 64Cu (PET tracer) to thiol anchoring groups of the dPGs. A small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR as targeting vector was attached (1). In parallel, a probe with similar surface characteristics but an EGFR unspecific sdAb (control) was synthesized (2). The conjugates were purified using affinity chromatography, which selectively separates the antibody-conjugated mul-timodal conjugates. In vitro and in vivo studies were conducted to assess its diagnostic potential. The in vitro results revealed a highly specific receptor mediate uptake of 1 in EGFR expressing A431 and FaDu cell lines using confocal microscopy and radio detection.
Intravenous injection of 1 and 2 on mouse xenografted models studies using PET and optical imaging revealed an overwhelming tumor accumulation of the EGFR-specific 1 in comparison to the EGFR-unspecific 2 and a minimum off-target accumulation of both conjugates. These results unveil the potential of dendritic polyglycerols as efficient multimodal platforms for theranostic applications.
Keywords: dendritic polyglycerols, cancer, biodistribution, radiolabeling, renal clearance, protein corona, biomedical applications.
  • Lecture (Conference)
    Nanotech France 2017, 28.-30.06.2017, PARIS, France

Publ.-Id: 25865 - Permalink


Comparison of lesion SUV and SUR test-retest variability in F-18 FDG PET
Hofheinz, F.; Apostolova, I.; Oehme, L.; Kotzerke, J.; van den Hoff, J.;
Quantitative assessment of radiation therapy response with FDG whole body PET has attracted increasing interest in recent years. Generally, the standardized uptake value (SUV) is utilized for quantitation. In this context, the substantial SUV test-retest variability (TRV) as demonstrated in recent studies is a major concern. The goal of our study was to investigate if standard uptake ratio (SUR) exhibits a lower TRV.

34 patients with non small cell lung cancer (ACRIN 6678 trial) were included. All patients underwent two FDG PET/CT scans prior to therapy. Maximum SUV of up to seven lesions was determined. SUR was computed as ratio of tumor SUV and blood SUV (determined in the aorta) and scan-time-corrected to 75 min p.i. TRV was assessed as the 95% confidence interval of the root mean square deviation of the paired fractional differences of SUV and SUR, respectively. The effect of blood normalization and scan time correction was inspected using the ratio RTRV=TRV[SUV]/TRV[SUR]. RTRV was correlated with the group averaged value dCFmean of the quantity dCF=|1-CF|, where CF is the factor that converts paired SUV ratios into the corresponding SUR ratios. Correlation analysis was performed by successively increasing a threshold value dCFmin and restricting the computation of dCFmean and RTRV to the respective sub-group of lesions with dCF>=dCFmin.

Overall, TRV was slightly lower for SUR than for SUV. TRV[SUR] decreases while TRV[SUV] increases with increasing dCF threshold (corresponding to larger blood SUV and scan time differences between paired scans), leading to a two-fold reduction of TRV[SUR] compared to TRV[SUV] for dCF>=15%. Correlation analysis revealed a pronounced correlation between RTRV and mean dCF (Spearman's rho=-0.99, P<0.001).

SUR is superior to SUV regarding TRV by eliminating two relevant factors contributing to TRV of SUV.
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Publ.-Id: 25863 - Permalink


Prognostische Relevanz der Asphärizität und des metabolischen Tumorvolumens beim Neuroblastom in der prätherapeutischen Iod-123-MIBG-SPECT
Rogasch, J.; Schatka, P.; Hundsdoerfer, P.; Furth, C.; Wedel, F.; Steffen, I.; Hofheinz, F.; Brenner, W.; Eggert, A.; Amthauer, H.;
Ziel: Die initiale Risikostratifikation und das daraus resultierende Therapieregime erfolgen bei Kindern mit Neuroblastom (NB) anhand klinischer und genetischer Faktoren. Ziel war nun die Evaluation des Stellenwerts der Asphärizität des Uptakes (ASP) und des metabolischen Tumorvolumens (MTV) in der prätherapeutischen Iod-123-MIBG-SPECT (IMS) zur Prädiktion des Therapieverlaufes.
Methodik: Retrospektive Analyse von 21 konsekutiv untersuchten Kindern (w:10, m:11; medianes Alter, 1,8 [0,3-6,8] a), bei denen eine IMS prätherapeutisch bei neu diagnostiziertem Neuroblastom erfolgt war. Im SPECT wurde mittels halbautomatischen, hintergrundadaptierten Schwellenwerts das MTV des Primarius und die ASP als relative Abweichung der MTV-Oberfläche von einer isovolumetrischen Kugel bestimmt. Uni- und multivariate Cox Regression, ROC-Analysen zur Cut-off-Findung sowie Kaplan-Meier (KM)-Analysen mit log-rank-Test bezüglich des ereignisfreien (EFS) und Gesamtüberlebens (OS) erfolgten für ASP, MTV, genetischer Faktoren, klinische Variablen (Alter, Stadium) und Tumormarker.
Ergebnisse: Das mediane Follow-up betrug 36 [6-102] Monate. Sechs Kinder erlitten einen Progress/Rezidiv, 3 davon verstarben. Die ASP (p=0,038; Hazard Ratio [HR], 1,03 je eine Einheit) und das MTV (p=0,031; HR, 1,012) waren die alleinigen signifikanten Prädiktoren des EFS in der univariaten Cox-Analyse; nur die ASP auch in der multivariaten Analyse (p=0,034; HR, 1,046). Bei einem Cut-off von >31,6% betrug das EFS für eine hohe vs. niedrige ASP 20 vs. 87 Monate (p=0,018), für ein hohes (>46,7 ml) vs. niedriges MTV 18 vs. 88 Monate (p=0,006). In der KM Analyse sagten eine hohe ASP (p=0,012) und ein hohes MTV (p<0,001; Cut-off, >97,5 ml) zudem ein geringeres OS voraus.
Schlussfolgerungen: In dieser explorativen Studie erlaubten die prätherapeutische Bestimmung von ASP und MTV des Primarius die Trennung von Kindern mit hohem und geringerem Risiko für einen Progress bzw. ein Rezidiv unter aktuellen Therapieregimen.
Keywords: NA
  • Contribution to proceedings
    Jahrestagung der DGN, 26.-29.04.2017, Dresden, Deutschland
    Proceedings der Jahrestagung der DGN

Publ.-Id: 25862 - Permalink


Adsorption of furfural from torrefaction condensate using torrefied biomass
Doddapaneni, T. R. K.; Jain, R.; Praveenkumar, R.; Rintala, J.; Romar, H.; Konttinen, J.;
Torrefaction is a biomass energy densification process that generates a major byproduct in the form of torrefaction condensate. Microbial conversion of TC could be an attractive option for energy integration within torrefaction process. However, TC contains several compounds, such as furfural, 5- hydroxymethylfurfural and guaiacol that are inhibitory to microbes. In this study, for the first time, we reported detoxification of TC, by removing the major inhibitory compound furfural, using torrefied biomass (TB) and later used the detoxified TC for anaerobic digestion. The effect of varying TB production temperature (225–300 ⁰C), TB dosage (25–250 g/L), initial pH (2–9), and contact time (1–12 h) on furfural adsorption was studied with batch adsorption experiments. Mechanism of furfural adsorption on torrefied biomass was best represented by pseudo second order kinetic model. The adsorption of furfural and other inhibitory compounds on TB was likely a hydrophobic interaction. A maximum of 60% of furfural was adsorbed from TC containing 9000 mg furfural/L using 250 g/L of TB in batch adsorption. For, column (20 mm internal diameter and 200 mm bed height), the saturation time for furfural adsorption was around 50 min. Anaerobic digestion of the detoxified TC shows that the lag phase in methane production was reduced from 25 d to 15 d for 0.2 VSsubstrate:VSinoculum loading. The study shows that TC can be effectively detoxified using TB for microbial conversion and can efficiently be integrated within the torrefied biomass pellet production process.
Keywords: Detoxification; Anaerobic digestion; pellets; torrefaction volatiles; Energy densification

Downloads:

  • Secondary publication expected

Publ.-Id: 25861 - Permalink


NMR investigations of paramagnetic effects in metal-organic complexes of trivalent and tetravalent actinides with soft-donor ligands
Radoske, T.; Adam, C.; Schöne, S.; Patzschke, M.; März, J.; Kaden, P.ORC
When NMR spectroscopy is applied to paramagnetic metal-organic complexes additional chemical shifts are observed on nuclei of the ligands that originate from electronic interactions between metal and ligand. The major two contributors to these paramagnetic chemical shifts are either due to delocalisation of unpaired electron density in molecular orbitals involving both metal and ligand orbitals (Fermi contact shift, FCS), or due to distance- and angle-dependent dipolar coupling of electron spins through space (pseudo contact shift, PCS). However, mathematical models for the treatment of paramagnetic chemical shifts are not yet applicable to actinide compounds.
Covalence is assumed to be the reason for some soft-donor ligands selectivity for the complexation of trivalent actinides over lanthanide ions. This long-kept notion was recently substantiated by evaluation of paramagnetic chemical shifts of respective Am(III) complexes1,2. The mathematical separation of contributions in complexes of the trivalent actinides, however, is hampered by the lack of a reliable diamagnetic reference in the actinide series. Furthermore, all available theories behind mathematical disentangling of contributions to the paramagnetic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution as well.
To assess the chemical bonding situation via the influences on paramagnetic chemical shifts we started to study metal-organic complexes of tetravalent actinides (An(IV)) with soft-donor ligands with Th(IV) as diamagnetic reference. With increasing number of unpaired electrons throughout the series additional effects to the observed chemical shift are expected. Herein we report the first results of investigations of N-donor ligand complexes of the An(IV) series.
References
1. C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak, M. A. Denecke, “Evidence for covalence in a N-donor complex of americium(III)”, Dalton Trans., 42, 14068-14074 (2013).
2. C. Adam, B. B. Beele, A. Geist, U. Müllich, P. Kaden, P. J. Panak, “NMR and TRLFS studies of Ln(III) and An(III) C5-BPP complexes”, Chemical Science, 6, 1548-1561 (2015).
Keywords: NMR, paramagnetic, diamagnetic reference, covalence, Fermi contact, pseudo-contact, U(IV), Th(IV), Am(III)
  • Lecture (Conference)
    Actinides 2017, 09.-14.07.2017, Sendai, Japan

Publ.-Id: 25860 - Permalink


MHD turbulence in shear flows and Keplerian disks - sustenance via interplay of linear nonmodal growth and nonlinear transverse cascade
Mamatsashvili, G.;
We investigate MHD turbulence in spectrally stable shear flows, including Keplerian disk flows, threaded by a non-zero net azimuthal/toroidal magnetic field. In order to gain a deeper insight into its sustaining mechanism, we performed a set of numerical simulations in the shearing box model and based on the simulation data, analyzed in detail the turbulence dynamics in Fourier/wavenumber k-space. Classical exponential/modal instabilities are absent in such flows and linear growth of perturbations has a transient nature due to shear flow non-normality, also referred to as nonmodal growth. Similarly, in the case of Keplerian flow with a net azimuthal field in the shearing box setup, the combination of rotation, shear and magnetic field, gives rise to the magnetorotational instability (MRI), which is dominated by the effects of non-normality and hence is of transient type too. This transient growth, which serves as the only energy supply to turbulence, is strongly anisotropic in Fourier space that, in turn, leads to anisotropy of nonlinear processes in Fourier space and, as a result, the main nonlinear process appears to be not an usual direct/inverse, but rather a new type of transverse/angular redistribution of perturbation modes in Fourier space, which we refer to as the nonlinear transverse cascade. We demonstrate that the turbulence is sustained by a subtle interplay of the linear nonmodal growth (transient MRI in the case of Keplerian disks) and the nonlinear transverse cascade. Analyzing this interplay, we reveal the basic subcycle of the sustenance scheme that clearly shows synergy of the linear and nonlinear processes in the self-organization of the magnetized flow system. This synergy is quite robust and persists for the considered four simulation boxes with different aspect ratios. The spectral characteristics of the dynamical processes in these boxes are qualitatively similar, indicating the universal character of the interplay that ensures the sustenance of the turbulence. Such an interplay of linear and nonlinear processes in the turbulence sustenance proposed here exemplifies the bypass concept of subcritical turbulence in spectrally stable shear flows, elaborated in the 1990s by the hydrodynamical community. Both the linear nonmodal growth and nonlinear transverse cascade mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space is crucial in the turbulence sustenance process and is called the vital area. Outside the vital area, both these processes are of secondary importance – the harmonics are transferred to dissipative scales by the usual nonlinear direct cascade only. In the conclusion, we discuss the application of this approach and results to the MRI-turbulence in Keplerian flows with vertical net nonzero or zero magnetic flux.
Keywords: MHD, nonmodal growth, magnetorotational instability, turbulence, accretion disks, numerical simulations
  • Invited lecture (Conferences)
    Invited seminar at the Niels Bohr Institute, University of Copenhagen, 24.-28.04.2017, Copenhagen, Denmark

Publ.-Id: 25859 - Permalink


Nonlinear evolution of helical magnetorotational instability
Mamatsashvili, G.; Stefani, F.;
We investigate the evolution of the helical magnetorotational instability in a magnetized Taylor-Couette flow from its linear growth to nonlinear saturation using numerical simulations. We show that the saturation occurs through modification (reduction) of the radial shear of the mean azimuthal velocity. The resulting saturated state is axisymmetric and represents a type of 2D MHD turbulence, whose (spectral) properties are characterized. The results are compared to the PROMISE experiment data.
Keywords: Taylor-Couette flow, helical magnetorotational instability, liquid metals, numerical simulations
  • Lecture (Conference)
    Bifurcation and instabilities in fluid dynamics, 11.-14.07.2017, Woodlands, Houston, Texas, USA

Publ.-Id: 25858 - Permalink


Increased FDG uptake on late-treatment PET in non-tumour-affected oesophagus is prognostic for pathological complete response and disease recurrence in patients undergoing neoadjuvant radiochemotherapy
Zschaeck, S.; Hofheinz, F.; Zöphel, K.; Bütof, R.; Jentsch, C.; Schmollack, J.; Löck, S.; Kotzerke, J.; Baretton, G.; Weitz, J.; Baumann, M.; Krause, M.;
Purpose

Early side effects including oesophagitis are potential prognostic factors in patients undergoing radiochemotherapy (RCT) for locally advanced oesophageal cancer (LAEC). We assessed the prognostic value of 18F-fluorodeoxyglucose (FDG) uptake within irradiated non-tumour-affected oesophagus (NTO) during restaging positron emission tomography (PET) as a surrogate for inflammation/oesophagitis.
Methods

This retrospective evaluation included 64 patients with LAEC who had completed neoadjuvant RCT and had successful oncological resection. All patients underwent FDG PET/CT before and after RCT. In the restaging PET scan maximum and mean standardized uptake values (SUVmax, SUVmean) were determined in the tumour and NTO. Univariate Cox regression with respect to overall survival, local control, distant metastases and treatment failure was performed. Independence of clinically relevant parameters was tested in a multivariate Cox regression analysis.
Results

Increased FDG uptake, measured in terms of SUVmean in NTO during restaging was significantly associated with complete pathological remission (p = 0.002) and did not show a high correlation with FDG response of the tumour (rho < 0.3). In the univariate analysis, increased SUVmax and SUVmean in NTO was associated with improved overall survival (p = 0.011, p = 0.004), better local control (p = 0.051, p = 0.044), a lower rate of treatment failure (p < 0.001 for both) and development of distant metastases (p = 0.012, p = 0.001). In the multivariate analysis, SUVmax and SUVmean in NTO remained a significant prognostic factor for treatment failure (p < 0.001, p = 0.004) and distant metastases (p = 0.040, p = 0.011).
Conclusions

FDG uptake in irradiated normal tissues measured on restaging PET has significant prognostic value in patients undergoing neoadjuvant RCT for LAEC. This effect may potentially be of use in treatment personalization.
Keywords: Oesophageal cancer Radiochemotherapy Side effects Inflammation FDG pet

Publ.-Id: 25857 - Permalink


Nonmodal and nonlinear dynamics of helical magnetorotational instability
Mamatsashvili, G.; Stefani, F.;
The helical magnetorotational instability (HMRI), a relative of standard MRI (SMRI), has become a subject of active research in recent years in connection with the experiments on magnetized cylindrical Taylor-Couette (TC) flows. It occurs in the presence of helical magnetic field, consisting of azimuthal and axial components and, like SMRI with only axial magnetic field, taps into the rotational energy of the flow. However, a main advantage of HMRI is that, being governed by the Reynolds (Re) and Hartmann (Ha) numbers, it persists even at very small magnetic Prandtl numbers typical to liquid metals, in contrast to SMRI. The linear development of HMRI has been widely studied theoretically using both classical modal and more recently by nonmodal stability analysis, where a fundamental connection between nonmodal dynamics and dissipation-induced (double-diffusive) modal instabilities, such as HMRI, has been demonstrated. A series of specially designed liquid metal TC experiments provided the first experimental evidence of HMRI and reproduced the main results of the linear theory, such as the stability threshold and propagation speed (frequency) of HMRI-wave. More importantly, these experiments revealed much richer dynamics of HMRI as a function of system parameters (Re, Ha, etc.) than that obtained from the linear analysis only. These results prompted further theoretical studies of the nonlinear development of HMRI, but detailed physics of its saturation and sustenance still remains missing, especially when comparison with the experiment is concerned.
Motivated by the existing experimental results, we investigate the evolution of HMRI, from its linear growth to nonlinear saturation using numerical simulations.
We show that depending on the Reynolds number, two regimes of saturation can be realized. At Re below a certain critical value (but higher than the instability threshold), the saturation energy linearly depends on Re and the corresponding energy spectrum is dominated by the most unstable mode and its multiple wavenumbers, while at larger Re, the energy increases with Re, but not linearly, and the related spectrum looks like turbulent spectrum, being much smoother over wavenumbers. The nonlinear state remains markedly axisymmetric (m = 0)
and at high Re can be viewed as a 2D turbulence, whose (spectral) properties are further examined.
Keywords: MHD, turbulence, nonmodal growth, instabilities, numerical simulations
  • Lecture (Conference)
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice Castle, Czech Republic

Publ.-Id: 25856 - Permalink


Kinetic Modeling of the New σ1 Receptor Ligand (-)-[18F]Fluspidine in the Human Brain
Becker, G. A. F.; Meyer, P.; Patt, M.; Hesse, S.; Luthardt, J.; Patt, J.; Rullmann, M.; Fischer, S.; Kluge, A.; Steinbach, J.; Wünsch, B.; Brust, P.; Sabri, O.;
Objectives:
The σ1 receptor, a transmembrane protein located at the endoplasmatic reticulum is involved in a variety of neuropsychiatric diseases, e.g. depression, schizophrenia and drug addiction. The newly developed PET tracer (-)-[18F]Fluspidine was successfully applied to quantify σ1 receptors in the porcine brain [1]. Here we present the first PET quantification of σ1 receptors with (-)-[18F] Fluspidine in humans.
Methods:
After intravenous administration of 269.6±13.3 MBq (-)-[18F]Fluspidine PET brain imaging was performed in 10 healthy subjects (age 36.6±14.8 years; gender 5F/5M) using an ECAT EXACT HR+ system in 3D-acquisition mode. 26 frames were acquired from 0-210 min post injection and motion corrected with SPM2. Kinetic modeling using 1- and 2-tissue compartment models (1TCM, 2TCM) with metabolite corrected arterial input-function was applied to the volume of interest (VOI) based tissue time-activity curves (TACs) in 43 brain regions (anatomically defined via MRI co-registration). Time ranges from 0 to 90 and 0 to 210 min were investigated. Model-based receptor parameter was the total distribution volume VT (ml/cm-3), a linear function of receptor density.
Results:
TACs of all 43 regions could be described with the 1- and 2TCM. VT in all cortical regions could be reliably estimated from 90 min PET data already. In white matter longer measurements can be necessary. The distribution volume was highest in the cerebellar cortex (31.4±6.1), low in the centrum semiovale (17.7±7.1) and ranged in cortical structures between 20.9±3.9 in the orbitofrontal and 24.9±5.7 in the posterior cingulate cortex (pcc) (2TCM, 90 min). The distribution volumes computed from 210 min data were comparable to 90 min results, e.g. in pcc 25.7±5.9 (2TCM) and 25.7±6.0 (1TCM).
Conclusions:
σ1 receptor parameters in cortical structures can be estimated with a 1- or 2TCM from 90 min (-)-[18F]Fluspidine TACs. If a model derived receptor parameter is used in a classification problem, e.g., distinguishing patients with depression from healthy controls, the final model decision should be made on the basis of the PET data of both groups.
References:
P. Brust, ..., O. Sabri, Journal of Nuclear Medicine 2014, 55, 1730-1736
  • Open Access LogoAbstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S383
    DOI: 10.1002/jlcr.3508

Publ.-Id: 25855 - Permalink


Development of (S)-[18F]T1 as first PET tracer for imaging the α3β4 nicotinic acetylcholine receptor
Sarasamkan, J.; Fischer, S.; Deuther-Conrad, W.; Scheunemann, M.; Ludwig, F.-A.; Vajragupta, O.; Brust, P.;
Objectives:
Neuronal nicotinic acetylcholine receptors (nAChRs) are composed of diverse subtypes which have different functional properties, distributions and pharmacological profiles. The α7, α3β4 and α4β2 nAChRs are well recognized as drug targets implicated in cognitive disorders and addiction. Therefore, to image nAChRs in vivo, subtype-selective radiotracers need to be developed.
Methods:
A novel PET radiotracer for imaging nAChRs was developed based on the design and synthesis of six racemates (T1-T6) and its enantiomers based on the structure of triazole-quinuclidine QND8. All R enantiomers were found to be selective to α7 nAChR while their S counterparts were selective to α3β4 nAChR. (S)-T1 binds selectively to α3β4 nAChR (Ki 3.09 nM) with very modest off-target binding to α1 receptor, dopamine receptors and serotonin receptors. Radiosynthesis of (S)-[18F]T1 was achieved by two-step reaction, starting with the preparation of 18F-alkyne synthon (1-ethynyl-4-[18F]fluorobenzene; [18F]2), followed by the click reaction between [18F]2 and (S)-azidoquinuclidine.
Results:
The radiosynthesis of (S)-[18F]T1 was achieved in 130 min with the overall isolated radiochemical yield of 4.3±1.3%, radiochemical purity > 99%, and molar radioactivity > 158 GBq/µmol at end of synthesis. The brain uptake and brain-to-blood ratio of this tracer in mice at 30 min after injection were 6.06% ID/g and 6.1, respectively. The tracer remained intact > 99% in brain homogenates. Only one major radiometabolite was detected in plasma and urine samples. In vitro autoradiography on pig brain slices revealed high binding of (S)-[18F]T1 to brain regions consistent with the α3β4 nAChR distribution. Selective binding of (S)-[18F]T1 was evidenced by (i) the reduction of percent labeling of this tracer in the presence of a selective α3β4 nAChR partial agonist, AT-1001 and (ii) the retention of the tracer in the presence of α7 nAChR-specific SSR180711.
Conclusions:
These findings suggest the potential of (S)-[18F]T1 for imaging the α3β4 nAChR in the brain as a promising tool for both diagnosis and therapy monitoring of neurodegenerative diseases and addiction.
Acknowledgement:
This work was supported by Thailand Research Fund (TRF) through the Royal Golden Jubilee Ph.D. Program (grant no. PHD/0272/2552) to J.S. and O.V.
References:
[1] K. Arunrungvichian, V. V. Fokin, O. Vajragupta, P. Taylor. ACS Chem Neurosci. 2015, 6, 1317-1330.
[2] J. Sarasamkan, M. Scheunemann, N. Apaijai, S. Palee, W. Parichatikanond, K. Arunrungvichian, et al. ACS Med. Chem. Lett. 2016, 7, 890- 895.
  • Open Access LogoAbstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S50
    DOI: 10.1002/jlcr.3507

Publ.-Id: 25854 - Permalink


ElectroHydroDynamic emitters developments for improving Focused Ion Beam machines
Gierak, J.; Bischoff, L.; Mazarov, P.; Bruchhaus, L.; Blanchard-Desce, M.; Vaultier, M.; Lozano, P.;
The patterning of samples using Focused Ion Beams (FIB) is very popular, widely used both for industrial [1] and emerging nanoscience prototyping applications [2]. This FIB technique allows 3D and direct patterning of target materials using a finely focused pencil of ions having speeds of several hundreds of km/seconds at impact with a penetration range of a few tens of nanometres. Thanks to this, local information and/or modifications can be obtained at the target surface. In what the ion nature is concerned, apart that many elements can be used in FIB technology as pure elements or in the form of alloys, gallium (Ga+ ions) is often preferred.
Traditionally for several decades FIB technology has been mainly based on gallium Liquid Metal Ion Sources (LMIS). LMIS are also known as electrohydrodynamically (EHD) driven ion emitters operating in a cone-jet mode. The very high brightness, long lifespan, small source size, and easy handling of this emitter remain its chief and most decisive advantages. On the other hand, some weaknesses are also well known that inhibit the resolution of EHD/LMIS-based FIBs. Therefore progress on ion sources operational characteristics still remains very desirable.
In this presentation we will first summarize our work aiming at understanding, optimizing and evaluating gallium LMIS “needle type” performances. In particular stable operation at lowest possible emission currents will be detailed. The gains in terms of patterning resolution and beam selectivity [3], we will evaluate, are firm evidence that progresses can still be expected from this mature technology.
We will then review and detail the advantages of Liquid Metal Alloy Ion Sources (LMAIS) that represent a promising alternative to expand the already remarkable application field and potential of FIB machines in the field of nanosciences. Indeed selecting the best suited elements transported in a focused ion beam can open new nanofabrication routes. In this presentation we will explain that nearly half of the elements of the periodic table can already be made available to the FIB technology as a result of a continuous research effort in this area [4] and how, in our opinion, nanofabrication shall now take benefit of these capabilities. Finally we will introduce our new addition to the arsenal of EHD driven devices: The Ionic Liquid Ion Sources (ILIS). ILIS are capable to produce ion beams through field-evaporation, also in the cone-jet mode, but from room temperature molten-salts [5]. The possibility of extracting both positive and negative ions at
emission current several orders of magnitude below LMIS standards is already a very appealing perspective in terms of source virtual source size and brightness. Then we will show that ILIS allows to access new ionic species thanks to the almost limitless chemical engineering latitude of molten salts. Moreover subsequent tuning can be achieved via selecting the tip polarity, the ion emission current and the ion landing energy. We will show the possibility to achieve a new kind of FIB patterning using a beam of chemically reactive ion radicals native in the transported beam. This represents a formidable perspective for FIB technology.
In conclusion we will summarize our vision on the future of FIB technology based on electrohydrodynamically (EHD) driven emitters operating in the conejet mode, both in terms of performances, versatility and on the science frontiers these might help to push.

[1] J. Orloff, Scientific American Oct. 1994, pp.74-79
[2] J. Gierak Nanofabrication 2014; Volume 1: pp. 35–52
[3] J. Gierak and R. Jede, Patent US8546768 B2, WO2010029270A1; Sept 2008
[4] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 2016; 3: pp. 021101
[5] C. Perez-Martinez, J. Gierak, and P. C. Lozano, P106 (Invited), EIPBN Conference, May 31-
June 3, 2016, Pittsburgh, PA
Keywords: Focused Ion Beam; Liquid Metal Alloy Ion Source; Ionic Liquid Ion Source; FIB patterning
  • Lecture (Conference)
    Conference on ultracold ion and electron beams, 10.-12.07.2017, Eindhoven, The Netherlands
  • Lecture (Conference)
    61th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication EIPBN-2017, 30.05.-02.06.2017, Orlando, USA

Publ.-Id: 25853 - Permalink


Ion-Beam-Induced Atomic Mixing in Ge, Si, and SiGe, Studied by Means of Isotope Multilayer Structures
Bracht, H.; Radek, M.; Posselt, M.; Liedke, B.; Schmidt, B.; Voelskow, M.; Bischoff, L.; Böttger, R.; Prucnal, S.; Hansen, J. L.; Larsen, A. N.; Bougeard, D.;
Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing.
Keywords: silicon; germanium; ion beam; atomic mixing; thermal spike; radiation enhanced diffusion; amorphization; recrystallization; molecular dynamics

Publ.-Id: 25852 - Permalink


Modeling tumor control probability for spatially inhomogeneous risk of failure based on clinical outcome data
Lühr, A.; Löck, S.; Jakobi, A.; Stützer, K.; Bandurska-Luque, A.; Vogelius, I. R.; Enghardt, W.; Baumann, M.; Krause, M.;
Purpose

Objectives of this work are (1) to derive a general clinically relevant approach to model tumor control probability (TCP) for spatially variable risk of failure and (2) to demonstrate its applicability by estimating TCP for patients planned for photon and proton irradiation.
Methods and Materials

The approach divides the target volume into sub-volumes according to retrospectively observed spatial failure patterns. The product of all sub-volume TCPi values reproduces the observed TCP for the total tumor. The derived formalism provides for each target sub-volume i the tumor control dose (D50,i) and slope (γ50,i) parameters at 50% TCPi. For a simultaneous integrated boost (SIB) prescription for 45 advanced head and neck cancer patients, TCP values for photon and proton irradiation were calculated and compared. The target volume was divided into gross tumor volume (GTV), surrounding clinical target volume (CTV), and elective CTV (CTVE). The risk of a local failure in each of these sub-volumes was taken from the literature.
Results

Convenient expressions for D50,i and γ50,i were provided for the Poisson and the logistic model. Comparable TCP estimates were obtained for photon and proton plans of the 45 patients using the sub-volume model, despite notably higher dose levels (on average +4.9%) in the low-risk CTVE for photon irradiation. In contrast, assuming a homogeneous dose response in the entire target volume resulted in TCP estimates contradicting clinical experience (the highest failure rate in the low-risk CTVE) and differing substantially between photon and proton irradiation.
Conclusions

The presented method is of practical value for three reasons: It (a) is based on empirical clinical outcome data; (b) can be applied to non-uniform dose prescriptions as well as different tumor entities and dose-response models; and (c) is provided in a convenient compact form. The approach may be utilized to target spatial patterns of local failures observed in patient cohorts by prescribing different doses to different target regions. Its predictive power depends on the uncertainty of the employed established TCP parameters D50 and γ50 and to a smaller extent on that of the clinically observed pattern of failure risk.
Keywords: Radiotherapy, Dose–response modeling, TCP, Inhomogeneous dose, Head and neck cancer, Proton therapy

Downloads:

Publ.-Id: 25851 - Permalink


Superconducting Ferromagnetic Nanodiamond
Zhang, G.; Samuely, T.; Xu, Z.; Jochum, J. K.; Volodin, A.; Zhou, S.; May, P. W.; Onufriienko, O.; Kačmarčík, J.; Steele, J. A.; Li, J.; Vanacken, J.; Vacík, J.; Szabó, P.; Yuan, H.; Roeffaers, M. B. J.; Cerbu, D.; Samuely, P.; Hofkens, J.; Moshchalkov, V. V.;
Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature Tc ∼ 3 K and a Curie temperature TCurie > 400 K. In spite of the high TCurie, our nanodiamond films demonstrate a decrease in the temperature dependence of magnetization below 100 K, in correspondence to an increase in the temperature dependence of resistivity. These anomalous magnetic and electrical transport properties reveal the presence of an intriguing precursor phase, in which spin fluctuations intervene as a result of the interplay between the two antagonistic states. Furthermore, the observations of high-temperature ferromagnetism, giant positive magnetoresistance, and anomalous Hall effect bring attention to the potential applications of our superconducting ferromagnetic nanodiamond films in magnetoelectronics, spintronics, and magnetic field sensing.
Keywords: anomalous Hall effect; giant positive magnetoresistance; nanodiamond; spin fluctuations; superconductivity and ferromagnetism

Downloads:

Publ.-Id: 25850 - Permalink


Structural and optical properties of Gd implanted GaN with various crystallographic orientations
Macková, A.; Malinský, P.; Jagerová, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Pristovsek, M.; Mikulics, M.; Lorinčík, J.; Böttger, R.; Akhmadaliev, S.;
Structure, morphology, and optical properties of Gd implanted GaN epitaxial layers were studied for (0001), (11 − 20), and (11 − 22) orientations. The GaN layers grown by MOVPE on sapphire were subsequently implanted with 200 keV Gd+ ions using fluences of 5 × 1015 and 5 × 1016 cm− 2. Dopant depth profiling was accomplished by Rutherford Back-Scattering spectrometry (RBS). Structural and optical changes during subsequent annealing were characterized by RBS, Raman spectroscopy, and photoluminescence measurements. Post-implantation annealing induced a structural reorganization of GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the implantation fluence and on crystallographic orientation. The defect density depth distribution was evaluated by RBS. The surface morphology and optical properties depend on particular crystallographic orientation.
Keywords: GaN implantation; RBS channelling; Optical properties of Gd implanted GaN

Publ.-Id: 25849 - Permalink


Interplay between magnetic domain patterning and anisotropic magnetoresistance probed by magnetooptics
Osten, J.ORC; Lenz, K.; Schultheiss, H.ORC; Lindner, J.; McCord, J.; Fassbender, J.ORC
We study the correlation between the magnetic reversal and the anisotropic magnetoresistance (AMR) response in magnetic hybrid structures that were created by local modification of magnetic properties induced by ion implantation. The stripe pattern have been investigated simultaneously by dual-wavelength Kerr microscopy and magnetoresistance measurements. We observe that the switching of the stripe pattern introduces an additional AMR maximum. The domain wall in between the stripes provides a positive resistance contribution, whereas domains at the stripe edges lead to an asymmetric AMR response. A method for calculating the AMR response from the quantitative Kerr micrographs is demonstrated that allows the reconstruction of the AMR value within a region of interest only.
Keywords: anisotropic magnetoresistance, magnetic domain

Downloads:

Publ.-Id: 25848 - Permalink


Experimental and Numerical Modeling of Fluid Flow Processes in Continuous Casting: Results from the LIMMCAST-Project
Timmel, K.ORC; Kratzsch, C.; Asad, A.; Schurmann, D.; Schwarze, R.; Eckert, S.
The present paper reports about numerical simulations and model experiments concerned with the fluid flow in the continuous casting process of steel. This work was carried out in the LIMMCAST project in the framework of the Helmholtz alliance LIMTECH. A brief description of the LIMMCAST facilities used for the experimental modeling at HZDR is given here. Ultrasonic and inductive techniques and the X-ray radioscopy were employed for flow measurements or visualizations of two-phase flow regimes occurring in the submerged entry nozzle and the mold. Corresponding numerical simulations were performed at TUBAF taking into account the dimensions and properties of the model experiments. Numerical models were successfully validated using the experimental data base. The reasonable and in many cases excellent agreement of numerical with experimental data allows to extrapolate the models to real casting configurations. Exemplary results will be presented here showing the effect of electromagnetic brakes or electromagnetic stirrers on the flow in the mold or illustrating the properties of two-phase flows resulting from an Ar injection through the stopper rod.
Keywords: LIMTECH-alliance, Continuous Casting, numerical modeling, experimental modeling, liquid metal models, electromagnetic actuators, two-phase flow

Publ.-Id: 25847 - Permalink


Arterial spin labeling spatial coefficient of variation predicts carotid occlusion side
Mutsaerts, H. J.; Petr, J.; Bokkers, R.; Hendrikse, J.; Lazar, R.; Marshall, R.; Asllani, I.;
Collateral perfusion has been shown to be of key prognostic importance in carotid steno‐occlusive disease as it prevents irreversible ischemia1, 2. Arterial spin labeling ﴾ASL﴿ may provide a biomarker of collateral perfusion by measuring arterial transit time ﴾ATT﴿ in addition to cerebral blood flow ﴾CBF﴿. However, this leads to longer scanning times, lower signal‐to‐noise ratio3 and higher motion sensitivity4. We have developed a method to estimate the ATT from a single post‐labeling delay ﴾PLD﴿ ASL image using the spatial coefficient of variance ﴾CoV﴿5. Here, we investigate whether the spatial CoV lateralization through collateral perfusion can predict the side of carotid occlusion.
  • Lecture (Conference)
    34th Annual Scientific Meeting of European Society for Magnetic Resonance in Medicine and Biology, 19.10.2017, Barcelona, Spain
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 30(2017)Suppl 1, 198
    DOI: 10.1007/s10334-017-0633-0

Downloads:

Publ.-Id: 25846 - Permalink


ExploreASL: image processing toolbox for multi-center arterial spin labeling population analyses
Mutsaerts, H.; Petr, J.; Lysvik, E.; Schrantee, A.; Shirzadi, Z.; Zelaya, F.; Groote, I.; O'Daly, O.; Kuijer, J.; de Bresser, J.; Richard, E.; Caan, M.; van Osch, M.; Golay, X.; Reneman, L.; Macintosh, B.; Masellis, M.; Hendrikse, J.; Barkhof, F.; Bjørnerud, A.; Nederveen, A.; Asllani, I.; Groot, P.;
Arterial spin labeling (ASL) perfusion MRI1 is rapidly maturing as a research tool, potential future biomarker2 and pharmacological monitoring agent3 for many diseases including neurodegeneration. There is thus a growing need for standardization of ASL image processing and quality control (QC) for voxel-based (VBA) and region-of-interest (ROI)-based analyses. Here, we present ExploreASL, a non-commercial software package that aims to harmonize image processing for ASL perfusion images for single- and multi-center studies4, 5. In addition, ExploreASL combines key structural image processing tools from recent literature to differentiate perfusion from structural effects.
Initiated through the EU-funded COST-action "ASL In Dementia", ExploreASL is a collaborative framework of researchers and clinical investigators. It was already used to process ~4000 ASL images from all major MRI vendors and ASL sequences, and a large variety of patient populations. The ultimate goal is to combine data from a large number of studies and identify common and different perfusion patterns to enhance knowledge of ASL image analysis and of the role of perfusion and structural changes in neurodegenerative pathophysiology.
  • Lecture (Conference)
    34th Annual Scientific Meeting of European Society for Magnetic Resonance in Medicine and Biology, 19.10.2017, Barcelona, Spain

Publ.-Id: 25845 - Permalink


Perfusion changes following elective surgery in the elderly
Mutsaerts, H. J.; Kant, I.; Petr, J.; Winterer, G.; Spies, C.; Pischon, T.; Asllani, I.; Slooter, A.; Hendrikse, J.;
Purpose / Introduction
As society ages and medical technology advances, more and more elderly undergo elective surgery. However, older patients have an
increased risk of postoperative cognitive dysfunction, leading to impaired quality of life and an increased chance of becoming dependent 1.
The pathophysiology of these long‐term side effects is poorly understood. New imaging biomarkers may be used to study the postoperative
changes and evaluate the efficacy between different surgical or anesthetic strategies 1. In this study we explore the cerebral
blood flow ﴾CBF﴿ changes following elective surgery using arterial spin labeling ﴾ASL﴿ perfusion MRI.
Subjects and Methods
Data were drawn from the Biomarker Development for Postoperative Cognitive Impairment in the Elderly ﴾BioCog﴿ study. Sixty‐five elderly
﴾71.7 ± 5.2 yrs, 73.9% M﴿ were scanned before and approximately 3 months after various types of elective surgery, excluding brain surgery
and history of dementia. A background suppressed 2D EPI pseudo‐continuous ASL scan was performed, with labeling duration 1650 ms
and post‐labeling delay slice‐range 1525‐2225 ms. CBF maps were processed2 and transformed into standard space3 using ExploreASL4.
We investigated global CBF changes, cognitive decline regions and the spatial coefficient of variation ﴾CoV﴿5.
Results
CBF decreased with 11.4% in the white matter ﴾WM, p=0.004﴿ and with 7.6% in the gray matter ﴾GM, p=0.017﴿ ﴾Table 1﴿. We did not
identify regional CBF changes ﴾data not shown﴿, suggesting that CBF decreased to a similar degree across the brain. The 8.8% WB CBF
decrease was correlated with baseline WB CBF ﴾r=0.63, p<0.001﴿.
The spatial CoV did not change ﴾p=0.179﴿, implying that there were no major macro‐vascular changes. Visually, the CBF decrease was
subtle and slightly asymmetrical ﴾Figure 1﴿. Figure 2 shows that CBF decreased in the majority of the individuals. This effect seems to be
stronger for higher baseline CBF values, whereas for lower CBF baseline values there were also patients whose CBF increased.
Discussion / Conclusion
We identified global CBF decreases across the brain after elective surgery, which was related with baseline CBF. Future studies are
encouraged to confirm these explorative findings in larger samples, investigate the apparent perfusion asymmetry and whether subgroups
can be defined with different degrees of CBF changes. Such an analysis may differentiate to what extent our findings are related to the type
or duration of surgery or anesthetics. Furthermore, the clinical relevance of these changes should be investigated by studying long‐term
adverse outcomes after surgery such as postoperative cognitive dysfunction1.
  • Lecture (Conference)
    34th Annual Scientific Meeting of European Society for Magnetic Resonance in Medicine and Biology, 19.10.2017, Barcelona, Spain
  • Open Access LogoAbstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 30(2017)Suppl 1, 372
    DOI: 10.1007/s10334-017-0633-0

Downloads:

Publ.-Id: 25844 - Permalink


Comparison of two methods for atrophy-correction in perfusion imaging: Partial-volume correction versus gray matter volume covariate
Petr, J.; Mutsaerts, H. J.; Hofheinz, F.; Steketee, R. M.; Smits, M.; Nederveen, A. J.; van den Hoff, J.; Asllani, I.;
Purpose / Introduction
Partial volume (PV) effects, caused by the mixing of different tissue signals within a voxel, are a well-recognized confounder in arterial spin labeling (ASL) imaging1,2, and are especially relevant in populations with atrophy3,4. Although several PV-correction algorithms exist5,6,7, many investigators continue to account for PV by using gray matter volume (GM-vol) as a covariate in the analysis of PV-uncorrected cerebral blood flow (CBF) images. To gain insight into this issue, we compared the performance of PV-correction5 vs GM-vol covariate using data based on acquired images that were simulated to reflect decreases in GM-vol and CBF.
Subjects and Methods
A total of 88 3D T1w images with 1x1x1mm3 resolution were acquired on twenty-two healthy volunteers8 (22.6±2.1 years, 9 men) who were scanned twice on two 3T scanners (GE Discovery and Philips Intera). T1w images were segmented, and CBF images were simulated to reflect GM-vol and CBF decrease with age, which was randomly and uniformly assigned to each subject (range 40-80 years). Sixteen different combinations of linear GM-volume and CBF decrease of 0, 0.25, 0.5 and 1% per year were simulated. The GM-vol decrease was simulated as cortical thinning using the high-resolution PV maps (Figure 1). The PV maps were then downsampled to the 3x3x7mm3 resolution. CBF images were simulated assuming baseline GM-CBF of 80±4 mL/min/100g and age-independent GM/WM-CBF ratio of 3. Additionally, pixelwise Gaussian noise (s.d. ±4 mL/min/100g) was added to the simulated CBF images11 (Figure 2). The mean CBF in voxels with GM content above 70% was analyzed with the two methods using a multivariate linear regression with age as fixed effect. The estimated slope of CBF change with age was compared with the simulated (ground truth) value.
Results
The PV-correction outperformed the GM-covariate method in all cases, and the PV-correction relative error was under 0.5% (Table 1). The error of the GM-covariate method increased with increasing atrophy and reached a maximum value of 10%.
Discussion / Conclusion
In the presence of atrophy, PV correction allowed for detection of CBF changes relatively independent of atrophy and with higher accuracy than the GM-volume covariate method. The reason is probably that the underestimation of PV-uncorrected CBF in the presence of atrophy does not perfectly correlate with the GM-vol decrease as it depends on additional factors such as cortical thickness. Further studies should evaluate the effect of global and local segmentation errors, and focal atrophy on the efficacy of both methods.
  • Poster
    34th Annual Scientific Meeting of European Society for Magnetic Resonance in Medicine and Biology, 19.10.2017, Barcelona, Spain
  • Open Access LogoAbstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 30(2017)Suppl 1, 395
    DOI: 10.1007/s10334-017-0633-0

Downloads:

Publ.-Id: 25843 - Permalink


Theranostic mercury 197(m)Hg: comparing different Hg/Au separation methods
Wang, C.; Červenák, J.; Walther, M.; Lebeda, O.; Preusche, S.; Pietzsch, H. J.; Steinbach, J.;
Objectives: The access to no-carrier-added 197(m)Hg for imaging and therapy research based on proton or deuteron irradiation of gold was recently reported1,2. The development of a rapid, reliable method for Hg/Au separation represents an important prerequisite for increasing yields. Ideally would be, a reversible interaction at least of one of the two metal ions, allowing for the product elution into a small volume. Besides the liquid-liquid extraction with methyl isobutyl keton (MIBK)1, the solid phase extraction using LN resin (LaNthanides) containing di(2-ethylhexyl)orthophosphoric acid as extractant was examined for this application2.
Methods: The gold target was irradiated for 120 minutes with a 25 µA beam current of 10 MeV protons resulting in 200 MBq of 197(m)Hg or with 15.6 MeV deuteron beam at 7.8 µA beam current for 180 min resulting in ca 800 MBq of of 197(m)Hg (EOB). The irradiated gold foil was dissolved after 1 h in 700 µl of aqua regia (freshly prepared 1 h before EOB from 525 µl 30% HCl + 175 µl 65% HNO3) at room temperature. The column preparation was carried out directly before use by loading 3.6 g LN resin slurried with 10 ml of 6M HCl onto the column and rinsing with additional 30 ml of 6M HCl. After dilution of the 700 µl product solution with 300 µl 6M HCl, this mixture was loaded onto the column and eluted with 6M HCl in 1 ml aliquots.
Results: Comparing with the previously described liquid-liquid extraction1, the solid phase extraction using the LN resin showed shorter performance time. After loading the mixture of chloroauric acid and n.c.a. mercury chloride, the colored gold solution was observed to rapidly distribute in the upper part of the column and then slowly proceeds down during the stepwise elution with 6M HCl. After the addition of 5–6 ml of HCl, the yellow chloroauric acid extended roughly two thirds down the column and almost stopped to move, while over 90% of n.c.a. radiomercury chloride (higher than 60-80% extracted with 4×500 µl MIBK) eluted in the following 2 ml of HCl. The separated 197(m)Hg has excellent radionuclidic purity with no detectable traces of 198Au. It is massively produced in the deuteron activation of gold and acts as a very sensitive tracer of the separation process efficiency.
Conclusions: In contrast to the liquid-liquid extraction, LN resin based method is significantly more efficient and provides product of high radionuclidic purity. Another major advantages compared to the liquid-liquid extraction are obviously 1) better handling and easy automation that shorten the separation time and minimize radiation burden, 2) negligible product losses 3) open possibility to collect and recycle the target material.
  • Poster
    22nd International Symposium on Radiopharmaceutical Sciences, 14.-19.05.2017, Dresden, Deutschland

Publ.-Id: 25842 - Permalink


Liquid metal batteries - materials selection and fluid dynamics
Weier, T.; Bund, A.; El-Mofid, W.; Horstmann, G.; Lalau, C.-C.; Landgraf, S.; Nimtz, M.; Starace, M.; Stefani, F.; Weber, N.;
Liquid metal batteries are possible candidates for massive and economically feasible large-scale stationary storage and as such could be key components of future energy systems based mainly or exclusively on intermittent renewable electricity sources. The completely liquid interior of liquid metal batteries and the high current densities give rise to a multitude of fluid flow phenomena that will primarily influence the operation of future large cells, but might be important for today’s smaller cells as well. The paper at hand starts with a discussion of the relative merits of using molten salts or ionic liquids as electrolytes for liquid metal cells and touches the choice of electrode materials. This excursus into electrochemistry is followed by an overview of investigations on magnetohydrodynamic instabilities in liquid metal batteries, namely the Tayler instability and electromagnetically excited gravity waves. A section on electro-vortex flows complements the discussion of flow phenomena. Focus of the flow related investigations lies on the integrity of the electrolyte layer and related critical parameters.
Keywords: liquid metal batteries, Tayler instability, metal pad role instability, electro-vortex flows

Publ.-Id: 25841 - Permalink


Numerical simulations of convection in the titanium reduction reactor
Teimurazov, A.; Frick, P.; Weber, N.; Stefani, F.;
We introduce a hydrodynamic model of convective flows in a titanium reduction reactor. The reactor retort is a cylindrical vessel with a radius of 0.75 m and a height up to 4m, filled with liquid magnesium at a temperature of 850°C. The exothermic chemical reaction on the metal surface, cooling of the side wall and heating of the lower part of the retort cause strong temperature gradients in the reactor during the process. These temperature gradients cause intensive convective flows inside the reactor. As a result of the reaction, a block of titanium sponge grows at the retort bottom and the magnesium salt, whose density is close to the density of magnesium, settles down. The process of magnesium salt settling in a titanium reduction reactor was numerically studied in a two-dimensional (full size model) and three-dimensional (30% size of the real model) non-stationary formulation. A detailed analysis was performed for configurations with and without presence of convective flow due to work of furnace heaters. It has been established that magnesium salt is settling in drops with sizes from ~3 cm to ~10 cm. It was shown that convective flow can entrain the drop and carry it with the vortex.

Publ.-Id: 25840 - Permalink


A fluorescence anisotropy-based assay to characterize the GTP-binding site of tissue transglutaminase
Hauser, C.; Kasprzyk, R.; Wodtke, R.; Jemielity, J.; Löser, R.; Pietsch, M.;
High activity of tissue transglutaminase (TGase 2) in various tumors is associated with both their increased metastatic and invasive potential and their resistance towards chemotherapy and radiation. This renders TGase 2 an attractive target for the development of agents that are capable of targeting the tumor-associated TGase 2 for both imaging and therapeutic approaches [1]. TGase 2 exists in two different conformations, with the closed one being the major intracellular form. It functions as a GTP-binding protein (Gh protein) at low Ca2+ levels, whereas transition to the open conformation (initiated by an increase in Ca2+ concentration) allows for the transamidase activity leading to protein-protein crosslinking [2].
Characterization of the GTP-binding activity of TGase 2 was done by means of a new fluorescence anisotropy assay using the literature known BODIPY FL-GTPγS [3]. This compound, internally quenched by an intramolecular stacking of the BODIPY and the guanosin moieties, is commonly used in fluorescence-based assays that make use of the unfolding and thereby dequenching of the fluorophore upon binding, leading to an increase in fluorescence. [3] Such behavior, however, interferes with the analysis of fluorescence anisotropy as the measured data have to be corrected [4].
To optimize the new assay, we investigated a small series of newly developed GTP- and GDP-analogues labeled with fluorescein for TGase affinity and change in fluorescence upon protein binding. All compounds show a significantly smaller increase in fluorescence intensity compared to the BODIPY FL-labeled nucleotide and – in some cases – an up to ten-fold superior binding affinity towards TGase 2. The fluorescence anisotropy assay was then validated for inhibition studies by investigation of GTP and GTPγS, which both show IC50 values (64 nM and 109 nM, respectively) that are in agreement with literature data [5,6].
Further investigations included titration of the GTP/TGase 2 interaction with CaCl2 to determine the Ca2+ concentration needed to shift TGase 2 to the extended conformation and inhibition studies with GDP and ATP as well as compounds targeting the acyltransferase domain of TGase 2.
References:
[1] Pietsch, M. et al. Bioorg. Med. Chem. Lett. 2013, 23, 6528.
[2] Kerr, C. et al. Oncogene 2016, doi: 10.1038/onc.2016.452.
[3] McEwen, D. P. et al. Methods Enzymol. 2002, 344, 403.
[4] Jameson, D. M. & Mocz, G. Methods Mol. Biol. 2005, 305, 301-322.
[5] Datta, S. et al. Biochemistry 2007, 46, 14819.
[6] Schaertl, S. et al. J. Biomol. Screen. 2010, 15, 478.
  • Poster
    Debrecen University Symposium 2017 - Transglutaminases in Medicine, 03.-05.08.2017, Debrecen, Ungarn

Publ.-Id: 25839 - Permalink


Radiosynthesis and in vitro characterisation of a potent 18F-fluorinated Nε-acryloyllysine as activity-based probe for transglutaminase 2
Wodtke, R.; Bauer, D.; Pufe, J.; Hauser, S.; Hauser, C.; Pietsch, M.; Pietzsch, J.; Löser, R.;
Transglutaminase 2 (TGase 2) represents an interesting target for the development of PET tracers for functional imaging of tumours. Among the TGase 2 inhibitors described in the literature, Nα-phenylacetyl-Nε-acryloyl-L-lysine-4-(6-methylpyridin-2-yl)piperazide (1) [1] seems to be most suitable for radiotracer development as this compound exhibits both strong inhibitory potential and selectivity towards human (h) TGase 2. Extensive structure-activity relationship studies by our group revealed some potent fluorinated analogues of 1, of which compound 3 (methyl group is substituted by fluorine) is a potential candidate for PET tracer development due to its great inhibitory potency and promising pharmacokinetic properties.
For the radiosyntheses of [18F]3, 6-nitro (2a) and 6-trimethylammonio-pyridines (2b) were envisaged as precursors for direct 18F-fluorination. The fluorination reactions using [18F]fluoride were performed under various conditions. Labelling of 2a by [18F]fluoride resulted in only moderate radiochemical yields (≈20%) accompanied by the formation of two 18F-labelled side products. In contrast to this, 18F-fluorination of 2b yielded exclusively [18F]3 in high radiochemical yields (≈70%). Therefore, precursor 2b was chosen for further radiosyntheses. In vitro characterisation of [18F]3 with regards to its reactivity towards hTGase 2 as well as its selectivity and specificity was done by radio-TLC and radio-SDS-PAGE. Kinetic investigations by radio-TLC provided values for kinact/KI that are in good agreement with values obtained by fluorimetric activity assays. Incubation of whole cell lysates of different human tumour cell lines exhibiting a high expression of TGase 2 with [18F]3, followed by SDS-PAGE and measurement of the 18F activity revealed essentially a single band around the molecular mass of hTGase 2 (≈77 kDa). Accordingly, no band was observed for those tumour cells which do not express TGase 2. Further experiments with [18F]3 will include cell uptake studies in living tumour cells as well as stability, biodistribution and PET studies in mice.
[1] J. Wityak et al. ACS Med. Chem. Lett. 2012, 3, 1024-1028
  • Lecture (Conference)
    Deberecen University Symposium 2017 - Transglutaminases in Medicine, 03.-05.08.2017, Debrecen, Ungarn

Publ.-Id: 25838 - Permalink


Magnetic field dynamos and magnetically triggered flow instabilities
Stefani, F.; Albrecht, T.; Arlt, R.; Christen, M.; Gailitis, A.; Gellert, M.; Giesecke, A.; Goepfert, O.; Herault, J.; Kirillov, O.; Mamatsashvili, G.; Priede, J.; Rüdiger, G.; Seilmayer, M.; Tilgner, A.; Vogt, T.;
The project A2 of the LIMTECH Alliance aimed at a better understanding of those magnetohydrodynamic instabilities that are relevant for the generation and the action of cosmic magnetic fields. These comprise the hydromagnetic dynamo effect and various magnetically triggered flow instabilities, such as the magnetorotational instability and the Tayler instability. The project was intended to support the experimental capabilities to become available in the framework of the DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN). An associated starting grant was focused on the dimensioning of a liquid metal experiment on the newly found magnetic destabilization of rotating flows with positive shear. In this survey paper, the main results of these two projects are summarized.

Publ.-Id: 25837 - Permalink


Strategies for the radiosynthesis of potent fluorinated Nε-acryloyllysines as potential PET tracers for transglutaminase 2
Wodtke, R.; Jäckel, E.; Bauer, D.; Lohse, M.; Wong, A.; Pufe, J.; Ruiz-Gómez, G.; Hauser, C.; Hauser, S.; Steinbach, J.; Teresa Pisabarro, M. T.; Pietsch, M.; Pietzsch, J.; Löser, R.;
Objectives: Various kinds of tumour entities are characterised by increased activity of transglutaminase 2 (TGase 2), which contributes to enhanced invasive potential of the tumour cells and their resistance to chemo- and radiotherapy. Therefore, this enzyme represents an interesting target for the development of PET tracers for functional imaging of tumours. Among the TGase 2 inhibitors described in the literature, Nε-acryloyllysine 1 [1] seems to be most suitable for radiotracer development as this compound exhibits both strong inhibitory potential and selectivity towards human TGase 2. Extensive structure-activity relationship studies by our group revealed some potent fluorinated analogues of 1, of which compounds 2 and 4 were identified as potential candidates for PET tracer development due to their great inhibitory potencies and promising pharmacokinetic properties.
Methods: Reference compounds 2 and 4 as well as the precursor 3 were synthesised in a modular synthetic route. For the radiosynthesis of [18F]2, thienyl and anisyl iodonium salts were envisaged as precursors for prosthetic labelling groups, which were synthesised starting from iodophenylacetates. The fluorination reactions using [18F]F- were performed under various conditions to maximise the radiochemical yield (RCY).
Results: Although a wide range of conditions for radiolabelling of the phenylacetic acid-derived iodonium salts were applied, no incorporation of [18F]F- could be observed. To identify possible reasons for this, the two other regioisomeric phenylacetic acid-derived iodonium salts were synthesised and subjected to labelling with [18F]F-. As a result of these efforts, the CH acidity of the benzylic methylene group was supposed to have a detrimental effect on the labelling reaction. In contrast to this, labelling of precursor 3 was successful with RCYs (non-isolated crude product) of up to 15%. Due to the difficult separation of 3 and [18F]4, the nitro group was reduced to the respective amino group by tin(II) chloride prior to purification by RP-HPLC.
Conclusions: After identifying fluorinated Nε-acryloyllysines as potential PET tracer candidates, strategies for their radiosynthesis were developed. While attempts for the incorporation of fluorine-18 at the non-activated phenylacetic acid moiety revealed inherent structural limitations, labelling at the 2-nitropyridine-derived precursor led to a promising PET tracer candidate.
References:
[1] J. Wityak et al. ACS Med. Chem. Lett. 2012, 3, 1024-1028
  • Open Access LogoAbstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S419-S419
    DOI: 10.1002/jlcr.3508

Publ.-Id: 25836 - Permalink


Improving Stability of Cathepsin B Endopeptidase Substrates as Potential Cleavage Sites in Activatable Cell-Penetrating Peptides
Kuhne, K.; Behring, L.; Birgit Belter, B.; Wodtke, R.; Steinbach, J.; Pietzsch, J.; Löser, R.;
Objectives: The cysteine protease cathepsin B, whose expression in tumors correlates with increased metastasis, therapy resistance, and a generally poor prognosis, represents an excellent target for molecular imaging using radiotracers [1]. We aim to develop a cathepsin B specific, substrate-based radiotracer derived from poly-d-arginine-based activatable cell penetrating peptides [2]. With in vivo application of peptides being often limited by short biological half-life, stabilization against proteolytic degradation is a key aspect in the development of this agent.
Methods: Octapeptide substrates containing the FRET pair aminobenzoyl/dinitrophenyl (Abz/Dnp) were synthesized by solid phase peptide synthesis in high purities and good yields, using non-proteinogenic and N-methylated amino acids (AA) for stabilization. All substrates were evaluated for cleavage efficiency by cathepsin B in orientation to [3]. In vitro stability studies were performed in human serum, with analysis by UPLC-ESI-MS, using the UV absorbance of Dnp (λ = 365 nm) for quantification and subsequent ESI-MS analysis for identification of degradation products.
Results: Rapid degradation has been observed for the endopeptidase substrate Abz-Gly-Ile-Val-Arg-Ala-Lys(Dnp)-Gly-Ser-NH2 in the in vitro serum stability assay (T1/2 = 3.7 min), which was due to cleavage at the P1-P1’ cleavage site (Arg-Ala) as indicated by LC-MS analysis. In a first step, arginine was substituted by citrulline to decrease susceptibility to trypsin-like serum proteases, which increased serum stability (T1/2 = 8.9 min). The non-proteinogenic AA homoarginine, homocitrulline and O-carboxybenzylserine are being tested as further potential substitutes for arginine. Secondary cleavage sites, identified at P4-P3 (Gly-Ile) and P2’-P3’ (Lys-Gly), were suppressed by insertion of Nα-methyl-isoleucine and Nα-methyl-glycine.
Conclusions: After the optimization of the endopeptidase substrate with regards to cathepsin B-specific cleavage, substrate stabilization against other proteases is a crucial step to a peptide-based radiotracer. We have demonstrated the potential for stabilization by introduction of citrulline, with further stabilization by insertion of N-methylated and non-proteinogenic amino acids ongoing, which will pave the way to the envisaged substrate-based imaging probes.
References:
1. Löser & Pietzsch, Front. Chem. 2015, 3, 37
2. Jiang et al., PNAS 2004, 101, 17867
3. Cotrin et al., Anal. Biochem. 2004, 335, 244
  • Open Access LogoAbstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, S221-S221
    DOI: 10.1002/jlcr.3508

Publ.-Id: 25835 - Permalink


Brain volume and perfusion changes in healthy tissue of glioblastoma patients treated with radiochemotherapy
Petr, J.;
Brain volume and perfusion changes in healthy tissue of glioblastoma
patients treated with radiochemotherapy
  • Invited lecture (Conferences)
    Invited talk at Leiden University Medical Center, 17.01.2017, Leiden, Netherlands

Publ.-Id: 25834 - Permalink


Resolution and deformation issues of the partial volume correction of ASL data
Petr, J.; Mutsaerts, H.; de Vita, E.; Maus, J.; van den Hoff, J.; Asllani, I.;
  • Invited lecture (Conferences)
    Invited lecture at UCL Institute of Neurology, 15.03.2016, London, United Kingdom

Publ.-Id: 25833 - Permalink


Thermal convection of liquid metal in the titanium reduction reactor
Teimurazov, A.; Frick, P.; Stefani, F.;
The structure of the convective flow of molten magnesium in a metallothermic titanium reduction reactor has been studied numerically in a three-dimensional non-stationary formulation with conjugated heat transfer between liquid magnesium and solids (steel walls of the cavity and titanium block). A nonuniform computational mesh with a total of 3.7 million grid points was used. The Large Eddy Simulation technique was applied to take into account the turbulence in the liquid phase. The instantaneous and average characteristics of the process and the velocity and temperature pulsation fields are analyzed. The simulations have been performed for three specific heating regimes: with furnace heaters operating at full power, with furnace heaters switched on at the bottom of the vessel only, and with switched-off furnace heaters. It is shown that the localization of the cooling zone can completely reorganize the structure of the large-scale flow. Therefore, by changing heating regimes, it is possible to influence the flow structure for the purpose of creating the most favorable conditions for the reaction. It is also shown that the presence of the titanium block strongly affects the flow structure.

Publ.-Id: 25832 - Permalink


Stability of MR Brain Perfusion Measurement Using Arterial Spin Labeling
Petr, J.; Hofheinz, F.; Platzek, I.; Schramm, G.; van den Hoff, J.;
Reproducibility of ASL perfusion measurements.
  • Lecture (Conference)
    Meeting of the ASL COST Action, 03.02.2015, Les Diablerets, Switzerland

Publ.-Id: 25831 - Permalink


Transitions in a magnetized quasi-laminar spherical Couette flow
Kasprzyk, C.; Kaplan, E.; Seilmayer, M.; Stefani, F.;
First results of a new spherical Couette experiment are presented. The liquid metal flow in a spherical shell is exposed to a homogeneous axial magnetic field. For a Reynolds number Re=1000, we study the effect of increasing Hartmann number Ha. The resulting flow structures are inspected by ultrasound Doppler velocimetry. With a weak applied magnetic field, we observe an equatorially antisymmetric jet instability with the azimuthal wave number m=3. As the magnetic field strength increases, this instability vanishes. When the field is increased further, an equatorially symmetric return flow instability arises. Our observations are shown to be in good agreement with linear stability analysis and non-linear flow simulations.
  • Open Access LogoMagnetohydrodynamics 53(2017)2, 393-401

Downloads:

Publ.-Id: 25830 - Permalink


Comparison of MLAA-derived attenuation maps with and without utilisation of time-of-flight information in the attenuation estimation step
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation
errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches. As A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is required to eliminate possible ”crosstalk” between the estimated activity and attenuation distribution. On the other hand, it is widely believed that use of the TOF information during attenuation estimation does not result in image quality improvement and thus is unnecessary, see for example ref. [2]. However, so far this assumption has never been thoroughly tested. We address this issue in the present investigation. To this end, we have compared TOF and non-TOF versions of the attenuation estimation algorithm as part of MLAA within the framework of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [3].

METHODS
MLAA is an image reconstruction algorithm, which maximizes the Likelihood function by alternately updating activity distribution and attenuation map. Maximum-Likelihood Estimation-Maximization (MLEM) is normally used for the
activity estimation and Maximum-Likelihood Transmission Reconstruction (MLTR) for the attenuation estimation. In order to investigate the potential impact of using TOF-MLTR instead of nonTOF-MLTR in the MLAA workflow both of them were implemented as a part of our THOR application. List-mode MLEM algorithm was used for activity reconstruction and accelerated by utilizing ordered subsets. For scatter correction (SC), the time-of-flight extension of the Single Scatter Simulation algorithm (SSS) was used, see ref [4]. Attenuation map reconstruction was performed by ordered subsets accelerated list-mode version of MLTR, which is equivalent to the standard sinograms based MLTR in the non-TOF case. For the initial attenuation map estimate the MR-derived outline of the scanned object was uniformly filled with the attenuation coefficient of water. During reconstruction, attenuation map estimates were augmented by a pre-computed template of the patient bed. The main difference between TOF- and nonTOF-MLTR is the way how scatter and randoms corrections are handled. TOF information allows to individually compute this correction for each event (or TOF-bin) depending on event position along the LOR, while this correction is assumed to be the same for all the events within the LOR in the non-TOF algorithm. Consequently, any differences between both MLTR versions should be most pronounced for high contrast objects as is the case, e.g., if the bladder is within the field-of-view. Therefore, two different configurations of the whole body phantom L981602 were used. The phantom in configuration A has two cylindrical air-filled inserts and one cylindrical bone-like insert. This phantom allows to assess accuracy of the attenuation map estimate under low-contrast conditions. The phantom in configuration B comprises a large spherical ”bladder” insert with high target-to-background contrast and a small ”lesion” insert with lower contrast. The attenuation map is uniform in this case, which facilitates detection of scatter-related artifacts in the MLAA reconstructed attenuation image. Transmission scans of the phantoms with the Siemens HR+ scanner were performed and used as ground-truth for the attenuation maps.

RESULTS
The whole body phantom in both configurations was scanned with the Time-Of-Flight capable Philips Ingenuity-TF PET/MR scanner (TOF resolution (FWHM): ∼600 ps). Acquired data were reconstructed with THOR MLAA and TOF-MLTR and nonTOF-MLTR, respectively. In the case of configuration A (low activity contrast, high attenuation contrast) TOF-MLTR does not improve attenuation coefficients estimate significantly. Reconstructed attenuation values differ by less than 1% for bone and less than 15% for air. The situation is different for configuration B (high activity contrast, homogeneous attenuation). Due to presence of the large hot object in the field-of-view a massive artifact appears in the transaxial plane of the reconstructed attenuation map containing the ”bladder” insert. In the coronal view this artifact appears as a rather large area of apparently reduced attenuation in the middle of the phantom. The difference between the attenuation coefficient of the water background in the central and the peripheral zones depends on the reconstruction method used. Specifically, the use of TOF-MLTR instead of nonTOF-MLTR yields twofold decrease of the artifact. On the other hand, the attenuation coefficient inside the ”bladder” is about 12% higher than the reference value with TOF-MLTR compared to a 6% overestimate with nonTOF-MLTR (where this reduced deviation probably is due to the influence of the mentioned attenuation artifact).

CONCLUSION
Our preliminary results indicate that the use of TOF-MLTR within the MLAA framework provides only small improvements in terms of attenuation map accuracy if activity contrasts are modest. However, it can distinctly decrease scatter related artifacts in the presence of high activity contrast such as is frequently observed in the pelvis region. We hypothesize the advantages of TOF-MLTR will become even more apparent with increasing TOF resolution. A more detailed investigation of the benefits of TOF-MLTR usage within the MLAA workflow is under way.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Rezaei and J. Nuyts, “Simultaneous reconstruction of the activity image and registration of the CT image in TOF-PET,” IEEE Nuclear Science Symposium Conference Record, vol. 1852, p. 1852, 2016.
[3] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[4] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transactions on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
Keywords: PET, TOF-PET, PET/MR, MLAA, MRAC, Attenuation Correction
  • Poster
    PSMR 2017 - 6th Conference on PET-MRI and SPECT-MRI, 29.-31.05.2017, Lisbon, Portugal

Publ.-Id: 25829 - Permalink


Sun - Batteries - Sun
Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.;
Liquid metal batteries (LMBs) are presently discussed as cheap means for the storage of wind and solar energy. Among other drivers of undesired fluid motion that could destroy the three-fluids stratification, the Tayler instability (TI) sets some upper limit for the upscalability of LMBs. We present the principles of the TI, its possible effects on LMBs, and some simple ways to suppress it. We focus on the peculiar saturation mechanism of the TI at low magnetic Prandtl numbers, which relies on the change of the hydrodynamic base state. We discuss the recently found helicity oscillations of the m=1 velocity field of the TI which, in turn, might have consequences for stellar dynamo models for which the TI had originally been discussed. We show that these helicity oscillations can be resonantly excited by certain m=2 perturbations which would result, e.g., from planetary tidal forces. It is this high sensitivity of the helicity oscillations that could empower those very weak tidal forces to synchronize the entire solar dynamo.
  • Lecture (Conference)
    International workshop on liquid metal battery fluid dynamics (LMBFD 2017), 16.-17.05.2017, Dresden, Germany

Publ.-Id: 25828 - Permalink


The DRESDYN project: planned experiments and present status
Stefani, F.; Eckert, S.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Räbiger, D.; Seilmayer, M.; Weier, T.;
The Dresden sodium facility for dynamo and thermohydraulic studies (DRESDYN) is a platform for large-scale liquid sodium experiments devoted to fundamental geo- and astrophysical questions as well as to various applied problems related to the conversion and storage of energy. Its most ambitious part is a precession driven dynamo experiment, comprising 8 tons of liquid sodium supposed to rotate with up to 10 Hz and to precess with up to 1 Hz. Another large-scale set-up is a Tayler-Couette experiment with a gap width of 0.2 m and a height of 2 m, whose inner cylinder rotates with up to 20 Hz. Equipped with a coil system for the generation of an axial field of up to 120 mT and two different axial currents through the center and the liquid sodium, this experiment aims at studying various versions of the magnetorotational instability and their combinations with the Tayler instability. We discuss the physical background of these two experiments and delineate the present status of their technical realization. Other installations, such as a sodium loop and a test stand for In-Service-Inspection experiments, will also be sketched.
  • Lecture (Conference)
    88th GAMM Annual Meeting, 06.-10.03.2017, Weimar, Germany

Publ.-Id: 25827 - Permalink


Ultrasound propagation in bond frustrated HgCr2S4 spinel in magnetic fields
Felea, V.; Prodan, L.; Stefanet, E.; Cong, P. T.; Zherlitsyn, S.; Tsurkan, V.;
Ultrasound and magnetization studies of bond frustrated spinel HgCr2S4 are performed as a function of temperature in static magnetic fields. Beside the anharmonic effect, the sound velocity shows pronounced anomaly at the antiferromagnetic (AFM) transition at TN = 23 K with an additional significant increase of the order of 0.5 % indicating a strong spin-lattice coupling. External magnetic fields enhance the ferromagnetic (FM) correlations and shift the anomalies to lower temperatures concomitantly with the reduction of the Néel temperature. The constructed H–T Phase diagram beside the long-range AFM states reveals the state with induced FM order and regimes with short-range AFM and FM correlations as well.

Publ.-Id: 25826 - Permalink


Comparison of arterial spin labeling registration strategies in the multi-center GENetic frontotemporal dementia initiative (GENFI)
Mutsaerts, H. J. M. M.; Petr, J.; Thomas, D. L.; de Vita, E.; Cash, D. M.; van Osch, M. J. P.; Golay, X.; Groot, P. F. C.; Ourselin, S.; van Swieten, J.; Laforce, R.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J. B.; Graff, C.; D. Pizzini, F. B.; Finger, E.; Sorbi, S.; Castelo Branco, M.; Rohrer, J. D.; Masellis, M.; Macintosh, B. J.;
Purpose: To compare registration strategies to align arterial spin labeling (ASL) with 3D T1-weighted (T1w) images, with the goal of reducing the between-subject variability of cerebral blood flow (CBF) images.
Materials and Methods: Multi-center 3T ASL data were collected at eight sites with four different sequences in the multi-center GENetic Frontotemporal dementia Initiative (GENFI) study. In a total of 48 healthy controls, we compared the following image registration options: (I) which images to use for registration (perfusion-weighted images [PWI] to the segmented gray matter (GM) probability map (pGM) (CBF-pGM) or M0 to T1w (M0-T1w); (II) which transformation to use (rigid-body or non-rigid); and (III) whether to mask or not (no masking, M0-based FMRIB software library Brain Extraction Tool [BET] masking). In addition to visual comparison, we quantified image similarity using the Pearson correlation coefficient (CC), and used the Mann-Whitney U rank sum test.Results: CBF-pGM outperformed M0-T1w (CC improvement 47.2% 6 22.0%; P < 0.001), and the non-rigid transformation outperformed rigid-body (20.6% 6 5.3%; P < 0.001). Masking only improved the M0-T1w rigid-body registration (14.5% 6 15.5%; P 5 0.007).
Conclusion: The choice of image registration strategy impacts ASL group analyses. The non-rigid transformation is promising but requires validation. CBF-pGM rigid-body registration without masking can be used as a default strategy.
In patients with expansive perfusion deficits, M0-T1w may outperform CBF-pGM in sequences with high effective spatial resolution. BET-masking only improves M0-T1w registration when the M0 image has sufficient contrast.

Downloads:

Publ.-Id: 25825 - Permalink


Scatter correction in TOF and non-TOF PET image reconstruction in THOR
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches but, as A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is then required to eliminate possible ”crosstalks” between the estimated activity and attenuation distribution. We are aiming at implementation of MLAA for the Philips Ingenuity-TF PET/MR scanner as part of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [2]. As a prerequisite we are currently modifying THOR to make full use of the available TOF information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue and compare TOF-SC techniques with conventional non-TOF SC method.

METHODS
One possible implementation of TOF-SC uses a straight forward extension of Watson’s well-known Single Scatter Simulation (SSS) algorithm [3] but this approach results in about an order of magnitude increase of computational burden compared to standard SSS. Alternatively, one can use standard SSS to estimate the number of scattered events in each Line Of Response (LOR) and use an additional algorithm to estimate the shape of the time distribution of scattered events within each LOR (scatter mask). To integrate TOF-SC into our THOR reconstruction, four different approaches to scatter mask calculation have been investigated:
A. Simple scatter scaling
This approach assumes that scattered and unscattered events have identical time distribution within each single LOR.
B. Attenuation based SC
In this approach the object is modeled as a set of “scatter points” which are generated by SSS. Each scatter point is then also assumed to be a scatter source. For each detector pair and scatter point the geometric path difference from scatter source to both detectors is calculated and an effective position of the scattered event within the corresponding LOR is determined. By repeating this procedure for a large number of scatter points and post-processing the results by smoothing or using a TOF-binning technique one can compute the required scatter mask.
C. Attenuation and activity based SC
While approach B allows to properly handle the shape of the attenuating object it does not take into account the given activity distribution. To fix this issue scatter sources and scatter points should be separated. To do this in a simple and fast way we introduce a small set of “emission points” for approximation of the given activity distribution. The activity distribution/object is then described as superposition of suitable 3D Gaussian distributions around these emission
points. Calculation of the scatter masks is similar to the previous approach, but now scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. In this approach the intensity of each source is proportional to the intensity of corresponding emission point and decreases according to a Gaussian as a function of the distance between them.
D. TOF-SSS Time-Of-Flight extension of Single Scatter Simulation by Watson.

RESULTS
All four approaches have been integrated into THOR and tested in dedicated phantom and patient studies. Approach A does not yield quantitatively correct scatter distributions for big objects. Approach B is superior to A but notable artifacts remain in the presence of high-contrast. Approach C is able to eliminate part of these artifacts but requires more computation time. Approach D is the most accurate and computationally most expensive.

CONCLUSION
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[3] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transations on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC, Single Scatter Simulation, SSS
  • Lecture (Conference)
    Seminar on PET image reconstruction, 28.-30.09.2016, Leuven, Belgium

Publ.-Id: 25824 - Permalink


Effect of Brain Extraction of Low Resolution Arterial Spin Labeling (ASL) Fmri Images on Realignment and Coregistration
Liao, J.; Petr, J.; Lazar, R. M.; Marshall, R. S.; Asllani, I.;
ASL is an fMRI method that maps cerebral blood (CBF), which is a key parameter of brain physiology. In ASL, flow-weighted images are computed by subtracting a “labeled” image from a contiguously acquired unlabeled control image. The difference is then converted to a CBF image using partial volume (PV) maps obtained from the segmentation of the anatomical T1w image. It follows that the quality of ASL data is dependent on the quality of motion correction and coregistration of the high-resolution T1w image to the low-resolution ASL. We tested whether applying brain-extraction on the low-resolution ASL would improve both these processes. The test was performed on 8 patients with carotid occlusive disease. Improvement in motion realignment was defined as % change averaged over the 6 degrees of freedom and across patients; improvement in coregistration was assessed as a difference in the mutual information (MI) value between the T1w and extracted and original ASL, respectively. There was a noticeable effect of brain extraction on both realignment and coregistration.
Keywords: MR neuroimaging, Brain image analysis, Rigid-body image registration, ASL
  • Contribution to proceedings
    39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 11.-15.07.2017, Jeju Island, Korea
  • Poster
    39th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 11.07.2017, Jeju Island, Korea

Publ.-Id: 25823 - Permalink


SUR: a superior alternative to SUV as a surrogate of tumor glucose metabolism
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Symposium Nuclear Medicine & Molecular Imaging, Katholieke Universiteit Leuven, 10.01.2017, Leuven, Belgien

Publ.-Id: 25822 - Permalink


Standardised Uptake Ratio (SUR): die robuste Variante des SUV
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Jahrestagung der Bayrischen Gesellschft für Nuklearmedizin, 01.07.2016, Regensburg, Deutschland

Publ.-Id: 25821 - Permalink


Magnetohydrodynamic instabilities in liquid metal batteries
Stefani, F.;
The increasing deployment of strongly fluctuating renewable energies requires a corresponding large-scale expansion of electricity storage. Liquid metal batteries (LMBs) are presently discussed as a possible route of economical grid-scale energy storage. They consist of two liquid metal electrodes and a molten salt ionic conductor sandwiched between them. The density ratios allow for a stable stratification of the three layers. In the talk, we concentrate on the magnetohydrodynamic aspects of this cell type, with special focus on electro-vortex flows, the sloshing instability, and possible effects of the Tayler instability.
  • Lecture (Conference)
    XXth Winter School on Continuous Media Mechanics, 13.-16.02.2017, Perm, Russia

Publ.-Id: 25820 - Permalink


Upconverting Nanophosphors for bioimaging: Preparation Strategies for hydrophilic colloidal Stable Particles
Nsubuga, A.; Sgarzi, M.; Joshi, T.; Stephan, H.;
Currently, there is a widespread interest to use neodymium containing upconverting nanophosphors (UCNPs) for bioimaging applications. The infatuation of these nanoparticles derives from their capacity for excitation in the biologically transparent window (700-1000 nm), exceptional ability to convert near infrared radiation into visible light (upconversion), which prevents autofluorescence and over-heating effect of biological tissues and capability for deep tissue, high contrast imaging related to minimum autofluorescence in this spectral range [1]. Despite the fast progress in lanthanide-doped upconversion nanoparticles, the preparation of ultrasmall, monodisperse and hydrophilic UCNPs that display intense luminescence is still a challenging issue. Only a few examples of ultrasmall and hydrophilic UCNPs have been reported [2-3]. Here, we report the elaboration, synthesis and surface modification of sub-10 nm UCNPs with an excitation wavelength of 795 nm, which are composed of a host lattice of crystalline NaYF4 doped with Nd3+ and Yb3+ as sensitizers, and Er3+,Ho3+ or Tm3+ as emitter ions. Established strategies for synthesizing UCNPs yield mainly hydrophobic particles[1]. We report the conversion of these into hydrophilic, colloidally-stable, and biocompatible by using mainly ligand exchange strategies, and the influence of the coating on the UCNPs’ photophysical properties. This study will also allow establishing information about biodistribution, pharmacokinetics and formation of protein corona for ultrasmall UCNPs.
Keywords: Upconversion, lanthanide, Sub 10 nm particles, surface functionalization, Bio imaging
  • Lecture (Conference)
    NANOTECH France 2017, 28.-30.06.2017, Paris, France

Publ.-Id: 25819 - Permalink


Time efficient scatter correction in Time-Of-Flight PET image reconstruction
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
Aim
We are currently modifying our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [1], to make full use of the available Time-of-Flight (TOF) information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue.

Methods
Four different, partly newly developed approaches to estimation of scatter time distribution have been investigated: A. Simple scatter scaling: this approach assumes that scattered and unscattered events have identical time distribution within each single LOR. B. Attenuation based SC (new approach): in this approach the object is modeled as a set of “scatter points”. Each scatter point is also assumed to be a scatter source. C. Attenuation and activity based SC (new approach): in this approach a small set of “emission points” for approximation of the given activity distribution is introduced. Calculations are similar to B except that scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. D. TOF-SSS Time-Of-Flight extension of Single Scatter Simulation by Watson.

Results
All four approaches have been integrated into THOR and tested in dedicated phantom and patient studies. Approach A does not yield quantitatively correct scatter distributions for big objects. Approach B is superior to A but notable artifacts remain in the presence of high-contrast. Approach C is able to eliminate part of these artifacts but requires more computation time. Approach D is the most accurate and computationally most expensive.

Conclusion
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications.

Literature
[1] A. Lougovski, F. Hofheinz, J. Maus, et al., Physics in Medicine
and Biology 59(3), 561 (2014)
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC
  • Poster
    NuklearMedizin 2017, 26.-29.04.2017, Dresden, Germany

Publ.-Id: 25818 - Permalink


Liquid metal experiments on hydromagnetic dynamos and magnetically triggered flow instabilities
Stefani, F.;
The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Magnetic fields play, in turn, an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects had been the subject of purely theoretical investigations. The lecture gives an overview about the recent liquid metal experiments on dynamo action and magnetically triggered instabilities. An outlook on future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project, is also given.
  • Invited lecture (Conferences)
    XXth Winter School on Continuous Media Mechanics, 13.-16.02.2017, Perm, Russia

Publ.-Id: 25817 - Permalink


Time efficient scatter correction in Time-Of-Flight PET image reconstruction
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.; Maus, J.ORC; van den Hoff, J.
INTRODUCTION
As is well known, quantitative combined PET/MR imaging depends on accurate MR-based attenuation correction (MRAC). While a mostly satisfactory state of affairs has been reached today, problems persist regarding segmentation errors including unsatisfactory bone identification and residual systematic differences in comparison to PET/CT. Alternative or complementary strategies for attenuation correction (AC), therefore, are of considerable relevance. In this context, Maximum Likelihood reconstruction of Attenuation and Activity (MLAA) is one of the most promising approaches but, as A. Rezaei et al. have shown [1], Time-Of-Flight (TOF) image reconstruction is then required to eliminate possible ”crosstalks” between the estimated activity and attenuation distribution. We are aiming at implementation of MLAA for the Philips Ingenuity-TF PET/MR scanner as part of our previously developed Tube of response High resolution OSEM Reconstruction (THOR), see ref [2]. As a prerequisite we are currently modifying THOR to make full use of the available TOF information. The most critical point in this context is accurate and computational efficient TOF Scatter Correction (TOF-SC). Here, we report on our approach to solving this issue.

METHODS
One possible implementation of TOF-SC uses a straight forward extension of Watson’s well-known Single Scatter Simulation (SSS) algorithm [3] but this approach results in about an order of magnitude increase of computational burden compared to standard SSS. Alternatively, one can use standard SSS to estimate the number of scattered events in each Line Of Response (LOR) and use an additional algorithm to estimate the shape of the time distribution of scattered events within each LOR (scatter mask). To integrate TOF-SC into our THOR reconstruction, three different approaches to scatter mask calculation have been investigated which are modifications/improvements of key ideas from article [4]:
A. Simple scatter scaling
This approach assumes that scattered and unscattered events have identical time distribution within each single LOR.
B. Attenuation based SC
In this approach the object is modeled as a set of “scatter points” which are generated by SSS. Each scatter point is then also assumed to be a scatter source. For each detector pair and scatter point the geometric path difference from scatter source to both detectors is calculated and an effective position of the scattered event within the corresponding LOR is determined. By repeating this procedure for a large number of scatter points and post-processing the results by smoothing or using a TOF-binning technique one can compute the required scatter mask.
C. Attenuation and activity based SC
While approach B allows to properly handle the shape of the attenuating object it does not take into account the given activity distribution. To fix this issue scatter sources and scatter points should be separated. To do this in a simple and fast way we introduce a small set of “emission points” for approximation of the given activity distribution. The activity distribution/object is then described as superposition of suitable 3D Gaussian distributions around these emission
points. Calculation of the scatter masks is similar to the previous approach, but now scatter sources are determined as projections of emission points onto straight lines connecting selected scatter point and detectors. In this approach the intensity of each source is proportional to the intensity of corresponding emission point and decreases according to a Gaussian as a function of the distance between them.

RESULTS
All three approaches have been integrated into our THOR reconstruction and tested in phantom and patient studies. Simple scatter scaling (approach A) does not yield quantitatively correct scatter distributions for big objects such as whole body phantoms. Attenuation based SC (approach B) does not have this problem due to proper handling of the object shape, but notable artifacts appear in the presence of high-contrast such as in the pelvis/bladder region. The combined attenuation and activity based algorithm (approach C) is able to eliminate part of the latter artifacts but requires more computation time.

CONCLUSION
Our preliminary results indicate that attenuation based SC might be the best compromise between computation time and image quality for a wide range of applications. A more detailed investigation of the efficiency and accuracy of the implemented TOF-SC methods is currently in progress.

REFERENCES
[1] A. Rezaei, M. Defrise, G. Bal, C. Michel, M. Conti, C. Watson, and J. Nuyts, “Simultaneous reconstruction of activity and attenuation in time-of-flight PET.” IEEE transactions on Medical Imaging, vol. 31, no. 12, pp. 2224–33, dec 2012.
[2] A. Lougovski, F. Hofheinz, J. Maus, G. Schramm, E. Will, J. van den Hoff, and J. van den Hoff, “A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction,” Physics in Medicine and Biology, vol. 59, no. 3, pp. 561–577, feb 2014.
[3] C. C. Watson, “Extension of Single Scatter Simulation to Scatter Correction of Time-of-Flight PET,” IEEE Transations on Nuclear Science, vol. 54, no. 5, pp. 1679–1686, 2007.
[4] M. Conti, B. Bendriem, M. Casey, M. Chen, F. Kehren, C. Michel, and V. Panin, “First experimental results of time-of-flight reconstruction on an LSO PET scanner.” Physics in medicine and biology, vol. 50, no. 19, pp. 4507–4526, oct 2005.
Keywords: PET, TOF-PET, Scatter Correction, TOF-SC
  • Lecture (Conference)
    PSMR 2016 - 5th Conference on PET/MR and SPECT/MR, 23.-25.05.2016, Cologne, Germany

Publ.-Id: 25816 - Permalink


DRESDYN: Liquid metal experiments on dynamo action and magnetorotational instability
Gundrum, T.; Eckert, S.; Gerbeth, G.; Stefani, F.; Steglich, C.;
We report on two large-scale liquid sodium experiments on precession-driven dynamo action and magnetorotational instability that are planned in the framework of the DRESDYN project.
  • Poster
    Nuclear Astrophysics at the Dresden Felsenkeller, 26.-28.06.2017, Dresden, Germany

Publ.-Id: 25815 - Permalink


Can planetary tides synchronize the solar dynamo?
Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.;
While the traditional explanation of the Hale cycle of the solar magnetic field relies on intrinsic features of the solar dynamo, we presently witness an increased interest in the question of whether gravitational forces of planets could influence the length and intensity of the cycle. Although tidal forces are usually considered as much too weak to play any role, one should note the large gravitational acceleration at the tachocline that amounts to 500 m/s². This translates the apparently tiny tidal heights of the order of 1 mm to equivalent velocities of 1 m/s. Such velocities, when allowed to coherently develop in the quiet regions of the tachocline, might indeed be relevant for the dynamo.
In our quest for a viable physical mechanism that could link the weak planetary force with solar dynamo action, we focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability that is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantly excited by m=2 perturbations that reflect tidal oscillations. Specifically, we speculate that the 11.07 years tidal oscillation induced by the tidally dominant Venus--Earth--Jupiter system may lead to a 1:1 resonant excitation of the oscillation of the associated alpha-effect. In the framework of a reduced, zero-dimensional alpha-Omega dynamo model, including a weak non-oscillatory and a resonantly excited oscillatory part of alpha, we recover the 22.14-year cycle of the solar dynamo. We finally show that the synchronization model can produce the correct orientation of the butterfly diagram even in case that the product of the non-oscillatory part of alpha with Omega is positive.
  • Poster
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice, Czech Republic

Publ.-Id: 25814 - Permalink


Spectroscopic and microscopic approach of U(VI) sorption on Acidovorax facilis for remediation purpose
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Müller, K.; Moll, H.; Rossberg, A.; Merroun, M. L.;
The Gram-negative betaproteobacterium Acidovorax facilis is a suitable candidate for in situ bioremediation of contaminated waste waters and environments [1]. For spectroscopic and microscopic studies kinetic U(VI) sorption experiments were performed under aerobic conditions at 30°C by adjusting an initial U(VI) concentration to 0.1 mM at a neutral pH range by adding UO2(NO3)2 to the batch culture.
A high-resolution image of the cellular localization of U by A. facilis was achieved by using electron microscopy (STEM/HAADF). The elemental distribution analysis of phosphorus and uranium clearly indicates that U is entirely present in the cell membrane. By cryo-Time-resolved laser-induced fluorescence spectroscopy (cryo-TRLFS) studies the spectra deconvolution indicates a fast binding of U(VI) on phosphorylic functionality groups during the first hour with a subsequent formation of Uranyl-carboxylic species in addition to the Uranyl-phosphorylic species. Compared to emission spectra of the Uranyl-lipopolysaccharide [2] we suggest an interaction of UO22+ with cell membrane components of the outer membrane of A. facilis cells, whereas lipopolysaccharide will form the most stable complex. These results support those obtained by Extended X-ray absorption fine structure spectroscopy (EXAFS), where a relative short average U-Oeq bond length of 2.35 Å were observed for the U(VI) interaction with lipopolysaccharide indicating a binding of the U(VI) via organic phosphate groups in a monodentate fashion. The strong interaction of U(VI) with phosphorylic and carboxylic groups was reinforced by in-situ attenuated total reflection Fourier-transform (ATR FT-IR) spectroscopic studies due to the presence of characteristic phosphoryl vibrations. Most of the bound U(VI) presumably remained on the cells, more precisely on the phosphorylic functionalities at the cell membrane.
[1] Gerber et al. (2016). J. Hazard. Mater. 317, 127–134.
[2] Barkleit et al. (2008). Appl. Spectrosc. 62(7), 798-802.
Keywords: Uranium, Acidovorax facilis, TRLFS, EXAFS, ATR FT-IR, STEM/HAADF
  • Lecture (Conference)
    Goldschmidt2017, 13.-18.08.2017, Paris, France

Publ.-Id: 25813 - Permalink


Laboratory experiments on dynamo action and magnetically triggered flow instabilities
Stefani, F.;
Magnetic fields of planets, stars and galaxies are known to be generated by the homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can foster cosmic structure formation by destabilizing, via the magnetorotational instability (MRI) or the Tayler instability (TI), those rotating flows that would be otherwise hydrodynamically stable. The mutual reinforcement of dynamo action and magnetic instabilities leads to interesting concepts such as the MRI-dynamo or the Tayler-Spruit-dynamo.
For a long time, all these topics had been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. Further liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed important findings related to the alpha, beta and Omega effects as well as to various wave phenomena in magnetized rotating fluids. MRI-related research was partly successful with the observation of the helical MRI and the azimuthal MRI at the PROMISE facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability in a liquid metal was also obtained.
The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered flow instabilities. It concludes with an overview about future experiments, with special focus on the precession driven liquid sodium experiment and the large-scale Tayler-Couette experiment that are under construction in the framework of the DRESDYN project at HZDR.The prospects for experimental validation of the recently discussed magnetic destabilization of flows with positive shear are also discussed.
  • Invited lecture (Conferences)
    2nd Conference on Natural Dynamos, 25.06.-01.07.2017, Valtice, Czech Republic

Publ.-Id: 25812 - Permalink


Evaluation of hemodynamic impairments in healthy elderly participants and patients with high-grade unilateral carotid artery stenosis
Kaczmarz, S.; Göttler, J.; Griese, V.; Petr, J.; van de Ven, K.; Helle, M.; Kooijman, H.; Kluge, A.; Karampinos, D.; Zimmer, C.; Sorg, C.; Preibisch, C.;
Internal carotid-artery stenosis (ICAS) causes complex and not yet well understood physiological impairments. We present preliminary data from an ongoing clinical study in ICAS patients and healthy, age-matched participants. The major aims were to evaluate the reliability of a multimodal MRI-protocol and investigate physiological changes. For ICAS patients, regionally impaired vascular-reactivity as well as hypo-perfusion were found. In accordance with literature, we did not find ICAS-induced changes in oxygen extraction on group level. The presented preliminary results thus imply successful application of multimodal MRI methods and are highly promising with respect to gaining a deeper insight into ICAS-related physiological changes.
Keywords: stenosis, ASL, perfusion, MRI
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Proceedings of the 25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Lecture (Conference)
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii, USA

Publ.-Id: 25811 - Permalink


Perfusion decrease during radiochemotherapy is not fully explained by volumetric gray matter changes
Petr, J.; Mutsaerts, H.; Hofheinz, F.; Asllani, I.; van Osch, M.; Platzek, I.; Seidlitz, A.; Krause, M.; van den Hoff, J.;
Radiochemotherapy in brain-tumor patients was shown to cause gray matter (GM) volume and cerebral blood flow (CBF) changes. The interaction of these two effects, however, remains unclear. Here, we investigated GM volume and ASL CBF changes and their interaction in the healthy hemisphere of 38 glioblastoma patients undergoing radiochemotherapy with Temozolomide. We found a statistically significant CBF decrease with dependence on the RT-dose. PV-corrected results indicated that, while to a certain extent the apparent CBF decrease measured by ASL is caused by GM atrophy, there still remain significant CBF changes that cannot be explained by structural changes alone.
Keywords: ASL, perfusion, glioblastoma, radiochemotherapy, atrophy, partial volume
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Proceedings of the 25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
  • Poster
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii, USA

Publ.-Id: 25810 - Permalink


Brain volume loss in glioblastoma patients following photon and proton radiochemotherapy
Petr, J.; Hofheinz, F.; Gommlich, A.; Raschke, F.; Troost, E.; Beuthien-Baumann, B.; Seidlitz, A.; Platzek, I.; Baumann, M.; Krause, M.; van den Hoff, J.;
Gray matter (GM) atrophy in healthy brain tissue following radiochemotherapy was shown in brain-tumor patients in several studies. Here, we aimed to study GM and white matter (WM) changes in glioblastoma patients undergoing photon (n=43) and proton (n=12) radiochemotherapy. In photon-therapy patients, a statistically significant decrease of both GM (~2%) and WM (1.3-2.3%) volume was found with a positive influence of the RT-dose on the GM volume loss. In proton-therapy patients, no significant changes in GM and WM volumes were observed after therapy. This indicates that the proton-therapy has the potential to reduce structural GM changes in healthy tissue.
Keywords: radiochemotherapy, proton therapy, atrophy, morphometrics
  • Contribution to proceedings
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.-27.04.2017, Honolulu, Hawaii, USA
    Brain volume loss in glioblastoma patients following photon and proton radiochemotherapy
  • Lecture (Conference)
    25th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 22.04.2017, Honolulu, Hawaii

Publ.-Id: 25809 - Permalink


Kinetic Modeling
van den Hoff, J.;
A mathematical description of the time-dependent tissue uptake and tissue clearance after injection of contrast agents or radioactively labeled tracers with suitable models (kinetic modeling) allows a detailed analysis of transport processes and metabolism in vivo. Such an analysis can provide at once quantitative information for several interesting parame- ters such as local blood volume, blood flow, distribution volumes, metabolic rates, binding potentials, and so forth. While the mathematical techniques are – with some reservations – in principle suited for data analysis in other tomographic modalities as well (notably CT and MRI), the broadest field of application is found in PET. We will focus especially on small animal PET in the following.
Keywords: PET, Kinetic Modeling, Small Animal Imaging
  • Book chapter
    Fabian Kiessling, Bernd J. Pichler, Peter Hauff: Small Animal Imaging: Basics and Practical Guide, Heidelberg: Springer International Publishing, 2017, 978-3-319-42200-8, 559-580
    DOI: 10.1007/978-3-319-42202-2_21

Publ.-Id: 25808 - Permalink


Steering magnons by non-collinear spin textures
Schultheiss, K.; Wagner, K.; Kákay, A.; Schultheiss, H.;
One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives [1], it turned out to be challenging to transport spin information without great losses [2]. With magnonics a visionary concept inspired researchers worldwide: Utilize spin waves - the collective excitation quanta of the spin system in magnetically ordered materials - as carriers for information [3-8]. Spin waves, which are also called magnons, are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers.
While macroscopic prototypes of magnonic logic gates have been demonstrated [9,10], the full potential of magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium. Spin textures are robust, non-volatile and still reprogrammable on ultra short timescales. The vast possibilities offered by combining these magnetic phenomena, add value to both magnonics and the fundamental understanding of complex spin textures.
The scope of this chapter is about experimental studies on magnon transport in metallic ferromagnetic microstructures with focus on actively controlling the magnon propagation. Two inherent characteristics of magnons enable for lateral steering: the anisotropy of the magnon dispersion and its sensitivity to changes in the internal magnetic field distribution. We intend to give an idea of how these magnon features can be utilized towards realizing functionalized magnonic networks.
Keywords: spin waves, magnonics, spintronics, magneto-optics, spin textures, domain walls
  • Book chapter
    Sergej Demokritov: Spin Wave Confinement: Propagating Waves (2nd Edition), Singapore: Pan Stanford Publishing Pte. Ltd., 2017, 9789814774352

Publ.-Id: 25807 - Permalink


EXILL - a high efficiency, high resolution setup for γ-spectroscopy at an intense cold neutron beam
Jentschel, M.; Blanca, A.; de France, G.; Köster, U.; Leoni, S.; Mutti, P.; Simpson, G.; Soldner, T.; Ur, C.; Urban, W.; Ahmed, S.; Astieri, A.; Augey, L.; Back, T.; Baczyk, P.; Bajoga, A.; Balabanski, D.; Belgya, T.; Benzoni, G.; Bernards, C.; Biswas, D.; Bocchi, G.; Bottoni, S.; Britton, R.; Bruyneel, B.; Burnett, J.; Cakirli, R. B.; Carroll, R.; Catford, W.; Cederwall, B.; Celikovic, I.; Cieplicka, N.; Clement, E.; Cooper, N.; Crespic, F.; Csatlos, M.; Czerwinski, M.; Danu, L.; Davies, A.; Didierjean, F.; Drouet, F.; Duchene, G.; Ducoin, C.; Eberhardt, K.; Erturk, S.; Fraile, L. M.; Gottardo, A.; Grente, L.; Grocutt, L.; Guerrero, C.; Guinet, D.; Hartig, A.-L.; Henrich, C.; Ignatov, A.; Ilieva, S.; Ivanova, D.; John, B.; John, R.; Jolie, J.; Kisyov, S.; Konstantinopoulos, T.; Korgul, A.; Krasznahorkay, A.; Kröll, T.; Kurpeta, J.; Kutiu, I.; Lalkovski, S.; Larijani, C.; Leguillon, R.; Lica, R.; Litaize, O.; Magron, C.; Mancuso, C.; Ruiz Martinez, E.; Massarczyk, R.; Mazzocchi, C.; Melon, B.; Mengoni, D.; Million, B.; Mokry, C.; Mukhopadhyay, S.; Mulholland, K.; Nannini, A.; Napoli, D. R.; Olaizola, B.; Orlandi, R.; Patel, Z.; Paziy, V.; Petrache, C.; Pfeiffer, M.; Podolyak, Z.; Ramdhane, M.; Redon, N.; Regan, P.; Regis, J. M.; Regnier, D.; Oliver, R. J.; Rudigier, M.; Runke, J.; Rzaca-Urban, T.; Saed-Samii, N.; Salsacq, M. D.; Scheck, M.; Schwengner, R.; Sengele, L.; Simpson, G.; Singh, P.; Smith, J.; Stezowski, O.; Szpak, B.; Thomas, T.; Thürauf, M.; Timaru, J.; Toml, A.; Tomandl, I.; Tornyi, T.; Townsley, C.; Tuerler, A.; Valenta, S.; Vancraeyenest, A.; Vandone, V.; Vanhoy, J.; Vedia, V.; Warr, N.; Werner, V.; Wilmsen, D.; Wilson, E.; Zerrouki, T.; Zielinska, M.;
In the EXILL campaign a highly efficient array of HPGe detectors was operated at the cold neutron beam instrument PF1B of the Institut Laue-Langevin to carry out nuclear structure studies, via measurements of -rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent
flux of about 108 s-1 cm-2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM clover detectors, four to six
anti-Compton shielded large coaxial GASP detectors and two smaller clover detectors. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The trigger-less acquisition system allowed an event collection rate of up to 6 × 105 Hz. From triggerless collected data it was possible to construct decay schemes and in combination with the FATIMA array of LaBr3 detectors to analyze half-lives of excited levels in the pico- to micro-second range. Precise energy and efficiency calibrations of EXILL were performed using 27Al(n,γ)28Al and 35Cl(n,γ)36Cl reactions in the energy range from 30 keV up to 10 MeV.
Keywords: neutron-induced fission; 235U; 241Pu; (n,γ)-reactions; Ge detectors; angular correlations; multiple-γ coincidences.

Publ.-Id: 25806 - Permalink


Nuclear-Physics Experiments at the Bremsstrahlung Facility γELBE
Schwengner, R.; Wagner, A.;
The γELBE facility at HZDR is described.
Keywords: electron accelerator, bremsstrahlung, HPGE detectors

Publ.-Id: 25805 - Permalink


Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263]