Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
On the surface wettability heterogeneities in fine particle separation technologies - inverse Gas Chromatography investigations and interface interaction studies
Rudolph, M.; Sygusch, J.;
Fine particle separation is a challenging task and relies on a proper understanding of interfacial properties. In our research the focus lies on the process of flotation, which is a heterocoagulation separation method for fine particles in aqueous dispersions (size range approx. 5 µm < x <200 µm). It has been used in large extent for several decades and with billions of tons of particles processed per annum in the mining industry to separate valuable mineral particles from worthless ones. The main principle of separation is the particles' differences in wettability. This wettability is influenced by controlled selective adsorption of amphiphilic molecules rendering most typically the valuable containing minerals hydrophobic. Usually the particle property "wettability" is being quantified with a water contact angle. However, this value is not only difficult to assess for particles but furthermore through Young's equation a function of the surface free energy, which is a complex parameter as a result of various interatomic/intermolecular interactions. Using iGC we show how to characterize these complex wettability properties of particles assessing the heterogeneity of disperse and acid base specific surface free energies. These complex values are used in accordance to an approach by van Oss to formulate a new wettability parameter for flotation which is the specific free energy of interaction between a particle and a gas bubble immersed in water. We are presenting the general approach and results from various mineral collector systems and give insights to the boundary conditions and the general calculation scheme. In a recent trial we show the predictive power of the results. Furthermore we show how iGC can be put in context to other interaction investigations using flotability, contact angle measurements and colloidal probe atomic force microscopy.
  • Invited lecture (Conferences)
    1st European Symposium on Sorption Science, 05.-07.09.2018, Wien, Österreich

Publ.-Id: 28381 - Permalink


The Effect of Tin on the Formation and Properties of Pt/MgAl(Sn)Ox Catalysts for Dehydrogenation of Alkanes
Belskaya, O. B.; Stepanova, L. N.; Nizovskii, A. I.; Kalinkin, A. V.; Erenburg, S. B.; Trubina, S. V.; Kvashnina, K. O.; Leont’Eva, N. N.; Gulyaeva, T. I.; Trenikhin, M. V.; Bukhtiyarov, V. I.; Likholobov, V. A.;
The MgAl(Sn) layered double hydroxides (LDH) with the atomic ratios Mg/(Al+Sn) = 3 and Sn/(Sn+Al) = 0, 0.002, 0.005, 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 1.0 were synthesized and the ratio Sn/(Sn+Al) ≤ 0.1 was shown to provide the formation of systems with uniform phase composition. Mixed oxides derived from LDH retain the high specific surface area of 150-200 m2/g and the basic properties when some aluminium atoms are replaced with tin. It was found that the Sn-containing mixed oxides are able to restore the layered structure during rehydration and intercalate the anion precursors of platinum into the interlayer space of the formed LDH.
The emerging platinum sites initiate the reduction of tin at temperatures below 723 K. TEM, EXAFS and XPS studies demonstrated that tin introduction in the support increases the dispersion of supported platinum. An extreme dependence of the activity of Pt/MgAl(Sn)Ox catalysts in propane and n-decane dehydrogenation on the tin content in the support was revealed. The active catalysts are characterized by the phase and elemental uniformity of the support, highly disperse state of Pt(0), and the absence of a noticeable amount of reduced tin and bimetallic particles.

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  • Secondary publication expected from 05.12.2019

Publ.-Id: 28380 - Permalink


An investigation of the recovery and kinetics during the flotation of residual petroleum coke in lime calcination exhaust tailings
Vaziri Hassas, B.; Guven, O.; Hassanzadeh, A.;
Flotation is one of the feasible separation methods suggested for recovery of petroleum coke from the tailings of lime calcination furnaces. In this study, analyses of ash content and calorific value of petroleum coke in lime calcination tailings were used to measure its floatability and product quality. In addition, seven most common flotation kinetics models were fitted to the obtained experimentalm data. Based on the maximum recovery, minimum ash content, and maximum calorific value of the flotation products, optimum dosages for collector (kerosene) and frother (MIBC) were found 30 g/t and 60 g/t, respectively. Regarding the flotation kinetic modeling and the obtained sum of squared errors (SSEs), Agar and Klimpell models were found to have the best and the poorest fits to the experimental data, respectively. Finally, it was concluded that new statistical concepts such as information criteria (IC) and non-linear generalized least squares estimation (NLGLSE) must be applied to the process of model selection owing to consideration of goodness of fit, complexity of a model and model consistency.
Keywords: Reagent optimization; flotation rate constant; flotation kinetic model; petroleum coke

Publ.-Id: 28379 - Permalink


Explaining metal zonation at the Lisheen deposit
Frenzel, M.ORC; Burisch, M.; Röhner, M.; Gilbert, S.; Cook, N. J.; Ciobanu, C. C.; Güven, J.; Gutzmer, J.
  • Lecture (others)
    16th Freiberg Shortcourse in Economic Geology - "Zinc Deposits", 04.12.2018, Freiberg, Deutschland

Publ.-Id: 28378 - Permalink


Stratified and Segregated Flow Modelling - AIAD 2018
Höhne, T.;
Today: Limits in simulating stratified & segregated two phase flow
Algebraic Interfacial Area Density Model (AIAD)
Free Surface Drag
Turbulence Damping
Sub-grid wave turbulence (SWT)
Verification and Validation is going on – more experimental data are required for the validation
Keywords: AIAD, Free Surface Drag, Sub-grid wave turbulence (SWT)
  • Lecture (Conference)
    16th Short Course “Multiphase Flow: Simulation,Experiment and Application", 13.-16.11.2018, Dresden, Deutschland
  • Contribution to proceedings
    16th Short Course “Multiphase Flow: Simulation,Experiment and Application, 13.-16.11.2018, Dresden, Deutschland
  • Poster
    16th Short Course “Multiphase Flow: Simulation,Experiment and Application, 13.-16.11.2018, Dresden, Deutschland

Publ.-Id: 28377 - Permalink


Spin-Wave Modes in Transition from a Thin Film to a Full Magnonic Crystal
Langer, M.; Gallardo, R. A.ORC; Schneider, T.; Stienen, S.; Roldán-Molina, A.; Yuan, Y.; Lenz, K.ORC; Lindner, J.; Landeros, P.ORC; Fassbender, J.ORC
Surface-modulated magnonic crystals are the natural link between continuous films with sinusoidal spin-wave eigenmodes and one-dimensional magnonic crystals composed of individual nanowires. Nevertheless, the transformation process of the spin-wave modes in this transition remains yet unclear. Here, spin-wave modes in their entire transition from a flat film to a ‘full’ (one-dimensional) magnonic crystal are studied by ferromagnetic resonance (FMR) and micromagnetic simulations. For this purpose, the surface of a pre-patterned thin permalloy film was sequentially ion milled resulting in hybrid structures, referred to as surface-modulated magnonic crystals, with increasing modulation depth. After each step, FMR measurements were carried out in backward-volume and Damon-Eshbach geometry. The evolution of each spin-wave resonance is studied together with the corresponding mode profile obtained by micromagnetic simulations. Simple rules describing the transition of the modes from the film to the modes of the full magnonic crystal are provided unraveling the complexity of spin-wave states in these hybrid systems.
Keywords: spin waves, ferromagnetic resonance, magnonic crystals, band structure, magnonics, thin films, magnetism

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Publ.-Id: 28375 - Permalink


On the Chemistry and Diffusion of Hydrogen in the Interstitial Space of Layered Crystals h‐BN, MoS2, and Graphite
An, Y.; Kuc, A. B.ORC; Petkov, P.; Lozada-Hidalgo, M.; Heine, T.
Recent experiments have demonstrated transport and separation of hydrogen isotopes in layered materials, such as hexagonal boron nitride and molybdenum disulphide. Here, based on first-principles calculations combined with well-tempered metadynamics simulations, we report the chemical interactions and mobility of protons (H+) and protium (H atoms) in the interstitial space of these layered materials. We show that both H+ and H can be transported between the layers of h-BN and MoS2 with low free energy barriers, while they are immobilized in graphite, in accordance with the experimental observations. In h-BN and MoS2, the transport mechanism involves a hopping process between the adjacent layers, which is assisted by the low- energy phonon shear modes. Defects present in MoS2 suppress the transport and act as traps for H species.

Publ.-Id: 28373 - Permalink


Functionalized DNA Origami Structures for Molecular Electronics
Bayrak, T.; Helmi, S.; Ye, J.; Martinez-Reyes, A.; Samano-Tirado, E.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nano-electronics and nano-photonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanomolds and nanosheets are used for the fabrication of nano-electronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanomolds and nanosheets create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanomold and nanosheet based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires based on nanomold structure showed metallic conductance. The other wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Poster
    IHRS NanoNET Annual Workshop, 05.-07.09.2018, Bad Gottleuba, Germany

Publ.-Id: 28372 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Ye, J.; Helmi, S.; Martinez-Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nano-electronics and nano-photonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanomolds and nanosheets are used for the fabrication of nano-electronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanomolds and nanosheets create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanomold and nanosheet based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires based on nanomold structure showed metallic conductance . The other wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Poster
    CECAM/Psi-k research conference: BioMolecular Electronics (BIOMOLECTRO), 27.-31.08.2018, Madrid, Spain

Publ.-Id: 28371 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Ye, J.; Helmi, S.; Martinez-Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications.
This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanoMOLDS are used for the fabrication of nanoelectronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanoMOLDS and create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanoMOLD based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires showed metallic conductance. The other two wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Poster
    13th HZDR PhD Seminar, 05.-07.11.2018, Usti nad Labem, Czech Republic

Publ.-Id: 28370 - Permalink


Electrical transport study as a function of temperature on a C-shape gold nanowire templated by a DNA origami
Bayrak, T.; Martinez-Reyes, A.; Ruiz-Arce, D.; Kelling, J.; Samano, E.; Erbe, A.;
Small DNA origami templates 90 nm x 70 nm DNA origami nanosheets with three functionalized sides holding a total of eight capture strands for decoration with gold nanoparticles were fabricated. Electroless gold growth is applied to selectively grow the gold nanoparticles until they merge into continuous nanowires. Finally, this work demonstrates the application of shape-controlled C-shaped gold wires as precisely tailored metal contacts to single, isolated nanowires to better understand the charge transport characteristics at different temperatures.
  • Lecture (Conference)
    DNA Mitteldeutschland, 24.05.2018, Leibniz IPHT Jena, Germany

Publ.-Id: 28369 - Permalink


DNA Origami templated assembly of metallic nanowires
Bayrak, T.; Erbe, A.;
The DNA origami method provides a programmable bottom up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nano-electronics and nano-photonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanomolds1,2 and nanosheets are used for the fabrication of nano-electronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanomolds and nanosheets create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanomold and nanosheet based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires based on nanomold structure showed metallic conductance.1 The other wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Lecture (Conference)
    PhD Seminar HZDR, 07.05.2018, Dresden, Germany

Publ.-Id: 28368 - Permalink


DNA origami sheet based C-shaped conducting nanowires
Bayrak, T.; Martinez-Reyes, A.; Ruiz-Arce, D.; Kelling, J.; Samano, E.; Erbe, A.;
Small DNA origami templates 90 nm x 70 nm DNA origami nanosheets with three functionalized sides holding a total of eight capture strands for decoration with gold nanoparticles were fabricated. Electroless gold growth is applied to selectively grow the gold nanoparticles until they merge into continuous nanowires. Finally, this work demonstrates the application of shape-controlled C-shaped gold wires as precisely tailored metal contacts to single, isolated nanowires to better understand the charge transport characteristics at different temperatures.
  • Lecture (Conference)
    BAC Retreat, 25.06.2018, Rathen, Germany

Publ.-Id: 28367 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Helmi, S.; Ye, J.; Kelling, J.; Schönherr, T.; Erbe, A.; Seidel, R.;
The DNA origami method provides a programmable bottom up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications.
This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanoMOLDS are used for the fabrication of nanoelectronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanoMOLDS and create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanoMOLD based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires showed metallic conductance. The other two wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Poster
    DPG Meeting Berlin, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 28366 - Permalink


Functionalized DNA Origami Nanostructures for Molecular Electronics
Bayrak, T.; Helmi, S.; Ye, J.; Martinez-Reyes, A.; Samano-Tirado, E.; Seidel, R.; Erbe, A.;
The DNA origami method provides a programmable bottom up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nano-electronics and nano-photonics device fabrications. This technique enables the precise positioning of metallic and semiconducting nanoparticles along the DNA nanostructures. In this study, DNA origami nanomolds1,2 and nanosheets are used for the fabrication of nano-electronic devices. To this end, electroless gold deposition is used to grow the AuNPs within the DNA origami nanomolds and nanosheets create eventually continues nanowires. In order to contact the fabricated nanostructues electrically, a method using electron-beam lithography was developed. The DNA origami nanomold and nanosheet based metallic wires were electrically characterized from room temperature down to 4.2K.
Temperature-dependent characterizations for four wires exhibiting different conductance at RT were performed in order to understand the dominant conductance mechanisms from RT to 4.2K. Two of these nanowires based on nanomold structure showed metallic conductance.1 The other wires deviated from pure metallic behavior and they showed thermionic, hopping and tunneling charge transport mechanism.
  • Lecture (Conference)
    3rd Functional DNA Nanotechnology Workshop, 06.-08.06.2018, Rome, Italy

Publ.-Id: 28364 - Permalink


Thermal dependence of large scale freckle defect formation
Kao, A.; Shevchenko, N.; Alexandrakis, M.; Krastins, I.; Eckert, S.; Pericleous, K.;
The fundamental mechanisms governing macroscopic freckle defect formation during directional solidification are studied experimentally in a Hele-Shaw cell for a low melting point Ga-25wt.%In alloy, and modelled numerically in 3D using a microscopic parallelised Cellular Automata lattice Boltzmann method. The size and distribution of freckles (long solute channels, or chimneys) is shown to be strongly dependent on the thermal profile of the casting, with flat, concave and convex isotherms being considered. For the flat isotherm case, no large-scale freckles form, while for concave or convex isotherms large freckles appear but in different locations. The freckle formation mechanism is as expected buoyancy-driven, but the chimney stability, its long-term endurance and its location, are shown to depend critically on the detailed convective transport through the inter-dendritic region. Flow is generated by curved isopleths of solute concentration. As solute density is different from that of the bulk fluid, gravity causes ‘uphill´ or ‘downhill’ lateral flow from the sample centre to the edges through the mush, feeding the freckle. An excellent agreement is obtained between the numerical model and real-time x-ray observations of a solidifying sample under strictly controlled temperature conditions.
Keywords: Freckle defect formation, Ga-In alloy, Convective transport

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  • Secondary publication expected from 22.04.2020

Publ.-Id: 28363 - Permalink


Organische Chemie XV - Stereoselektive Reaktionen, Naturstoffsynthese, Syntheseplanung - Retrosynthese
Mamat, C.;
Im ersten Teil dieses letzten Studienheftes wollen wir uns mit Reaktionen vertraut machen, bei denen aus einer prochiralen Verbindung selektiv chirale Verbindung gebildet wird, bei der ausschließlich eines der beiden Stereoisomere mit Chiralitätszentrum entsteht. Aus den Studienheften davor wissen wir schon, dass aus nichtchiralen Verbindungen mit prochiralem Zentrum meist Racemate entstehen. Faktoren, die zu einer Bevorzugung eines der beiden Stereoisomere führen, werden wir uns genau anschauen.
Im zweiten Teil wollen wir uns mit Retrosynthese und Syntheseplanung beschäftigen. Ausgehend von teils komplizierten Molekülen und Strukturen werden Sie sehen, wie durch eine gedankliche „Rückwärtsreaktion“ (Zerlegung in Bestandteile) ein Syntheseplan erstellt werden kann. Dazu wird das Zielmolekül immer weiter in seine Bestandteile, also hypotetische Ausgangsstoffe, zerlegt.
Keywords: Wittig-Reaktion, Walden-Umkehr, Auxiliar, Zerlegung, Totalsynthese
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    44 Seiten

Publ.-Id: 28362 - Permalink


Organische Chemie XIV - Metallorganische Verbindungen und Übergangsmetallkatalyse
Mamat, C.;
Elementorganische Verbindungen sind uns schon ganz am Anfang dieses Studiums seit dem ersten Studienheft über den Weg gelaufen. Bisher haben wir uns auf Substanzen beschränkt, die Hauptgruppenmetalle wie Magnesium, Natrium oder Lithium beinhalten. Denken Sie dabei zum Beispiel an die Aldol-Reaktion. Aber auch ein typisches Nebengruppenelement, nämlich das Zink, haben wir uns angeschaut.
Für Sie ist wichtig zu wissen, welche Bindungsverhältnisse in diesen metallorganischen Verbindungen vorherrschen. Das betrifft insbesondere die Umpolung der Bindung des Kohlenstoffs, wenn er an Metallen gebunden ist im Vergleich zur Bindung von elektronegativeren Elementen, wie den Halogenen, Stickstoff, Sauerstoff oder auch Schwefel. Damit soll klarwerden, dass dieses Kohlenstoffatom dann carbanionisch reagiert.
Keywords: Grignard, Kreutzkupplung, Metallorganyle, Komplexe, Katalysatoren
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0045 Seiten

Publ.-Id: 28361 - Permalink


Organische Chemie XIII - Umlagerungen und Elektrocyclische Reaktionen
Mamat, C.;
Das Ziel des ersten Teils dieses Studienheftes besteht darin, ein Gefühl beziehungsweise Verständnis von Nebenreaktionen zu bekommen, die beispielsweise bei nucleophilen Substitutionsreaktionen oder Additionen und Eliminierungen auftreten. Diese Nebenreaktionen sind meist Umlagerungen, haben teilweise ihren eigenen Mechanismus und führen vielfach zu unerwarteten Produkten, wie wir schon in der Vergangenheit sehen konnten. Wir werden uns intensiv damit beschäftigen, ob und wie diese Umlagerungen beeinflusst werden können und welche Varianten es gibt.
Des Weiteren werden wir schauen, welche weiteren Umlagerungen existieren und welche Produkte zu erwarten sind. Am Ende werden wir einen Blick auf elektrocyclische Reaktionen werfen und sehen, dass durch deren Übergangszustände und Zwischenstufen stereoselektiv Produkte gebildet werden.
Keywords: Wasserstoffwanderung, Alkylgruppenwanderung, Claisen-Reaktion,Cope-Reaktion, Abbaureaktionen
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0043 Seiten

Publ.-Id: 28360 - Permalink


Organische Chemie XII - Stereoisomerie
Mamat, C.;
Nachdem wir uns in der Organischen Chemie I in der Hauptsache mit Stoffklassen, funktionellen Gruppen und wichtigen Reaktionen beschäftigt haben und in der Organischen Chemie II die Reaktionsmechanismen genau beleuchteten, wollen wir uns im dritten Teil mit speziellen Themen der organischen Chemie beschäftigen. In diesem Studienheft wollen wir uns einzig und allein mit der Anordnung der Atome in Molekülen und den damit verbundenen Besonderheiten dieser Moleküle beschäftigen. Doch warum brauchen wir das ganze Wissen über den exakten Aufbau der Moleküle? Es ist speziell für die Pharmazie und Biochemie von grundlegender Bedeutung, genau zu wissen, wie Moleküle aufgebaut sind. Denn mit exakt der gleichen Summenformel, selbst mit gleicher Aneinanderreihung der Atome können unterschiedliche Wirkungen auftreten.
Deshalb werden wir noch einmal genau beleuchten, was Isomere sind und welche Arten es gibt. Dann werden wir uns die Auswirkungen anschauen, die vier unterschiedliche Substituenten an einem Kohlenstoffatom haben. Wichtig ist, dass Sie verstehen, dass unterschiedliche Stoffe oder Verbindungen da sind, wenn Sie die Stellung (Anordnung) der Substituenten im Molekül „vertauschen“. Zudem sollten Sie mit dem Begriff Stereoisomerie sicher umgehen können und wissen, was für Isomere da existieren und was das für Folgen auf die Reaktivität des Moleküls hat. Darauf aufbauend finden wir Moleküle, in denen mehr als ein Chiralitätszentrum existiert. Welche Auswirkungen das auf die Eigenschaften des Moleküls hat, werden wir am Schluss sehen.
Keywords: Isomere, Enantiomere, prochiral, Chiralität
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0039 Seiten

Publ.-Id: 28359 - Permalink


Symmetry Breaking of Azimuthal Magnetorotational Instability Caused by Thermal Boundary Conditions
Seilmayer, M.; Stefani, F.;
The first evidence of azimuthal magnetorotaional instability was given some years ago by Seilmayer et al. (2014). A Taylor Couette Setup, filled with liquid metal, was exposed to magnetic field Bφ ~ r^ -1. The necessary current was supplied by a large frame of copper rods which caused a residual m=1 field disturbance. This imperfection caused a stationary dominant background flow. Since then, several changes took place to circumvent external asymmetries and influences. The main improvement was the symmetric current return path which eliminates the m=1 background flow and reduces stray fields. Now the AMRI wave is mainly located at the top of the cylinder, which is surprising since the theoretical prediction allows a symmetric wave with m=±1 configuration. However, the wave component from below is missing. Recent work indicate that thermal convection could be a possible source of symmetry breaking. We present experimental results which give evidence to the strong dependency on thermal boundary conditions which affect AMRI action in the volume.
Keywords: AMRI, MRI, Taylor Couette, magnetorotational instability
  • Poster
    MHD Days and GDRI Dynamo Meeting, 26.-28.11.2018, Dresden, Deutschland

Publ.-Id: 28358 - Permalink


Thallium pollution in China and removal technologies for waters: A review
Liu, J.; Luo, X.; Sun, Y.; Tsang, D. C. W.; Qi, J.; Zhang, W.; Li, N.; Yin, M.; Wang, J.; Lippold, H.; Chen, Y.; Sheng, G.;
Thallium (Tl) is a typical toxic metal, which poses a great threat to human health through drinking water and the food chain (biomagnification). China has rich Tl-bearing mineral resources, which have been extensively explored and utilized, leading to release of large amounts of Tl into the environment. However, research on Tl pollution and removal techniques is relatively limited, because Tl has not been listed within the scope of environmental monitoring in China for several decades. This paper reviewed Tl pollution in wastewater arising from various industries in China, as well as the latest available methods for treating Tl-containing industrial wastewater, in order to give an outlook on effective technologies for controlling Tl pollution. Conventional physical and chemical treatment technologies are efficient at removing trace amounts of Tl, but it proved to be difficult to achieve the stringent environmental standard (≤0.1–5 μg/L) cost-effectively. Adsorption by using newly developed nanomaterials, and metal oxide modified polymer materials and microbial fuel cells are highly promising and expected to become next-generation technologies for remediation of Tl pollution. With the potential for greater Tl contamination in the environment under accelerated growth of industrialization, researches based on lab-scale implementation of such promising treatment technologies should be further expanded to pilot and industrial scale, ensuring environmental protection and the safety of drinking water for sustainable development. Comprehensive insights into experiences of Tl pollution in China and in-depth perspectives on new frontier technologies of Tl removal from wastewaters will also benefit other nations/regions worldwide, which are susceptible to high exposure to Tl likewise.
Keywords: Thallium pollution; Industrial wastewater treatment; Anthropogenic source; Nanomaterials

Publ.-Id: 28357 - Permalink


Fine grinding characteristics of a cassiterite-bearing skarn ore
Buchmann, M.; Leißner, T.; Kern, M.; Schach, E.; Tolosana-Delgado, R.; Rudolph, M.; Gutzmer, J.; Peuker, U. A.;
The grinding characteristic of a cassiterite-bearing skarn ore was investigated for the fine particle size range using an agitated ball mill. The applicability of Mineral Liberation Analyzer was investigated for the fine particle range. The appropriate liberation of cassiterite was determined with the help of tangible parameters such as the degree and coefficient of liberation and grade-recovery diagrams. The liberation of cassiterite was found to be in a satisfying range for downstream upgrading. A more etailed analysis of the liberation characteristics of the potential valuables together with a better understanding of the breakage characteristics of the gangue minerals will help to optimize the operation of the subsequent upgrading process. Therefore, the breakage behavior of the most important gangue minerals was analyzed. The effect of selectivity in breakage for the different minerals became visible.
A clear spreading for the mineral recovery versus size class indicated a mineral specific accumulation during milling. These trends lead to the assumption that the separation of the minerals into different particle size classes can be optimized by applying a specific energy input.
  • Contribution to proceedings
    European Mineral Processing and Recycling Congress (EMPRC) 2018, 22.06.2018, Essen, Germany

Publ.-Id: 28355 - Permalink


Evaluation of Magnetic Separation Efficiency on a Cassiterite-Bearing Skarn Ore by Means of Integrative SEM-Based Image and XRF–XRD Data Analysis
Buchmann, M.; Schach, E.; Tolosana-Delgado, R.; Leißner, T.; Astoveza, J.; Kern, M.; Möckel, R.; Ebert, D.; Rudolph, M.; van den Boogaart, K. G.;
Image analysis data obtained from scanning electron microscopy provided data for a detailed evaluation of the separation efficiency for various processes involving the beneficiation of particulate materials. A dry magnetic separation by a drum type magnetic separator served as a case study to visualize effects of processing of a skarn ore with a high content of cassiterite as ore mineral (~4 wt%). For this material, iron oxides and silicates are the main gangue mineral groups. Based on the obtained data, partition curves were generated with the help of local regression.
From the partition curves, the separation efficiency was evaluated and the relevant particle properties deduced. A detailed analysis of the bias of the quantitative mineralogical data is presented. This bias was monitored and further analyzed in detail. Thorough analysis of feed and products of magnetic separation enabled identification of the most important factors that control losses of cassiterite to the magnetic product, namely the association with iron oxides and particle sizes below ~40 µm.
The introduced methodology is a general approach applicable for the optimization of different separation processes and is not limited to the presented case study.
Keywords: SEM-based image analysis; MLA (Mineral Liberation Analyzer); magnetic separation; cassiterite; partition curve; local regression

Publ.-Id: 28354 - Permalink


The inherent link between ore formation and geometallurgy as documented by complex tin mineralization at the Hämmerlein deposit (Erzgebirge, Germany)
Kern, M.; Kästner, J.; Tolosana-Delgado, R.; Jeske, T.; Gutzmer, J.;
A comprehensive quantitative mineralogical study on the Hämmerlein tin deposit in the Erzgebirge, Germany, not only yields insights into the genesis of Sn mineralization but also provides also important clues for beneficiation. The lithological units of the skarn and greisen deposit show significant differences in modal mineralogy and Sn deportment. These systematic differences are attributed to several stages of ore formation. Of greatest significance is a paragenetically late cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage replaces pre-existing skarn lithologies and also forms stockwork mineralization in greisen-type ores developed at the expense of mica schist that surrounds the skarn. The co-genetic formation of the cassiterite-chlorite-fluorite-sulfide assemblage is captured by the mineral association parameter—a parameter that can be easily quantified from data acquired during automated mineralogy studies. To document the preferred mineral association, a ratio is introduced that illustrates how closely cassiterite—the only Sn mineral of economic relevance—is associated with chlorite, fluorite, and sulfides. This socalled MAMA ratio illustrates the strongly preferred association between cassiterite and chlorite. The results also illustrate that the abundance of rock-forming chlorite may be used as a proxy for the abundance of the much less common cassiterite. This proxy is well-suited to sort ore from poorly mineralized/unmineralized rock fragments early during the beneficiation process. Such separation may well be achieved by using a short wave infrared detector that is already deployed in commercially available sorting equipment. The case study illustrates the inherent link between the processes responsible for ore genesis, the definition of geometallurgical domains, and the selection of suitable beneficiation strategies.

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  • Secondary publication expected

Publ.-Id: 28351 - Permalink


Reconfigurable spin-wave non-reciprocity induced by dipolar interaction in a coupled ferromagnetic bilayer
Gallardo, R. A.ORC; Schneider, T.; Chaurasiya, A. K.; Oelschlägel, A.; Arekapudi, S. S. P. K.ORC; Roldáan-Molina, A.; Hübner, R.; Lenz, K.ORC; Barman, A.ORC; Fassbender, J.ORC; Lindner, J.; Hellwig, O.; Landeros, P.ORC
Non-reciprocity of wave phenomena describes the situation where wave dispersion depends on the sign of the wave-vector, i.e., counter-propagating waves exhibit di↵erent wavelengths for the same frequency. Such behavior has been recently observed in heavy-metal/ferromagnetic interfaces with Dzyaloshinskii-Moriya coupling, and has also been known for coupled magnetic bilayers, where non-reciprocity is enhanced when the two layers are antiparallel aligned. Besides the conventional uses of spin-waves, non-reciprocity adds further functionalities, such as its potential applications in communications technologies and logical operations. In the current manuscript, we thus examine the spin-wave non-reciprocity induced by dipolar interactions in a coupled bilayer consisting of two ferromagnetic layers separated by a non-magnetic spacer. We derive an easy-to-use formula to estimate the frequency di↵erence provided by the non-reciprocity, which allows for choosing an optimal system in order to maximize the e↵ect. For small wave-numbers, non-reciprocity scales linearly, while for larger wave-vectors the non-reciprocity behaves non-monotonically, with a well-defined maximum. The study is carried out by means of analytical calculations that are complemented by micromagnetic simulations. Furthermore, we confirmed our model by experimental investigation of the spin-wave dispersion in a prototype antiparallel-coupled bilayer system. Since the relative magnetic orientation can be controlled through a bias field, the magnon non-reciprocity can be then turned on and o↵, which lends an important functionality to the coupled ferromagnetic bilayers.
Keywords: non-reciprocity, spin waves, ferromagnetic resonance, Brillouin Light Scattering, magnetism, Dzyaloshinskii-Moriya interaction, dispersion relation

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Publ.-Id: 28349 - Permalink


Synthese von deuterierten Oxocortisolderivaten
Hocke, V.;
Ziel dieser Masterarbeit war die Synthese der Steroidderivate 18-Oxocortisol (8a) und dessen deuteriertes Analogon 1,2-2H2-18-Oxocortisol (8b). Die Darstellung erfolgte ausgehend vom strukturell ähnlichen Prednisolon (1). Dazu mussten zunächst orthogonale Schutzgruppen eingeführt werden, um selektiv Modifizierungen an der Steroidstruktur vornehmen zu können. Im Anschluss musste die 18-Methylgruppe funktionalisiert werden um die Einführung der Aldehydfunktion zu ermöglichen. Nach der darauffolgenden Entschützung sollte Derivat 7 erhalten werden, das sich von 8a und 8b lediglich in der C=C-Doppelbindung zwischen den Kohlenstoffatomen C-1 und C-2 unterschiedet und durch selektive Hydrierung oder Deuterierung dieser zu den Zielverbindungen umgesetzt werden kann.
Keywords: 18-Oxocortisol, Deuterium
  • Master thesis
    HTW Dresden, 2018
    Mentor: Dr. habil. Constantin Mamat
    0063 Seiten

Publ.-Id: 28348 - Permalink


Process Analytical Techniques
Hampel, U.;
The lecture gives an introduction to modern process analytical techniques in the industry and research.
Keywords: process analytical techniques
  • Invited lecture (Conferences)
    TOMOCON 1st Summer School, 26.-28.09.2018, Lublin, Poland

Publ.-Id: 28347 - Permalink


High-Resolution Flow Measurement Techniques for the Generation of Validation Data in Nuclear Thermal Hydraulics Experiments
Hampel, U.;
The past years have seen a tremendous increase in computational power and hence a trend to employ more and more advanced numerical tools for the analysis of nuclear thermal hydraulics. Primary applications are accident analyses as well as safety assessment for new reactor systems and prominent directions are 3D computational multiphase fluid dynamics, coupled codes, and advanced BEPU analyses. While years ago it was believed that one day such tools may be able to replace experiments fully or in part, it is meanwhile commonly accepted, that a focus must be given on validation experiments for single effect problems and that such validation experiments should be preferably at original system t/h conditions to account for difficult upscaling conditions, and that such experiments need new instrumentation in order to get CFD grade data. The latter means field quantities of phase fraction, velocity and temperature at high spatial and temporal resolution.
The lecture gives an in-depth overview over novel field measuring techniques for nuclear thermal hydraulics experiments. We will briefly touch the field of distributed sensors for phase fraction, temperature and velocity and then dive into the field of advanced imaging techniques. We will discuss the application of well-known imaging techniques, such as high speed videometry, PIV and IR thermography and then come to computed tomography techniques, which are very useful to study multiphase problems. The methodological description of the basic physics and technology will be accompanied by application examples in nuclear safety research being pursued at the TOPFLOW facility at Helmholtz-Zentrum Dresden-Rossendorf.
Keywords: Flow measurement, multiphase flow, reactor safety, nuclear thermal hydraulics, tomography
  • Invited lecture (Conferences)
    The Frédéric Joliot / Otto Hahn Summer School on Nuclear Reactors "Maximizing the Benefits of Experiments for the Simulation, Design and Analysis of Reactors", 22.-31.08.2018, Aix en Provence, Frankreich

Publ.-Id: 28346 - Permalink


Recent developments and future trends in tomographic imaging for multiphase flows
Hampel, U.;
The presentation gives a overview over recent activities in the field of tomographic imaging for multiphase flows.
Keywords: Multiphase flow, imaging techniques, process tomography
  • Invited lecture (Conferences)
    International Workshop on Multiphase Flow Imaging and Measurement, 13.-14.08.2018, Tianjin, China

Publ.-Id: 28345 - Permalink


TOMOCON: A Marie Skłodowska-Curie European Training Network on Tomography-based Control in Industrial Processes
Hampel, U.; Wondrak, T.; Fjeld, M.; Mudde, R.; Portela, L. M.; Kenjeres, S.; Legendre, D.; Link, G.; Koiranen, T.; Hlava, J.; Babout, L.; Jackowska-Strumiłło, L.; Soleimani, M.; Vauhkonen, M.; Lähivaara, T.; Rymarczyk, T.; Trepte, M.; Voutilainen, A.; Rodriguez, M.; Bos, J.; Betz, S.; Hysky, J.; Pennerstorfer, P.; Goldammer, M.; Matten, C.; Hoffmann, R.; Gingras, J.-P.; van der Plas, D.; Veenstra, P.; Nurmi, J.; Pudack, C.; Da Silva, M. J.;
The European Doctoral Training Network “Smart Tomographic Sensors for Advanced Industrial Process Control (TOMOCON)” gathers academic and industrial partners from different sectors with the mission to develop new fundamentals and technological solutions of advanced industrial control by tomographic sensors. It has received funding by the EU under the Marie Skłodowska-Curie scheme as an Innovative Training Network. It runs from September 2018 to August 2022 with 15 Early Stage Researchers, who are working as PhD students in 10 different European academic institutions. Within their research projects the doctoral students receive an extensive training in various fields of engineering and natural sciences being carried out in the frame of so called secondments at different industrial and academic partners as well as via three dedicated Summer Schools. The network is further supported by an Advisory Board with members from leading institutions in the field of process tomography.
Keywords: Marie Skłodowska-Curie Innovative Training Network, Process Tomography, Process Control, Process Modelling, Doctoral Education and Training
  • Lecture (Conference)
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
  • Open Access LogoContribution to proceedings
    9th World Congress on Industrial Process Tomography, 02.-06.09.2018, Bath, UK
    Proceeding of the 9th World Congress on Industrial Process Tomography

Publ.-Id: 28344 - Permalink


Leaching of U(VI) and Cm(III) doped calcium (aluminum) silicate hydrate gel (C-(A)-S-H) and tobermorite in saline brines
Wolter, J. M.; Schmeide, K.; Huittinen, N.; Bok, F.; Weiss, S.; Brendler, V.; Stumpf, T.;
To evaluate the retention potential of concrete inside a nuclear waste repository for actinides under saline and hyperalkaline conditions, leaching experiments with actinide doped cementitious phases were performed in repository-relevant brines. Therefore, U(VI) and Cm(III) doped calcium silicate hydrate (C-S-H) phases with different calcium-to-silicon (C/S) ratios (1.0−2.0) were synthesized directly in presence of either U(VI) or Cm(III) and characterized by time-resolved laser-induced luminescence spectroscopy (TRLFS), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The time-dependent release of Ca, Si, U or Cm from CSH phases into brines that contained either 2.5 M NaCl, 2.5 M NaCl/0.02 M Na₂;SO₄, 2.5 M NaCl/0.02 M NaHCO₃ or 0.02 M NaHCO₃ for U(VI) doped CSH phases or 2.5 M NaCl/0.02 M NaHCO₃ or 0.02 M NaHCO₃ for Cm(III) doped CSH phases was monitored in batch leaching experiments for 30 to 60 days. Subsequently, leaching induced changes of the C-S-H structure and of the U(VI) or Cm(III) coordination environment were investigated with TRLFS, IR spectroscopy and XRD. Results indicated that the U(VI) retention by C-S-H phases is maintained in the presence of NaCl rich solutions due to the formation of uranophane [1]. The presence of carbonate in saline leaching solutions increased the U(VI) mobility due to formation of Ca₂UO₂(CO₃)₃(aq) at moderate alkaline pH values [1]. Furthermore, an influence of the secondary CaCO₃ phases calcite, vaterite and aragonite was detected. Calcite contributed to the U(VI) retention which was shown with TRLFS [1]. The binding study of Cm(III) incorporated into C-S-H gel revealed at least two Cm(III) species: (i) Cm(III) substituted against Ca2+ from the C-S-H interlayer and (ii) Cm(III) incorporated in the polyhedral CaO plane of the C-S-H structure. Additionally, a luminescence line narrowing effect was observed indicating variations of the local surrounding of Cm(III) in C-S-H gel. Leaching experiments showed that Cm(III) is not mobilized by carbonate but becomes partially incorporated into secondary CaCO₃ phases. Recently, we started to investigate the Al and U(VI) incorporation into C-S-H phases at different Al/Si ratios (0.025−0.2) and synthesis temperatures (25°C or 200°C). The obtained phases were investigated with ² ⁷Al NMR, TRLFS, XRD and Raman microscopy. First results indicated an influence of the Al starting material and synthesis temperature on the Al incorporation.
Keywords: C-S-H, Aluminum, TRLFS, XRD, Raman, IR, Leaching, Saline, Carbonate
  • Contribution to proceedings
    5th International Workshop on Mechanisms and Modelling of Waste/Cement interactions, 25.-27.03.2019, Karlsruhe, Deutschland
    Proceedings of the 5th International Workshop on Mechanisms and Modelling of Waste/Cement interactions
  • Poster
    5th International Workshop on Mechanisms and Modelling of Waste/Cement interactions, 25.-27.03.2019, Karlsruhe, Deutschland

Publ.-Id: 28342 - Permalink


Lattice relaxation effects of the spin-ice Dy2Ti2O7
Stoeter, T.; Nomura, T.; Granovsky, S.; Doerr, M.; Petrenko, O. A.; Balakrishnan, G.; Zherlitsyn, S.; Wosnitza, J.;
Dy2Ti2O and Ho2Ti2O7 have attracted enormous scientific interest because of the unusual spin-ice ground state and exotic excitations – magnetic monopoles. In this work, we investigated how the lattice reacted to the change of the monopole density from the spin-ice through the Kagome ice to the saturated monopole phase and whether the very slow monopole dynamics predicted in theory were also detectable in lattice effects. We have performed magnetostriction and thermal-expansion measurements with a capacitive dilatometer on Dy2Ti2O7 at temperatures down to 0.28 K to explore the lattice effects in the different regimes: Indeed, we have observed a field-dependent lattice anomaly and have found lattice relaxation effects which could be related to previously proposed monopole dynamics. This research has been supported by the DFG within project C01 of SFB 1143.
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28341 - Permalink


Magnetic ground state of the cubic perovskite Ba3NiNb2O9
Yamamoto, S.; Aslan Cansever, G.; Gottschall, T.; Uhlarz, M.; Blum, C. G. F.; Wolter-Giraud, A.; Aswartham, S.; Wurmehl, S.; Herrmannsdörfer, T.; Seiro, S.;
We investigated the magnetic spin-1 perovskite Ba3NiNb2O9 by means of complex ac susceptibility measurements at extreme sample conditions. Ba3NiNb2O9 with cubic perovskite structure (Pm-3m) has a random occupation of Nb(66 %)/Ni(33 %) at the center of the cubic perovskite unit cell. Different from the isostoichiometric sister compound, Ba3NiNb2O9 with P-3m1 structure which shows both uud-spin configuration and multiferroicity, the magnetic properties of the investigated system have not been studied below 2 K yet. For our single crystals, we observe a spin freezing transition at around 0.7 K. Furthermore, the peak of 𝜒’ is suppressed by applying an external dc field of 200 mT and 𝜒” shows a sudden onset near the freezing temperature.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28340 - Permalink


Thermal and thermal-Hall conductivity study of SrCu2(BO3)2
Arsenijevic, S.; Dabkowska, H.; Gaulin, B.; Stern, R.; Wosnitza, J.;
We present measurements of the thermal and the thermal-Hall conductivity as a function of temperature and magnetic field in the twodimensional dimer spin system SrCu2(BO3)2. The thermal conductivity in zero magnetic field shows a pronounced peak around 4 K which is ascribed to a spin-gap opening. The low-temperature maximum is strongly suppressed by the application of magnetic field. This result implies that the majority of heat is conducted by phonons which interact with the magnetic excitations. Furthermore, a theoretical study predicted a strong thermal Hall signature due to anisotropies originating from the Dzyaloshinskii-Moriya interactions which lead to a topological character of triplon excitations [1]. Our detailed experimental investigation did not reveal such effect disproving the existence of topological transitions in the triplon band structure.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28339 - Permalink


Inverted hysteresis within the antiferromagnetic all-in-allout state of the pyrochlore Nd2Hf2O7
Opherden, L.; Bilitewski, T.; Hornung, J.; Herrmannsdörfer, T.; Samartzis, A.; Islam, A. T. M. N.; Anand, V. K.; Lake, B.; Moessner, R.; Wosnitza, J.;
We report the observation of an anisotropic and inverted hysteresis loop in the antiferromagnetic all-in-all-out ordered phase of Nd2Hf2O7 having a negative remnant magnetization. The hysteresis emerges once exceeding a characteristic magnetic-field strength 𝐻(𝑇) below the Neél temperature. The very unusual appearance of a negative remnant magnetization is observed for a field parallel to the [111] and [110] direction. However, for field parallel to [001] no hysteresis can be seen. For this orientation the projection of the field onto all four local spin directions is equal and, hence, both realizations of the all-in-all-out state gaining equal Zeeman energy through a canting of their spins. We show further, that the underlying all-in-all-out phase is established in Nd2Hf2O7 for temperatures below 𝑇𝑁 = 0.48 K and persists up to fields of 0.27 T. We account for the inverted hysteresis in terms of a theory of uncompensated domain-wall spins of spherical Domains forming inside a fully polarized single-domain state.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28338 - Permalink


Electronic structure of the B20 compound CrGe
Klotz, J.; Götze, K.; Bruin, J.; Geibel, C.; Weber, K.; Schmidt, M.; Rosner, H.; Wosnitza, J.;
CrGe is a nonmagnetic transition-metal germanide with the B20 noncentrosymmetric cubic structure. In contrast, the isostructural MnGe and FeGe both show a helical spin order. We present dHvA-effect data on CrGe that were obtained employing capacitive torque Magnetometers in a 18 T/30 mK and a 33 T/340 mK system. In combination with our fplo calculations, we provide a detailed picture of the Fermisurface topology of CrGe. Furthermore, by comparing the calculated band structures of CrGe and MnGe, we discuss possible reasons for the absence of magnetic order in CrGe. Finally, our calculations indicate that substituting Ge by As or Sn will not lead to magnetic order.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28337 - Permalink


Reversibility of minor hysteresis loops in magnetocaloric Heusler alloys
Gottschall, T.; Stern-Taulats, E.; Manosa, L.; Planes, A.; Skokov, K. P.; Gutfleisch, O.; Skourski, Y.; Wosnitza, J.;
The unavoidable existence of thermal hysteresis in these magnetocaloric materials is one of the central challenges limiting their implementation in cooling devices. Transforming the material in minor loops of the thermal hysteresis, however, allows achieving significant reversible effects even when the hysteresis is relatively large. In this work, we focus on the magnetocaloric properties of Heusler alloys under cycling. We compare thermometric measurements of the adiabatic temperature change in low magnetic fields and pulsed field experiments with calorimetric measurements of the isothermal entropy change when moving in minor hysteresis loops driven by magnetic fields [1, 2].
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berline, Deutschland

Publ.-Id: 28336 - Permalink


Exploring the Quantum Limit of Weyl semimetal candidates
Förster, T.; Klotz, J.; Wosnitza, J.; Shekhar, C.; Yan, B.; Felser, C.;
Non-centrosymmetric transition-metal mono-pnictides such as NbAs, NbP and TaAs attracted a lot of attention because their bandstructures show linear non-degenerate band crossings, dubbed Weyl nodes [1,2]. Additionally, for certain magnetic-field orientations, the highest de Haas-van Alphen frequencies observed are smaller than 50 T. For that reason, all bands are expected to be in the quantum limit at fields easily reachable by pulsed magnetic fields. Thus, these semimetals constitute an ideal playground to study the quantum limit by electric transport and magnetic-torque measurements. Our first results for NbP show an unexpected linear increase in magnetic-torque measurements. In our contribution we show the results of our magnetic-torque measurements on NbP, NbAs, TaP and TaAs in pulsed fields up to 70 T.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28335 - Permalink


NMR of the two-dimensional 𝑆 = 1/2 Heisenberg antiferromagnet CuPOF
Dmytriieva, D.; Zhang, Z. T.; Uhlarz, M.; Landee, C. P.; Wosnitza, J.; Kühne, M.;
The metal-organic compound [Cu(pz)2(2-OHpy)2](PF6)2 (CuPOF) is a molecular-based analog of the two-dimensional quantum 𝑆 = 1/2 Heisenberg antiferromagnet (2D QHAF) with well-isolated Cu(pz) layers and a very low 𝑘𝐵𝑇𝑁/𝐽 = 0.21 ratio (𝐽/𝑘𝐵 = 6.8 K, 𝑇𝑁 = 1.38 K). We present a focus study of the low-temperature phase transition to long-range order performed via 1H and 31P nuclear magnetic resonance (NMR), as well as high-field magnetometry. A low-temperature Minimum of the temperature-dependent local and uniform magnetizations at 𝑇𝑚𝑖𝑛 indicates a presence of the magnetic order. Within the ordered state, a splitting of the 1H NMR spectra reveals commensurate AF order, presumably of checkerboard type. The phase transition, manifested as a sharp maximum of the temperature-dependent 31P nuclear spin-lattice relaxation rate 1/𝑇1, occurs at temperatures slightly lower than 𝑇𝑚𝑖𝑛, indicating an easy-plane anisotropy as well as a crossover between isotropic and XY behavior.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28334 - Permalink


Exploring the magnetic phase diagram of a metal-organic S = 1 triangular spin system.
Chattopadhyay, S.; Herrmannsdörfer, T.; Kanungo, S.; Zvyagin, S.; Uhlarz, M.; Manna, K.; Schnelle, W.; Sannigrahi, J.; Wosnitza, J.; Patra, R.;
We report on magnetic properties of a novel metal-organic S = 1 antiferromagnetic triangular spin compound with isolated Ni2+ triangles entitled as BHAP-Ni3. Specific heat measurements reflect an onset of magnetic correlation at low temperatures without any long-range order down to 300 mK, indicating the presence of an unusual magnetic ground state. ESR measurements performed at 1.5 K advocate this ground state to be a gapped one. Field-dependent magnetization measured on the single crystal shows anisotropic behavior with field applied parallel and perpendicular to the triangle plane. However, a clear plateau-like region is seen in both directions above 8 T which corresponds to half of the fully polarized value of Ni2+ moment. The presence of such half-magnetization plateau is quite unusual in the family of triangular magnets. High-field magnetization measurements using pulsed magnet show another field-induced plateau above 30 T corresponding to the fully polarized state of S = 1 triangles.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28333 - Permalink


High-field ESR studies of the honeycomb-lattice material 𝛼-RuCl3
Ponomaryov, A. N.; Schulze, E.; Wosnitza, J.; Lampen-Kelley, P.; Banerjee, A.; Yan, J. Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Kolezhuk, A. K.; Zvyagin, S.;
We present high-field electron spin resonance (ESR) studies of the honeycomb-lattice material 𝛼-RuCl3, a prime candidate to exhibit Kitaev physics. Two modes of antiferromagnetic resonance were detected in the zigzag ordered phase, with magnetic field applied in the 𝑎𝑏 plane. A very rich excitation spectrum was observed in the field-induced Quantum paramagnetic phase. The obtained data are compared with results of recent numerical calculations, strongly suggesting a very unconventional multiparticle character of the spin dynamics in 𝛼-RuCl3. The frequency-field diagram of the lowest-energy ESR mode is found consistent with the behavior of the field-induced energy gap, revealed by thermodynamic measurements. This work was supported by DFG (project ZV 6/2-2).
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28332 - Permalink


A brief discussion of the magnetocaloric effect in thin films of manganite doped with chromium.
Campillo, G.; Figueroa, A. I.; Arnache, O.; Osorio, J.; Marín Ramírez, J. M.; Fallarino, L.;
In this work we report on the magnetocaloric effect of La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3Mn0.94Cr0.06O3 (LCMCrO) manganite thin films grown by DC magnetron sputtering on LaAlO3 (100) substrates. X-ray diffraction shows that both doped and undoped films crystallize in the orthorhombic structure. Magnetic measurements show a decrease in both the Curie temperature, TC, and the saturation magnetization, MS, for the LCMCrO sample. The change in the magnetic entropy (deltaSm) was extracted from hysteresis loops at different temperatures around the ferromagnetic to paramagnetic transition, displaying a maximum of entropy change (deltaSm)max near TC in both films. Moreover, a shift in (deltaSm)max toward temperatures above TC with increasing magnetic field and a broadening of the entropy change curve were observed. Results of refrigeration cooling power show a lower efficiency for LCMCrO. In order to obtain a local insight into the magnetic interactions of these films, measurements of X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) were performed. XMCD suggests that an antiferromagnetic coupling between Mn4+ - Mn3+ is favored with Cr3+ incorporation, which reduces the Mn L2,3 XMCD signal and results in a decrease of MS and (deltaSm)max in LCMCrO films.
Keywords: Magnetocaloric effect , epitaxial La2/3Ca1/3MnO3 (LCMO) thin films, epitaxial La2/3Ca1/3Mn0.94Cr0.06O3 (LCMCrO) thin films
  • Open Access LogoContribution to proceedings
    VI Congreso Nacional de Ingeniería Física, 22.-26.10.2018, Bucaramanga, Colombia
    Journal of Physics: Conference Series (JPCS).: IOP
    DOI: 10.1088/1742-6596/1247/1/012013

Publ.-Id: 28331 - Permalink


Magnetoelastic phenomena in antiferromagnetic uranium intermetallics: The UAu2Si2 case
Valiska, M.; Saito, H.; Yanagisawa, T.; Tabata, C.; Amitsuka, H.; Uhlirova, K.; Prokleska, J.; Proschek, P.; Valenta, J.; Misek, M.; Gorbunov, D. I.; Wosnitza, J.; Sechovsky, V.;
Thermal expansion, magnetostriction, and magnetization measurements under magnetic field and hydrostatic pressure were performed on a UAu2Si2 single crystal. They revealed a large anisotropy of magnetoelastic properties manifested by prominent length changes, leading to a collapse of the unit-cell volume accompanied by breaking the fourfold symmetry (similar to that in URu2Si2 in the hidden-order state) in the antiferromagnetic state as consequences of strong magnetoelastic coupling. The magnetostriction curves measured at higher temperatures confirm a bulk character of the 50K weak ferromagnetic phase. The large positive pressure change of the ordering temperature predicted from Ehrenfest relation contradicts the more than an order of magnitude smaller pressure dependence observed by the magnetization and specific heat measured under hydrostatic pressure. A comprehensive magnetic phase diagram of UAu2Si2 in magnetic field applied along the c axis is presented. The ground-state antiferromagnetic phase is suppressed by a field-induced metamagnetic transition that changes its character from second to first order at the tricritical point

Publ.-Id: 28330 - Permalink


Chronic low dose ethanol induces an aggressive metastatic phenotype in TRAMP mice, which is counteracted by parthenolide
Morel, K.; Ormsby, R.; Solly, E.; Tran, L.; Sweeney, C.; Klebe, S.; Cordes, N.; Sykes, P.;
Despite advances in prostate cancer therapy, dissemination and growth of metastases results in shortened survival. Here we examined the potential anti-cancer effect of the NF-B inhibitor parthenolide (PTL) and its water soluble analogue dimethylaminoparthenolide (DMAPT) on tumour progression and metastasis in the TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model of prostate cancer. Six-week-old male TRAMP mice received PTL (40mg/kg in 10% ethanol/saline), DMAPT (100mg/kg in sterile water), or vehicle controls by oral gavage thrice weekly until palpable tumour formation. DMAPT treatment slowed normal tumour development in TRAMP mice, extending the time-to-palpable prostate tumour by 20%. PTL did not slow overall tumour development, while the ethanol/saline vehicle used to administer PTL unexpectedly induced an aggressive metastatic tumour phenotype. Chronic ethanol/saline vehicle upregulated expression of NF-B, MMP2, integrin 1, collagen IV, and laminin, and induced vascular basement membrane degradation in primary prostate tumours, as well as increased metastatic spread to the lung and liver. All of these changes were largely prevented by co-administration with PTL. DMAPT (in water) reduced metastasis to below that of water-control. These data suggest that DMAPT has the potential to be used as a cancer preventive and anti-metastatic therapy for prostate cancer. Although low levels of ethanol consumption have not been shown to strongly correlate with prostate cancer epidemiology, these results would support a potential effect of chronic low dose ethanol on metastasis and the TRAMP model provides a useful system in which to further explore the mechanisms involved.
Keywords: Parthenolide; DMAPT; Metastasis; TRAMP; Prostate cancer; Ethanol

Publ.-Id: 28329 - Permalink


Investigations on potential methods for the long-term monitoring of the state of fuel elements in dry storage casks
Hampel, U.; Kratzsch, A.; Rachamin, R.; Wagner, M.; Schmidt, S.; Fiß, D.; Reinicke, S.;
Extended dry storage of spent nuclear fuel is a relevant issue in many countries operating nuclear power plants. Beside regulatory and security aspects there are questions with respect to the long-term integrity of the spent fuel as this is of relevance for final transportation and reloading to final waste repository casks. Within the frame of the BMWi project DCS-MONITOR, we investigate the potentials of different methods for non-intrusive monitoring of dry cask storage containers with spent nuclear fuel. These are thermography, radiation-based methods, and acoustic methods. For all of them we study the sensitivity and cross-sensitivity with respect to defined changes in the nuclear fuel distribution inside the containers. The analyses are mainly based on numerical simulations but also include some dedicated experimental studies.
Keywords: extended storagy, spent fuel, monitoring
  • Kerntechnik 83(2018)6, 513-522
    DOI: 10.3139/124.110949
  • Lecture (Conference)
    2nd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 06.-08.06.2018, Garching, Deutschland
  • Contribution to proceedings
    2nd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel, 06.-08.06.2018, Garching, Germany
    Proceedings of 2nd Workshop on Safety of Extended Dry Storage of Spent Nuclear Fuel

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  • Secondary publication expected from 31.12.2019

Publ.-Id: 28328 - Permalink


Effect of neutron flux on the microstructure of irradiated RPV steels
Ulbricht, A.; Bergner, F.;
This invited talk about the effect of neutron flux on the microstructure of irradiated RPV steels was given to the participants of a Training School in the Framework of the European project SOTERIA.
Keywords: Pressure vessel steels, neutron irradiation, neutron flux, microstructure
  • Invited lecture (Conferences)
    International SOTERIA Training School, 03.07.-07.09.2018, Valencia, Spain

Publ.-Id: 28327 - Permalink


Metallische Verbundwerkstoffe mit funktionellen Eigenschaften
Weissgärber, T.; Schubert, T.; Hutsch, T.; Hilger, I.; Bergner, F.; Kieback, B.;
Der Vortrag umfasst Aspekte der Herstellung, Mikrostruktur, Eigenschaften und Anwendung von pulvermetallurgisch hergestellten Werkstoffen. Als Beispielsysteme werden ODS-Fe-Cr-Legierungen, Verbundwerkstoffe für die Elektronikkühlung und Aluminiumverbundwerkstoffe betrachtet.
Keywords: ODS Legierungen
  • Invited lecture (Conferences)
    7. Dresdner Werkstoffsymposium 2018, 06.-07.12.2018, Dresden, Deutschland

Publ.-Id: 28326 - Permalink


Comparative assessment of different image processing methods to determine the gas-liquid interfacial area in froth regimes of sandwich packings from ultrafast X-ray tomography image data
Sohr, J.; Bieberle, M.; George, G. R.; Flechsig, S.; Kenig, E. Y.; Schubert, M.; Hampel, U.;
Sandwich packings consist of alternatingly stacked structured packing layers of different specific surface area. In such packings froth two-phase flow appears when the packing is operated between the loading limits of the layers. For this highly agitated flow regime, there is a lack of hydrodynamic data, in particular on gas-liquid interfacial area. Ultrafast X-ray tomography, a cross-sectional imaging technique with a frame rate of more than 1000 cross-sectional images per second, is applied to visualize the gas-liquid flow and to extract the gas-liquid interfacial area data via image post-processing methods. For that, we assessed different segmentation methods, that are, level set and gray level contour techniques.
Keywords: Sandwich packing, ultrafast X-ray tomography, image segmentation, gas-liquid interfacial area

Publ.-Id: 28324 - Permalink


Machbarkeitsstudie zur MRT-integrierten Protonentherapie: Strahlablenkung, Sekundärteilchen und Bildqualität
Schellhammer, S. M.ORC; Gantz, S.; Lühr, A.; Pawelke, J.; Karsch, L.; Smeets, J.; Quets, S.; Burigo, L. N.; Oborn, B.; Bussmann, M.; Hoffmann, A. L.
Einleitung
Ungefähr 50% der Krebspatienten werden durch Strahlentherapie behandelt, und die Protonentherapie (PT) bietet hier aufgrund der begrenzten Eindringtiefe und des steilen Dosismaximums eine sehr gezielte Behandlungsform mit potentiell reduzierten Nebenwirkungen. Die Treffgenauigkeit der Protonentherapie kann jedoch durch Bewegungen und anatomische Veränderungen während der Therapie stark kompromittiert werden. Eine gleichzeitige Bildgebung mittels Echtzeit-Magnetresonanztomographie (MRT) wäre deshalb ideal. Bis heute existieren jedoch keine kombinierten Systeme für MRT und PT. Ziele dieser Studie waren die erste Integration eines MR-Scanners in eine PT-Strahlführung, die experimentelle Verifizierung der Ablenkung des Strahls und der Sekundärteilchen im Magnetfled des MRT-Scanners, die Überprüfung der Machbarkeit einer gleichzeitigen MR-Bildgebung und Bestrahlung, und die Kontrolle der MR-Bildqualität mit und ohne Strahleinfluss.

Material & Methoden
Ein offener MR-Scanner mit einem vertikalen Magnetfeld von 0.22 T (MRJ2200, Paramed Medical Systems SpA) wurde an einer strahldüsenlosen horizontalen Strahlführung (Ion Beam Applications SA) installiert, und durch einen kompakten Faraday-Käfig von Hochfrequenz-Interferenzen abgeschirmt (Abb. 1). Die Strahlablenkung und der Einfluss des Magnets auf die Sekundärteilchen im Strahl wurden mithilfe an einem PMMA-Phantom befestigter radiochromischer Filme (EBT3, Ashland) in einem 1 T Magneten gemessen und mit Monte-Carlo-simulationsbasierten Vorhersagen verglichen. Zur Überprüfung der MR-Bildgebung wurden anatomische MR-Bilder eines Probanden bei ausgeschalteter Strahlführung sowie MR-Bilder eines Gewebephantoms und eines dedizierten Bildqualitätsphantoms mit und ohne Strahleinfluss (bei 125 MeV und 5 nA) aufgenommen.

Ergebnisse
Die gemessene Ablenkung des Strahls sowie lokale Dosiserhöhung durch Sekundärteilchen im Magnetfeld waren gering (< 1 cm bzw. 2%) und zeigten sehr gute Übereinstimmung mit simulationsbasierten Vorhersagen. Die MR-Aufnahmen (Abb. 2) zeigten die für den verwendeten Scanner übliche Bildqualität. Es wurde keine Veränderung der Bildqualität durch die Strahlführungsmagneten und den Protonenstrahl beobachtet, jedoch eine gleichförmige, korrigierbare Bildverschiebung (< 1 mm) in Frequenzkodierrichtung.

Diskussion
Die Integration eines offenen MR-Scanners in den experimentellen Strahlengang einer Protonentherapie-Anlage war erfolgreich. Die Einflüsse des Magnetfelds des MRT-Scanners auf den Strahl sind vorhersagbar und eine gleichzeitige MR-Bildgebung und Bestrahlung ohne Bildverzerrung ist möglich. Dies rechtfertigt die Entwicklung eines ersten Prototyps für die MRT-integrierte Protonentherapie.
  • Poster
    1. Deutscher KrebsForschungsKongress (DKFK) | 1st German Cancer Research Congress (GCRC), 04.-05.02.2019, Heidelberg, Deutschland

Publ.-Id: 28323 - Permalink


Including anatomical variations in robust optimization for head and neck proton therapy can reduce the need of adaptation
Cubillos-Mesías, M.; Troost, E. G. C.; Lohaus, F.; Agolli, L.; Rehm, M.; Richter, C.; Stützer, K.ORC
Background and purpose: Classical robust optimization considers uncertainties in patient setup and particle range. However, anatomical changes occurring during the treatment are neglected. Our aim was to compare classical robust optimization (cRO) with anatomical robust optimization (aRO), to quantify the influence of anatomical variations during the treatment course, and to assess the need of adaptation.
Materials and methods: Planning CT and weekly control CTs (cCTs) from 20 head and neck patients were analysed. Three intensity-modulated proton therapy (IMPT) plans were compared: conventional PTV-based plan; cRO, using solely the planning CT, and aRO, including additionally the first 2 cCTs in the optimization. Weekly and total cumulative doses, considering anatomical variations during the treatment, were calculated and compared with the nominal plans.
Results: Nominal plans fulfilled clinical specifications for target coverage (D98% ≥ 95% of prescribed dose). The PTV-based and cRO approaches were not sufficient to account for anatomical changes during the treatment in 10 and 5 patients, respectively, resulting in the need of plan adaptation. With the aRO approach, in all except one patient the target coverage was conserved, and no adaptations were necessary.
Conclusion: In 25% of the investigated cases, classical robust optimization is not sufficient to account for anatomical changes during the treatment. Adding additional information of random anatomical variations in the optimization improves plan robustness.
Keywords: Robust optimization; head and neck cancer; proton therapy; treatment planning; anatomical variations; dose accumulation; plan adaptation

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  • Secondary publication expected from 31.12.2019

Publ.-Id: 28322 - Permalink


McSAFE - High Performance Monte Carlo methods for safety demonstration
Vocka, R.; Sanchez, V.; Mercatali, L.; Malvagi, F.; Smith, P.; Dufek, J.; Seidl, M.; Milisdorfer, L.; Leppänen, J.; Hoogenboom, E.; Kliem, S.ORC; van Uffelen, P.; Kerkar, N.
The main objective of the McSAFE project is the development of the Monte Carlo based multiphysics coupled methodologies for reactor analysis and safety investigations of different reactor systems. Key-research areas are e.g. advanced depletion methods, optimal coupling of MC-codes to thermalhydraulic solvers, time-dependent Monte Carlo and methods and algorithms for massively parallel simulations. The project has started in September 2017 under the coordination of KIT. Among the other partners are European research institutes and technical support organizations (VTT, JRC, CEA, HZDR, NRI, KTH,WOOD), electricity providers (CEZ, PreussenElektra) and consultants (DNC). The software developed within the project should allow for the high precision evaluation of core safety parameters and will be applicable also to VVER reactor types.
  • Contribution to proceedings
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic
    Proceedings of the 28. Symposium of AER, Budapest: MTA EK, 9789637351303, 237-238

Publ.-Id: 28321 - Permalink


Development of highly affine 18F-labelled radiotracers for PET imaging of the adenosine A2A receptor
Lai, T. H.; Schröder, S.; Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Scheunemann, M.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Steinbach, J.; Brust, P.;
Objectives: The adenosine A2A receptor (A2AR) is a G-protein-coupled-receptor which is mainly expressed in the basal ganglia (including striatum) of the brain and in cells of the immune system. Radiotracers for A2AR imaging have emerged as promising candidates for the diagnosis of neurodegenerative and neurooncological diseases. Aiming at the development of such radiotracer with improved molecular imaging properties, a library of 21 fluorinated pyrazolo[2,3-d]pyrimidine derivatives was synthesized based on a recently published lead compound [1]. Among those, the highly affine 4 fluorobenzyl derivate 1 (Ki(hA2A) = 5.3 nM; Ki(hA1) = 220 nM) and the 2 fluorobenzyl derivate 2 (Ki(hA2A) = 2.1 nM; Ki(hA1) = 147 nM) were chosen for 18F isotopoic labelling although the introduction of 18F at non-activated aromatic positions is challenging. Herein, we report on the radiosyntheses of [18F]1 and [18F]2 via an alcohol-enhanced copper-mediated one-step radiofluorination and their first biological evaluation.

Methods: Three different labelling strategies for the synthesis of [18F]1 have been investigated (Fig. 1). The first two were using [18F]fluorobenzaldehyde ([18F]B) as intermediate, which was produced by nucleophilic radiofluorination of a trimethylammonium precursor of type A (step a). Compound [18F]B was used either in a reductive amination reaction (step b) or it was further reduced to the corresponding alcohol (step c) followed by an Appel bromination to get [18F]C (step d) which was finally used in a benzylation reaction (step e). The third strategy, a one-step approach, started from the boronic acid pinacol ester precursor of type D employing [18F]TBAF and Cu(OTf)2(py)4 in n-BuOH/DMA (step f). The specific binding of [18F]1 and [18F]2 was evaluated in vitro by autoradiography of mice brain slices using 1, 2 and ZM241385 as different blocking agents.

Results: The two- and four-step labelling strategies resulted in an overall radiochemical yield of only 1.4% and 10%, respectively for [18F]1 (non-isolated). Therefore, [18F]1 and [18F]2 were prepared by an alcohol-enhanced copper-mediated one-step radiolabelling approach starting from the corresponding boronic acid pinacol ester precursor D. Compound [18F]1 was obtained with a radiochemical yield of 52+7% (n = 5, EOB), a molar activity of 135+64 GBq/µmol (n = 4, EOS) and a radiochemical purity of >98%. Compound [18F]2 was synthesized with a radiochemical yield of 9+1% (n = 2, EOB), a molar activity of 132 GBq/µmol (n = 1, EOS) and a radiochemical purity of >98%. In vitro autoradiography performed with [18F]2 showed high binding in the striatum, which could be blocked by selective A2AR ligands thus proving the specificity of the new radiotracer (Fig. 1).

Conclusions: An efficient copper-mediated one-step radiolabelling procedure was established for two new highly affine A2AR radiotracers. In a first in vitro study on mice brain slices, [18F]2 demonstrated excellent imaging properties. Further biological in vitro and in vivo investigations are needed to completely evaluate the potential of both A2AR radiotracers.

Acknowledgments: This work has been supported by the the European Regional Development Fund and Sächsische Aufbaubank (project no. 100226753).

References: [1] Gillespie et al., Bioorg. Med. Chem. Lett. 2008, 18, 2924-2929.
Keywords: adenosine, A2A, PET, 18F, radiofluorination
  • Lecture (Conference)
    The 23rd International Symposium on Radiopharmaceutical Sciences (ISRS2019), 26.-31.05.2019, Peking, China

Publ.-Id: 28320 - Permalink


Synthesis, Receptor Affinity, and Antiallodynic Activity of Spirocyclic σ Receptor Ligands with Exocyclic Amino Moiety
Bergkemper, M.; Kronenberg, E.; Thum, S.; Börgel, F.; Daniliuc, C.; Schepmann, D.; Nieto, F. R.; Brust, P.; Reinoso, R. F.; Alvarez, I.; Wünsch, B.;
In order to detect novel σ receptor ligands, the rigit spiro [[2]benzopyran-1,1'-cyclohexan]-4'-one was connected with amino moieties derived from σ2 receptor preferring lead compounds resulting in mixtures of trans- and cis-configured amines 6, 18, and 27. In a four step synthesis the methyl acetals 6 were converted into fluoroethyl derivatives 13 and 30. The most promising σ2 receptor ligand is the methyl acetal 6a bearing a 2,4-dimethylbenzylamino moiety. The fluoroethyl derivatives 13c and 13d reveal high σ1 affinity but moderate selectivity over the σ2 subtype. In mice 13c and 13d showed antiallodynic activity that is stronger than that of the reference σ1 antagonist BD-1063 (34). Since the antiallodynic activity of 13c could only be partially reversed by the σ1 agonist PRE-084 (35), it is postulated that a second mechanism contributes to its overall antiallodynic effect. In contrast, the antiallodynic effect of its diastereomer 13d can be totally explained by a σ1 antagonism.

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  • Secondary publication expected from 12.10.2019

Publ.-Id: 28319 - Permalink


The Serial Interface Package -- v2.0
Seilmayer, M.ORC
The 'serial' package as an extension to the programming language R enables reading and writing binary and ASCII data to RS232/RS422/RS485 or any other virtual serial interfaces of the computer.
Keywords: serial interface, RS232, RS422, RS485, R
  • Software in external data repository
    Publication year 2018
    Programming language: R
    System requirements: Windows, Mac, Unix
    License: GPL-2
    Hosted on r-project.org: Link to location

Publ.-Id: 28318 - Permalink


Characterization and beneficiation of pyrolyzed black mass from lithium ion batteries
Vanderbruggen, A.; Gilbricht, S.; Möckel, R.; Rudolph, M.;
The lithium-ion battery (LiB) market is growing rapidly. Consequently, LiB wastes will increase in the future and LiB components such as Co, Li, but also graphite, are forecast to be critical materials. These critical materials are contained in the black mass produced by LiBs recycling. This original research focuses on graphite beneficiation from cathode lithium metal oxides by flotation. Detailed characterization of the pyrolyzed black mass (inculding MLA, XRF and XRD) shows that the graphite particles are fully liberated from the copper foils, and the organic layer PVDF is removed. Batch flotation shows that pretreatment, such as attritioning, improves process efficiency while preserving the shape of spheriodized graphite. Concentrate impurities mainly comprise fine particles from cathode active materials, which can be removed with desliming and flotation cleaner stages. As an outlook, this reasearch is expected to bring about an innovative and useful process for the recycling industry.
Keywords: Attritionning, black mass, characterization, flotation, graphite, mineral liberation analysis (MLA), pre-treatment, recycling, spent lithium ion battery, surface analysis
  • Poster
    Minerals Engineering International (MEI) conference: Process Mineralogy '18, 19.-21.11.2018, Cape Town, South Africa

Publ.-Id: 28316 - Permalink


Serpent solution of the X2 VVER-1000 benchmark fresh core experiments
Bilodid, Y.; Fridman, E.;
The X2 VVER-1000 benchmark describes first 4 fuel cycles of the Khmelnitsky NPP 2nd unit with VVER-1000 reactor as well as some operational transients. The benchmark specifications contain description of the reactor core material, geometry and operational history supplemented by measured operational data and startup experiments. In this work, the hot zero power experiments conducted during the fresh core startup are modelled with the Serpent-2 Monte Carlo code. The numerical results are validated against the available measured core data. The calculated and measured values of a critical boron concentration, temperature reactivity effect, and control rod worth are in a very good agreement while the deviations lay within the measurement uncertainties. Since the power distribution was not measured at the hot zero power state, the obtained Serpent solution could be used as a reference for a deterministic codes verification.
Keywords: X2 benchmark, VVER-1000, Serpent
  • Contribution to proceedings
    PHYSOR 2018: Reactor Physics Paving The Way Towards More Efficient Systems, 22.-26.04.2018, Cancun, Mexico, 1982-1989

Publ.-Id: 28315 - Permalink


Doping issues in silicon nanowires by ion implantation and flash lamp annealing
Berencen, Y.; Prucnal, S.; Wang, M.; Rebohle, L.; Helm, M.; Zhou, S.; Skorupa, W.;
Semiconducting nanowires (NWs) hold promises for functional nanoscale devices. Although several applications have been demonstrated in the areas of electronics, photonics and sensing, the doping of NWs remains challenging. Ion implantation is a standard doping method in top-down semiconductor industry, which offers precise control over the areal dose and depth profile as well as allows for the doping of all elements of the periodic table even beyond their equilibrium solid solubility. Yet its major disadvantage is the concurrent material damage. A subsequent annealing process is commonly used for the healing of implant damage and the electrical activation of dopants. This step, however, might lead to the out-diffusion of dopants and eventually the degradation of NWs because of the low thermal stability caused by the large surface–area-to-volume ratio.

In this work, we report on non-equilibrium processing (flash lamps) for controlled doping of drop-casted Si/SiO2 core/shell NWs with shallow- and deep-level dopants below and above their equilibrium solid solubility. The approach lies on the implantation of either shallow-level dopants, such as B and P, or deep-level dopants like Se followed by millisecond flash lamp annealing. In case of amorphization upon high-fluence implantation, recrystallization takes place via a bottom-up template-assisted solid phase epitaxy. Non-equilibrium Se concentrations lead to intermediate-band Si/SiO2 core/shell NWs that have room-temperature sub-band gap photoresponse when configured as a photoconductor device [1]. Alternatively, the formation of a cross-sectional p-n junction is demonstrated by co-implanting P and B in individual NWs at different depth along the NW core.
[1] Y. Berencén, et al. Adv. Mater. Interfaces 2018, 1800101
Keywords: doping, nanowires, semiconductor, silicon, ion implantation, flash lamp annealing
  • Lecture (Conference)
    22nd International Conference on Ion Implantation Technology, 16.-21.09.2018, Würzburg, Deutschland

Publ.-Id: 28313 - Permalink


Advanced doping issues using nonequilibrium processing
Skorupa, W.; Rebohle, L.; Prucnal, S.; Berencen, Y.; Zhou, S.; Helm, M.;
In this talk I will introduce with a short view on the background of the transistor invention as a key element driving the topic of semiconductor doping. After that I will discuss examples of advanced doping including ion beam based and other methods: doping and alloying of germanium, hyperdoping of silicon, doping from deposited layers, doping of silicon nanowires, doping from deposited layers. In all cases the experiments were performed in correlation to nonequilibrium thermal processing using flash lamps in the millisecond time range.
Keywords: semiconductor doping, ion beam based methods, flash lamp annealing
  • Lecture (others)
    Eingeladener Seminarvortrag an der Marie-Curie-Universität Lublin/Polen, 11.10.2018, Lublin, Polen

Publ.-Id: 28311 - Permalink


Dataset on characterization, ion irradiation and nanoindentation of ODS Fe14Cr-based alloys
Bergner, F.;

The dataset comprises raw data of the nanoindentation tests and processed data on the ion irradiations and irradiation-induced hardness changes. File formats are excel, word, origin and ascii.


Related publications
Nanoindentation of single- (Fe) and dual-beam (Fe and He) … (Id 28308) has used this publication of HZDR-primary research data
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-12-04
    DOI: 10.14278/rodare.72

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Publ.-Id: 28310 - Permalink


Bonding and stability analysis of tetravalent f-element complexes with mixed N-, O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands re- flecting natural bonding motifs.
This study shows the different bonding behaviour of tetravalent f-elements with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent inter- actions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are presented. The obtained results are a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the inter- action between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possi- ble to understand the chemical properties of the f-elements and predict yet unknown complexes.
Keywords: Bonding analysis, Theoretical Chemistry, DFT, QTAIM, Actinides
  • Poster
    Symposium on Theoretical Chemistry, 17.-20.09.2018, Halle, Deutschland

Publ.-Id: 28309 - Permalink


Nanoindentation of single- (Fe) and dual-beam (Fe and He) ion-irradiated ODS Fe-14Cr-based alloys: Effect of the initial microstructure on irradiation-induced hardening
Heintze, C.; Hilger, I.; Bergner, F.ORC; Weissgärber, T.; Kieback, B.
Although the view that nm-sized oxide particles modify and essentially improve the irradiation resistance of Fe-Cr-based alloys is widely accepted, the correctness of this view has only been demonstrated in singular cases. An extension of the field of considered microstructures, irradiation conditions, and measures of irradiation resistance is required. The present study is focused on nanostructured ferritic Fe-14%Cr-based alloys, with and without the addition of 0.6 wt% Y2O3, produced via mechanical alloying and consolidation by spark plasma sintering. The materials were exposed to single-beam (Fe) and dual-beam (Fe+He) ion irradiations at room temperature. The initial microstructures were characterized, bimodal grain size distributions were observed and nanoindentation was applied to measure irradiation hardening for fine-grained and coarse-grained areas separately. We have found that grain size governs irradiation hardening for single-beam irradiation, while oxide nanoparticles play a dominant role for dual-beam irradiations. This sheds a light on the role of particle-matrix interfaces on helium management.
Keywords: Nanostructured ferritic alloys, oxide dispersion strengthening, ion irradiation, dual-beam irradiation, helium, nanoindentation, irradiation hardening
Related publications
Dataset on characterization, ion irradiation and … (Id 28310) HZDR-primary research data are used by this publication

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  • Secondary publication expected from 04.03.2020

Publ.-Id: 28308 - Permalink


Bonding and stability analysis of tetravalent actinide and lanthanide complexes with N,O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study shows the different bonding behaviour of tetravalent actinide and lanthanide complexes with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are done being a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possible to understand the chemical properties of the f-elements and predict yet unknown complexes.
Keywords: Bonding, Salen, Actinides, theoretical chemistry, DFT, QTAIM
  • Lecture (Conference)
    International Symposium on Nano and Supramolecular Chemistry, 09.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28307 - Permalink


The Study and Development of Pulsed High-field Magnets for Application in Laser-plasma Physics
Kroll, F.;
The thesis at hand addresses design, characterization and experimental testing of pulsed high-field magnets for utilization in the field of laser-plasma physics. The central task was to establish a technology platform that allows to manipulate laser-driven ion sources in a way that the accelerated ions can be used in complex application studies, e.g. radiobiological cell or tumor irradiation.

Laser-driven ion acceleration in the regime of target normal sheath acceleration (TNSA) offers the unique opportunity to accelerate particles to kinetic energies of few 10MeV on the micrometer scale. The generated bunches are short, intense, show broad exponentially decaying energy spectra and high divergence. In order to efficiently use the generated particles, it is crucial to gain control over their divergence directly after their production. For most applications it additionally is favorable to reduce the energy spread of the beam. This work shows that the developed pulsed high-field magnets, so-called solenoids (cylindrical magnets), can efficiently capture, transport and focus laser-accelerated protons. The chromaticity of the magnetic lens thereby provides for energy selection.

Three prototype solenoids, adapted to fit different application scenarios, and associated current pulse drivers have been developed. The magnets generate fields of several 10 T. Pulse durations are of the order of one millisecond and thus the fields can be considered as quasi-static for laser-plasma interaction processes taking place on the ps- to ns-scale. Their high field strength in combination with abandoning magnetic cores make the solenoids compact and light-weight.

The presented experiments focus on a solenoid magnet designed for the capture of divergent laser-driven ion beams. They have been carried out at the 6MV tandetron accelerator and the laser acceleration source Draco of Helmholtz-Zentrum Dresden – Rossendorf as well as at the PHELIX laser of GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The results show that the developed technology platform breaks ground for a variety of practical applications of laser ion acceleration. It is shown that laser-driven ion beams can be efficiently injected into conventional accelerator structures to allow for phase space modulation. Furthermore, first practical studies on medical beam guidance systems are presented. Hence, the developed magnets allow to investigate feasibility and potential of the frequently proposed laser-based ion beam therapy of tumor diseases. The pulsed high-field magnets bring us one step closer to the realization of this ambitious endeavor, as they pave the way for compact and efficient beam guidance toward the patient but also, in the phase of translational research, allow to study the radiobiological properties of the novel particle source. In this context, worldwide first irradiation studies with laser-accelerated protons on volumetric tumors in the mouse model have been prepared and their feasibility studied, identifying already met radiobiological criteria and hurdles yet to overcome.
Keywords: Pulsed magnets, high-field magnets, beam transport, laser-acceleration, laser acceleration, TNSA, laser particle acceleration, laser-radiooncology
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-094 2018

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Publ.-Id: 28306 - Permalink


Photo-induced THz response of VO2 under high pressures
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.ORC
We apply ultrafast optical pump – THz probe spectroscopy in order to investigate the nature of the high pressure metallic state of VO2 single crystal. The pump excitation was performed using near-infrared pulses at the wavelength of 800 nm. The probe pulses with a frequency of 30 THz were generated by difference frequency mixing and focused on the sample mounted inside a diamond anvil pressure cell. Using the probe photon energy far below the bandgap of VO2 we were able to explore the response of free charge carriers near the Fermi level.
  • Lecture (Conference)
    Non-equilibrium Dynamics of Condensed Matter in the Time Domain, 03.-06.09.2018, Kerkrade, Netherlands

Publ.-Id: 28305 - Permalink


Photoinduced non-thermal insulator-to-metal transition in NbO2 epitaxial thin films
Rana, R.; Klopf, M. J.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.ORC
Ultrafast insulator-to-metal transition in the correlated oxides such as vanadium dioxide (VO2) has been extensively explored for rich physics and potential applications. In this regard, its isovalent counterpart niobium dioxide (NbO2) with considerably higher transition temperature (Tc = 1080 K) can be envisaged as a potential candidate. We have performed time-resolved optical pump – terahertz (THz) probe measurements on NbO2 epitaxial thin at room temperature.
The onset of the THz conductivity is followed by an exponential decay on a timescale of 400 fs. The photoinduced change in THz transmission at later delay times exhibits excitation threshold of 17.5 mJ/cm2. Notably, in contrast to VO2, the pump energy required for the switching into a metastable metallic state is smaller than the energy necessary for heating NbO2 up to Tc providing a strong evidence for the non-thermal character of the photoinduced insulator-to-metal transition in this system. The transient optical conductivity in the metastable state can be modelled using the Drude model confirming its metallic character.
  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 28304 - Permalink


Development of a new 18F-labeled radioligand for imaging of sigma2 receptors by positron emission tomography
Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Deuther-Conrad, W.; Kranz, M.; Schepmann, D.; Jia, H.; Wünsch, B.; Brust, P.;
Objectives: Sigma2 receptors (S2R) have been found in CNS, liver, kidney, as well as endocrine glands and are suggested to play important roles in the regulation of cell differentiation. Besides their overexpression in various tumor cell lines, derived from e.g. breast, brain, colon, lung, pancreas, and prostate, they show a 10-fold higher expression in the proliferating vs quiescent status and thus are possible markers of solid tumor’s proliferative status. To quantify the S2R availability in living subjects, we aim for the development of a new class of S2R ligands that could be labeled by fluorine-18.
Methods: Starting from structural motifs known for S2R ligands [1, 2], we modified the indole ring system in A and synthesized a novel series of fluorine containing indole and aza-indole derivatives (1a-d and 2-6 in Fig. 1). Their binding affinities towards sigma2 and sigma1 receptors were determined by radioligand-binding assays, and 2 was selected for synthesis of a boronic acid pinacol ester precursor for radiolabeling. Synthesis of [18F]2 was optimized starting from 100-500 MBq of 18F-fluoride, using Kryptofix (K2.2.2.)/ K2CO3 (0.18-1.8 µmol/ 0.04-0.35 µmol) as well as TBAHCO3 (2.3 and 7.5 µmol) and 2-4 mg of precursor 7, in the presence of Cu(OTf)2py4 (0.4-6.8 eq.) in various solvent systems at 80-135 °C, monitored for 5-20 min. For monitoring, several analytical methods (radio-UHPLC, -HPLC, and -TLC) have been established, e.g. on the basis of RP18 und RP8 stationary phases for LC systems. Besides, different techniques for purification and isolation were investigated, including a substitution of semi-preparative HPLC by time-saving cartridge systems.
Results: By altering the heterocyclic system of A, a small series of fluorinated aza-indoles was synthesized (Fig. 1), of which 2 showed most promising binding affinity and selectivity (Ki(S2R) = 1.6 nM; Ki(S1R) = 691 nM). Radiosynthesis of [18F]2 was achieved with RCYs in a range of 20-45% (n = 2, all non-isolated, radio-UHPLC) by use of 2.0 mg of precursor 7 (4.1 µmol) and 3.6 eq. of Cu(OTf)2py4 at 115 °C within 10 min. The reaction was accompanied by the formation of a by-product (bp) which increased over time. Using the K2.2.2./ K2CO3 system resulted in RCYs of 21.5% (bp 5.5%) and 27.7 % (bp 4.6%), in DMF and DMA/ n-BuOH, respectively. Application of TBAHCO3 showed further increased conversions, represented by a RCY of 44.8% (bp 9.1%) in DMA/ n-BuOH. For subsequent semi-preparative HPLC, separation conditions were optimized, but still lack from low recoveries. As an alternative, SPE procedures using cartridge systems (SiO2, RP18) are being established and could be used as a time saving technique for the isolation of [18F]2.
Conclusions: A novel S2R-affine aza-indole derivative 2 was synthesized and radiofluorination of the appropriate boronic acid pinacol ester precursor afforded [18F]2 in RCYs of up to 45% (non-isolated). The optimal parameters for the radiosynthesis, conducted in a synthesis automat or module, have to be determined to setup a procedure for the production of [18F]2, which enables detailed preclinical in vitro and in vivo studies of this promising radioligand.
Acknowledgement: The authors would like to thank the Deutsche Forschungsgemeinschaft (DFG) for financial support (BR 1360/13-1).
References:
[1] Georgiadis, M.-O. et al. Molecules 2017, 22, 1408;
[2] Wang, L. et al. Bioorg Med. Chem. 2017, 25, 3792-3802
Keywords: Positron emission tomography, PET, fluorine-18, sigma2, indole, aza-indole
  • Poster
    23. International Symposium on Radiopharmaceutical Sciences (ISRS 2019), 26.-31.05.2019, Peking, China
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 62(2019), 181

Publ.-Id: 28303 - Permalink


Electron dynamics in InxGa1-xAs shells around GaAs nanowires probed by terahertz spectroscopy
Fotev, I.; Balaghi, L.; Schmidt, J.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.ORC
We present the electrical properties of GaAs/InxGa1-xAs core/shell nanowires measured by ultrafast optical pump - terahertz probe spectroscopy.
This contactless technique was used to measure the photoconductivity of nanowires with shell compositions of x = 0.20, 0.30 and 0.44. The results were fitted with the model of localized surface plasmon in a cylinder in order to obtain electron mobilities, concentrations and lifetimes in the InxGa1-xAs NW shells.
The estimated lifetimes are about 80 - 100 ps and the electron mobility reaches 3700 cm2/Vs at room temperature. This makes GaAs/InGaAs nanowires good candidates for the near-future realization of InGaAs based high-electronmobility transistor.
Keywords: GaAs nanowires, terahertz spectroscopy, ultrafast dynamics, electron mobility, plasmon, carrier lifetime

Publ.-Id: 28302 - Permalink


Nonthermal nature of photo-induced insulator-to-metal transition in NbO2
Rana, R.; Klopf, J. M.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.;
We study the photo-induced metallization process in niobium dioxide NbO2. This compound undergoes the thermal insulator-to-metal transition at the remarkably high temperature of 1080 K. Our optical pump ¬– terahertz probe measurements reveal the ultrafast switching of the film on a sub-picosecond timescale and the formation of a metastable metallic phase when the incident pump fluence exceeds the threshold of ~10 mJ/cm2. Remarkably, this threshold value corresponds to the deposited energy which is capable of heating NbO2 only up to 790 K, thus, evidencing the non-thermal character of the photo-induced insulator-to-metal transition. We also observe an enhanced formation of the metallic phase above the second threshold of ~17.5 mJ/cm2 which corresponds to the onset of the thermal switching. The transient optical conductivity in the metastable phase can be modeled using the Drude-Smith model confirming its metallic character. The present observation of non-thermal transition in NbO2 can serve as an important test bed for understanding photo-induced phenomena in strongly correlated oxides.
Keywords: metal-insulator transition, pump-probe spectroscopy, transition metal oxides

Downloads:

Publ.-Id: 28301 - Permalink


Optical Pump – THz Probe Response of VO2 under High Pressure
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.;
We present the ultrafast THz response of VO2 under high pressures. A clear anomaly is observed around 8 GPa indicating a pressure-induced phase transition. Our observations can be interpreted in terms of a bandwidth-controlled Mott-Hubbard transition.
Keywords: metal-insulator transition, high pressure, VO2, pump-probe spectroscopy
  • Open Access LogoContribution to proceedings
    XXI International Conference on Ultrafast Phenomena, 15.-20.07.2018, Hamburg, Deutschland
    Proceedings of Ultrafast Phenomena XXI, 91944 Les Ulis cedex A - France: EDP Sciences Web of Conferences
    DOI: 10.1051/epjconf/201920504003

Publ.-Id: 28300 - Permalink


Optical Pump – THz Probe Response of VO2 under High Pressure
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.; Marvel, R. E.; Haglund, R. F.; Pashkin, A.ORC
We present the ultrafast THz response of VO2 under high pressures. Pump-probe signals and a photoexcitation threshold are detected even in a metallic state. Our observations can be described as a pressure-driven Mott-Hubbard transition.
Keywords: vanadium dioxide, high pressure, pump-probe spectroscopy
  • Lecture (Conference)
    XXI. International Conference on Ultrafast Phenomena, 15.-20.07.2018, Hamburg, Deutschland

Publ.-Id: 28299 - Permalink


Freie Software in der Wissenschaft: Prototypen, Reproduzierbarkeit, Infrastruktur
Huebl, A.ORC
Beitrag zur Ringvorlesung der FSFW im Wintersemester 2018 an der HTW, TU Dresden und Bürgeruniversität.
Keywords: open science, open source, open infrastructure, open data
  • Lecture (others)
    Ringvorlesung WS2018: Freie Software und Freies Wissen als Beruf, 27.11.2018, Dresden, Germany
    DOI: 10.5281/zenodo.1884442

Publ.-Id: 28298 - Permalink


Measurement of torsional and sloshing modes in Rayleigh-Bénard convection using contactless inductive flow tomography
Wondrak, T.; Stefani, F.; Galindo, V.; Eckert, S.;
Flows driven by temperature differences play an important role in geo- and astrophysics as well as in many metallurgical applications. The dynamics of the large scale circulation (LSC) of Rayleigh-Bénard (RB) convection include azimuthal reorientations, cessations, torsional and sloshing modes. In this presentation we will show that the contactless inductive flow tomography (CIFT) is able to visualise these features. This will be shown using numerical simulations as well as measurements at a small model filled with GaInSn.
Keywords: contactless inductive flow tomography, liquid metal, flow measurement, Rayleigh-Bénard convection
  • Lecture (Conference)
    MHD Days and GDRI Dynamo Meeting, 26.-28.11.2018, Dresden, Deutschland

Publ.-Id: 28297 - Permalink


AER Working Group Meeting on VVER safety analysis - report of the 2018 meeting
Kliem, S.ORC
The AER Working Group D on VVER reactor safety analysis held its 27th meeting in Rossendorf, Germany, during the period 12-13 June, 2018. The meeting was hosted by Helmholtz-Zentrum Dresden-Rossendorf. Altogether 19 participants from nine AER member organizations attended the meeting of the working group D. The co-ordinator of the working group, Mr. S. Kliem, served as the chairperson of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given 13 presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking
• Severe accident analyses
• Future activities
The Working Group decided to include also in future the severe accident analyses into the scope of the activities.
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairperson.
  • Contribution to proceedings
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic
    Proceedings of the 28. Symposium of AER, Budapest: MTA EK Budapest, 9789637351303, 665-671
  • Lecture (Conference)
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic

Publ.-Id: 28295 - Permalink


Aerosol particle deposition and resuspension in turbulent air channel flows
Lecrivain, G.; Hampel, U.;
The deposition of aerosol graphite particles in a turbulent channel flow obstructed with periodic steps is here investigated et experimentally at Reynolds number Re = 8,000. Particles in the size range d = 1...100µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. The numerical results compare well with the experimental data.
  • Invited lecture (Conferences)
    Workshop on particle resuspension, 04.09.2018, Nice, France

Publ.-Id: 28294 - Permalink


Numerical Models for the DRESDYN Precession Dynamo Experiment
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.;
More than 100 years ago, Henri Poincare in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

In the present study we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around Rm_c ≈ 430, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precission are able to excite dynamo action when their structure is sufficient complex, i.e. the forcing is sufficient strong.

More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment. Finally, we discuss the role of turbulent flow fluctuations for the occurrence of dynamo action.
Keywords: Dynamo, DRESDYN
  • Poster
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA
  • Open Access LogoContribution to proceedings
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA

Publ.-Id: 28293 - Permalink


Numerical simulations for the DRESDYN precession dynamo
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.;
More than 100 years ago, Henri Poincar{\'e} in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

Here we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around ${\rm{Rm}}_{\rm{c}} \approx 430$, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precession are able to excite dynamo action when their structure is sufficiently complex, i.e. the forcing is sufficiently strong.
More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment.
Keywords: Dynamo, DRESDYN
  • Lecture (Conference)
    MHD Days 2018, 26.-29.11.2018, Dresden, Germany

Publ.-Id: 28292 - Permalink


Kopplung von CFD, Elektrochemie und Elektrodynamik am Beispiel Flüssigmetallbatterie
Weber, N.; Personnettaz, P.; Weier, T.;
Flüssigmetallbatterien (FMB) werden seit etwa 10 Jahren als preisgünstige stationäre Speicher für die Energiewende diskutiert. Der Aufbau aus zwei flüssigen Metallen, welche nur durch eine dünne Salzschmelze getrennt sind, erlaubt extreme Stromdichten und eine potentiell sehr hohe Lebensdauer. Für einen optimalen Wirkungsgrad muss die Salzschicht möglichst dünn sein – ohne jedoch einen Kurzschluss zuzulassen. Weiterhin ist effektiver Massetransport durch Konvektion von zentraler Bedeutung.

Im ersten Teil des Vortrags soll Aufbau und Funktionsweise einer FMB kurz erklärt werden. Anschließend werden verschiedene physikalische Phänomene an Hand von OpenFOAM-Simulationen diskutiert (thermische und solutale Konvektion, magnetohydrodynamische Instabilitäten, Elektrochemie, Stromverteilung in der Zelle). Im letzten Teil des Vortrags wird auf die Kopplung von CFD mit Elektrodynamik sowie von Massetransport mit der Potential- und Stromverteilung detailiert eingegangen.
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe Computational Fluid Dynamics mit OpenFOAM Workshop, 19.03.2019, Frankfurt, Deutschland

Publ.-Id: 28291 - Permalink


Liquid Metal Batteries: coupling electrochemistry, heat and mass transfer with magnetohydrodynamics
Weber, N.; Herreman, W.; Horstmann, G. M.; Nore, C.; Personnettaz, P.; Weier, T.;
Liquid metal batteries (LMBs) are discussed as cheap stationary energy storage. Built as a stable density stratification of two liquid metals separated by a molten salt, such cells offer extreme current densities at a potentially unlimited life time. Beyond that, it is especially the low price which makes LMBs an ideal candidate for balancing highly fluctuating renewable energy sources. The efficiency of LMBs is mainly determined by two aspects. Most importantly, the electrolyte layer must be as thin as possible as it has a high ohmic resistance. Still, it needs to be thick enough to prevent a short-circuit. Secondly, efficient mass transfer needs to be ensured. Optimising an LMB means therefore understanding the interplay of thermal and solutal convection, mass transfer, electrochemistry and electrodynamically driven flow with the current distribution in the cell. The talk will start with an introduction to built-up and operation of LMBs. The different physical effects will be discussed using simulations performed in OpenFOAM. Numerical details will be provided on coupling hydro- and electrodynamics, magnetic field calculation as well as the coupling of electrochemistry with current and potential distributions.
  • Lecture (Conference)
    Congress on Numerical Methods in Engineering, 01.07.2019, Guimarães, Portugal

Publ.-Id: 28290 - Permalink


Antihypertensive drug classes, not blood pressure, are associated with cerebral perfusion. Results from the PREvention of Dementia by Intensive VAscular care (PREDIVA) study
van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.;
Background: Constant cerebral blood flow (CBF) is fundamental to cerebral function. With aging and chronic hypertension, arteriolar damage may disrupt the CBF autoregulatory capacity. This might cause CBF to fluctuate with blood pressure (BP) levels, low BP and antihypertensive medication (AHM), potentially evoking hypoperfusion. We investigated the cross-sectional and longitudinal relations of BP and AHM with cerebral perfusion using arterial spin labeling (ASL).
Methods: In 186 community-dwelling individuals with hypertension (77±3 years, 53% female), 125 (67%) with 3-year follow-up (Figure 1), we assessed grey matter (GM) and white matter (WM) CBF (ml/100g/min) and the spatial coefficient of variation (CoV; SD CBF/mean CBF). Cross-sectional associations were assessed combining baseline and follow-up data using mixed models, longitudinal associations using linear regression assessing change, adjusted for baseline. We additionally adjusted for age, sex, AHM, stroke and parenchymal fraction.
Results: Cross-sectionally, higher diastolic BP was associated with lower GM and WM CBF (Table 1). AHM were associated with lower GM CBF and higher spatial CoV. Since calcium channel blockers (CCB) and angiotensin receptor blockers (ARB) in our main study were specifically associated with lower dementia risk compared to other AHM, we assessed these separately. Other AHM were associated with lower GM and WM CBF, while CCBs and ARBs were not. There were no correlations between BP change and perfusion changes (Table 2). We observed no J-shaped relationships.
Discussion: We found no evidence for any direct relation between BP and cerebral perfusion. Possibly, higher diastolic BP was associated with lower CBF by being a marker of more severe long-standing hypertension evoking vascular damage. Our finding that ARBs and CCBs are relatively protective of CBF compared to other AHM is consistent with findings of a protective effect of these AHM classes on dementia incidence, and could influence future treatment.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28289 - Permalink


Cognitive complaints associated with spatial coefficient of cerebral blood flow in community-dwelling older people in the PREvention of Dementia by Intensive VAscular care (PREDIVA) study
van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.;
Background: Low cerebral perfusion is cross-sectionally associated with dementia and predicts accelerated dementia progression. Hypothetically, impaired cerebral autoregulation, associated with aging and hypertension, and consequent cerebral hypoperfusion may contribute to the development of old-age cognitive decline. We investigated the cross-sectional and longitudinal relation between cognition and cerebral perfusion in older people without dementia using arterial spin labeling (ASL).
Methods: We included 186 community-dwelling individuals with hypertension (77 ±3 years, 53% female), 125 (67%) with 3-year follow-up neuroimaging (Figure 1). Cognitive measures included the mini-mental state examination (MMSE), visual association test (VAT) and subjective memory complaints (SMC) assessed using one question. Perfusion measures included grey matter (GM) cerebral blood flow (CBF, ml/100g/min), white matter (WM) CBF and spatial coefficient of variation (CoV; SD CBF/mean CBF, a potential proxy of vascular insufficiency). Cross-sectional analyses combined baseline and follow-up data using mixed models. Longitudinal analyses comprised linear regression of follow-up values adjusted for baseline. We additionally adjusted for age, sex, antihypertensives, WM hyperintensity volume and brain parenchymal fraction.
Results: Participants with memory complaints had a significantly higher CoV (Table 1). Furthermore, participants with better VAT scores had lower CoV, although this was attenuated after adjustment. Cerebral perfusion did not predict change in cognition (Table 2) but increasing CoV was associated with declining MMSE and, to a lesser extent, VAT scores. There were no significant relations between CBF and cognition.
Discussion: Our results suggest that higher CoV is associated with worse cognitive function and CoV changes concordantly with cognitive function. Spatial CoV may be a more sensitive cerebral hemodynamic parameter related to cerebral function compared to CBF. None of the cerebral perfusion parameters predicted future cognitive decline, suggesting that low perfusion does not precede cognitive decline in non-demented older people or that the perfusion measures employed were insufficiently sensitive.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28288 - Permalink


ASL-vascular insufficiency parameters can differentiate healthy controls from Alzheimer’s and Parkinson’s diseases
Ingala, S.; Petr, J.; Pålhaugen, L.; Gajdos, M.; Fladby, T.; Selnes, P.; Barkhof, F.; Bjørnerud, A.; Rektorova, I.; Mutsaerts, H.;
Decreased/Poor vascular health - e.g. increased vascular resistance, tortuosity - may lead to a delayed arrival of labelled blood to brain tissue causing vascular artefacts on arterial spin labeling (ASL) images [Figure 1]. Although these artefacts are traditionally treated as a nuisance, their presence can be quantified by the spatial coefficient of variance (CoV) parameter and used as an indication of vascular insufficiency. . Here, the goal was to investigate the ability of spatial CoV to assess the vascular health by comparing it between healthy controls and subjects with Alzheimer’s (AD) and Parkinson’s (PD) diseases.

Methods: We analyzed the MRI scans of 143 APGeM study participants, including healthy controls (HC, n=56) and subjects with AD- (n=41) or PD-related (n=46) mild cognitive impairment or dementia [Table]. We calculated CBF, spatial CoV, and WMH volume using ExploreASL [ref]. Pearson’s correlations of spatial CoV with age and WMH volume were investigated, as well as a t-test for the relation between spatial CoV and sex. A linear regression model was used to evaluate whether spatial CoV was able to discriminate HC vs. AD, HC vs. PD, and AD vs. PD after correction for age and sex.

Results: Spatial CoV measures showed a positive correlation with age (cor=0.35, p <0.001 and with WMH volume (cor=0.38, p <0.001 [Figure 2A], and differed between sexes (p <0.001). Differences in spatial CoV values were detected between HC and AD and between HC and PD subjects (p<0.05 in both cases) [Figure 2B]. With our model, spatial CoV was not able to discriminate between AD and PD.

Conclusions: These findings suggest that spatial CoV can provide insight in the vascular component of AD and PD pathologies. Validation of these results in larger cohorts and across a wider range of disorders might provide further insight in the relation between cerebrovascular health and neurodegeneration.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28287 - Permalink


Effects of intracranial stenosis on brain perfusion and cognitive performance in a memory clinic population
Hilal, S.; Mutsaerts, H.; Ferro, D.; Petr, J.; Kuijf, H.; Biessels, G.; Chen, C.;
Background: Intracranial stenosis (ICS) contributes to cognitive dysfunction possibly via decreased cerebral blood flow (CBF). However, CBF measurements by Arterial Spin Labelling (ASL) are affected by vascular artefacts making it difficult to apply in elderly with large vessel disease. Recently, spatial coefficient of variance (CoV) is proposed as a robust estimate to quantify vascular artifacts and may be used as a proxy marker of large vessel insufficiency. We investigate the association of ICS with ASL measurements and its eventual effects on cognition in a memory clinic population.
Methods: We included 403 participants (mean age=72.3±7.9years, women=53.7%). ICS was graded as ≥50% stenosis in any intracranial vessel on 3D Time of Flight Magnetic Resonance Angiography. Gray matter spatial CoV and gray matter CBF were analyzed with ExploreASL from 2D EPI pseudo-continuous ASL images. Global cognition was assessed by a detailed neuropsychological test.
Results: ICS was present in 70 (17.4%) individuals. Persons with ICS had higher GM spatial CoV (mean difference (β)= 0.17, 95%CI: 0.07; 0.28, p=0.001) and lower CBF (β= -0.21, 95%CI: -0.33; -0.09), p=<0.001). This association persisted after partial volume correction of spatial CoV and CBF. The lateralization of spatial CoV and CBF (asymmetry index) (β for CoV: 0.23, 95%CI: 0.05; 0.40, p=0.013 and β for CBF: -0.22, 95%CI: -0.33; -0.11, p=<0.001) were correlated with ipsilateral stenosis. Spatial CoV was associated with worse cognition independent of CBF (β= -0.76, 95%CI: -1.09; -0.43, p=<0.001). Moreover, ICS was associated with global cognition, independent of gray matter CoV and CBF, although this effect attenuated in the presence of cortical microinfarcts (β= -0.23, 95%CI: -0.49; 0.02, p=0.072).
Conclusion: These findings suggest an association of ASL perfusion with ICS and cognition, which has a predominant component of large vessel insufficiency. Moreover, cortical microinfarcts mediate the link between ICS and cognition independent of large vessel insufficiency.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28286 - Permalink


Tissue inhibitor of proteinase-1 and cerebral blood flow in predementia
Pålhaugen, L.; Selnes, P.; Kirkeby, E.; Tecelao, S.; Ingala, S.; Petr, J.; Bjørnerud, A.; Mutsaerts, H.; Fladby, T.;
Background
Cerebrovascular disease (CVD) can increase the risk of dementia and is frequently seen in Alzheimer’s disease. Tissue inhibitor of proteinase-1 (TIMP-1) measured in cerebrospinal fluid (CBF) is considered a promising biomarker of subcortical small vessel disease (SSVD). In addition to inhibition of matrix metalloproteases, it occurs in several biological processes, such as protection of the blood brain barrier. This study explores how TIMP-1 is associated with CBF in amyloid and non-amyloid pre-dementia cases as well as in controls.

Methods
Cases and controls, aged 40-80, were included from the Norwegian multi-site study “DDI” (n=69, age=63.2 +/- SD, m/f=26/43). Participants underwent cognitive assessment, MRI and lumbar puncture. Cases were staged as Subjective Cognitive Decline (SCD) or Mild Cognitive Impairment (MCI). We stratified by A1-42 pathology (A+/-) using an amyloid-PET verified CSF cutoff. Cerebral blood flow (CBF) was measured with arterial spin labeling and analyzed using ExploreASL. Linear regression analysis was performed with TIMP-1 and CBF in total gray matter (GM), total white matter (WM) and several GM regions (frontal, temporal, insula, parietal, occipital, thalamus, putamen and caudate nucleus), adjusting for age and sex. CBF was log-transformed.

Results
In the A- group (n=50, age=61.6, m/f=17/33, Controls/SCD/MCI=21/22/7) there was a significant positive relationship between TIMP-1 and CBF in total GM (=-0.46, p=0.001), total WM (=-0.44, p=0.002), frontal (=-0.41, p=0.004), temporal (=-0.45, p=0.001), insula (=-0.39, p=0.006), parietal (=-0.48, p<0.001), occipital (=-0.45, p=0.001), thalamus (=-0.53, p<0.001), putamen (=-0.41, p=0.004) and caudate nucleus (=-0.48, p=0.001) GM regions. There were no significant associations in the A+ group (n=19, age=67.4, m/f=9/10, Controls/SCD/MCI=2/7/10) or in the whole sample.

Conclusion
We found that TIMP-1 correlates positively with CBF in the A- group, whereas there were no significant association in the A+ group. Putatively, this may reflect different mechanisms for vascular pathology in the two groups.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28285 - Permalink


Cortical microinfarcts in memory clinic patients are associated with reduced cerebral perfusion
Ferro, D.; Mutsaerts, H.; Hilal, S.; Kuijf, H.; Petersen, E.; Petr, J.; van Veluw, S.; Venketasubramanian, N.; Biessels, G.; Chen, C.;
Background: Cerebral cortical microinfarcts (CMIs) are small ischemic lesions visible on autopsy and structural MRI. As CMIs occur/are observed more frequently in the cortical watershed areas, we hypothesize that hypoperfusion plays a role in their development. We investigated whether CMI presence is associated with decreased cerebral perfusion using arterial spin labeling (ASL).
Methods: We have analyzed 180 memory clinic patients (mean age 72 ± 9y, 51% male, 72% CMIs present ) with pCASL acquired at 3T MRI (PLD=xx ms, labeling duration=xx ms). Cerebral blood flow (CBF) was quantified (in ml/100g/min) and mean CBF and spatial coefficient of variation (CoV, quantitative proxy of transit time, expressed as SD of the CBF/mean CBF) was calculated in gray matter in each vascular territory. Vascular artefacts were observed in 33 patients due to prolonged transit time, and these were excluded from the CBF but not CoV analysis. CMIs were rated according to previously established criteria.
Results: In this cohort, CMIs presence was associated with a higher burden of cerebrovascular disease (Table 1). Patients with CMIs had lower CBF and a higher spatial CoV in the anterior circulatory territory, indicating a decreased perfusion and a delayed transit time (Table 1, Figure 1). The total number of CMIs was correlated to a lower CBF and a higher spatial CoV (p<.02). A sub-analysis in patients with unilateral CMI presence revealed no significant inter-hemisphere differences in CBF (n=27, .56 ±.7 ml/100g/min) or in CoV (n=36, .05 ±.25).
Conclusion: This is the first study to demonstrate that CMIs presence is associated with reduced global cerebral perfusion. Further research should identify at which level of the vascular tree the cause of hypoperfusion originates.
  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Lecture (Conference)
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28284 - Permalink


µTRLFS: Spatially-resolved sorption studies of Eu(III) on Eibenstock granite with time-resolved laser fluorescence spectroscopy
Molodtsov, K.; Schymura, S.; Rothe, J.; Dardenne, K.; Krause, J.; Schmidt, M.;
Finding a safe long-term repository for high-level nuclear waste is a highly relevant global issue. To that end, the interaction of radionuclides with mineral phases contained in possible host rocks and construction materials must be understood. On a time scale of up to one million years, especially the scenario of a water intrusion into the repository and thus dissolution of radionuclides has to be considered.

To investigate the sorption behaviour of actinides (e.g. Cm(III) and U(VI)O22+) and lanthanides (e.g. Eu(III)), time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method, because of its trace concentration sensitivity and capability to distinguish multiple species in complex systems. On the one hand this method gives the spectral information of the emitted fluorescence light, which allows determining the symmetry and the grade of complexation of the sorbed Ln/An. On the other hand the lifetimes of the excited electronic states provide information about the surrounding quenchers, mainly water. Typically, TRLFS investigations will focus on the interaction of an actinide with one relevant mineral phase. For a real rock formation, e.g. granite, sorption will however be a competitive process involving multiple mineral phases at the same time.

In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS. By doing so, it is possible to separate the multi-phase system into discrete single-phase systems and therefore to make a step beyond model systems by investigating, for example whole natural granite rock with TRLFS. Because of its advantageous fluorescence properties, we use Eu(III) as an analogue for the trivalent actinides Am and Cm. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused laser beam at a wavelength of 394 nm, and scanned through the laser’s focal point by an XYZ-stage with a resolution of approximately 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, F2/F1-band ratios, as well as fluorescence lifetimes.

A combination of spatially-resolved X-ray fluorescence spectroscopy (µXRF) and electron probe microanalysis (EPMA) is used to reveal the mineral phase composition in each point of measurement which can then be correlated to the µTRLFS maps. In addition, these methods provide impurity distributions of e.g. Fe or Mn as additional quenchers. By doing so, µTRLFS mapping of sorption capacity, complexation strength and surrounding quenchers can be correlated to phase distribution mappings and thus provide information about the sorption behaviour of each phase within the complete multi-phase system. The µTRLFS data can be directly compared to single phase TRLFS data of the main granite components quartz, feldspar, and mica. For verification, the Eu(III) distribution obtained from µTRLFS data will be compared to autoradiography images.
Keywords: µTRLFS, europium, sorption, granite
  • Poster
    10th International Conference on f-elements, 03.-06.09.2018, Lausanne, Schweiz
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28283 - Permalink


µTRLFS: Spatially- and time-resolved laser fluorescence spectroscopy with Eu(III) as a fluorophore on Eibenstock granite
Molodtsov, K.; Schmidt, M.;
Time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method to obtain information about the surrounding chemical environment of fluorophores with trace concentration sensitivity. This method allows determining the symmetry and grade of complexation of the fluorophore and provides information about the surrounding quenchers, mainly water as well. For highly heterogeneous systems however distinguishing and separating multiple binding species becomes an unsolvable problem. In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS, giving the possibility to separate a multi-phase system into discrete single-phase systems. Because of its advantageous fluorescence properties we use europium as an analogue for Am(III) and Cm(III) to study the sorption behaviour of granite as a possible host rock for high-level nuclear waste repositories. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused and pulsed UV laser beam, and scanned with a resolution of 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, band ratios, as well as lifetimes.
Keywords: µTRLFS, europium, sorption, granite
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung, 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 28282 - Permalink


The muon flux in the Felsenkeller shallow underground laboratory
Ludwig, F.; Wagner, L.; Al-Abdullah, T.; Barnaföldi, G. G.; Bemmerer, D.; Degering, D.; Surányi, G.; Zuber, K.;
The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany
have been studied using a portable muon detector based on the closed cathode chamber design. Data has been taken at
four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and
in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the
eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere
with 0.85 ◦ angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock
overburden, corresponding to 140 meters water equivalent.
The angular data are matched by two different simulations taking into account the known geodetic features of the
terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon
energy spectrum, and second, in a GEANT4 simulation propagating the muons through a column of rock equal to the
known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the
planning of an active veto for accelerator-based underground nuclear astrophysics experiments.
Keywords: Muon intensity, Underground laboratories, GEANT4, nuclear astrophysics, wire chambers, muon tomography, muon radiography

Publ.-Id: 28281 - Permalink


Trivalent Actinide Incorporation into Zirconium(IV) oxide – Eu3+ and Cm3+ luminescence spectroscopic studies
Eibl, M.; Shaw, S.; Morris, K.; Hennig, C.; Stumpf, T.; Huittinen, N.;
In a final repository for spent nuclear fuel (SNF), the mobilization of actinides from the UO2 matrix is a great concern for safety considerations. The SNF rods are surrounded by zircalloy cladding material, which, similarly to the UO2 waste matrix, has a very low solubility in aqueous solution. Despite the very good corrosion resistance of the cladding material, corrosion and dissolution are expected to occur together with the leaching of radionuclides from the SNF over geological timescales. Therefore, the dissolution of zircalloy and the formation of a corrosion layer mainly composed of zirconia (ZrO2) on the cladding surface may be accompanied by reactions with dissolved, long-lived radionuclides from the SNF matrix.
At ambient conditions zirconium oxide has a monoclinic (m) crystal structure. However, the incorporation of metal cations can stabilize the high-temperature zirconia phases, i.e. the tetragonal (t) and the cubic (c) phases, leading to the formation of stable structures at ambient conditions.[1] Such phase transformation may be expected when actinides from the SNF become incorporated and thus, immobilized within the zirconia corrosion layer.
In the present study the incorporation of aliovalent actinides in zirconia, and their stabilizing influence on the crystal structure, have been investigated. The crystallinity and structural properties of the resultant actinide-doped zirconia solids were investigated with powder x-ray diffraction (PXRD), while the local structure around the incorporated dopant was studied with laser-induced luminescence spectroscopy (TRLFS). Cm3+ and Eu3+ were taken as representatives for the trivalent actinides.
The PXRD results of calcined Eu3+ doped zirconia samples show that a systematic transformation of the monoclinic to the cubic phase via the tetragonal structure occurs as a function of increasing Eu3+ doping (Fig. 1, left) whilst the Eu3+ TRLFS results show a 7F1, 7F2 emission band splitting corresponding to a low symmetry environment despite the cubic bulk symmetry (Fig. 1, middle).

The Cm3+ co-doped luminescence spectra show strong red-shifts of the emission spectra in the cubic bulk system with a peak maximum of 643.9 nm (Fig. 1, right) which have been observed before.[2] Both spectroscopic methods point towards a strongly distorted local structure, caused by the effect of oxygen vacancies and lattice stress induced by the largely oversized dopant ions.
  • Lecture (Conference)
    4th International Workshop on Advanced Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28280 - Permalink


Pressure-tuning of the magnetic properties of the Heusler compound Mn2PtGa
Salazar Mejia, C.; Najak, A. K.; Felser, C.; Nicklas, M.;
We report on the pressure-tuning of the magnetic properties of the Heusler alloy Mn2PtGa. At ambient pressure, Mn2PtGa orders ferrimagnetically below TC ≈ 222 K, followed by a first-order ferrimagnetic to antiferromagnetic transition around TFI-AF ≈ 102 K upon cooling. Magnetization measurements up to 1.2 GPa evidence a stabilization of the ferrimagnetic phase, i.e., TC increases while TFI-AF decreases upon application of pressure. The magnetic properties in the ferromagnetic phase are not altered upon increasing pressure. However, the fraction of the ferrimagnetic phase present in the inhomogeneous antiferromagnetic low-temperature phase increases with pressure.

Publ.-Id: 28279 - Permalink


Entwicklung einer alternativen Methode zur selektiven Laugung von Seltenen Erden aus Zirkonsilikaten
Balinski, A.; Scharf, C.;
Zirkonsilikate spielen als Quelle für Seltene Erden trotz der geringen Belastung mit Uran und Thorium, des günstigeren Verhältnisses von schweren zu leichten Seltenen Erden und der Anwesenheit von wertvollen Begleitelementen immer noch eine untergeordnete Rolle. Eine industriell rentable Gewinnung von Seltenen Erden aus dieser Rohstoffgruppe hat sich trotz vieler initiierter Projekte bis auf eine Lagerstätte in Russland bisher nicht durchgesetzt. Der Grund dafür liegt in den geringen Konzentrationen der Zielelemente, der Kieselgelbildung während der Laugung und der Entstehung von komplexen Multielement-Laugungslösungen begründet. Die Arbeit beschäftigt sich mit der Entwicklung einer alternativen Methode zur Gewinnung von Seltenen Erden und der relevanten Begleitelemente unter Anwendung des unterschiedlichen Verhaltens der Sulfate der beiden Metallgruppen. Als Zwischenprodukte werden wässrige Phasen angereichert mit jeweils wertvollen Metallen beziehungsweise Seltenen Erden zur weiteren Raffination erzeugt.
  • Poster
    Jahrestreffen der Processnet-Fachgruppen Extraktion und Rohstoffe, 12.-13.03.2018, Frankfurt am Main, Deutschland

Publ.-Id: 28278 - Permalink


SE-FLECX-Projekt: alternative Ansätze zur Gewinnung von Seltenen Erden
Balinski, A.; Scharf, C.;
Seltene Erden (Lanthanoide), eine Gruppe von 17 Elementen mit ähnlichen Eigenschaften, sind aus einer Vielzahl heutiger Produkte nicht mehr wegzudenken. Dazu gehören sowohl Gegenstände des täglichen Bedarfs wie z.B. LCD-Bildschirme oder Akkus für Laptops als auch hochspezifische Anwendungen wie z.B. Dauermagneten in Windkraftanlagen.
Um eine sichere Versorgung mit Seltenen Erden zu gewährleisten, müssen neue und innovative Methoden sowohl zur Aufbereitung von Erzen und Konzentraten als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Das Forscherteam von „SE-FLECX“ nimmt die beiden Herausforderungen an, wobei drei Hauptziele im Fokus stehen: die Aufbereitung von unkonventionellen Rohstoffen, die Abtrennung der Actinoide und die selektive Auftrennung einzelner Seltenen Erden. Aufgrund der ähnlichen Eigenschaften der Elemente und der steigenden Komplexität der Erze ist die Bewältigung dieser Aufgaben entscheidend für die Erarbeitung von zukünftig durchsetzbaren Prozessen.
Keywords: Seltene Erden, Calixarene, unkonventionelle Rohstoffe, Flüssig-Flüssig-Extraktion
  • Lecture (Conference)
    r4-Clusterworkshop 2018, 10.-11.10.2018, Hannover, Deutschland

Publ.-Id: 28277 - Permalink


A Parallel Cellular Automata Lattice Boltzmann Method for Convection-Driven Solidification
Kao, A.; Krastins, I.; Alexandrakis, M.; Shevchenko, N.; Eckert, S.; Pericleous, K.;
This paper presents a novel coupling of numerical techniques that enable 3D convection-driven microstructure simulations to be conducted on practical time scales appropriate for small size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient hydrodynamic CFD solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso/macro-scale phenomena.
Keywords: Lattice Boltzmann method, large-scale simulations, convection-driven solidification, fluid flow

Publ.-Id: 28276 - Permalink


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene
Balinski, A.; Scharf, C.;
Zur Gewährleistung der sicheren Versorgung mit Seltenen Erden (Sc, Y und Lanthanoide) müssen innovative Methoden sowohl zur Aufbereitung von Rohstoffen als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Im SE-FLECX-Projekt sollen diese Ziele durch die Anwendung der besonderen Eigenschaften von Calix[4]arenen und eine gezielte Aufbereitung der unkonventionellen Rohstoffquellen erreicht werden.
Die Entwicklung neuartiger Extraktionsmittel erfolgte durch die gezielte Substitution an makrocyclischen Calix[4]arenen. Zwei Typen von Liganden wurden für die effiziente Trennung der Actinoide (Typ A) und der Seltenen Erden (Typ B) synthetisiert, charakterisiert und erprobt.
Im Laufe des Projektes wurden zwei Vertreter gefunden, die aus einfach zusammengesetzten Systemen (Modelllösungen) sowohl Seltene Erden quantitativ in einer Stufe extrahieren (FG20) als auch U(VI) sehr effizient abtrennen können (AJ46).
Bei AJ46 wurde neben der Fähigkeit zur Uranabtrennung ebenso eine starke Affinität zu Schweren Seltenen Erden festgestellt. Sein industrieller Einsatz wurde jedoch aufgrund der hohen Synthesekosten als unwirtschaftlich bewertet. Diese konnten durch die Entwicklung einer alternativen Syntheseroute signifikant reduziert werden.
Keywords: Seltene Erden, Calixarene,, Flüssig-Flüssig-Extraktion
  • Lecture (Conference)
    r4-Statuskonferenz, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    r4-Statuskonferenz 2018, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    24 Stunden für Ressourceneffizienz", Ressourceneffizienz-Kongress für Nachwuchsforscherinnen und Nachwuchsforscher, 14.-15.02.2017, Pforzheim, Deutschland

Publ.-Id: 28275 - Permalink


X-ray visualisation of melt flow effects on dendritic solidification
Shevchenko, N.; Keplinger, O.; Grenzer, J.; Rack, A.; Eckert, S.;
X-ray radiography is an effective tool for investigating flow phenomena and solidification processes in opaque metallic alloys. This work is devoted to complex interaction between dendritic growth and melt flow during solidification of Ga-In alloys under natural and forced convection. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. The conventional X-ray radioscopic experiments with sufficient spatial resolution (5-10 µm) deliver simultaneous information of both the dendrite structure and the flow patterns ahead of the solidification front and especially near the mushy zone. Melt convection alters the solutal field near the solidification front leading to different microstructures or even to the formation of freckle defects. The coarsening stage of dendritic structure is characterized by transformation of the sidearm morphology present after growth. The direct investigation of dendritic sidearm evolution during coarsening appears to be rather complex and impose high requirements with respect to the spatial and temporal resolution and sensitivity of the detector. The synchrotron imaging experiments with solidifying Ga-In alloys were performed at the BM20 and ID19 beamlines (ESRF, France) at a spatial resolution of < 1 µm. The present measurements provide real-time in-situ data on three phenomena that are of major importance in coarsening of dendrites: sidearm retraction, pinch-off and coalescence of neighboring sidearms. Using an advanced image analysis of high temporal and spatial resolution experimental data allows us to verify existing microstructural models.
Keywords: X-ray radiography, dendritic growth, melt flow, sidearm evolution
  • Lecture (Conference)
    32nd International Congress on High Speed Imaging and Photonics, 09.-12.10.2018, Twente, The Netherlands

Publ.-Id: 28274 - Permalink


In-situ observation of dendritic growth under the influence of electromagnetically driven flow
Shevchenko, N.; Keplinger, O.; Eckert, S.;
Many studies have demonstrated that the application of electromagnetic stirring enhances the area of equiaxed grains and reduces the mean grain size (see e.g. [1-2]). It is widely accepted that flow-induced grain refinement and the CET (columnar to equiaxed transition) in metallic alloys is triggered by the appearance of additional dendrite fragments originating from the columnar front. The mechanism for grain multiplication by melt convection is supposed to be complex and is not fully understood until now.
The X-ray radiography was used for an in-situ study of the effect of electromagnetic stirring during the solidification of a Ga-25wt%In alloy in a Hele-Shaw cell [3]. The experimental setup was extended by a magnetic wheel, which allowed for controlled excitation of a melt flow in the liquid phase. The forced flow induces different effects on dendrite morphology, such as the uneven growth of primary trunks or lateral branches, remelting of single dendrites and also of lager dendrite ensembles, freckle formation, changes the inclination angle of the dendrites and leads to an increasing arm spacing. These effects are primarily governed by the convective redistribution of solute. Figure 1 demonstrates an interesting effect of "repairing" of a segregation channel (see the right-hand side part of Fig. 1a) after switching off the magnetic wheel (Fig 1b). It can be seen that an area with equiaxed or fine dendrites was formed instead of a segregation channel. The appearance of small equiaxed grains in the undercooled melt in the segregation pools is triggered by quick redistribution of solute after stopping the magnetic pump.
References
1. B. Willers et al, Materials Science and Engineering A 402 (2005) 55-65
2. T. Campanella et al, Metallurgical and Materials Transactions A 35 (2004) 3201-3210
3. N. Shevchenko et al, Journal of Crystal Growth 417 (2015) 1-8
Keywords: Electromagnetic stirring, solidification, X-ray radiography, freckle formation, Ga-In alloy
  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji, Hyogo, Japan

Publ.-Id: 28273 - Permalink


Characterization of Isostructural An(IV) Complexes with Hetero-donor Imine Ligands
Radoske, T.ORC; Schöne, S.ORC; Kaden, P.; Ikeda-Ohno, A.ORC; Stumpf, T.
The coordination chemistry of actinides (An) serves as fundamental knowledge for chemical engineering and environmental science related to the nuclear industry.[1] However, as compared with other transition metals, the basic chemistry of An is far less explored. The chemistry of An is complicated by, e.g., various possible oxidation states ranging from II to VII for the early An. One possible approach to understand the chemical nature of the An series is the comparison of isostructural compounds containing different actinides with the same oxidation state.[2,3,4] With this approach, the relative changes observed among the An series could allow us to gain insight into their unique chemical nature, such as electronic properties originating from their f-electron orbitals. One major question remaining in the field of An chemistry is the degree of “covalency” across the An series.[5] In order to study the “covalency” across the An series, one would require to perform a systematic study on a wide series of An, including transuranium (TRU) elements. Nonetheless, precedent studies covering TRU elements are rather scarce. This background motivates us to perform the current study focusing on a systematic comparison of the isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which is dominant particularly under anoxic environmental conditions.[1] Synthesis of their compounds and the experiments should be conducted under inert and water-free atmosphere. The ligands used in this study are a hetero-donor imine ligand of salen and its derivatives (Fig. 1). These ligands have a capability to coordinate to metal ions tetradentately and exhibit both the hard- (oxygen) and medium-donor (nitrogen) characters, which could be a simple analog of natural occurring organic molecules. The eightfold coordination, which is often preferred for An complexes, can be readily achieved with these ligands by coordination of two ligand molecules. Salen and its derivatives have also been employed as a framework for catalytic and extraction agents.[6,7]
  • Lecture (Conference)
    Plutonium Futures 2018, 11.09.2018, San Diego, Vereinigte Staaten von Amerika

Publ.-Id: 28271 - Permalink


Actinide Bonding – Comparative Study of Isostructural An(IV) Imine Complexes
Radoske, T.ORC; Kaden, P.; Schöne, S.ORC; Ikeda-Ohno, A.ORC; Stumpf, T.
Because of their unique electronic properties originating from 5f-orbitals, the coordination chemistry of actinides (An) is still an attractive research field in terms not only of nuclear engineering but also of basic chemistry. In particular, the early An show profound complex chemistry due to a wide variety of possible oxidation states ranging from +II to +VII, which is in contrast to the dominant trivalent state for their chemical analog of lanthanides. The aim of our research activities is to gain knowledge about the interaction of An with a variety of hard- and soft-donor ligands, eventually providing a comprehensive understanding of the electronic nature of actinide compounds. The ligands used in this study possess both O- (i.e. hard) and N-donor (soft) containing functionalities (Fig.1) and could also be considered as a simplified model of naturally relevant organic O/N-donor ligands.
A series of single crystals of [AnIV(Lp)2] complexes were synthesized from the tetrachloride compounds of An = Th, U and Np. SC-XRD measurements on the obtained crystals reveal their crystal structures, all showing the eight-fold coordination of the metal centre with the ligands on their primary coordination sphere, forming a trigonal dodecahedral geometry around the metal centre.
1H-NMR spectra of the dissolved complexes [ThIV(Le)2], [UIV(Le)2], [CeIV(Le)2] and the pure ligand in solution were recorded. The observed shifts show unique features when comparing isostructural diamagnetic compounds of lanthanides and actinides, which can not be explained by charge density differences.
  • Lecture (Conference)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 10.07.2018, Dresden, Deutschland

Publ.-Id: 28270 - Permalink


Atomic-level thermodynamics and kinetics in solids: Examples for Si, Ge, and SiC
Posselt, M.;
In this talk examples of atomistic simulations on thermodynamics and kinetics in Si, Ge, and SiC are presented.
Keywords: Atomic-level simulations, thermodynamics, Si, Ge, SiC
  • Lecture (others)
    Seminar "Topical Problems in Theoretical Physics", 28.11.2018, Chemnitz, Deutschland

Publ.-Id: 28269 - Permalink


Age and genesis of polymetallic veins in the Freiberg district, Erzgebirge, Germany: constraints from radiogenic isotopes
Ostendorf, J.; Henjes-Kunst, F.; Seifert, T.; Gutzmer, J.;
The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.
Keywords: Erzgebirge, Freiberg district, Pb isotopesRb-Sr sphalerite dating, Sm-Nd fluorite dating, Vein-type deposit

Publ.-Id: 28268 - Permalink


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