Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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28745 Publications
Influence of the bubble size distribution on the stability of bubble columns
Ziegenhein, Thomas; Schipp, Johanna; Lucas, Dirk
Bubble columns are a fundamental operation unit in chemical engineering; nevertheless, their dimensioning is still based on empirical models. Here, one of the most important parameter is the point of change from the homogenous to the heterogeneous regime. Despite intensive research in the past decades, no deeper understanding of the underlying, local processes was gained. From theoretical deliberations, the lift force was identified as the possibly crucial parameter for the stability in bubble columns in the past (Lucas et al. 2005). The pre-factor of the lift force, the lift force depends on the shear rate, changes its sign when the bubbles reach a certain size (Tomiyama et al. 2002). Consequently, large bubbles tend to velocity peaks in a bubble column, which amplify the heterogeneous character; small bubbles, on the other hand, are driven away from velocity peaks, which homogenizes the flow.
Based on experiments, the turnover from the homogeneous regime to the heterogeneous by solely changing the bubble size distribution (BSD) is shown. For this purpose, the volume flow in a bubble column with evenly distributed needle spargers is kept constant; the BSD is varied by using different needles. By means of the BSD and the liquid velocity at different heights, the theoretically obtained stability criterion (Lucas et al. 2005) is compared to the experiments. The findings presented help to better understand the local process in a bubble column that lead to the turnover to the heterogeneous regime. In the end, with general, local models for these processes, bubble columns of arbitrary shape and other facilities can be specially designed to reach the desired homogenous regime at higher gas hold ups.
Keywords: bubbly flow, bubble column, stability, lift force
  • Poster
    Jahrestreffen Dresden - Jahrestreffen der ProcessNet-Fachgruppen Mehrphasenströmungen, Partikelmesstechnik, Zerkleinern und Klassieren, Computational Fluid Dynamics, Mischvorgänge und dem TAK Aerosoltechnologie, 14.-17.03.2017, Dresden, Germany

Registration No. 26507 - Permalink


Prediction of bubble size distributions in large-scale bubble columns using computational fluid dynamics
Besagni, G.; Inzoli, F.; Ziegenhein, Thomas; Lucas, Dirk
A precise estimation of bubble size distributions is of fundamental and practical importance to understand the fluid dynamics and to estimate the mass transfer in bubble columns. Multiphase computational fluid dynamic simulations, in the Eulerian multi-fluid framework, are able to predict the local bubble size distributions from the fluid flow conditions by using coalescence and breakage kernels. In particular, this study concerns the prediction of the bubble size distributions in the “pseudo-homogeneous” flow regime, which is characterized by a wide spectrum of bubble sizes and is generally observed in industrial applications. Reliable predictions of the “pseudo-homogeneous” flow regime are, however, limited up to now: one important drawback concerns the selection of appropriate models for the coalescence and break-up. A set of closure relations was collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been further extended to the “pseudo-homogeneous” flow regime by comparing experimental and numerical bubble size distributions at different axial positions in a large-diameter and large-scale bubble column. The results have been critically analysed and may serve as basis to improve the coalescence and break-up closures.
Keywords: Bubbly flow, bubble shape, bubble column, CFD
  • Contribution to proceedings
    14th INTERNATIONAL CONFERENCE MULTIPHASE FLOW IN INDUSTRIAL PLANT, 13.09.2017, Desenzano del Garda, Italy

Registration No. 26496 - Permalink


Dependency of bubble column flow regime on bubble size distribution
Ziegenhein, T.; Lucas, D.
The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. As shown by Lucas et al.
(2005) the lateral lift force may have an important influence on this transition. Interactions between local and global instabilities of a bubble column were discussed by Lucas et al. (2007).
As shown experimentally by Tomiyama et al. (2002) and by numerous direct numerical simulations (e.g. Dijkhuizen et al., 2010) the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions (Ziegen-hein et al., 2017 and Ziegenhein and Lucas, 2017a). The well-known correlation of Tomiyama et al. (2002) fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water, deionized water was used in the experiments. Replacing the Wellek- correlation by a correlation based on bubble shapes that are observed in bubble columns (Ziegenhein and Lucas, 2017b) the critical diameter for the change of the sign is about 5.14 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. (2005) derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The sparger consists of 6 holes that can be equipped with different needles. The holes are separated into two groups that hold different needle sizes to produce a certain poly-disperse flow. The total gas volume flow was fixed to 1.0 l/min for all experiments. The gas flow through the sparger group was varied to vary the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive.


The liquid velocity profile was determined by particle tracking using microbubbles and 100 µ m PMMA particles. The bubble sizes and the gas volume fraction were determined by high-speed camera observations. Measurements were done for different height positions in
the column. Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. (2005) these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.
Keywords: bubble size, lift force, stability
  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Germany

Registration No. 26494 - Permalink


Eulerian multiphase flow modelling – Advanced concepts
Lucas, D.
Advanced concepts for Euler-Euler-modelling of gas-liquid flow were presented. The inhomogeneous MUSIG model is a basic framework for modelling bubbly flows. A baseline model for polydisperse bubbly flows was established at HZDR. For segragated flows the AIAD model can be used. The innovative GENTOP concept allows the consideration of different flow morphologies and transitions between them.
Keywords: Poly-disperse flows, Large interfaces, Multi-scale modelling, Flow pattern transition
  • Lecture (others)
    Computational Fluid Dynamics in Metallurgy - Advanced Seminar, 04.-06.12.2017, Köln, Deutschland

Registration No. 26489 - Permalink


Euler-Euler-modelling of poly-disperse bubbly flows
Lucas, D.
Bubbly flows occur in various industrial processes. For medium and large industrial scales the Euler-Euler approach is frequently applied in CFD-simulations. To derive the corresponding balance equations for mass, momentum and energy averaging procedures are applied and in the result information on the gas-liquid interface gets lost. Models reflecting the physics at the non-resolved scale are required to close the problem. This concerns the momentum transfer between bubbles and liquid (bubble force models), modulation of turbulence by the bubbles (BIT – bubble induced turbulence), bubble-bubble interactions (coalescence and breakup) and mass and heat transfer between the phases (boiling, condensation, heterogeneous chemical reactions). Most of these closure models sensitively depend on the bubble size and even may change their sign in dependency on the bubble size (lateral lift force). Correspondingly an appropriate modelling requires the consideration of the bubble size distribution and in general also the sub-division of the gas phase in phases representing bubbles of a specific range of sizes.
Still there is no consensus on the closure models in literature. Often closures and open parameters are tuned to obtain agreement with experimental data. To achieve a consolidation of the modelling and more reliable predictions the so-called baseline model concept was proposed by HZDR. In the baseline model all closure models including constants are well defined and the fixed model is used for the simulation of different flow situations involving bubbles in the mm-range and larger without any modification.
The lecture presents the baseline model concept, introduces the baseline model for poly-disperse bubbly flows (including the definition of closures for bubble forces, BIT, coalescence and breakup), the inhomogeneous MUSIG model for the consideration of the bubble size distribution and the modelling of phase transfer and chemical reaction. The baseline model for poly-disperse bubbly flows was validated for more than 150 single experiments. Examples for the validation are given and perspectives of the future modelling are discussed.
Keywords: CFD, Euler-Euler, bubbly flow, baseline model
  • Lecture (others)
    ERCOFTAC Best Practice Guidance Seminar, CFD for Dispersed Multi-Phase Flows, 20.-21.11.2017, Magdeburg, Deutschland

Registration No. 26488 - Permalink


CFD-model for industrial bubbly flows
Lucas, D.; Rzehak, R.; Ziegenhein, T.; Krepper, E.; Liao, Y.
Computational Fluid Dynamics (CFD) is an accepted tool for design and optimisation in many single-phase flow applications, e.g. in automotive or aviation industries. In principle, CFD has the same potential also for multiphase flows, but it is not yet mature for routine applications because of the complexity of such flows. For medium and large scale industrial applications the Euler-Euler approach is most suited and the interactions between the phases have to be reflected by closure models. In bubbly flows such interactions between the liquid flow field and the deformable bubble interfaces have an important influence on the flow characteristics. CFD-models should depend on local flow characteristics as e.g. shear rate, turbulence, and bubble sizes. Locally such properties may be very similar even in quite different flow situations like bubbly pipe flows, bubble columns or air-lift reactors. Instead of case by case tuning the development of a unified model for bubbly flows seems to be a promising way to increase the reliability of predictions obtained from CFD-simulations. Such a model was established at HZDR and has been applied to many different bubbly flow situations without any modification. This contribution presents this model and some examples for application to different industrial relevant bubbly flows.
Keywords: CFD, Euler-Euler, bubbly flow, polydispers, baseline
  • Contribution to proceedings
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy
  • Lecture (Conference)
    14th International Conference on MULTIPHASE FLOW IN INDUSTRIAL PLANTS (MFIP17), 13.-15.09.2017, Desenzano del Garda, Italy

Registration No. 26487 - Permalink


Influence of the bubble size distribution on bubble column stability
Lucas, D.; Ziegenhein, T.; Schipp, J. F.
Bubble columns are widely used in industrial processes. The performance in case of chemical reactions between liquid and gaseous substances depends on characteristic parameters as interfacial area density, turbulence level, or kLa-values. Transitions between the homogeneous and the heterogeneous operating regime dramatically change such characteristic parameters and are for this reason subject of many investigations. Many of them tried to correlate the transition with the gas superficial velocity Jg or equivalent integral parameters, but there is no general valid critical value for the transition. Lucas et al. (2005) discussed the influence of the bubble size distribution on the stability of a homogeneous bubbly flow. Depending on the sign of the lateral lift force, which changes with the bubble size (Tomiyama et al., 2002), it can stabilize (positive lift force coefficient – small bubbles) or destabilize (negative lift force coefficient – large bubbles) the flow. Basing on a linear stability analysis finally a criterion was obtained for the stability of a homogeneous bubbly flow in dependence on the bubble size distribution. Indirectly it also depends on Jg since usually bubble sizes increase with increasing Jg caused by larger size of the injected bubbles and by increased coalescence. Lucas et al. (2007) discussed the complex relations between local and global instabilities that may be quite complex basing on CFD-simulations. Akbar et al. (2013) showed the influence of injection and bubble size on the flow structure in a rectangular bubble column.
The bubble size distribution clearly has an influence on the transition between the homogeneous and heterogeneous regime in bubble columns which can be explained by effects of the lateral lift force. It interacts with other phenomena like inlet induced instabilities and coalescence processes. A detailed investigation on these effects is presented in this contribution.
Keywords: bubble column, flow regime, regime transition, lift force, bubbly flow
  • Contribution to proceedings
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brussels, Belgium

Registration No. 26486 - Permalink


Simulation of flow pattern transitions in the Euler-Euler framework
Lucas, D.; Krepper, E.; Höhne, H.; Oertel, R.; Schlegel, F.
Two-phase flows occurring in nature or industrial applications frequently involve gas-liquid interfaces which vary over a wide range of scales. Simultaneously, within one flow domain there might be very small bubbles or droplets, but also large interfaces as e.g. caused by stratification due to gravity. In addition transitions between these different morphologies may occur such as bubble entrainment by jets or breaking waves, droplet generation from wave crests or the generation of large gas structures out of smaller ones by coalescence. Such flow situations are very challenging from the modelling point of view. At least for medium and large size flow domains it is not possible to resolve all interfacial scales down to the smallest ones because this would lead to a number of cells of the numerical grid which would exceed todays computing capacity by far. Consequently there will be interfaces smaller and larger than the computational grid. Clearly the smaller ones should be considered by appropriate sub-grid models while the larger ones should be simulated.
Up to now there is no CFD approach established for such flow situations. One promising approach is the so-called GENeralized TwO-Phase Flow concept (GENTOP) which was recently developed at Helmholtz-Zentrum Dresden – Rossendorf. It bases on the two-fluid multi-field approach. Beside one or several fields representing the dispersed morphologies of gas and/or liquid potentially continuous phases for gas and liquid are introduced. Interfaces between these potentially continuous fields are statistically resolved if the local volume fraction is large enough. If this is not the case, closure models for the disperse phase are applied. For this reason it is called potentially continuous phase. The coupling of the dispersed and potentially continuous fields is done basing on a population balance. The knowledge on the typical length scale of a gas or liquid structure allows its presentation in the corresponding field. Transitions can be modelled as coalescence and breakup processes which are in agreement with the involved physical phenomena.
The concept was previously implemented in the CFX-code of ANSYS and tested considering only one continuous field for liquid, but disperse fields and a potentially continuous field for gas. Demonstration cases involve the bubble entrainment by a plunging liquid jet, generation of large bubbles out of small ones due to coalescence in a bubble column, collapse of a water column with transitions from continuous to disperse morphologies of the gas in the beginning and the vice versa process in the later phase and the simulation churn-turbulent pipe flows. Recently first simulations were done for boiling in a side wall heated vertical pipe. Single phase liquid enters the pipe from below with slight sub-cooling. Steam bubbles are generated at the wall and continue to increase and coalesce producing large bubbles which migrate to the pipe center caused by the inversion of the lateral lift force. Finally large gas structures are observed in the pipe center leasing to a transition to annular flow. The simulation involves the transition between bubbly flow and churn-turbulent flow regime and a starting transition to annular flow. In the talk the GENTOP concept and selected demonstration cases with focus on the new simulations on boiling in the heated pipe are presented. Also some recent developments to implement a similar approach in OpenFOAM are presented.
Keywords: multiscale, modelling, GENTOP, CFD, two-phase, boiling
  • Invited lecture (Conferences)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, ICNMMF-III, 26.-29.06.2017, Tokyo, Japan

Registration No. 26485 - Permalink


Dependency of bubble column flow regime on bubble size distribution
Ziegenhein, T.; Lucas, D.
The regime transition from homogenous to heterogeneous is one of the most important design parameters of bubble columns. The lateral lift force may have an important influence on this transition. As shown experimentally and by numerous direct numerical simulations the lateral lift force changes its sign in dependence on the bubble size. Recently the findings of Tomiyama et al. obtained for single bubbles in a linear laminar shear flow for a system with high Morton number (high viscosity) were also confirmed for low the viscid air-water system and turbulent conditions. The well-known correlation of Tomiyama et al. fits very well also for these conditions, provided the Eötvös number based on the major axis is used. With the Tomiyama correlation combined with the Wellek correlation for the bubble shape the critical diameter for the change of the sign of the lift force is about 5.8 mm for the air-water system. While the Wellek-correlation is valid for contaminated water deionized water was used in the new HZDR experiments. Replacing the Wellek- correlation by a correlation based on the observed bubble shape the critical diameter for the change of the sign is about 4.5 mm.
With a positive sign of the lift force coefficient – which is valid for bubbles smaller than the critical diameter a homogeneous bubbly flow is stabilized while larger bubbles destabilize the flow. Lucas et al. derived a stability criterion also for bubble size distributions that include small and large bubbles.
Experiments investigating the effect of the bubble size distribution were conducted in a high aspect ratio bubble column for air/purified water. The gas flow through the sparger groups was varied to modify the partial gas fraction of the small and large bubbles. Due to this variation, the stability criterion was manipulated from ‘strong’ negative to ‘strong’ positive. Measurements were done for different height positions in the column.
Completely different flow structures and profiles were observed by only changing the bubble size. Homogeneous flow characterized by flat profiles for gas volume fraction and liquid velocity were observed for a bubble size distribution with mainly small bubbles, while a center peak characterizing the heterogeneous regime occurs for the distribution with large bubbles. Applying the stability criterion of Lucas et al. these two situations correspond to ‘strong’ negative and ‘strong’ positive meaning homogeneous and heterogeneous flow regime, respectively. Beside these extreme cases also the transition region was investigated. Here the measurements are made difficult because coalescence changes the bubble size distribution along the column height resulting in a transient behavior. In any case, the lift force seems to be the key for a local criterion on the regime transition.
Keywords: bubble column, flow regime, lift force, bubbly flow, stability
  • Lecture (Conference)
    53rd European Two-Phase Flow Group Meeting, 22.-24.05.2017, Gdansk, Poland

Registration No. 26484 - Permalink


SOS Metallurgy - Save our Smelters
Reuter, M. A.
Maintaining European metallurgy know-how and how to integrate metallurgy into sustainable primary and secondary raw material industry.
  • Invited lecture (Conferences)
    Europe—From Mine to Market, 28.09.2017, Dresden, Deutschland

Registration No. 26482 - Permalink


Opportunities & Limits of the Circular Economy
Reuter, M. A.
Metallurgy is a key enabler of a circular economy, its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a circular economy, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a circular economy, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency of the circular economy system, connecting all stakeholders via digitalization.
Keywords: circular economy
  • Invited lecture (Conferences)
    Strategic Materials for a Low-Carbon Future: From Scarcity to Availability / Resource Availability Conference, 02.-03.11.2017, Oxford, United Kingdom

Registration No. 26480 - Permalink


Construction and validation of a long-channel membrane test cell for representative monitoring of performance and characterization of fouling over the length of spiral-wound membrane modules
Siebdrath, N.; Ding, W.; Pietsch, E.; Kruithof, J.; Uhl, W.; Vrouwenvelder, J.
Corresponding author: Uhl, W.
A long-channel membrane test cell (LCMTC) with the same length as full-scale elements was developed to simulate performance and fouling in nanofiltration and reverse osmosis spiral-wound membrane modules (SWMs). The transparent LCMTC enabled simultaneous monitoring of SWM performance indicators: feed channel pressure drop, permeate flux and salt passage. Both permeate flux and salt passage were monitored over five sections of the test cell and were related to the amount and composition of the accumulated foulant in these five sections, illustrating the unique features of the test cell. Validation experiments at various feed pressures showed the same flow profile and the same hydraulic behaviour as SWMs used in practice, confirming the representativeness and suitability of the test cell to study SWM operation and fouling. The importance to apply feed spacers matching the flow channel height in test cell systems was demonstrated. Biofouling studies showed that the dosage of a biodegradable substrate to the feed of the LCMTC accelerated the gradual decrease of membrane performance and the accumulation of biomass on the spacer and membrane sheets. The strongest permeate flux decline and the largest amount of accumulated biomass was found in the first 18 cm of the test cell. The LCMTC showed to be suitable to study the impact of biofilm development and biofouling control strategies under representative conditions for full-scale membrane elements.
Keywords: Feed spacer; RO spiral-wound module; NF; Permeate production; Membrane performance; Biofouling

Registration No. 26479 - Permalink


Modeling of Reactive Mass-Transfer in Bubbly Flows
Rzehak, R.; Krauß, M.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. Concerning the fluid dynamics of bubbly flows a certain degree of predictive capability has been reached recently. However, concerning mass transfer both with and without an accompanying chemical reaction only few studies have been performed to date.
The present contribution focusses on the so-called enhancement factor which describes the effect of a chemical reaction on the mass transfer. Different models available from the literature are compared. The reactive absorption of CO2 in aqueous NaOH is considered as an example. Simulations are compared with a set of experimental data reported by Darmana et al. [Chemical Engineering Science 62 (2007), 2556 - 2575]. Using an adequate model for the enhancement factor and taking into account the complete reaction network, an improved match with the data is obtained. Experimental conditions are suggested, for which further aspects of the system behavior become manifest.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics, Mischvorgänge, 16.-17.03.2017, Dresden, Deutschland

Registration No. 26477 - Permalink


Euler-Euler Modeling of Reactive Bubbly Flows
Rzehak, R.; Krauß, M.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. To achieve predictive capability, all details of the closure models have to be fixed in advance without reference to any measured data.
Concerning the fluid dynamics of bubbly flows a baseline model has recently been proposed to this end and shown to work for a range of different applications in a unified manner [1,2]. This provides a reliable background which is well suited to add more complex physics.
Concerning mass transfer in bubbly flows both with and without an accompanying chemical reaction only few studies have been performed to date [e.g. 3 and Refs. therein]. For the mass transfer coefficient, a variety of entirely different closures have been applied in rather similar situations. To facilitate predictive applications, a standard model which is validated for a broad range of conditions yet has to be developed. The effect of a chemical reaction on the mass transfer is described by an enhancement factor which depends on the type of the reaction. As an example for which some measured data are available for comparison [4], the absorption of CO2 in NaOH is considered.

[1] Rzehak, R., Ziegenhein, T., Kriebitzsch, S., Krepper, E., and Lucas, D. (2017), Unified modeling of bubbly flows in pipes, bubble columns, and airlift columns, Chem. Eng. Sci. 157, 147-158.
[2] Rzehak, R., Krauß, M., Kovats, P., and Zähringer, K. (2017), Fluid dynamics in a bubble column: New experiments and simulations, Int. J. Multiphase Flow 89, 299-312.
[3] Rzehak, R., and Krepper, E. (2016), Euler-Euler simulation of mass-transfer in bubbly flows, Chem. Eng. Sci. 155, 459-468.
[4] Darmana, D., Henket, R., Deen, N. and Kuipers, J. (2007), Detailed modelling of hydrodynamics, mass transfer and chemical reactions in a bubble column using a discrete bubble model, Chem. Eng. Sci. 62, 2556–2575.
Keywords: mass transfer, chemical reaction, chemisorption, enhancement factor, dispersed gas-liquid multiphase flow, Euler-Euler two-fluid model, CFD simulation
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Brüssel, Belgien

Registration No. 26476 - Permalink


Guest Editorial Special Issue on Sensors for Process Imaging
Bieberle, A.; Tan, C.; Soleimani, M.; Silva, M. J. D. (Editors)
Sustainable industrial production requires the use of advanced sensors and controls. In many industrial activities, the sensing and monitoring of processes provides valuable information for controlling and decision-making strategies as well as supporting the understanding and modeling of the phenomena involved. Since safety and efficiency requirements are continuously growing, the quality of information is becoming more and more important. A current trend to accomplish such requirements is the use of imaging sensors and systems generating and processing multidimensional data to extract key information from the processes. Further work is required to ensure that these imaging technologies are actually providing information that can be easily adapted and used in process control. This requires a holistic look at these sensing methods and data analysis.
Keywords: Special issues and sections Tomography Sensor phenomena and characterization Mechanical sensors Magnetic sensors Optoelectronic and photonic sensors Sensor systems and applications

Registration No. 26474 - Permalink


Defining the recovery potential for residual ore minerals from flotation tailings based on automated mineralogy data
Büttner, P.; Osbahr, I.; Zimmermann, R.; Leißner, T.; Satge, L.; Gutzmer, J.
The extraction of valuable (ore) minerals from fine-grained flotation tailings is a commercially interesting but technologically challenging endeavor that needs to be supported by a full technical and economic feasibility study. A novel approach to such the technological assessment is introduced here. It is illustrated by the example of an historic tailing storage facility containing ca. 0.2 weight percent of Sn as cassiterite. Mineral processing test work identified flotation as a suitable technology route to recover the residual cassiterite. The viability of flotation was attributed to three material parameters, namely grade, liberation and grain size of cassiterite. These parameters were quantified for a set of ten exploration drill cores by chemical assay and mineral liberation analysis. For each of the three relevant parameters an optimum range was defined by a weighting function that was applied to the data set. The data was then geo-referenced and combined to construct a 3-D model illustrating a depreciated grade, i.e., the amount of tin (as cassiterite) that could realistically be recovered from the tailings storage facility.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach
  • Lecture (Conference)
    Process Mineralogy '17, 20.-22.03.2017, Cape Town, South Africa

Registration No. 26440 - Permalink


Recovery potential of flotation tailings assessed by spatial modelling of automated mineralogy data
Büttner, P.; Osbahr, I.; Zimmermann, R.; Leißner, T.; Satge, L.; Gutzmer, J.
Corresponding author: Büttner, P. HZDR
The extraction of ore minerals from fine-grained flotation tailings is a commercially interesting but technologically challenging endeavor that needs to be supported by a full technical and economic feasibility study. A novel approach to such an assessment is introduced here. It is illustrated by the example of a historic tailing storage facility containing on average 0.2. wt% of Sn as cassiterite. Mineral processing test work identified flotation as a suitable technology route to recover this cassiterite. The viability of flotation was attributed to three material parameters, namely grade, liberation and particle size of cassiterite. These parameters were quantified for a set of ten exploration drill cores by chemical assay and mineral liberation analysis. For each of the three relevant parameters a suitable weighting function was defined that was applied to the entire data set. The data was then geo-referenced and combined to construct a 3D model illustrating a depreciated grade, i.e., the amount of cassiterite-bound tin that can realistically be recovered from the tailings. Results of the case study illustrate the importance of combining chemical grade data with quantitative mineralogical and microfabric information in any effort to objectively assess the residual value contained in industrial tailings or any other residue considered for re-processing.
Keywords: 3D modelling, Altenberg, Automated mineralogy, Cassiterite, Erzgebirge, Geometallurgy, Mine waste, Mineral liberation analysis, MLA, Processing, Re-mining, Re-processing, Recycling, Remediation, Remining, Reprocessing, Spatial modelling, Tailing, Tailing storage facility, Tin, Tin recovery, TSF, Zero waste approach

Registration No. 26439 - Permalink


A comparative study of machine learning methods for time-To-event survival data for radiomics risk modelling
Leger, S.; Zwanenburg, A.; Pilz, K.; Lohaus, F.; Linge, A.; Zöphel, K.; Kotzerke, J.; Schreiber, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; Krause, M.; Baumann, M.; Troost, E.; Löck, S.; Richter, C.
Corresponding author: Leger, S. OncoRay
Radiomics applies machine learning algorithms to quantitative imaging data to characterise the tumour phenotype and predict clinical outcome. For the development of radiomics risk models, a variety of different algorithms is available and it is not clear which one gives optimal results. Therefore, we assessed the performance of 11 machine learning algorithms combined with 12 feature selection methods by the concordance index (C-Index), to predict loco-regional tumour control (LRC) and overall survival for patients with head and neck squamous cell carcinoma. The considered algorithms are able to deal with continuous time-to-event survival data. Feature selection and model building were performed on a multicentre cohort (213 patients) and validated using an independent cohort (80 patients). We found several combinations of machine learning algorithms and feature selection methods which achieve similar results, e.g., MSR-RF: C-Index = 0.71 and BT-COX: C-Index = 0.70 in combination with Spearman feature selection. Using the best performing models, patients were stratified into groups of low and high risk of recurrence. Significant differences in LRC were obtained between both groups on the validation cohort. Based on the presented analysis, we identified a subset of algorithms which should be considered in future radiomics studies to develop stable and clinically relevant predictive models for time-to-event endpoints.

Registration No. 26437 - Permalink


4D Delivery - Treatment verification in particle therapy
Richter, C.; Jakobi, A.; Meijers, A.; Knopf, A.
4D delivery verficiation, mainly focussing on machine log-file based 4d dose reconstruction using 4D-CT and motion surrogate information
  • Invited lecture (Conferences)
    4D Treatment (Planning) Workshop, 04.-05.12.2017, Wien, Österreich

Registration No. 26427 - Permalink


Scale dependent soil erosion dynamics in a fragile loess landscape
Baumgart, P.; Eltner, A.; Domula, A. R.; Barkleit, A.ORC; Faust, D.
Loess landscapes provide highly fertile soils in temperate zones and thus are often under intensive agricultural use with a high susceptibility to soil degradation. Magnitudes of soil erosion on different spatio-temporal scales are hard to recognise or were even ignored due to the restricted human perception. Precise and reliable soil erosion measurements are still very scarce, especially for intense single precipitation. In this study, present-day soil erosion is investigated as a complex process on different spatial and temporal scales, such as a short-term observation on plot scale and a medium-term observation on slope scale, which lead to long-term indications for the catchment scale. Classical soil drillings, 7Be and 137Cs radionuclide tracer investigations and non-invasive unmanned aerial vehicle (UAV) photogrammetry were performed for two cultivated field sections within the Saxon Loess Province (Eastern Germany). The main findings are: (1) for a short-term intense precipitation event interrill soil erosion reaches up to 4.69 ± 0.73 mm on plot scale and mean total erosion values reach 1.45 mm on catchment scale; (2) medium-term soil erosion exhibit values up to 33 cm on slope scale within the last 50 years, indicating a strong landscape liability to agricultural use; (3) climatic pressure with increasing temperature and precipitation shifts towards seasons with bare soil surfaces favours the soil erosion process and increases the fragility of the landscape substantially. In conclusion, soil erosion is the driving factor of present-day landscape evolution in the Saxon Loess Province.
Keywords: Saxon Loess Province, Beryllium-7, Caesium-137, unmanned aerial photogrammetry (UAV)
  • Contribution to external collection
    in: Zeitschrift für Geomorphologie, Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung, 2017, 191-206
    DOI: 10.1127/zfg/2017/0409

Registration No. 26423 - Permalink


Bioassociation of uranium onto an extremely halophilic microorganism relevant in nuclear waste repositories in rock salt
Bader, M.
Microorganisms indigenous to rock salt must be considered for the safety analysis of a final repository for radioactive waste in a salt rock formation. Metabolic activity can cause microbial induced redox processes and influence radionuclide speciation and solubility. Additionally, passive biosorption onto living as well as dead biomass may affect the migration of radionuclides [1].
An extremely halophilic archaeon indigenous to rock salt was used for this study. Two similar strains with different origin were compared concerning their interaction processes with uranium. Halobacterium noricense DSM 15987 was originally isolated from an Austrian salt mine [2], the second strain Halobacterium putatively noricense was isolated from the Waste Isolation Pilot Plant (WIPP) [3].
[1] Lloyd, J. R. et al., Interactions of Microorganisms with Radionuclides (Eds. M. J. Keith-Roach, F. R. Livens), 313-342 (2002).
[2] Gruber, C. et al., Extremophiles, 8, Page 431-439 (2004).
[3] Swanson, J. S. et al., Status Report on the Microbial Characterization of Halite and Groundwater Samples from the WIPP - Status report Los Alamos National Laboratory, Page 1ff. (2012).
  • Lecture (Conference)
    Kompetenzzentrum Ost für Kerntechnik, 07.12.2017, Dresden, Deutschland

Registration No. 26420 - Permalink


Biomineralization of uranium(VI) by fungi - alternative for remediation approaches?
Schäfer, S.; Gerber, U.; Krawczyk-Bärsch, E.; Merroun, M. L.
Uranium pollution of soils and waters within the environment is from big concern. A range of remediation strategies were developed using chemicals and industrial equipment. As a consequence, the conventional remediation of polluted sites is elaborated and time-consuming. Microorganisms can affect the solubility of uranium and thus they could be an appropriate alternative in bioremediation approaches. It is well described that microorganisms could interact with metals in different ways. One of these is called biomineralization, and is defined as an interaction mechanism between microorganisms and metals whereby biological produced minerals capture pollutants within stable solid phases.
We investigated natural occurring fungi which were directly isolated from the flooding water of the former uranium mine Königstein in Germany. The isolated strain KS1 Penicillium simplicissimum displayed the ability to immobilize high amounts of uranium from surrounding solutions. Metabolism-dependent uranium removal experiments revealed in different interaction mechanisms of KS1 with uranium(VI). By transmission electron microscopy (TEM) we observed that the immobilization of the soluble uranium(VI) took place by bioaccumulation within the cells and furthermore by biomineralization outside of the cells. EDX investigations resulted in amorphous phosphate-minerals inside and outside the cells. In addition, enzymatic analysis displayed organic acids which were produced by the fungi and released to the solution. The results of our investigations revealed that the isolated fungi KS1 could be a suitable candidate for further bioremediation studies. Uranium was immobilized effectively, fast and possibly within stable solid phases. Compared to conventional remediation approaches the use of microorganisms should be taken into account.
Keywords: Bioremediation, Uranium, Biomineralization
  • Invited lecture (Conferences)
    16. Remediation Colloquium Jena, 05.-06.10.2017, Jena, Germany

Registration No. 26416 - Permalink


Wechselwirkungen zwischen U(VI) und Ca-Bentonit sowie Cm(III) und CSH-Phasen unter dem Einfluss alkalischer und hochsalinarer Porenwässer
Philipp, T.; Wolter, J.-M.; Schmeide, K.; Stumpf, T.
Der Vortrag fasst den aktuellen Stand der Untersuchungen innerhalb des BMWi-Verbundprojektes GRaZ zusammen. Es werden im Wesentlichen Ergebnisse zu zwei Systemen vorgestellt: U(VI) / Ca-Bentonit, sowie Cm(III) / CSH - Phasen. Die U(VI)-Rückhaltung an Ca-Bentonit zeigt eine große Variabilität im pH-Bereich 8-13 und ist stark vom Carbonat-Gehalt abhängig. Eine Erniedrigung der U(VI)-Rückhaltung bei pH > 8 in Gegenwart von Carbonat durch Bildung schwach sorbierender Uranyl-Carbonat-Komplexe wurde nur bis zu einem bestimmten pH Wert beobachtet. Bei höherem pH wird die aquatische Speziation widerrum durch Uranyl-Hydroxo-Komplexe dominiert, was zu einer erhöhten U(VI)-Rückhaltung führt. Der zugrunde liegende Rückhaltemechanismus konnte noch nicht eindeutig geklärt werden. Erste spektroskopische Untersuchungen der Oberflächenkomplexe deuten aber darauf hin, dass Oberflächenausfällung und/oder der Bildung oligomerer Oberflächenkomplexe zur Rückhaltung beitragen.
Cm(III)-dotierte CSH-Phasen konnten erfolgreich hergestellt und mittels TRLFS characterisiert werden. Anschließende Leaching-Versuche mit 0,02 M NaHCO3 und 2,5 M NaCl zeigten, im Gegensatz zu vergleichbaren Untersuchung mit U(VI), keinerlei remobilisierung des Curiums. Grund dafür ist der Einbau des freigesetzten Curiums in bei der Alteration neu gebildete Calcit- und Vateritmineralphasen.
  • Lecture (others)
    5. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 15.11.2017, Potsdam, Deutschland

Registration No. 26414 - Permalink


Quantitative prediction of critical heat flux initiation in pool and flow boiling
Ding, W.; Krepper, E.; Hampel, U.
Corresponding author: Ding, W.
Boiling is a very efficient heat transfer mechanism with a large heat transfer coefficient and it is widely found in industrial systems. However, boiling heat transfer is limited by the critical heat flux (CHF), also termed as boiling crisis. It leads to a rapid decrease of the heat transfer coefficient in temperature controlled heat transfer or to a significant jump in heater surface temperature in power controlled heat transfer cases. While the earlier effect clearly lowers efficiency the latter may even jeopardize safety. A clear understanding of the basic mechanisms leading to CHF is still lacking. In this paper a new model of priori critical heat flux(CHF-) is derived from the bubble dynamics of nucleate boiling. It holds for pool boiling and forced convective boiling and incorporates a mutual effect model and a shear stress model. The comparison between predicted and experimental results under different thermal hydraulic conditions shows a good agreement. The model is capable to explain the initiating mechanism of the boiling crisis and impacts from different variables. It can be also implemented as a sub-model in CFD codes.
Keywords: Critical heat flux (CHF), boiling heat transfer, pool boiling, forced convective boiling, cavity activation

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  • Secondary publication expected from 28.11.2018

Registration No. 26411 - Permalink


Investigation of pore and network formation in spin-on ultra low-k dielectrics by spectroscopic techniques
Koehler, N.; Liedke, M. O.; Attallah, A. G.; Butterling, M.; Anwand, W.; Wagner, A.; Krause-Rehberg, R.; Schulz, S. E.
Positronium annihilation spectroscopy has become more and more important in microelectronics industry as one of the few methods to characterize engineered nanopores in next-generation (k < 2.4) interlayer dielectrics (ILD). With the addition of infrared spectroscopy a way is found to investigate the pore and network formation during the curing process.
1. Introduction
Porous spin-on glasses are one great candidate for the integration as ultra low-k (ULK) dielectrics in Back-End of Line (BEOL) for advanced technology nodes. They offer the possibility of a structured pore network by using “Block Polymer Templated Inorganic Oxides” (USP 6,592,764) [1]. Therefore, it is possible to adjust the physical properties of these thin films [1] as well as pore size and porosity. However, these materials are also prone to dielectric damage [2,3] during the integration into back-end of Line. In addition, these material degradations will increase with porosity [3]. It follows, that beside the damage mechanism also the pore and network formation of ULK materials need to be investigated more in detail to comprehend integration damage from the very first time of appearance. This work will evaluated the formation of spin-on glasses during curing by positron annihilation spectroscopy to observe the pore formation and by Fourier Transform Infrared spectroscopy to study the network formation.
2. Experimental
2.1 Preparation of spin-on dielectrics
For preparation of spin-on ULK material a solution from SBA Materials, Inc. was used. The ULK liquid precursor consists of an amphiphilic block copolymer with silicon alkoxide esters [1]. The final thickness is supposed to be 500 nm with an initial k-value of 2.2. The solution was spin-coated on 6-inch silicon wafers with 2000 rpm for 60 s. The spin-coated samples were soft baked for 120 s at 150 °C. The curing procedure was performed with the quartz glass oven PEO 603 from ATV technologies for different curing times at 450 °C under nitrogen atmosphere. The heat ramp of curing was chosen to be 7 °C/min.
2.2 Measurement techniques of pore and network structure
Fourier Transform Infrared (FTIR) spectroscopy was used to determine the chemical and structural changes before and after different curing times. The measurements were performed in transmission mode in the mid-range from 400 to 4000 cm-1, using the Bruker Tensor 27 spectrometer. The optical response is given as absorbance and normalized to thickness as well as treated by a baseline subtraction. Thus a comparison of the different processes can be achieved. Furthermore, a deconvolution of the FTIR peaks at the oxide region (1300 cm-1 to 950 cm-1) was accomplished with the Peak-Fit Module of ORIGIN 8.5 software. As it is described in literature the oxide region is used to be deconvoluted into the following peaks: the suboxide-, network-, cage-peak [4,5] and the Si-O-C peak [6]. The area was normalized to the total area of the Si-O-Si area.
The characterization of the nanopores were carried out at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) with positron annihilation spectroscopies (PAS). For determination of different pore components the Elbe Positron Source (EPOS) was used; a pulsed positron source with high repetition rate, high intensity and choosable energies for depth profile measurements [7,8]. Furthermore, by using the The Slow-Positron System of Rossendorf (SPONSOR) Doppler broadening spectroscopy was used to acquire also information about the atomic surrounding of the pores.
Since the possibility of diffusing out of ortho-positronium (o-Ps) from film surface through open, interconnecting pores the ULK films were covered with a 20 nm thick carbon layer by evaporating using a pre-shaped carbon rod.
3. Results
Fig. 1 shows the FTIR spectrum of the uncured and cured samples after 5 min, 30 min, 60 min and 90 min at 450 °C. The curing process at 450 °C for 90 min can be considered as complete cure. The uncured sample shows the –OH absorbance peak at 3400 cm-1 and the Si-OH peak at 914 cm-1 [9], which is characteristic for spin-on glasses in sol-gel science [10]. During the curing process the methylsilsesquioxane (MSQ) based Si-OH groups condensate and cross-linking occurs to form a 3D network [11]. Besides the Si-OH peak in the uncured sample the region from 3000 cm-1 to 2800 cm-1 is more pronounced compared to the cured samples. There are located the C-Hx vibration bands, which mostly correspond to porogen to form a porous network. The region from 900 cm-1 to 700 cm-1 is called the fingerprint region, where mostly the different Si-C vibration modes are dominate [9]. The absorbance peak at 1277 cm-1 belongs to the Si-CH3 vibration band.
The two main mechanism during the curing of spin-on ULK are the cross-linking of the Si-OH groups to form a mechanically stable thin film and the porogen removal to form a porous network. The cross-linking of Si-OH to form the Si-O-Si linkage can be seen in Fig 1. in the range of 1250 cm-1 to 960 cm-1. Already after 5 min of curing the Si-O-Si region is formed almost completely and only little changes during further curing are observed. By taking a closer look at the Si-O-Si region, a shift from 1047 cm-1 to 1052 cm-1 can be observed. Within this region four peaks are overlapping: the suboxide-, network-, cage- [4,5] and the Si-O-C peak [6]. To distinguish between those peaks a deconvolution was done, where the results are shown in Fig. 2. With increasing curing time the network peak rises whereas the cage and the suboxide peak decreases. This behavior is likely due to the cross-linking of the network material and is less pronounced after 30 min of curing. The Si-O-C peak seams not to be affect by curing time.
Fig. 3 and Fig. 4 show the results from the DBS and PALS measurements. From the DBS measurements two specific line parameters can be calculated: the S- and W-parameter. The S-parameter is a measurement of the open volume and the W-parameter is a measurement of the atomic environment of the annihilation site. The mean implantation depth for the positrons is given in nanometer scale at the upper x-axes based on the density of silica. The first 20 nm (until 1.2 keV) the S- and W-parameter corresponds to the carbon capping layer and retain unchanged for all treatments. The W-parameter for the uncured sample shows the highest values. Only for 20 nm Carbon layer the W-parameter is higher. Within the first minutes of curing, the porogen is almost removed and the W-parameter decreases. From 30 min to 90 min no change in W-parameter is visible anymore. Compared to the FTIR spectra (Fig. 1) in the region of 3000 cm-1 to 2800 cm-1 no change for all curing times are visible which shows the sensitive behavior of PAS measurements for nanopore evaluations. For the cross-linking behavior (Fig. 2) the dependence on curing time can still be observed in detail by FTIR. Therefore, it can be concluded that the porogen extraction at 450 °C with a slow heating ramp is completed within the first 30 min, whereas the cross-linking of the network takes places over the complete curing time.
The calculated pore components from PALS measurements are shown in Fig. 4. Two different lifetime components were found. The upper diagrams show the diameter of the pores and the lower diagrams show the intensities of the pore components. The first pore component has a diameter of around 0.8 nm which does not change for all curing treatments and positron energies, whereas the intensities of the component 1 decrease from the uncured to the cured state. With regard to the FTIR results (Fig. 1 and Fig. 2), this pore component intensities shows the inverse behavior of the oxide region, where the network is formed. Therefore, this component is likely due to the unreacted Si-OH groups, which decreases during the curing. The second pore component arises from the pores itself and was not observed at the uncured sample. The mean diameter is about 3.4 nm, which lowers to 3 nm near the surface of the film. This can be due to the carbon capping layer deposition and needs further considerations. Also it can be seen that the pore diameter from 5 min to 30 min still increases and reaches a final value after 30 min. In addition, the intensity of the pore component 2 changes marginal. That confirms that the porogen extraction as well as the pore formation takes place within the first 30 min.
4. Summary
In this work, the pore formation of spin-on ULK materials with an initial k-value of 2.2 was studied for a thermal curing process at 450 °C with a slow heat ramp for curing. After 5 min of curing most of the porogen is extracted and the network is formed almost completely, which can be seen by PAS and FTIR. The porogen extraction as well as the pore formation appear to be complete after 30 min, whereas the remaining time is needed to form the network.
All the investigations are running right now for faster heat ramp of curing as well as for different curing temperatures to slow down the pore formation process and get a better understanding of the processes taking place inside the material during curing.
References
[1] P. Garrou, Solid State Technology, p. 10, Nov. 2010, Accessed 22 May 2017
[2] J.L. Shohet et al., ECS Transactions, 60 (1) p. 733-738 (2014)
[3] M.R. Baklanov et al., Journal of Applied Physics 113, p. 041101, (2013)
[4] L. Zhang et al., ECS Solid State Lett. 2 (2), p. N5 (2013)
[5] A. Grill et al., J. Appl. Phys. 94 (10), p. 6697 (2003).
[6] Y. Lin et al., J. Electrochem. Soc. 153 (7), p. F144 (2010)
[7] A. Uedono et al. Applied Surface Science, Bd. 368, pp 272-276 (2016)
[8] A. Wagner et al., Defect and Diffusion Forum, Bd. 331, pp. 25-40, (2012)
[9] B. Xie et al., Microelectron. Eng, 76 (1-4) p. 52-59 (2004)
[10] P. Eaton et al., J. Appl. Polym. Sci. 82 (8), p. 1097-4628 (2001)
[11] A. Zenasni et al., J. Electrochem. Soc. 154 (1) p. G6 –G12 (2007)
Keywords: low-k materials, dielectrics, positron annihilation spectroscopy, positron lifetime, Fourier Transform Infrared Spectroscopy, Doppler broadening spectroscopy, pores, networks
  • Poster
    2017 Advanced Metallization Conference, 13.-14.09.2017, Austin, TX, USA

Registration No. 26409 - Permalink


Assembly Behavior of Organically Interlinked Gold Nanoparticle Composite Films: A Quartz Crystal Microbalance Investigation
Daskal, Y.; Tauchnitz, T.; Güth, F.; Dittrich, R.; Joseph, Y.
Corresponding author: Daskal, Yelyena Technische Universität Bergakademie Freiberg
Thin films based on dodecylamine stabilized gold nanoparticles interlinked with different organic molecules are prepared by automatic layer-by-layer self-assembly in a microfluidic quartz crystal microbalance (QCM) cell, to obtain an in situ insight on the film formation by ligand/linker exchange reactions. The influence of interlinking functional groups and the length of the organic linker molecule on the assembly behavior is investigated. Alkyldithiols with different lengths are compared to alkyldiamines and alkylbisdithiocarbamates with a C8 alkylic molecular backbone. The stepwise layer-by-layer assembly occurs independently of the linker molecule, while the largest frequency changes always correspond to the gold nanoparticle step.
During the solvent rinsing and ligand/linker exchange reaction step, the frequency is almost constant with slight increases or decreases dependent on the molar mass of the linker compared to the exchanged ligand. The assembly efficiency is higher for shorter molecules and for molecules with stronger interacting functional groups. The densities of the composite films are calculated from QCM data and independent thickness measurements. They reflect the higher fraction of organic material in the films comprising longer organic linkers. The plasmon resonance band of the gold nanoparticles in the final assemblies is measured with UV/vis spectroscopy. Band positions in films prepared from dithiols and diamines of comparable lengths are very similar, while the spectrum of the bisdithiocarbamate film exhibits a distinct blue-shift. This observation is explained by the longer molecular structure of the linker due to a larger binding group, in conjunction with a delocalization of particle charge on the organic molecule. Obtained results play an essential role in the understanding of thin film layer-by-layer self-assembly processes, and enable the formation of new gold nanoparticle networks with organic diamine and bisdithiocarbamate molecules.

Registration No. 26407 - Permalink


Synthese und Charakterisierung von funktionalisierten Calix[4]arenen zur Chelatisierung von Barium und Radium
Steinberg, J.
Die Entwicklung von Ra2+-Komplexen für den Einsatz der radiopharmazeutisch interessanten Radiumnuklide Ra-223 und Ra-224 in Radiotherapeutika, beispielsweise zur Behandlung eines breiten Spektrums an Tumoren, steht im Fokus dieser Arbeit. Um einen Einbau des calciummimetischen Ra2+ in den Hydroxyapatit des Knochengewebes zu unterbinden, müssen die Radiometallkomplexe hohe Komplexstabilitäten aufweisen. Bifunktionelle Chelatoren mit einer hochaffinen Targeteinheit zum Zielgewebe sollen den Transport zum pathogenen Gewebe möglich machen. Die emittierte α-Strahlung des Radiums führt zur Zerstörung des Zielgewebes.
Vielversprechend stellen sich überbrückte und funktionalisierte p-tert-Butylcalix[4]arenderivate dar. Die erforderliche hohe Stabilität des Komplexes soll dabei besser als mit offenkettigen und einfach cyclischen Verbindungen erreicht werden, da eine definierbare Kavität selektiver und stabiler Metalle bindet. Durch die sterischen Effekte, die durch zusätzliche Modifikationen eintreten, soll der Komplex vor Dissoziation geschützt werden. Einerseits lassen die p-tert-Butyl-Gruppen der upper rim-Seite keinen Angriff auf die Metallionen zu, andererseits werden sie zusätzlich durch die sterisch anspruchsvollen Substituenten der lower rim-Seite festgehalten. Zudem sollen deprotonierbare Positionen an Funktionalisierungen gute Bindungsstellen für Ra2+ zur Komplexbildung darstellen. Aufgrund ähnlicher chemischer Eigenschaften wird Ba2+ als Surrogat für diese Untersuchungen eingesetzt, um das Komplexierungsverhalten der Calixarene zu studieren.
Keywords: Radium, Barium, Calix[4]arene
  • Diploma thesis
    TU Dresden, 2017
    Mentor: Dr. Constantin Mamat
    0120 Seiten

Registration No. 26403 - Permalink


Desertification Susceptibility Mapping Using Logistic Regression Analysis in the Djelfa Area, Algeria
Djeddaoui, F.; Chadli, M.; Gloaguen, R.
Corresponding author: Gloaguen, Richard Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology
The main goal of this work was to identify the areas that are most susceptible to desertification in a part of the Algerian steppe, and to quantitatively assess the key factors that contribute to this desertification. In total, 139 desertified zones were mapped using field surveys and photo-interpretation. We selected 16 spectral and geomorphic predictive factors, which a priori play a significant role in desertification. They were mainly derived from Landsat 8 imagery and Shuttle Radar Topographic Mission digital elevation model (SRTM DEM).
Some factors, such as the topographic position index (TPI) and curvature, were used for the first time in this kind of study. For this purpose, we adapted the logistic regression algorithm for desertification susceptibility mapping, which has been widely used for landslide susceptibility mapping. The logistic model was evaluated using the area under the receiver operating characteristic (ROC) curve. The model accuracy was 87.8%. We estimated the model uncertainties using a bootstrap method. Our analysis suggests that the predictive model is robust and stable. Our results indicate that land cover factors, including normalized difference vegetation index (NDVI) and rangeland classes, play a major role in determining desertification occurrence, while geomorphological factors have a limited impact. The predictive map shows that 44.57% of the area is classified as highly to very highly susceptible to desertification. The developed approach can be used to assess desertification in areas with similar characteristics and to guide possible actions to combat desertification.
Keywords: desertification; logistic regression; steppe; Djelfa

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Registration No. 26402 - Permalink


Pressure-induced insulator-to-metal transition in VO₂ studied by near-infrared pump – mid-infrared probe spectroscopy
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
The strongly correlated electron material VO₂ shows an insulator-to-metal transition (IMT) when heated above Tc = 340 K accompanied by a lattice transformation from monoclinic to rutile structure. The mechanism of the temperature-driven IMT in VO₂ is very complex and involves a Peierls instability facilitated by a strong Coulomb interaction. However, the hierarchy of these processes during the IMT is still under discussion.

Ultrafast time-resolved techniques allow to study the photo-induced IMT in VO₂ that occurs on a femtosecond time scale. At sufficient pump fluences the insulating gap closes almost instantaneously due to the screening of the Coulomb repulsion [1] and the lattice evolves on a sub-picosecond timescale to a rutile structure indicating the existence of a transient monoclinic metallic phase [2].

On the other hand, application of external pressure also can induce an equilibrium monoclinic metallic phase [3]. Therefore, the mechanism of the pressure-induced IMT in VO₂ must be qualitatively different compared to the temperature-driven IMT. However, until now the information about the electronic band structure of the pressurized metallic phase remains obscure due to incompatibility of photoemission spectroscopy with high-pressure techniques.

Here we use ultrafast near-infrared pump – mid-infrared probe spectroscopy in order to unravel the changes in the electronic structure of VO₂ across the pressure-induced IMT. The nonlinear spectroscopy allows us to extract information about the response of localized and free charge carriers. In this case the non-degenerate pump-probe scheme is essential: The probe photon energy of 0.12 eV is well below the band gap (0.6 eV) at ambient conditions while the pumping with photon energies of 1.5 eV photo-excites additional charge carriers across the band gap.

The probe radiation is focused on a VO₂ single crystal inside a diamond anvil cell to a nearly diffraction limited spot. We measure the transient reflectivity change in mid-infrared induced by the near-infrared pumping. In agreement with previous studies the pump-probe traces indicate the onset of a long-living metallic state when the excitation fluence exceeds a certain threshold 𝛷th [4]. The results for three independent experimental runs of different VO₂ crystals are shown in Figure 1 together with the linear transmissivity of the probe beam. Initially the threshold grows with pressure increase, but at a critical pressure pc of 6-8 GPa a sudden drop is observed. It coincides with the vanishing of the linear transmissivity (measured without pumping) indicating the pressure-induced IMT in the sample. Remarkably, there is a remnant threshold behavior even for pressures above pc. By pumping it is still possible to enhance the conductivity of the pressure-induced metallic phase. Such behavior is fundamentally different from the temperature-driven IMT, where all t2g bands overlap with the Fermi level leading to the vanishing of the pump-probe response in the metallic phase.

We suggest that the pressure-induced changes of the threshold and linear transmission agree well to a scenario of a bandwidth-driven Mott-Hubbard transition [5]. In this scenario of a purely electronic IMT, pressure-induced increase of the bandwidth leads to a spectral weight transfer from the Hubbard bands to a quasiparticle peak at the Fermi level causing metallic conductivity and a gradual filling of the insulating gap. As a large portion of the spectral weight is still located in the Hubbard bands, the number of charge carriers still can be increased by photoexcitation.

Figure 1. Threshold fluence 𝛷th for three samples and linear transmissivity (bottom curve) as functions of pressure.

[1] D. Wegkamp et al., Phys. Rev. Lett. 2014, 113, 216401.
[2] V. R. Morrison et al., Science 2014, 346, 445.
[3] E. Arcangeletti et al., Phys. Rev. Lett. 2007, 98, 196406.
[4] C. Kübler et al., Phys. Rev. Lett. 2007, 99, 116401.
[5] J. M. Braun et al., in preparation (2017).
Keywords: ultrafast pump-probe spectroscopy, bandwidth-driven Mott-Hubbard transition, vanadium dioxide, VO₂, insulator-to-metal transition, pressure-induced metallization, high pressure, diamond anvil cell
  • Lecture (Conference)
    55th European High Pressure Research Group (EHPRG) Meeting on High Pressure Science and Technology, 03.-08.09.2017, Poznań, Poland

Registration No. 26401 - Permalink


Pressure-Induced Metallization in VO₂ Studied by Optical Pump – THz Probe Spectroscopy
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
We have investigated pressurized VO₂ using optical pump – THz probe spectroscopy. Distinct pump-probe signals and an excitation threshold are observed even in the metallic state. Our results are consistent with a pressure-driven Mott-Hubbard transition.
Keywords: pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂, optical pump - THz probe spectroscopy
  • Lecture (Conference)
    CLEO 2017 (Conference on Lasers and Electro-Optics), 14.-19.05.2017, San Jose, USA

Registration No. 26400 - Permalink


Bandwidth-controlled metallization in pressurized VO₂ revealed by optical pump – THz probe spectroscopy
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
Vanadium dioxide (VO₂) is a classic example of a transition metal oxide showing a sharp first- order insulator-to-metal transition (IMT) around 340 K accompanied by a pronounced structural transformation. Pressure-induced metallization of VO₂ has been demonstrated by infrared spectroscopy [1] and resistivity measurements [2]. Remarkably, in contrast to the temperature-driven IMT, the crystal structure is not affected and remains monoclinic in the metallic phase [1-3].

Here we apply ultrafast optical pump – THz probe spectroscopy in order to reveal the nature of the pressure-induced IMT in a single crystal of VO₂. The probe pulses with a central frequency of 30 THz were generated by difference frequency mixing and focused down to a 35-𝜇m-spot on the sample mounted inside a diamond anvil pressure cell. Using THz radiation with photon energies far below the bandgap of VO₂ gives us an extremely sensitive probe of the dynamics of metallization [4].

Fig. 1(a) demonstrates that above a certain excitation fluence, a non-zero pump-probe signal survives on a multi-ps timescale indicating the long-lived photoinduced metallic state [4]. Here we define the threshold fluence 𝛷th as a crossing point of linearly extrapolated pump-probe signals in the low- and high-excitation regimes, as shown in Fig. 1(b). Surprisingly, the threshold behavior typical for the insulating state of VO₂ is also observed above the IMT that occurs between 6 and 8 GPa. This indicates a strongly correlated character of the pressure-induced metallic phase in which a part of the electrons remains localized - as predicted for a bandwidth-controlled Mott-Hubbard transition.

Fig. 1(c) shows that 𝛷th initially increases with pressure evidencing that the monoclinic structure stabilizes under hydrostatic compression. However, at the pressure-induced IMT, we observe a sudden drop of 𝛷th. This may be related to the partial screening of Coulomb correlations by delocalized electrons in the metallic state that lowers the critical excitation density necessary for a complete closure of the correlation gap. Our results attest to a purely electronic pressure-induced Mott-Hubbard transition in VO₂ and yield important insights into the nature of the correlated metallic state.

Figure 1: (a) Typical pump-probe response of VO₂ under a pressure of 2.9 GPa at different excitation fluences 𝛷;
(b) Amplitude of pump-probe in the metastable photoinduced state 1 ps after the excitation at different pressures;
(c) Dependence of the threshold fluence 𝛷th as a function of applied pressure. pc marks the region of the insulator-metal
transition.

[1] E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 (2007).
[2] L. Bai et al., Phys. Rev. B. 91, 104110 (2015).
[3] W.-P. Hsieh et al., Appl. Phys. Lett. 104, 021917 (2014).
[4] C. Kübler et al., Phys. Rev. Lett. 99, 116401 (2007).
Keywords: optical pump - THz probe spectroscopy, pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂
  • Lecture (Conference)
    Optical Terahertz Science and Technology (OTST 2017), 02.-07.04.2017, London, United Kingdom

Registration No. 26398 - Permalink


The nature of the pressure-induced metallization in VO₂
Braun, J. M.; Schneider, H.; Helm, M.; Mirek, R.; Boatner, L. A.ORC; Marvel, R. E.; Haglund, R. F.; Pashkin, A.
We utilize ultrafast optical pump - THz probe spectroscopy in order to investigate the pressure-driven insulator-to-metal transition (IMT) in vanadium dioxide (VO₂). The probe pulses with central frequency of 30 THz enable a sensitive detection of the photoinduced metallization.
The threshold pump fluence necessary for generation of a metastable metallic phase has been systematically measured for pressures up to 19GPa. Initial pressure application leads to a notable increase of the threshold fluence. This contrasts the thermally-driven IMT in VO₂ where it decreases on approaching the transition temperature. Above the IMT, that occurs at approximately 6-8GPa, we observe a sharp drop of the threshold fluence. However, the clear threshold behavior characteristic for systems with cooperative electronic localization still could be observed also in the metallic state up to the highest applied pressure.
Our results support a view of the pressure-induced IMT in VO₂ as a purely electronic bandwidth-driven Mott-Hubbard transition, that does not involve any change in the crystal structure.
Keywords: pressure-induced metallization, bandwidth-controlled Mott-Hubbard transition, insulator-to-metal transition, high pressure, diamond anvil cell, vanadium dioxide, VO₂, optical pump - THz probe spectroscopy
  • Lecture (Conference)
    DPG-Frühjahrstagung 2017, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26397 - Permalink


Outlook on a new combined MRI/TI experiment
Seilmayer, M.; Stefani, F.; Gundrum, G.; Köppen, S.
In the project framework of DRESDYN a sodium based experiment investigating magneto rotational instability (MRI) an Tayler instability (TI) is going to be built. Since both instabilities are based on hydrodynamically stable but magnetized Taylor Couette flow, the magnetic field configuration distinguishes the different types of instabilities. The past experimental research successfully worked out helical MRI with a combination of axial and azimuthal magnetic field and azimuthal MRI with only a pure azimuthal field. In both cases the relevant field B[phi] ~ 1/r is
generated by a rather large insulated current running on the symmetry axis of the experiment. The most challenging type of instability still remains standard MRI (SMRI) which relays on pure axial magnetic field B[z]. Here the necessary high rotation rates and large dimensions do limit the experimental feasibility to trigger SMRI until now. Besides that, even a non-rotating fluid with zero velocity can be destabilized by Tayler instability. Here the current is driven through the liquid which gives a B[phi] ~ r dependence. Concluding, the aim of new experimental is to investigate the whole parameter space for the mentioned instabilities and corresponding transitions.

We like to present the latest stage of construction of a large scale liquid sodium Taylor-Couette experiment with a height of 2m and diameter of 0.8 m. In a rough approximation, the achievable boundary conditions will be up to 20 Hz rotation rate and up to 50kA of electrical current. In a more detail, there are some specific topics we like to discus.

First, there is the quasi coaxial system consisting of a central current carrying copper rod and five symmetric return paths which provides homogeneous magnetic field to the Taylor-Couette flow.
One challenging part is the design of the current distributor, which is supposed to divide the current into several equally weighted lines. Because of the individual characteristic resistance of all involved conductors an initial imbalance in the current distribution affecting the symmetry of the magnetic field is the result. So the adjustment of current distribution becomes mandatory to ensure maximum field homogeneity. An indirect access to set the current in all five return paths is to control the outflow temperature of the required water cooling. This is done by thermostatically operated valves in conjunction with the temperature dependent branch resistance. Finally, the calibrated system achieves less than 1% field in-homogeneity and works in a wide range of currents. Additional benefits of the presented approach will be the minimal stray field of the installation and cheap components.

Second, we designed a stacked magnetic field system to generate the axial component. Here 27 individual coils provide an almost homogeneous field with B[z] < 150 mT in the relevant volume. The most challenging aspect is the huge amount of electrical power (approximately 120 kW) which have to be cooled. The main advantage of the present geometry is the guaranteed access to all the sensors mounted on the outer cylinder surface. This is achieved by a special geometry to partially levitate the coil system.

[1]F. Stefani et al., PRE, 80(6), 2009.
[1]M. Seilmayer et al., PRL, 108(24), 244501, 2012.
[1]M. Seilmayer et al., IEEE Sensors Journal, DOI 10.1109/JSEN.2017.2765671, 2017.
Keywords: Experiment, Sodium, DRESDYN, Taylor-Couette
  • Poster
    GDRI DYNAMO MEETING, 26.-29.11.2017, Paris, Frankreich

Registration No. 26393 - Permalink


ns-laser driven magnetic phase transition in FeAl
Liedke, M. O.; Bali, R.; Gradauskaite, E.; Ehrler, J.; Wang, M.; Potzger, K.; Zhou, S.; Wagner, A.
FeAl alloys show temperature dependent magnetic phase transition (MPT) from a ferromagnetic disordered A2-phase to a paramagnetic ordered B2-phase. The B2-phase can be reversed back to the A2-phase, e.g, by ion irradiation. The most plausible explanation of MPT points in direction of the anti-site disorder (ASD), i.e., more Fe-Fe nearest neighbors due to disordering. However, variations of the lattice parameter, defects concentration, and secondary phases may play an important role, too. Here, we employ an excimer UV ns-laser to examine the role of ASD and defects onto magnetic properties. Three sample series with different initial order conditions were irradiated by several laser fluences: (i) as-grown semi-, (ii) Ne irradiated fully-disordered, and (iii) vacuum annealed ordered alloys. Two magnetic regimes were found depending on laser fluence: (i) in the low fluence range magnetization initially decreases, followed by (ii) subsequent monotonic increase for larger fluences. The positron annihilation spectroscopy measurements reveal changes of defects surrounding from Al- to Fe dominant, respectively, as well as of defects concentration. The results obtained by MOKE, VSM, AFM, and TEM will be discussed in detail.
Keywords: FeAl alloys, PAS, magnetic phase transition, ns-laser, anti-site disorder, positron annihilation spectroscopy
  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26391 - Permalink


EPR studies of the triangular-lattice antiferromagnet Cs2CuBr4
Schulze, E.; Ponomaryov, A. N.; Wosnitza, J.; Tanaka, H.; Zvyagin, S. A.
Corresponding author: Zvyagin, S. A. Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
The spin dynamics of the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4 is probed by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy. Temperature dependences of EPR parameters are studied in a broad temperature range between 1.4 and 200 K for different orientations of the applied magnetic field. In the high-temperature regime (T >> J/kB), an unusually broad and anisotropic resonance line is detected, suggesting a sizeable Dzyaloshinskii–Moriya interaction. Employing the theory of exchange narrowing, the ratio of the Dzyaloshinskii–Moriya vector components, Dc/Da ≈ 0.3, is estimated.
  • Low Temperature Physics 43(2017), 1642-1646

Downloads:

  • Secondary publication expected from 25.09.2018

Registration No. 26383 - Permalink


Nonlinear THz spectroscopy of low-dimensional materials
Helm, M.; König-Otto, J.; Schmidt, J.; Dimakis, E.; Winnerl, S.; Schneider, H.
Thanks to the development of powerful THz sources, both table-top and accelerator-based, highly nonlinear THz investigations of materials are possible today. Here we will present two recent examples of nonlinear spectroscopy on low-dimensional materials: resonant four-wave mixing in graphene under a magnetic field, and nonlinear THz spectroscopy of intersubband transitions in a semiconductor quantum well.
Graphene is predicted to be a highly nonlinear material due to its linear dispersion. Clear experimental observations are relatively scarce, however. In a magnetic field, the band structure splits up into non-equidistant Landau levels, giving rise to resonant behavior of the optical properties. We demonstrate resonantly enhanced four-wave-mixing (FWM) at a photon energy of 78 meV, resonant at a magnetic field of B = 4.5 T. The chi(3) character is clearly demonstrated by the power dependence of the four-wave-mixing signal and the narrower line shape as compared to the linear absorption. The FWM signal, proportional to the induced microscopic polarization, decays faster than the also measured pump-probe signal, beyond the time resolution of the experiment (4 ps).
Intersubband transitions in quantum wells, due to their similarities to atomic transitions, have been a playground for many fundamental optical and quantum mechanical effects as well as for novel devices for three decades. Nonlinear or quantum optical effects such as dressed states or electromagnetically induced transparency (EIT) were demonstrated, however, only in the mid-infrared range or probed in the near infrared. Here we employ our THz free-electron laser (FEL) in combination with THz time-domain spectroscopy to realize a true narrow-band pump – broad-band probe experiment: While pumping the 2-3 intersubband transition in a single GaAs/AlGaAs quantum well (at 3.5 THz = 15 meV), we probe the entire THz absorption up to 4 THz (including 1-2 and 2-3 transitions). The experiment allows one to extract the transmission change vs pump-probe time delay as well as the complete spectral shape of the transmission change at a specific time delay. We will discuss the observed spectra, including indications for the Autler-Townes splitting on the 1-2 transition.
Keywords: four-wave mixing, graphene., free-electron laser, pump-prbe, GaAs, quantum well, intersubband transition, Autler-Townes
  • Invited lecture (Conferences)
    MTSA 2017 & TeraNano-8, 19.-23.11.2017, Okayama, Japan

Registration No. 26381 - Permalink


Versatile Tri(pyrazolyl)phosphanes as Phosphorus Precursors for the Synthesis of Highly Emitting InP/ZnS Quantum Dots - Tri(pyrazolyl)phosphane als Vorstufen für die Synthese von stark emittierenden InP/ZnS-Quantenpunkten
Panzer, R.; Guhrenz, C.; Haubold, D.; Hübner, R.; Gaponik, N.; Eychmüller, A.; Weigand, J. J.
Corresponding author: Weigand, J. J. TU Dresden
Tri(pyrazolyl)phosphanes (5R1,R2) are utilized as an alternative, cheap and low-toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long-term stable stock solutions (>6 months) of P(OLA)3 (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)3 acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530-620 nm and photoluminescence quantum yields (PL QYs) between 51-62 %. A proof-of-concept white light-emitting diode (LED) applying the InP/ZnS QDs as a color-conversion layer was built to demonstrate their applicability and processibility.
Tri(pyrazolyl)phosphane werden als alternative kostengünstige und weniger toxische Phosphorquelle in der Synthese von InP/ZnS-Quantenpunkten (QDs) eingesetzt. Ausgehend von ihnen können langzeitstabile (>6 Monate) P(OLA)3-Stammlösungen (OLAH=Oleylamin) synthetisiert werden, aus denen sich die entsprechenden Pyrazole einfach zurückgewinnen lassen. P(OLA)3 fungiert in der Synthese von stark emittierenden InP/ZnS-QDs sowohl als Phosphorquelle als auch als Reduktionsmittel. Die erhaltenen Kern/Schale-Partikel zeichnen sich durch hohe Photolumineszenz-Quantenausbeuten von 51–62 % in einem Spektralbereich von 530-620 nm aus. Die Verarbeitung und Anwendung dieser InP/ZnS-QDs als Farbkonversionsschicht wurde anhand des Einsatzes in einer weißen Leuchtdiode demonstriert.
Keywords: hot injection, oleylamine, phosphorus, quantum dots, waste prevention - Heißinjektion, Oleylamin, Phosphor, Ressourcen-Schonung, Quantenpunkte

Registration No. 26377 - Permalink


Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2
Kumar, N.; Sun, Y.; Xu, N.; Manna, K.; Yao, M.; Süss, V.; Leermakers, I.; Young, O.; Förster, T.; Schmidt, M.; Borrmann, H.; Yan, B.; Zeitler, U.; Shi, M.; Felser, C.; Shekhar, C.
Corresponding author: Felser, C. Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings can lead to spectacular electronic properties such as large mobilities accompanied by extremely high magnetoresistance. In particular, two closely neighboring Weyl points of the same chirality are protected from annihilation by structural distortions or defects, thereby significantly reducing the scattering probability between them. Here we present the electronic properties of the transition metal diphosphides, WP2 and MoP2, which are type-II Weyl semimetals with robust Weyl points by transport, angle resolved photoemission spectroscopy and first principles calculations. Our single crystals of WP2 display an extremely low residual low-temperature resistivity of 3 nΩ cm accompanied by an enormous and highly anisotropic magnetoresistance above 200 million % at 63 T and 2.5 K. We observe a large suppression of charge carrier backscattering in WP2 from transport measurements. These properties are likely a consequence of the novel Weyl fermions expressed in this compound.

Registration No. 26376 - Permalink


Investigations of the Effects of the Variation of Fuel Assembly Positions in a core of a PWR
Konheiser, J.; Müller, S. E.; Seidl, M.
This work shows the impact of possible variations of the core geometry on the signal values of the ex-core instrumentation of a pressurized water reactor (PWR). Based on the potential influence on the signals, neutron fluxes have been determined for selected fuel assembly displacements using stationary Monte Carlo calculations. First, critical calculations were carried out for the chosen core configurations and corresponding surface sources on the core barrel were determined. In a second step transport calculations for the ionization chambers were performed using the surface sources. Typical data of a German PWR were used for the investigations.
Variation of fuel assembly positions in the outer region of the core were studied, which were directly opposite to the ex-core instrumentation. An increase of the neutron flux at the chambers of up to 4% has been calculated for a change in position of 1 mm between some fuel assemblies. The reason is an improved moderation of neutrons because of the larger water gap. This causes an increase in local power which leads to a greater leakage of neutrons over the core barrel. In addition, a dependence of this effect as a function of cycle burnup was analyzed.
Keywords: PWR type reactor; Monte Carlo calculation; safety analysis; ex-core instrumentation
  • Lecture (others)
    17. AAA Workshop, 04.12.2017, Garching, Germany

Registration No. 26372 - Permalink


Coupling of ferromagnetism and structural phase transition in V2O3/Co bilayers
Wang, C.; Xu, C.; Wang, M.; Yuan, Y.; Liu, H.; Dillemans, L.; Homm, P.; Menghini, M.; Locquet, J.-P.; Haesendonck, C. V.; Zhou, S.; Ruan, S.; Zeng, Y.-J.
Interfacial coupling in hybrid magnetic heterostructures is being considered as a unique opportunity for functional material design. Here, we present the temperature dependence of magnetic properties of V2O3/Co bilayers influenced by the structural phase transition that is accompanied by a metal–insulator transition in V2O3. Both the coercivity and the magnetization of Co layer are strongly affected by the interfacial stress due to the magnetostrictive effect in the ferromagnetic film. The observed change in coercivity is as large as 59% in a narrow temperature range. The changes in the magnetic properties are reproducible and reversible, which are of importance for potential applications.
Keywords: metal–insulator transition, magnetostrictive coupling, structural phase transition, heterostructure

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  • Secondary publication expected from 14.11.2018

Registration No. 26371 - Permalink


An orthotopic xenograft model for high-risk non-muscle invasive bladder cancer in mice: influence of mouse strain, tumor cell count, dwell time and bladder pretreatment
Huebner, D.; Rieger, C.; Bergmann, R.; Ullrich, M.; Meister, S.; Toma, M.; Wiedemuth, R.; Temme, A.; Novotny, V.; Wirth, M. P.; Bachmann, M.; Pietzsch, J.ORC; Fuessel, S.
Corresponding author: Fuessel, S. Uniklinikum Dresden
Background: Novel theranostic options for high-risk non-muscle invasive bladder cancer are urgently needed. This requires a thorough evaluation of experimental approaches in animal models best possibly reflecting human disease before entering clinical studies. Although several bladder cancer xenograft models were used in the literature, the establishment of an orthotopic bladder cancer model in mice remains challenging.
Methods: Luciferase-transduced UM UC 3LUCK1 bladder cancer cells were instilled transurethrally via 24G permanent venous catheters into athymic NMRI and BALB/c nude mice as well as into SCID-beige mice. Besides the mouse strain, the pretreatment of the bladder wall (trypsin or poly-L-lysine), tumor cell count (0.5×106 – 5.0×106) and tumor cell dwell time in the murine bladder (30 min – 2 h) were varied. Tumors were morphologically and functionally visualized using bioluminescence imaging (BLI), magnetic resonance imaging (MRI), and positron emission tomography (PET).
Results: Immunodeficiency of the mouse strains was the most important factor influencing cancer cell engraftment, whereas modifying cell count and instillation time allowed fine-tuning of the BLI signal start and duration – both representing the possible treatment period for the evaluation of new therapeutics. Best orthotopic tumor growth was achieved by transurethral instillation of 1.0×106 UM UC 3LUCK1 bladder cancer cells into SCID-beige mice for 2 h after bladder pretreatment with poly-L-lysine. A pilot PET experiment using 68Ga-cetuximab as transurethrally administered radiotracer revealed functional expression of epidermal growth factor receptor as representative molecular characteristic of engrafted cancer cells in the bladder.
Conclusions: With the optimized protocol in SCID-beige mice an applicable and reliable model of high-risk non-muscle invasive bladder cancer for the development of novel theranostic approaches was established.
Keywords: bioluminescence, luciferase, orthotopic xenograft models, small animal multimodal imaging, magnetic resonance imaging, optical imaging, positron emission tomography, transurethral instillation, UM-UC-3 cell line, urothelial carcinoma

Registration No. 26370 - Permalink


Potential of asphericity as a novel diagnostic parameter in the evaluation of patients with Ga-68-PSMA-HBED-CC PET-positive prostate cancer lesions
Meissner, S.; Janssen, J.; Prasad, V.; Brenner, W.; Diederichs, G.; Hamm, B.; Hofheinz, F.; Makowski, M.
Corresponding author: Meissner, S. Department of Radiology, Charité Universitätsmedizin Berlin, Berlin, Germany
Background: The aim of this study was to evaluate the diagnostic value of the asphericity (ASP) as a novel quantitative parameter, reflecting the spatial heterogeneity of tracer uptake, in the staging process of patients with Ga-68-PSMA-HBED-CC positron emission tomography (PET)-positive prostate cancer (PC). In this study, 37 patients (median age 72 years, range 52-82 years) with newly diagnosed PC, who received a Ga-68-PSMA-HBED-CC PET fused with computed tomography (Ga-68-PSMA-PET/CT), a magnetic resonance imaging (MRI) of the prostate, and a core needle biopsy (within 74.2 8 +/- 80.2 days) with an available Gleason score (GSc) were extracted from the local database. The ASP and the viable tumor volume (VTV) was calculated using the rover software (ABX GmbH, Radeberg, Germany), a segmentation tool for automated tumor volume delineation. Additionally, parameters including total lesion binding rate (TLB), maximum, mean and peak standardized uptake value (SUVmax/mean/peak), prostate-specific antigen (PSA), D'Amico classification, and prostate imaging reporting and data system (PI-RADS) were analyzed.

Results: The ASP mean differed significantly (p = 0.05) between the different GSc groups: GSc 6-7: 11.9 +/- 4.8%, GSc 8: 25.5 +/- 4.8%, GSc
9-10: 33.3 +/- 6.8%. A significant correlation between ASP and GSc (rho = 0.88; CI 0.78-0.94; p < 0.05) was measured. The ASP enabled an independent (p > 0.05) prediction of the GSc. A moderate correlation was measured between ASP and the D'Amico classification (rho = 0.6; CI 0.32-0.78; p < 0.05). The VTV showed a moderate correlation with the SUVmax (rho = 0.58; CI 0.32-0.76; p < 0.05) and the GSc (rho = 0.51; CI 0.23-0.72; p < 0.05).

Conclusion: The asphericity in Ga-68-PSMA-PET could represent a promising novel quantitative parameter for an improved non-invasive tumor staging of patients with PC.
Keywords: Prostatic neoplasms Positron emission tomography computed tomography Gleason score Asphericity Histopathology

Registration No. 26366 - Permalink


Feasible device architectures for ultra-scaled CNTFETs
Pacheco-Sanchez, A.; Fuchs, F.; Mothes, S.; Zienert, A.; Schuster, J.; Gemming, S.; Claus, M.
Corresponding author: Pacheco-Sanchez, A. TUD, cfaed
Feasible device architectures for ultra-scaled CNTFETs are studied down to 5.9 nm using a multiscale simulation approach covering electronic quantum transport simulations and TCAD numerical device simulations. Schottky-like and ohmic-like contacts are considered. The simplified approach employed in the numerical device simulator is critically evaluated and verified by means of comparing the results with electronic quantum simulation results of an identical device. Different performance indicators such as the switching speed, switching energy, the subthreshold slope, Ion/Ioff-ratio, among others, are extracted for different device architectures. These values guide the evaluation of the technology for different application scenarios. For high-performance logic applications, the buried gate CNTFET is claimed to be the most suitable structure.
Keywords: CNTFETs, Logic gates, Numerical models, Computer architecture, Performance evaluation, Electric potential, Effective mass

Registration No. 26363 - Permalink


Investigation of the environmental impact of nanoparticles using smart radiolabeling
Schymura, S.; Fricke, T.; Hildebrand, H.; Steudtner, R.; Hübner, R.; Mansel, A.; Franke, K.
The investigation of the environmental impact of nanoparticles is greatly hindered by a lack of suitable detection methods, especially at the low, environmentally relevant concentrations. The radiolabeling of nanoparticles can overcome these setbacks and provides a possibility of detecting nanoparticles at minimal concentrations against high elemental and particle backgrounds.
In addition to that the sophisticated use of different labeling strategies allows the direct measurement of processes such as dissolution and their relevant in, for example, plant uptake. Using different labeling stragies we produce radiolabeled CeO2 nanoparticles with different radioactivity release kinetics upon dissolution. This enabled us to measure the uptake and translocation of CeO2 nanoparticles in plants and to identify the predominant uptake pathway in the form of particles, as opposed to an uptake of their dissolved remains.
Keywords: Radiomarkierung/ radiolabeling Nanopartikel/ nanoparticles Umwelt/ environment Pflanzen/ plants
  • Lecture (Conference)
    13th Cycleur – European Network of Cyclotron Research Centers – Workshop, 23.-24.11.2017, Lissabon, Portugal

Registration No. 26360 - Permalink


Novel Humanized and Highly Efficient Bispecific Antibodies Mediate Killing of Prostate Stem Cell Antigen-Expressing Tumor Cells by CD8+ and CD4+ T Cells
Feldmann, A.; Arndt, C.; Töpfer, K.; Stamova, S.; Krone, F.; Cartellieri, M.; Koristka, S.; Michalk, I.; Lindemann, D.; Schmitz, M.; Temme, A.; Bornhäuser, M.; Ehninger, G.; Bachmann, M.
Prostate cancer is the most common noncutaneous malignancy in men. The prostate stem cell Ag (PSCA) is a promising target for immunotherapy of advanced disease. Based on a novel mAb directed to PSCA, we established and compared a series of murine and humanized anti-CD3–anti-PSCA single-chain bispecific Abs. Their capability to redirect T cells for killing of tumor cells was analyzed. During these studies, we identified a novel bispecific humanized Ab that efficiently retargets T cells to tumor cells in a strictly Ag-dependent manner and at femtomolar concentrations. T cell activation, cytokine release, and lysis of target cells depend on a cross-linkage of redirected T cells with tumor cells, whereas binding of the anti-CD3 domain alone does not lead to an activation or cytokine release. Interestingly, both CD8+ and CD4+ T cells are activated in parallel and can efficiently mediate the lysis of tumor cells. However, the onset of killing via CD4+ T cells is delayed. Furthermore, redirecting T cells via the novel humanized bispecific Abs results in a delay of tumor growth in xenografted nude mice.

Registration No. 26359 - Permalink


Retargeting of T Cells to Prostate Stem Cell Antigen ExpressingTumor Cells: Comparison of Different Antibody Formats
Feldmann, A.; Stamova, S.; Bippes, C. C.; Bartsch, H.; Wehner, R.; Schmitz, M.; Temme, A.; Cartellieri, M.; Bachmann, M.
BACKGROUND. Prostate cancer (PCa) is the most common malignant disease in men. Novel treatment options are needed for patients after development of metastatic, hormone-refractory disease or for those who have failed a local treatment. The prostate stem cell antigen (PSCA) is expressed in >80% of primary PCa samples and bone metastases. Its expression is increased both in androgen-dependent and independent prostate tumors, particularly in carcinomas of high stages and Gleason scores. Therefore, PSCA is an attractive target for immunotherapy of PCa by retargeting of T cells to tumor cells.
METHODS. Aseries of different bispecific antibody formats for retargeting of T cells to tumor cells were described but, only very limited data obtained by side by side comparison of the different antibody formats are available. We established two novel bispecific antibodies in different formats. The functionality of both constructs was analyzed by FACS and chromium release assays. In parallel, the release of pro-inflammatory cytokines was determined by ELISA.
RESULTS AND CONCLUSIONS. Irrespective of the underlying antibody format, both novel bispecific antibodies cause an efficient killing of PSCA-positive tumor cells by preand non-pre-activated T cells. Killing and release of pro-inflammatory cytokines requires an antigen specific cross-linkage of the T cells with the target cells.
Keywords: single chain bispecific antibodies; prostate cancer; T cell targeting; immunotherapy

Registration No. 26358 - Permalink


Retargeting of Human Regulatory T Cells by Single-Chain Bispecific Antibodies
Koristka, S.; Cartellieri, M.; Theil, A.; Feldmann, A.; Arndt, C.; Stamova, S.; Michalk, I.; Töpfer, K.; Temme, A.; Kretschmer, K.; Bornhäuser, M.; Ehninger, G.; Schmitz, M.; Bachmann, M.
Bispecific Abs hold great potential for immunotherapy of malignant diseases. Because the first components of this new drug class are now entering clinical trials, all aspects of their mode of action should be well understood. Several studies proved that CD8+ and CD4+ effector T cells can be successfully redirected and activated against tumor cells by bispecific Abs both in vitro and in vivo. To our knowledge, this study provides the first evidence that bispecific Abs can also redirect and activate regulatory T cells against a surface Ag, independently of their TCR specificity. After cross-linking, via a bispecific Ab, redirected regulatory T cells upregulate the activation markers CD69 and CD25, as well as regulatory T cell-associated markers, like CTLA-4 and FOXP3. The activated regulatory T cells secrete the immunosuppressive cytokine IL-10, but, in contrast to CD8+ and CD4+ effector T cells, almost no inflammatory cytokines. In addition, the redirected regulatory T cells are able to suppress effector functions of activated autologous CD4+ T cells both in vitro and in vivo. Therefore, the potential risk for activation of regulatory T cells should be taken into consideration when bispecific Abs are applied for the treatment of malignant diseases. In contrast, an Ag/tissue-specific redirection of regulatory T cells with bispecific Abs holds great potential for the treatment of autoimmune diseases and graft rejection.

Registration No. 26357 - Permalink


Retargeting of regulatory T cells to surface-inducible autoantigen La/SS-B
Koristka, S.; Cartellieri, M.; Arndt, C.; Bippes, C. C.; Feldmann, A.; Michalk, I.; Wiefel, K.; Stamova, S.; Schmitz, M.; Ehninger, G.; Bornhäuser, M.; Bachmann, M.
The nuclear autoantigen La can be detected on the surface of dying cells. Here we present an assay which enables us to show that La protein is not limited to the surface of dying cells but will be released upon stress-induced cell death. As released La protein tightly binds to the surface of neighboring intact cells we asked the question whether or not La protein could serve as a stress-inducible target e.g. for redirecting of regulatory T cells (Tregs) into damaged tissues to downregulate an immune response. In order to provide first proof of concept we developed a novel fully humanized single-chain bispecific antibody (bsAb) which on the one hand is directed to the La antigen and on the other hand to the CD3 complex of T cells. A cross-linkage of Tregs with La-decorated target cells mediated by this bsAb resulted indeed in the activation of the Tregs in a target-dependent manner. Moreover, such bsAb activated Tregs displayed a potent suppressive capacity and negatively influenced proliferation, expansion and cytokine production of autologous CD4+ and CD8+ Teff cells.
Keywords: La/SS-B, Regulatory T cells, Single-chain bispecific antibodies, Immunotherapy

Registration No. 26356 - Permalink


Combinatorial antigen recognition with balanced signaling promotes selective tumor eradication by engineered T cells
Kloss, C. C.; Condomines, M.; Cartellieri, M.; Bachmann, M.; Sadelain, M.
Current T-cell engineering approaches redirect patient T cells to tumors by transducing them with antigen-specific T-cell receptors (TCRs) or chimeric antigen receptors (CARs) that target a single antigen. However, few truly tumor-specific antigens have been identified, and healthy tissues that express the targeted antigen may undergo T cell–mediated damage. Here we present a strategy to render T cells specific for a tumor in the absence of a truly tumor-restricted antigen. T cells are transduced with both a CAR that provides suboptimal activation upon binding of one antigen and a chimeric costimulatory receptor (CCR) that recognizes a second antigen. Using the prostate tumor antigens PSMA and PSCA, we show that co-transduced T cells destroy tumors that express both antigens but do not affect tumors expressing either antigen alone. This ‘tumor-sensing’ strategy may help broaden the applicability and avoid some of the side effects of targeted T-cell therapies.

Registration No. 26353 - Permalink


Redirection of T cells with a first fully humanized bispecific CD33–CD3 antibody efficiently eliminates AML blasts without harming hematopoietic stem cells
Arndt, C.; von Bonin, M.; Cartellieri, M.; Feldmann, A.; Koristka, S.; Michalk, I.; Stamova, S.; Bornhäuser, M.; Schmitz, M.; Ehninger, G.; Bachmann, M.
Corresponding author: Bachmann, Michael Institute of Immunology, Medical Faculty ‘Carl Gustav Carus’, TU Dresden, Dresden, Germany
Redirection of T cells with a first fully humanized bispecific
CD33–CD3 antibody efficiently eliminates AML blasts without
harming hematopoietic stem cells

Registration No. 26352 - Permalink


Magnetohydrodynamic instabilites in aluminium reduction cells
Weber, N.; Herreman, W.; Horstmann, G.; Nore, C.; Weier, T.
Übersicht über Theorie und numerische Simulation von Aluminium-Reduktionszellen.
  • Lecture (others)
    Aluminium-Reduktions-Treffen, 16.11.2017, Wuppertal, Deutschland

Registration No. 26350 - Permalink


Magnetic nanomaterials
Josten, E.; Glavic, A.; Meertens, D.; Wetterskog, E.; Bersgtröm, L.; Brückel, T.; Lindner, J.
Magnetic nanomaterials and their assembly in highly correlated structures are of great interest for future applications as e.g. spin-based data storage media or as material for magnon-spintronics. These systems exhibit unique physical properties like superparamagnetism or symmetry breaking emerging due to their limited size. Individual nanomaterials can be combined as building blocks for so called superstructures where the combination of the different functionalities creates a novel multi-functional system.
Recently, more and more well-defined nanoobjects became available and the advances in measurement methods allow a characterization of these systems. For example, single micrometer-sized three-dimensional magnetic nanoparticle assemblies are available, exhibiting a high degree of structural order close to that of an atomic crystal [1,2]. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.
The work to be presented focuses on the fundamental structural and magnetic research on such objects and their functionalization. For the investigation we make use of different complementary measurement methods like small angle x-ray and neutron scattering or using microresonators, which provide the necessary sensitivity for the investigation of magnetic properties of a single nano- or micrometer-sized object using ferromagnetic resonance (FMR) [3].
Keywords: nanoparticles, scattering
  • Invited lecture (Conferences)
    JCNS Workshop 2017, 10.-13.10.2017, Tutzing, Deutschland

Registration No. 26349 - Permalink


Highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance
Josten, E.; Narkowicz, R.; Kakay, A.; Meertens, D.; Lennart, B.; Brückel, T.; Fassbender, J.; Lindner, L.
Magnetic nanoparticles and their assembly into highly correlated superstructures are of great interest for future applications, e.g. as material for magnon-spintronic. These systems are not only distinguished by the obvious miniaturization but by their novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks ordered like atoms in a crystal, which render them a new class of materials.
Recently, single micrometer-sized three-dimensional magnetic nanoparticle assemblies became available, exhibiting a high degree of structural order close to that of an atomic crystal. These systems provide a good basis for the magnetic investigation of nanoparticle superstructures.

Novel microresonators, provide the necessary sensitivity for the investigation of magnetic properties of nano- and micrometer-sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity gain. A focused ion beam was used to isolate an individual 3D mesocrystal from an ensemble and to transfer it into the microresonator loop (Fig. 1). The FMR study reveals the magnetic anisotropy of the single mesocrystal (Fig. 2), which is corroborated by micromagnetic simulations. It was possible for us to functionalize the system and to set the magnetic easy axis of the mesocrystal via pre-defining their shape.
Keywords: nanoparticle
  • Lecture (Conference)
    INTERMAG Europe 2017, 24.-28.04.2017, Dublin, Irland

Registration No. 26348 - Permalink


Felsenkeller 5 MV underground accelerator: Towards the Holy Grail of Nuclear Astrophysics 12C(α,γ)16O
Bemmerer, D.
Underground ion accelerator laboratories such as the LUNA 0.4 MV accelerator in Italy are indispensable in order to precisely measure charged particle induced nuclear reaction cross sections. The rock overburden attenuates the cosmic ray induced background and enables the measurement of very low interaction rates. The first of the new generation of higher-energy underground accelerators is the Felsenkeller 5 MV machine in Dresden/Germany, under construction and due to open late 2017. The cross sections of several nuclear reactions relevant to nucleosynthesis in a supernova and/or its precursor are not well known, with effects on the nucleosynthetic output of these events. Of these reactions, it is planned to study the 12C(alpha,gamma), 22Ne(alpha,gamma), 40Ca(alpha,gamma), and several other cases at Felsenkeller. The scientific motivation and state of work will be reviewed. It is hoped that the Felsenkeller accelerator will be widely used, including researchers from as many German universities as possible.
Keywords: Underground nuclear astrophysics Felsenkeller Helium burning
  • Invited lecture (Conferences)
    Arbeitstreffen Kernphysik, 02.-09.03.2017, Schleching, Deutschland
  • Lecture (Conference)
    Workshop on Nuclear Astrophysics at the Dresden Felsenkeller, 26.-28.06.2017, Dresden, Deutschland
  • Lecture (Conference)
    Nuclear Physics in Astrophysics VIII, 20.06.2017, Catania, Italien
  • Invited lecture (Conferences)
    16th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS16), 19.09.2017, Shanghai, China

Registration No. 26346 - Permalink


Felsenkeller 5 MV underground accelerator: Muon, neutron, 𝛾-ray background and project status
Bemmerer, D.
Motivated by the success of the world's only underground ion accelerator, LUNA 0.4 MV in Italy, a project for a higher-energy underground accelerator is underway in Dresden. A 5\,MV Pelletron accelerator with double charging chains and provision for intensive ^1H^+, ^4He^+, and ^{12}C^+ beams based on external and internal ion sources is currently being installed in the Felsenkeller underground site in Dresden. Civil construction work in Felsenkeller will be completed in August 2017. The nine Felsenkeller tunnels are shielded from cosmic rays by 45\,m rock overburden, attenuating the background in radiation detectors. New data on the muon, neutron, and $\gamma$ background in Felsenkeller will be shown, and used for a discussion on the feasibility of low-background experiments there. The new accelerator will be open for outside users, and its most important experimental capabilities will be summarized.
Keywords: Underground Nuclear Astrophysics Felsenkeller
  • Lecture (Conference)
    Frühjahrstagung, 30.03.2017, Münster, Deutschland

Registration No. 26344 - Permalink


Recent progress on hydrogen and helium burning at the LUNA 400 kV underground accelerator
Bemmerer, D.
n-beam radiative-capture experiments at low astrophysical energies require experiments in ultra-low background conditions. The Laboratory for Underground Nuclear Astrophysics (LUNA) 0.4\,MV accelerator at INFN Gran Sasso, Italy, is so far the only underground ion accelerator in the world. Recent progress at LUNA regarding the $^{22}$Ne(p,$\gamma$)$^{23}$Na [1,2], $^{22}$Ne($\alpha$,$\gamma$)$^{26}$Mg, and $^{17}$O(p,$\alpha$)$^{14}$N [3] reactions will be reviewed. The project for the new, 3.5 MV LUNA-MV accelerator is on track and will be summarized.
Keywords: Nuclear Astrophysics Hydrogen burning
  • Lecture (Conference)
    Frühjahrstagung, 27.03.2017, Münster, Deutschland

Registration No. 26343 - Permalink


Constraining the 7Be(p,gamma)8B S -factor with the new precise 7Be solar neutrino flux from Borexino
Takács, M. P.; Bemmerer, D.; Junghans, A. R.; Zuber, K.
Corresponding author: Bemmerer, Daniel
Among the solar fusion reactions, the rate of the 7Be(p,γ)8B reaction is one of the most difficult to determine rates. In a number of previous experiments, its astrophysical S-factor has been measured at E = 0.1-2.5 MeV center-of-mass energy. However, no experimental data is available below 0.1 MeV. Thus, an extrapolation to solar energies is necessary, resulting in significant uncertainty for the extrapolated S-factor. On the other hand, the measured solar neutrino fluxes are now very precise. Therefore, the problem of the S-factor determination is turned around here: Using the measured 7Be and 8B neutrino fluxes and the Standard Solar Model, the 7Be(p,γ)8B astrophysical S-factor is determined at the solar Gamow peak. In addition, the 3He(α,γ)7Be S-factor is redetermined with a similar method.
Keywords: Nuclear Astrophysics Solar neutrinos Nuclear reaction rate Solar fusion

Registration No. 26342 - Permalink


LUNA: Status and Prospects
Broggini, C.; Bemmerer, D.; Caciolli, A.; Trezzi, D.
Corresponding author: Broggini, Carlo INFN
The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of 12C+12C and of the two reactions which generate free neutrons inside stars: 13C(α,n)16O and 22Ne(α,n)25Mg.
Keywords: Nuclear Astrophysics LUNA Laboratory Underground for Nuclear Astrophysics

Registration No. 26341 - Permalink


Modification of surface properties of solids by femtosecond LIPSS writing: comparative studies on silicon and stainless steel
Varlamova, O.; Hoefner, K.; Ratzke, M.; Reif, J.; Sarker, D.
Corresponding author: Varlamova, O. LS Experimentalphysik II, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus
We investigate the implication of modified surface morphology on wettability of stainless steel (AISI 304) and silicon (100) targets covered by laser-induced periodic surface structures (LIPSS) on extended areas (10 × 10 mm2). Using multiple pulses from a Ti: Sapphire laser (790 nm/100 fs/1 kHz) at a fluence in the range of 0.35–2.1 J/cm2 on a spot of 1.13 × 10− 4 cm2, we scanned the target under the spot to cover a large area. A systematical variation of the irradiation dose by changing the scanning speed and thus dwelling time per spot results in the formation of surface patterns ranging from very regular linear structures with a lateral period of about 500–600 nm to complex patterns of 3D microstructures with several-µm feature size, hierarchically covered by nano-ripples.

Registration No. 26340 - Permalink


Surface modifications of crystal-ion-sliced LiNbO3 thin films by low energy ion irradiations
Bai, X.; Shuai, Y.; Gong, C.; Wu, C.; Luo, W.; Böttger, R.; Zhou, S.; Zhang, W.
Corresponding author: Wu, C. State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Single crystalline 128°Y-cut LiNbO3 thin films with a thickness of 670 nm are fabricated onto Si substrates by means of crystal ion slicing (CIS) technique, adhesive wafer bonding using BCB as the medium layer to alleviate the large thermal coefficient mismatch between LiNbO3 and Si, and the X-ray diffraction pattern indicates the exfoliated thin films have good crystalline quality. The LiNbO3 thin films are modified by low energy Ar+ irradiation, and the surface roughness of the films is decreased from 8.7 nm to 3.4 nm. The sputtering of the Ar+ irradiation is studied by scanning electron microscope, atomic force microscope and X-ray photoelectron spectroscopy, and the results show that an amorphous layer exists at the surface of the exfoliated film, which can be quickly removed by Ar+ irradiation. A two-stage etching mechanism by Ar+ irradiation is demonstrated, which not only establishes a new non-contact surface polishing method for the CIS-fabricated single crystalline thin films, but also is potentially useful to remove the residue damage layer produced during the CIS process.
Keywords: 128°Y-cut LiNbO3; Single crystalline thin films; Crystal ion slicing; BCB bonding; Ar+ irradiation

Registration No. 26339 - Permalink


Die Bestimmung des neutroneninduzierten Spaltquerschnitts von ²⁴²Pu
Kögler, T.
Präzise neutroneninduzierte Spaltquerschnitte von Actinoiden wie den Plutoniumisotopen haben für die Entwicklung zukünftiger Transmutationstechnologien eine große Bedeutung. Die Unsicherheiten des ²⁴²Pu-Spaltquerschnitts im schnellen Bereich des Spektrums betragen derzeit etwa 21 %. Aktuelle Sensitivitätsstudien haben gezeigt, dass nur eine Reduzierung dieser Unsicherheiten auf unter 5 % verlässliche neutronenphysikalische Simulationen zulässt.
Diese anspruchsvolle Aufgabe konnte im Rahmen der vorliegenden Arbeit an der Neutronen-Flugzeitanlage nELBE durchgeführt werden. Dünne, homogene und großflächige Actinoiden-Proben wurden dem Helmholtz-Zentrum Dresden - Rossendorf innerhalb des TRAKULA-Verbundprojektes zur Verfügung gestellt. Eingesetzt in eine neu entwickelte Spaltionisationskammer ermöglichten sie eine akkurate Bestimmung des Spaltquerschnitts relativ zu ²³⁵U. Die Flächendichten der Plutoniumschichten wurden anhand der spontanen Spaltrate von ²⁴²Pu bestimmt. Aufwändige Teilchentransportsimula-
tionen (durchgeführt mit Geant 4, MCNP 6 und FLUKA) wurden genutzt, um die auftretende Neutronenstreuung zu korrigieren. Die gewonnenen Ergebnisse sind im Rahmen ihrer Unsicherheiten in guter Übereinstimmung mit aktuellen Kerndatenevaluierungen. /
Neutron induced fission cross sections of actinides like the Pu-isotopes are of relevance for the development of nuclear transmutation technologies. For ²⁴²Pu, current uncertainties are of around 21 \%. Sensitivity studies show that the total
uncertainty has to be reduced to below 5\% to allow for reliable neutron physics simulations. This challenging task was performed at the neutron time-of-flight facility of the new German National Center for High Power Radiation Sources at HZDR, Dresden. Within the TRAKULA project, thin, large and homogeneous deposits of ²³⁵U and ²⁴²Pu have been produced successfully. Using two consecutively placed fission chambers allowed the determination of the neutron induced fission cross section of ²⁴²Pu relative to ²³⁵U. The areal density of the Plutonium targets was calculated using the measured spontaneous fission rate. Experimental results of the fast neutron induced fission of ²⁴²Pu acquired at nELBE will be presented and compared to recent experiments and evaluated data. Corrections addressing the neutron scattering are discussed by using
results of different neutron transport simulations (Geant4, MCNP6 and FLUKA).
Keywords: Kernspaltung, Wirkungsquerschnitt, schnelle Neutronen, nELBE, Spaltionisationskammern/ fission, cross section, fast neutrons, nELBE, fission ionization chambers
  • Doctoral thesis
    TU Dresden, 2017
    Mentor: Dr. Arnd R. Junghans
    187 Seiten

Registration No. 26338 - Permalink


Determination of the γ-Ray-Angular Distribution in the Inelastic Scattering of Fast Neutrons on ⁵⁶Fe at nELBE
Dietz, M.
The inelastic neutron scattering reaction on 56Fe was studied at the nELBE time-of-flight facility of HZDR. The incoming neutron energy ranges in the fast neutron spectrum from 100 keV to 10 MeV, where high precision nuclear data are needed. Regarding the recent CIELO evaluation on 56Fe, there is a great interest in improving the knowledge of inelastic scattering angular distribution and increasing the resolution on the few literature data of gamma-ray-angular distribution.
To investigate angular distributions of the emitted gamma-rays, a new detector setup has been installed. It contains five HPGe detectors and five LaBr3 scintillation detectors, which can be set under different angles. For this measurement they were positioned under 30°; 55°; 90°; 125° and 150°, relative to the beam axis. By cyclical measurement with and without the natural Fe-target the intrinsic and the neutron induced background from the setup, except the target, has been subtracted. Corrections for gamma-self-absorption inside the target and extended source effciency were achieved using GEANT4 simulations.
The gamma-ray-angular distribution data measured with the HPGe detectors are compared with data from D. L. Smith, Argonne, 1976. Due to the much better time resolution in LaBr3 detectors high resolution data have been obtained and very interesting resonant structures have been observed for the gamma-ray-angular distribution. In the end, the influence of angular distribution coeffcient a4 is demonstrated by a anisotropy correction factor for experiments, using only one detector under an angle of 125°.
Keywords: nELBE, inelastic neutron scattering, Fe-56, angular distribution
  • Master thesis
    TU Dresden, 2016
    Mentor: Arnd R. Junghans

Registration No. 26336 - Permalink


Orca for computational actinide chemistry
Patzschke, M.
The program package Orca will be introduced and the use in computational actinide chemistry will be demonstrated.
Keywords: computational chemistry, ab initio, DFT, relativistic effects
  • Invited lecture (Conferences)
    ThUL School 2017, 16.-20.10.2017, Jülich, Deutschland

Registration No. 26334 - Permalink


Computational Spectroscopy
Patzschke, M.
In the contribution we discuss the application of computational chemistry to calculate spectroscopical parameters. We first present the foundations of computational chemistry in a very short form. We will show problems and advantages of DFT. Then we will show how spectroscopical parameters (IR,UV-VIS,NMR) can be calculated and what accuracy can be expected.
Keywords: computational chemistry, DFT, ab initio, actinides, spin-orbit coupling, relativistic effects
  • Invited lecture (Conferences)
    ThUL School 2017, 16.-20.10.2017, Jülich, Deutschland

Registration No. 26333 - Permalink


VVER-1000 RPV lower head model related to late in-vessel phenomena in case of hypothetical severe accident
Gencheva, R.; Grudev, P.; Stefanova, A.; Jobst, M.; Wilhelm, P.
This work discusses the progress in the development of an ASTEC computational model for investigation of molten corium pool behaviour in the lower head of a VVER-1000 reactor in case of a hypothetical accident with core degradation. The model was tested with variation of characterizing parameters which could have an influence on the molten pool behaviour and respectively the response behaviour of the reactor pressure vessel wall. An accident scenario with external cooling of the RPV wall was analysed. The preliminary code results give an estimation of the thermal load on the RPV wall. The sensitivity of the model depending on RPV wall nodalization was investigated. The analysis is performed in support to the numerical investigations realized within the frames of the EU HORIZON 2020 IVMR project (grant agreement number 662157).
Keywords: VVER-1000, severe accident, RPV, lower head, in-vessel
  • Contribution to proceedings
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland, 205-213
  • Lecture (Conference)
    27th Symposium of AER on VVER Reactor Physics and Reactor Safety, 17.-20.10.2017, München, Deutschland

Registration No. 26332 - Permalink


The influence of bentonite colloids on neptunium(V) migration in granitic rock
Elo, O.; Hölttä, P.; Huittinen, N.
In Finland, the repository for spent nuclear fuel (SNF) will be excavated at a depth of about 500 meters in the fractured crystalline bedrock in Olkiluoto at Eurajoki implemented by Posiva Oy. The engineered barrier systems (EBS), consisting of a solid fuel capsule, a copper-iron canister and the bentonite buffer should prevent the migration of radionuclides to the biosphere. Montmorillonite, the main mineral of bentonite, is like other aluminosilicates known to retain radionuclides, thus, preventing them from migrating from the repository with the groundwater. Bentonite erosion resulting in the formation of colloids may have a direct impact on the overall performance of the bentonite buffer. The potential relevance of colloids for radionuclide transport is highly dependent on the formation of colloids, the stability and mobility of colloids in different chemical environments, and their interaction with radionuclides [1]. Stable and mobile bentonite colloids can be formed when the glacial meltwater dilutes the groundwater. In these mildly oxic conditions, neptunium(V) will be present in its pentavalent oxidation state as the neptunyl cation (NpO2+), which is rather soluble, highly mobile and poorly adsorbed. Due to the long half-life of Np-237 (2.144·106 y), it will be a major dose contributor after 100,000 years in the SNF repository.
In our previous study, the interaction of Np(V) with Na-montmorillonite purified from MX-80 bentonite and corundum was investigated [2]. Corundum was used as a reference mineral in order to study the aluminol surface sites present on clay minerals, which are regarded as the main adsorption sites for radionuclide attachment [3]. This study aimed at investigating two processes: retardation of Np(V) on the bentonite colloids and granitic rock and the effect of the stable and mobile bentonite colloids on the migration of Np(V) in intact and crushed granitic rock columns.
The materials used in this study were colloids prepared from MX-80 Volclay type bentonite (76% montmorillonite) and Kuru Grey granite. Np(V) sorption on these materials under stagnant conditions was studied as a function of pH, solid concentration, time, and Np(V) concentration. The sorption experiments as a function of pH (3-11), were performed at a constant Np(V) concentration of 10-6 M. The sorption isotherms as a function of Np(V) concentration were conducted at concentration from 10-9 to 5·10-6 M at pH 8, 9, and 10. Solid concentrations were 0.08 g/L and 0.8 g/L for colloids and 40 g/L for granite. The samples were prepared by adding a small aliquot of colloid stock solution or crushed granite, Np-237 tracer and the background electrolyte in 20 ml polypropylene vials. The solution was buffered to the desired pH and after one week equilibration time the solid phase was separated from the liquid by centrifugation and 1 ml aliquots were taken immediately for liquid scintillation counting (Perkin Elmer Tri-Carb 3100 TR or Quantulus liquid scintillation counter). All the batch sorption studies were conducted in 10 mM NaClO4 either in carbonate-free N2-atmosphere (bentonite colloids, 0.08 g/L) or under ambient air conditions (granite and bentonite colloids 0.8 g/L).
The effect of bentonite colloids on Np(V) migration was studied in column experiments, where the column material was either crushed granite (grain size 0.01-0.1 mm) or an intact drill core of the Kuru Grey granite. The crushed granite column diameter was 1.5 cm and the length 15 cm. Drill core columns were constructed from Kuru grey granite cores which were placed inside a tube to form a flow channel (L = 28 cm, w = 4.4 cm) representing an artificial fracture formed by the 0.5 mm gap between the core and the tube [3]. In the experiments, colloid solution was injected into the water flow and the colloid breakthrough was detected by photon correlation spectroscopy (PCS) measurements. The column experiments were performed under ambient air conditions in 10 mM NaClO4 solution using flowrates of 1.5 mL/h, 0.8 mL/h, and 0.3 mL/h. The Np-tracer was injected into the flow, through an injection loop of known volume. The flow conditions in the columns were determined using chloride (36Cl-) as a conservative tracer. The effect of bentonite colloids on Np(V) transport at pH 8 and pH 10 was determined in the absence and presence of colloids (0.7 and 0.9 g/L). The colloid concentration in the collected fractions was determined by PCS and the Np(V) concentration was determined after PCS measurements from the same samples by liquid scintillation counting.
Np(V) adsorption onto MX-80 bentonite colloids and crushed Kuru Grey granite in 10 mM NaClO4 is shown as a function of pH in Figure 1a and as a function of Np concentration in Figure 1b. Sorption onto colloids was rather weak (20%) at pH 8 and higher adsorption occurred only above pH 10. According to the pH-edge results, the sorption isotherms for bentonite colloids are as expected, linear and the slopes are close to one another. The weak sorption of Np(V) on the colloids indicates that Np(V) will be mobilized as a neptunyl cation in solution. Despite the low uptake of Np(V) by the bentonite colloids, the obtained column results show that Np(V) breakthrough from the granite columns is enhanced in the presence of colloids (Figure 2).
  • Poster
    16th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 10.-15.09.2017, Barcelona, Spain

Registration No. 26330 - Permalink


Complexation of trivalent actinides and lanthanides with aqueous phosphates at elevated temperatures (25-80°C)
Huittinen, N.; Jordan, N.; Lösch, H.
The incorporation of actinides in solid lanthanide phosphates crystallizing in the monazite structure has been intensely investigated in the past decades due to the relevance of these monazites as potential ceramic phases for the immobilization of specific high level radioactive waste (HLW) streams [1-3]. In recent years, understanding the incorporation behaviour of trivalent dopants in the LnPO4×nH2O rhabdophane structure, which is the hydrated phosphate precursor in the synthesis of monazites through precipitation routes and a potential secondary mineral controlling actinide solubility in dissolution and re-precipitation reactions of monazite host-phases, has been given more attention [4,5]. Despite the large interest in lanthanide phosphates and the interaction of actinides with these solids, very little data is available on the complexation of lanthanides and actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing HLW repositories. It also suffers from an almost systematic absence of independent spectroscopic validation of the stoichiometry of the proposed complexes. Both from the perspective of aqueous rhabdophane synthesis, which is often carried out at elevated temperatures, and heat-generating HLW immobilization in monazites, the lanthanide and actinide complexation reactions with aqueous phosphates under ambient conditions should be complemented with data obtained at higher temperatures.

In the present work, time-resolved laser fluorescence spectroscopy (TRLFS) has been employed to study the phosphate complexation of Eu3+ (5×10-6 M) and Cm3+ (5×10-7 M) as a function of total phosphate concentration (0-1 M ΣPO4) in the temperature regime 25-80°C, using NaClO4 as a background electrolyte. These studies have, in a first step, been conducted in the acidic pH-range (pH = 1) to avoid precipitation of solid Eu or Cm rhabdophane. Both trivalent metal cations form a complex with the anionic H2PO4- species, i.e. EuH2PO42+ and CmH2PO42+. As expected, the complexation reaction occurs at lower total phosphate concentration when increasing the temperature. In addition, our preliminary results show the presence of a second Eu-phosphate species which is tentatively assigned to Eu(H2PO4)2+. The presence of this species will be verified with mass-spectrometric methods.
Temperature-dependent complexation constants for the identified species will be derived from the recorded luminescence emission spectra. These will be recalculated to standard conditions with the van´t Hoff equation and the Specific Ion Interaction Theory. For this, the required ion interaction coefficients have been preliminary determined at 25 °C by varying the ionic strength (0.6 to 3 M).
  • Poster
    16th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 10.-15.09.2017, Barcelona, Spain

Registration No. 26329 - Permalink


Charaterization of actinide(IV) complexes with imine type ligands
Radoske, T.
The progress on the PhD thesis is presented in an oral talk. The results include complexes of tetradentate and hexadentate salen complexes with several actinides in tetravalent state.
Keywords: actinide, salen, complex, thorium, uranium, SC-XRD
  • Lecture (others)
    FENABIUM Projekttreffen, 10.05.2017, Leipzig, Deutschland

Registration No. 26328 - Permalink


European standard on small punch testing of metallic materials
Bruchhausen, M.; Holmström, S.; Altstadt, E.; Dymacek, P.; Jeffs, S.; Lancaster, R.; Lacalle, R.; Matocha, K.; Petzova, J.
Life extension of aging nuclear power plant components requires knowledge of the properties of the service-exposed materials. For instance, in long term service the tensile and creep properties might decline and the ductile-to-brittle transition temperature (DBTT) might shift towards higher temperatures. Monitoring of structural components in nuclear power plants receives much attention – in particular in the context of lifetime extension of current plants, where the amount of material available for destructive testing is limited. Much effort has therefore been invested in the development of miniature testing techniques that allow characterizing structural materials with small amounts of material. The small punch (SP) test is one of the most widely used of these techniques. It has been developed for nuclear applications but its use is spreading to other industries.
Keywords: small punch test; tensile properties; fracture; creep; standardization
  • Contribution to proceedings
    ASME 2017 Pressure Vessels and Piping Conference PVP2017, 16.-20.07.2017, Hawaii, USA
    Proceedings of the ASME 2017 Pressure Vessels and Piping Conference PVP2017
    DOI: 10.1115/PVP2017-65396

Registration No. 26327 - Permalink


Structure Analysis of Pipe Section Reactor for Pipe-Wall Reaction: A Computational Fluid Dynamics Analysis Approach
Hua, P.; Ma, S.; Ding, W.; Zhang, J.
Corresponding author: Zhang, J. Tech Univ Dresden, Inst Urban Water Management, D-01062 Dresden, Germany
Pipe section reactor (PSR) is a well-controlled laboratory reactor, which is used to simulate the water quality variations in drinking water distribution systems. However, the hydraulics condition within PSR, which is an essential prerequisite of the water quality studies, still remains unclear. Consequently, the objective of this study is to analyze the hydraulic conditions within PSR by means of a computational fluid dynamics (CFD) approach. The influences of configuration parameters on the hydraulic conditions were tested including propeller diameter, inclined angle of the propeller, distance between the top and inner cylinder, distance between the bottom and inner cylinder, outer cylinder length, baffle length, number of the baffles, rotational speed of the propeller, and inner and outer cylinder diameters. According to the CFD analysis, an optimal structure of PSR was suggested. The data presented here could facilitate the PSR application and improve the simulation of water quality in distribution systems
Keywords: Chlorine decay; Computational fluid dynamics; Pipe section reactor; Structure optimization

Registration No. 26325 - Permalink


On the Role of the Electrical Field in Spark Plasma Sintering of UO2+x
Tyrpekl, V.; Najii, M.; Holzhäuser, M.; Freis, D.; Prieur, D.; Martin, P.; Cremer, B.; Murray-Farthing, M.; Cologna, M.
Corresponding author: Tyrpekl, Vaclav JRC
The electric field has a large effect on the stoichiometry and grain growth of UO2+x during Spark Plasma Sintering. UO2+x is gradually reduced to UO2.00 as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions. The shape of the gradient depends unequivocally on the direction of the electrical field. The positive surface of the pellet shows a higher oxidation state compared to the negative one. An area with larger grain size is found close to the positive electrode, but not in contact with it. We interpret these findings with the redistribution of defects under an electric field, which affect the stoichiometry of UO2+x and thus the cation diffusivity. The results bear implications for understanding the electric field assisted sintering of UO2 and non-stoichiometric oxides in general.
Keywords: UO2, SPS, XANES

Registration No. 26323 - Permalink


Serpent-DYN3D solution of the X2 benchmark: fresh core at HZP
Bilodid, Y.; Fridman, E.
In this work, the hot zero power experiments conducted during the startup of the fresh core of Khmelnitsky-2 NPP are modelled with the Serpent and DYN3D codes.
  • Lecture (Conference)
    7th International Serpent User Group Meeting, 06.-09.11.2017, Gainesville, FL, USA

Registration No. 26322 - Permalink


Nuclear data uncertainty quantification for the FREYA fast critical experiments
Fridman, E.; Aufiero, M.
This study summarizes some initial results of nuclear data uncertainty quantification for the FREYA fast critical experiments
  • Lecture (Conference)
    7th International Serpent User Group Meeting, 06.-09.11.2017, Gainesville, FL, USA

Registration No. 26321 - Permalink


Modeling of Phenix EOL experiments with Serpent-DYN3D
Nikitin, E.; Fridman, E.
This study presents the Serpent-DYN3D solution of the Phenix EOL benchmark
Keywords: Serpent, DYN3D, SFR, Phenix
  • Lecture (Conference)
    7th International Serpent User Group Meeting, 06.-09.11.2017, Gainesville, FL, USA

Registration No. 26320 - Permalink


Evaluation of gamma-ray strength functions
Schwengner, R.
Gamma-ray strength functions deduced from nuclear resonance fluorescence (NRF) and from light-ion induced reactions are compared.
Model assumptions in the analysis and differences in the reaction mechanisms and their influence on the results are considered.
New results from NRF experiments at ELBE and from calculations within the shell model are presented.
Keywords: Nuclear resonance fluorescence, light-ion induced reactions, absorption cross sections, dipole strength functions.
  • Invited lecture (Conferences)
    2nd Research Coordination Meeting of the Coordinated Research Project on Updating the Photonuclear Data Library and generating a Reference Database for Photon Strength Functions, 16.-20.10.2017, Wien, Österreich

Registration No. 26317 - Permalink


FFLO States in Layered Organic Superconductors
Wosnitza, J.
Corresponding author: Wosnitza, J. Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
In this short review, the recently found experimental evidence that Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states are realized in quasi-two-dimensional (2D) organic superconductors is reported. At low temperatures and when a high magnetic field is aligned parallel to the conducting organic layers, an upturn of the upper critical field much beyond the Pauli limit is observed, as proven by thermodynamic measurements. Under certain conditions, a second thermodynamic transition emerges inside the FFLO state. Nuclear magnetic resonance (NMR) work has added strong microscopic support for the realization of the FFLO state. The NMR spectra in the FFLO phase can very well be explained by a nonuniform one-dimensionally modulated superconducting order parameter. All These features, appearing only in a very narrow angular region close to parallel-field orientation, give robust evidence for the realization of the FFLO state in organic superconductors.

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  • Secondary publication expected from 03.11.2018

Registration No. 26310 - Permalink


Pt and Au bimetallic and monometallic nanostructured amperometric sensors for direct detection of hydrogen peroxide: Influences of bimetallic effect and silica support
Liu, W.; Hiekel, K.; Hübner, R.; Sun, H.; Ferancova, A.; Sillanpää, M.
Corresponding author: Liu, W. TU Dresden
The non-enzyme direct electrochemical sensing of hydrogen peroxide (H2O2) by nanostructured electrodes of Pt- and Au-containing bimetallic or monometallic nanocatalysts including paramecium-like nanostructures of PtAu supported on silica nanorods, Pt and Au nanoparticles supported on silica nanorods, and the non-supported Pt and Au nanoparticles (NPs) is reported. The nanocatalysts modified electrodes were fabricated by simple self-assembling on 3-aminopropyl-trimethoxysilane (APTMS) modified glassy carbon. The cyclic voltammetric and amperometric results showed that PtAu supported on silica nanorods has superior performance over the corresponding monometallic counterparts, with a broad linear range from 5.0 µM to 72000 µM for H2O2, a detection limit of 2.6 µM, a sensitivity of 46.7 µA mM-1cm-2 at a lower working potential of -0.20 V vs SCE, and has good stability and reproducibility. In addition, a systematic test showed that the non-supported Pt NPs sensor has a surprisingly high performance, even better than the paramecium-like nanostructure of PtAu supported on silica nanorods, where the existence of silica nanorod templates in the nanocatalysts retards the electrocatalytic reduction/oxidation of H2O2. Among the nanocatalysts tested in this work, the Pt NPs sensor showed fastest response within 3 s, a broad linear response from 5 µM to 58000 µM, a detection limit of 4.2 µM, and the highest sensitivity of 110.3 µA mM-1cm-2 at the lowest working potential of -0.08 V vs SCE. Notably, the performance of the Pt NPs sensor is also among the best Pt-containing monometallic or bimetallic nanostructured electrochemical sensors toward H2O2 reported so far. This work shows a simple method to fabricate H2O2 electrochemical sensors of high performance and indicates the importance of considering not only bimetallic effects but also the influences of the nanostructure of nanocatalysts on the electrocatalytic performance and electrochemical sensing property.
Keywords: Platinum, Bimetallic effect, Support material, Electrocatalyst, Amperometric sensor, Hydrogen peroxide
  • Sensors and Actuators B 255(2018), 1325-1334

Registration No. 26307 - Permalink


Fast neutron measurements at the nELBE time-of-flight facility
Junghans, A. R.; Beyer, R.; Grosse, E.; Hannaske, R.; Kögler, T.; Massarczyk, R.; Schwengner, R.; Wagner, A.
The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf has been rebuilt. A new enlarged experimental hall with a flight path of up to 10 m is available for neutron time-of-flight experiments in the fast energy range from about 50 keV to 10 MeV.
nELBE is intended to deliver nuclear data of fast neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. The experimental programme consists of transmission measurements of neutron total cross sections, elastic and inelastic scattering cross section measurements, and neutron induced fission cross sections. The inelastic scattering to the first few excited states in 56Fe was investigated by measuring the gamma production cross section with an HPGe detector. The neutron induced fission of 242Pu was studied using fast ionisation chambers with large homogeneous actinide deposits.
Keywords: nELBE, neutron time of flight, transmission, total cross section, inelastic scattering, fission

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Registration No. 26306 - Permalink


Generation of high-avidity, WT1-reactive CD8+ cytotoxic T cell clones with anti-leukemic activity by streptamer technology
Tunger, A.; Wehner, R.; von Bonin, M.; Kühn, D.; Heidenreich, F.; Matko, S.; Nauerth, M.; Rücker-Braun, E.; Dietz, S.; Link, C. S.; Eugster, A.; Odendahl, M.; Busch, D. H.; Tonn, T.; Bonifacio, E.; Germeroth, L.; Schetelig, J.; Bachmann, M. P.; Bornhäuser, M.; Schmitz, M.
Summary: In summary, we demonstrated that the expansion of WT1 peptide-specific CD8+ T cells by peptide-loaded MoDCs followed by streptamer-based selection represents an attractive strategy to significantly enrich such T cells prior to cloning. By using this technology, we generated high-avidity, WT1 peptide-reactive CD8+T cell clones with anti-leukemic activity. This strategy may be particular useful for the generation of CD8+T cell clones from healthy donors, in which blood circulating T cells recognizing tumor-associated antigens are rare or not detectable.
Keywords: WT1, CD8+ cytotoxic T cell clones, streptamer technology

Registration No. 26305 - Permalink


Exploratory investigation of PSCA-protein expression in primary breast cancer patients reveals a link to HER2/neu overexpression.
Link, T.; Kuithan, F.; Ehninger, A.; Kuhlmann, J. D.; Kramer, M.; Werner, A.; Gatzweiler, A.; Richter, B.; Ehninger, G.; Baretton, G.; Bachmann, M.; Wimberger, P.; Friedrich, K.
Corresponding author: Kuhlmann, J. D. Department of Gynecology and Obstetrics, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
Background: Prostate stem cell antigen (PSCA) has been suggested as biomarker and therapeutic target for prostate cancer. Recent advances showed that PSCA is upregulated in other cancer entities, such as bladder or pancreatic cancer. However, the clinical relevance of PSCA-expression in breast cancer patients has not yet been established and is therefore addressed by the current study.
Methods: PSCA-protein expression was assessed in 405 breast cancer patients, using immunohistochemistry (PSCA antibody MB1) and tissue microarrays.
Results: PSCA-expression was detected in 94/405 patients (23%) and correlated with unfavorable histopathological grade (p=0.011) and increased Ki67 proliferation index (p=0.006). We observed a strong positive correlation between PSCA-protein expression and HER2/neu receptor status (p<0.001). PSCA did not provide prognostic information in the analyzed cohort. Interestingly, the distribution of PSCA-expression among triple negative patients was comparable to the total population.
Conclusion: We identified a subgroup of PSCA-positive breast cancer patients, which could be amenable for a PSCA-targeted therapy. Moreover, given that we found a strong positive correlation between PSCA- and HER/neu expression, targeting PSCA may provide an alternative therapeutic option in case of trastuzumab resistance.
Keywords: breast cancer, PSCA, HER2/neu, therapeutic target

Registration No. 26302 - Permalink


Deposition and properties of Fe(Se,Te) thin films on vicinal CaF2 substrates
Bryja, H.; Hühne, R.; Iida, K.; Molatta, S.; Sala, A.; Putti, M.; Schultz, L.; Nielsch, K.; Hänisch, J.
Corresponding author: Bryja, H. Institute for Metallic Materials, IFW Dresden & Institute of Materials Science, TU Dresden, Dresden, Germany
We report on the growth of epitaxial Fe1+δSe0.5Te0.5 thin films on 0°, 5°, 10°, 15° and 20° vicinal cut CaF2 single crystals by pulsed laser deposition. In situ electron and ex situ x-ray diffraction studies reveal a tilted growth of the Fe1+δSe0.5Te0.5 films, whereby under optimized deposition conditions the c-axis alignment coincides with the substrate [001] tilted axis up to a vicinal angle of 10°. Atomic force microscopy shows a flat island growth for all films. From resistivity measurements in longitudinal and transversal directions, the ab- and c-axis components of resistivity are derived and the mass anisotropy parameter is determined. Analysis of the critical current density indicates that no effective c-axis correlated defects are generated by vicinal growth, and pinning by normal point core defects dominates. However, for H||ab the effective pinning centers change from surface defects to point core defects near the superconducting transition due to the vicinal cut. Furthermore, we show in angular-dependent critical current density data a shift of the ab-planes maxima position with the magnetic field strength.

Registration No. 26300 - Permalink


Acoustic Properties of Crystals with Jahn–Teller Impurities: Elastic Moduli and Relaxation Time. Application to SrF2:Cr2+
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Shakurov, G. S.; Ulanov, V. A.; Surikov, V. T.
Corresponding author: Gudkov, V. V. Ural Federal University, Ekaterinburg, Russia
A new approach to evaluate the relaxation contribution to the total elastic moduli for crystals with Jahn–Teller (JT) impurities is worked out and applied to the analysis of the experimentally measured ultrasound velocity and attenuation in SrF2:Cr2+. Distinguished from previous work, the background adiabatic contribution to the moduli, important for revealing the impurity relaxation contribution, is taken into account. The temperature dependence of the relaxation time for transitions between the equivalent configurations of the JT centers has been obtained, and the activation energy for the latter in SrF2:Cr2+. as well as the linear vibronic coupling constant have been evaluated.

Registration No. 26299 - Permalink


Mass spectrometry-based identification of a naturally presented receptor tyrosine kinase-like orphan receptor 1-derived epitope recognized by CD8+ cytotoxic T cells
Heidenreich, F.; Rücker-Braun, E.; Walz, J. S.; Eugster, A.; Kühn, D.; Dietz, S.; Nelde, A.; Tunger, A.; Wehner, R.; Link, C. S.; Middeke, J. M.; Stölzel, F.; Tonn, T.; Stevanovic, S.; Rammensee, H. G.; Bonifacio, E.; Bachmann, M.; Zeis, M.; Ehninger, G.; Bornhäuser, M.; Schetelig, J.; Schmitz, M.
Corresponding author: Heidenreich, F. DKMS German Bone Marrow Donor Center, Clinical Trials Unit, Dresden, Germany; Department of Medicine I, University Hospital of Dresden, Germany
Mass spectrometry-based identification of a naturally presented receptor tyrosine kinase-like orphan receptor 1-derived epitope recognized by CD8+ cytotoxic T cells

Registration No. 26298 - Permalink


Microstructure and charge trapping in in ZrO2- and Si3N4-based superlattice layer systems with Ge nanoparticles
Seidel, S.; Rebohle, L.; Prucnal, S.; Lehninger, D.; Hübner, R.; Klemm, V.; Skorupa, W.; Heitmann, J.
Corresponding author: Seidel, S.
Ge was deposited on silicon as a superlattice with 10 layers of Ge embedded in Si3N4 or ZrO2 matrices via plasma enhanced chemical vapor deposition or RF-sputtering, respectively. Raman spectroscopy, transmission electron microscopy and capacitance-voltage (CV) measurements were performed in order to investigate the structural and electrical properties of the superlattices. It will be shown that, in contrast to furnace annealing, flash lamp annealing of Ge-ZrO2-superlattices leads to crystalline Ge nanoparticles in an amorphous matrix. As revealed by CV measurements, these layers show excellent charge storage capabilities. In comparison, a higher thermal budget is needed to crystallize Ge in case of Si3N4-based superlattices, and no significant charge trapping could be detected during CV measurements.
Keywords: Ge nanocrystals, zirconium oxide, silicon nitride, superlattice, flash lamp annealing

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Registration No. 26291 - Permalink


Topological Hall Effect in an Artificial Skyrmion Lattice
Murray, P.; Chen, Z.; Gilbert, D. A.; Zang, J.; Stuckler, T.; Lenz, K.; Maranville, B. B.; Fassbender, J.; Yu, H.; Borchers, J. A.; Liu, K.
Magnetic skyrmions have exciting potential for future device applications in low dissipation information storage [1-3]. While much research has been focused on DMI-stabilized skyrmions in bulk crystals or multilayers, we recently realized Bloch-type artificial skyrmion lattices which are stable at room temperature under zero magnetic field [4], offering a convenient platform for investigating transport characteristics such as the Topological Hall Effect (THE). Here, we report a study of the THE in a different type of planar skyrmion lattice, without any protruding magnetic dots on top.
Keywords: skyrmions, DMI, magnetism, topological hall effect
  • Poster
    62nd Annual Conference on Magnetism and Magnetic Materials, MMM 2017, 06.-10.11.2017, Pittsburgh, USA

Registration No. 26289 - Permalink


Synthesis and characterization of tetravalent actinide complexes with benzamidinates
Schöne, S.ORC; März, J.; Kaden, P.
The synthesis and characterization of tetravalent actinide complexes with different amidinates is presented. The synthesized thorium and uranium amidinates were characterized in solution with NMR and UV-Visible spectroscopy and in solid state with SC-XRD and IR spectroscopy. The molecular structures were discussed in detail showing differences between the coordination behavior of different amidinates.
  • Lecture (others)
    FENABIUM Projekttreffen, 10.05.2017, Leipzig, Deutschland

Registration No. 26288 - Permalink


Novel Radiolabeled Bisphosphonates for PET Diagnosis and Endoradiotherapy of Bone Metastases
Pfannkuchen, N.; Meckel, M.; Bergmann, R.; Bachmann, M.; Bal, C.; Sathekge, M.; Mohnike, W.; Baum, R. P.; Rösch, F. .
Corresponding author: Rösch, Frank . Institute of Nuclear Chemistry, Johannes Gutenberg University Mainz, Fritz-Strassmann-Weg 2, 55128 Mainz, Germany
Bone metastases, often a consequence of breast, prostate, and lung carcinomas, are characterized by an increased bone turnover, which can be visualized by positron emission tomography (PET), as well as single-photon emission computed tomography (SPECT). Bisphosphonate complexes of 99mTc are predominantly used as SPECT tracers. In contrast to SPECT, PET offers a higher spatial resolution and, owing to the 68Ge/68Ga generator, an analog to the established 99mTc generator exists. Complexation of Ga(III) requires the use of chelators. Therefore, DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), NOTA (1,4,7-triazacyclododecane-1,4,7-triacetic acid), and their derivatives, are often used. The combination of these macrocyclic chelators and bisphosphonates is currently studied worldwide. The use of DOTA offers the possibility of a therapeutic application by complexing the β-emitter 177Lu. This overview describes the possibility of diagnosing bone metastases using [68Ga]Ga-BPAMD (68Ga-labeled (4-{[bis-(phosphonomethyl))carbamoyl]methyl}-7,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl)acetic acid) as well as the successful application of [177Lu]Lu-BPAMD for therapy and the development of new diagnostic and therapeutic tools based on this structure. Improvements concerning both the chelator and the bisphosphonate structure are illustrated providing new 68Ga- and 177Lu-labeled bisphosphonates offering improved pharmacological properties.
Keywords: bisphosphonates; bone metastases; diagnosis; therapy; 68Ga; 177Lu

Registration No. 26287 - Permalink


Biological characterization of novel nitroimidazole-peptide conjugates in vitro and in vivo.
Bergmann, R.; Splith, K.; Pietzsch, J.; Bachmann, M.; Neundorf, I.
Corresponding author: Neundorf, Ines Department für Chemie, Institut für Biochemie, Mathematisch-Naturwissenschaftliche Fakultät, Universität zu Köln, Köln, Germany
Recently, we reported on the design of a multimodal peptide conjugate useful as delivery platform for targeting hypoxic cells. A nitroimidazole (2-(2-nitroimidazol-1-yl)acetic acid, NIA) moiety, which is selectively entrapped in hypoxic cells, was coupled to a cell-penetrating peptide serving as the transporter. Furthermore, attachment of a bifunctional linker allowed the introduction of a diagnostic or therapeutic radiometal. However, although selective tumor accumulation could be detected in vivo, a fast renal clearance of the compound was observed. The present study aims to improve the system by using the more proteolytically stable all-d version of the peptide carrier (DsC18), by attaching two NIA moieties instead of one (DsC18(NIA)2 ) to enhance the tumor uptake, and by incorporating the bifunctional chelator NODAGA instead of DOTA (NODAGA-DsC18(NIA)2 ) to optimize labeling chemistry. First, we characterized in vitro the novel all-d peptide compared with its parent l-version. Then, in order to investigate and compare the pharmacological profiles of the peptides, these were radiolabeled with 64 CuII and 68 GaIII , and the biodistribution and kinetics were evaluated in vivo. Our results show the versatility of the d-peptide as cell-penetrating peptide and transporter. However, attaching two NIA groups modified the system in such a way that no selective tumor uptake could be observed compared with the peptide without NIA moieties. Still, this work highlights new pharmacokinetic data on the biodistribution of such compounds in vivo.
Keywords: cell-penetrating peptides; drug delivery; positron emission tomography (PET); proteolytic stability; tumor hypoxia; tumor theranostics

Registration No. 26286 - Permalink


Detection of metal ions using fluorescent gold nanoclusters
Vogel, M.; Matys, S.; Pollmann, K.; Raff, J.
S-layer proteins appear to be suitable for wide variety of different technical applications due to their distinctive physico-chemical properties and their multifunctionality.Since several years the focus has been placed especially on their potential use for biosensor applications. There are many approaches under investigation to develop sensors that are highly specific and sensitive as well as robust, reliable and not expensive. Optical methods currently appear an attractive solution. Colloidal gold nanoparticle suspensions as sensory active systems, for instance, have been the subject of intensive investigations for many years. An additional promising approach is the use of proteins as template structures for the production of highly fluorescent, size-controlled gold nanoclusters. These gold nanoclusters can be synthesized directly at the protein by a simple chemical reaction. We present current investigations on different kind of proteins such as bovine serum albumin, calmodulin, and S-layer protein. In combination with the known S-layer or calmodulin mediated selective and specific binding of ionic analytes, e.g. rare earth elements as surrogates/analogues for intrinsic protein bound Ca2+, a subsequent analyte-induced change in the fluorescence intensity of the gold nanoclusters might be used as sensory system for the detection of such strategic relevant elements.
Keywords: S-layer proteins, BSA, gold nanoclusters, bio-sensing, fluorescence
  • Poster
    13. Sensor Symposium, 04.-06.12.2017, Dresden, Deutschland
  • Open Access LogoContribution to proceedings
    13. Sensor Symposium, 04.-06.12.2017, Dresden, Deutschland
    AMA Proceedings 2017
    DOI: 10.5162/13dss2017/P4.08

Registration No. 26285 - Permalink


Characterization of a switchable chimeric antigen receptor platform in a pre-clinical solid tumor model
Bejestani, E. P.; Cartellieri, M.; Bergmann, R.; Ehninger, A.; Loff, S.; Kramer, M.; Spehr, J.; Dietrich, A.; Feldmann, A.; Albert, S.; Wermke, M.; Baumann, M.; Krause, M.; Bornhäuser, M.; Ehninger, G.; Bachmann, M.; von Bonin, M.
Corresponding author: Bonin, Malte Von Medical Department I, University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
The universal modular chimeric antigen receptor (UniCAR) platform redirects CAR-T cells using a separated, soluble targeting module with a short half-life. This segregation allows precise controllability and flexibility. Herein we show that the UniCAR platform can be used to efficiently target solid cancers in vitro and in vivo using a pre-clinical prostate cancer model which overexpresses prostate stem cell antigen (PSCA). Short-term administration of the targeting module to tumor bearing immunocompromised mice engrafted with human UniCAR-T cells significantly delayed tumor growth and prolonged survival of recipient mice both in a low and high tumor burden model. In addition, we analyzed phenotypic and functional changes of cancer cells and UniCAR-T cells in association with the administration of the targeting module to reveal potential immunoevasive mechanisms. Most notably, UniCAR-T cell activation induced upregulation of immune-inhibitory molecules such as programmed death ligands. In conclusion, this work illustrates that the UniCAR platform mediates potent anti-tumor activity in a relevant in vitro and in vivo solid tumor model.
Keywords: Chimeric antigen receptors, immune checkpoints, immunoevasion, prostate stem cell antigen, solid tumors, targeting module

Registration No. 26282 - Permalink


Monovacancy paramagnetism in neutronirradiated graphite probed by 13C NMR
Zhang, Z. T.; Xu, C.; Dmytriieva, D.; Molatta, S.; Wosnitza, J.; Wang, Y. T.; Helm, M.; Zhou, S.; Kühne, H.
Corresponding author: Zhang, Z. T. Institute of Ion Beam Physics and Materials Research & Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
We report on the magnetic properties of monovacancy defects in neutron-irradiated graphite, probed by 13C nuclear magnetic resonance spectroscopy. The bulk paramagnetism of the defect moments is revealed by the temperature dependence of the NMR frequency shift and spectral linewidth, both of which follow a Curie behavior, in agreement with measurements of the macroscopic magnetization. Compared to pristine graphite, the fluctuating hyperfine fields generated by the defect moments lead to an enhancement of the 13C nuclear spin-lattice relaxation rate 1/T1 by about two orders of magnitude. With an applied magnetic field of 7.1 T, the temperature dependence of 1/T1 below about 10 K can well be described by a thermally activated form, 1/T1 α exp(−Δ/kBT), yielding a singular Zeeman energy of (0.41 ± 0.01) meV, in excellent agreement with the sole presence of polarized, non-interacting defect moments.

Registration No. 26279 - Permalink


Magnetic Properties of the Nanocrystalline Nd-Ho-Fe-Co-B Alloy at Low Temperatures: The Influence of Time and Annealing
Tereshina, I. S.; Kudrevatykh, N. V.; Ivanov, L. A.; Politova, G. A.; Tereshina, E. A.; Gorbunov, D.; Doerr, M.; Rogackie, K.
Corresponding author: Tereshina, I. S. Faculty of Physics, Lomonosov Moscow State University, Moscow, Russia and International Laboratory of High Magnetic Fields and Low Temperature, Wroclaw, Poland
A study is made of the effects of various factors such as time (7 years), temperature, high magnetic field up to 580 kOe and heat treatment (HT) on the morphological structure and magnetic hysteresis properties of a high-coercive nanocrystalline (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy with a low temperature coefficient of remanence. We find a rather weak time effect on (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2. After 7 years, the loss in the maximum magnetic energy product (BH)max is no more than 5%. Annealing of the sample at 250 °C for 30 min decreases the amount of amorphous phase from 7.2 to 1.7%, while the grains’ size of the 2-14-1 phase increases from 83 to 109 nm. For the HT alloy, a magnetization jump is observed at H ~ 500 kOe. It can be attributed to the first-order magnetization process or a spin-flip magnetic transition. Rectangularity of the hysteresis loop degrades after annealing. In case of the short-time heat treatment, losses in (BH)maxare ~ 10%.

Registration No. 26278 - Permalink


Influence of Co on the magnetism of HoFe5Al7
Andreev, A. V.; Gorbunov, D. I.; Sebek, J.; Nehnakhin, D. S.
Corresponding author: Andreev, A. V. Institute of Physics, Academy of Sciences, Prague, Czech Republic
Effects of the Co substitution for Fe on the strongly anisotropic ferrimagnet HoFe5Al7 are studied on single-crystalline samples with a tetragonal crystal structure of the ThMn12-type. For HoFe5-xCoxAl7, we found the homogeneity range up to x = 2.5. The Co substitution results in a shrinkage of the tetragonal lattice within the basal plane, whereas the c parameter does not change. The exchange interactions and magnetic anisotropy are strongly affected by the Co substitution. The detrimental effect of Co on the Curie temperature TC in HoFe5-xCoxAl7 compounds is very unusual. The Curie temperature linearly falls from 216 K for x = 0-67 K for x = 2.5, which is unexpected because the Co substitution for Fe in 3d-4f intermetallic compounds usually increases the magnetic ordering temperatures due to the strengthening of exchange interactions. At the same time, the compensation temperature changes very little between 65 K and 72 K. At 2 K, spontaneous magnetic moment increases from 2 µB at x = 0-4.2 µB at x = 2.5. Magnetization measurements have been performed in pulsed magnetic fields up to 58 T. The compounds exhibit a high magnetic anisotropy of the easy-plane type with the [110] axis as the easy-magnetization direction. Along the easy axis, two first-order field-induced magnetic transitions (at 17 T and 37 T) are observed for HoFe5Al7 and one transition at 27 T for HoFe4CoAl7. The magnetization curve has an S-shape for HoFe3Co2Al7.

Registration No. 26273 - Permalink


Meniscus Asymmetry and Chemo-Marangoni Convection in Capillaries
Eckert, K.; Shi, Q.; Seidel, K.; Schwarzenberger, K.
Corresponding author: Eckert, Kerstin
A liquid-liquid system inside a capillary in which an interfacial reaction leads to in situ production of a surfactant was studied experimentally. The resulting chemo-Marangoni convection induces periodic spreading-dewetting cycles in laboratory experiments. By selected experiments in microgravity, the individual phenomena of the system dynamics could be isolated. The spreading-dewetting cycles result from a complex interplay between the decrease in interfacial tension due to the production of surfactant, the chemo-Marangoni convection, and the gravity-driven deformation of the meniscus shape.
Keywords: Capillaries, Interfacial reactions, Marangoni convection, Meniscus deformation, Microgravity

Registration No. 26272 - Permalink


Kinematic dynamo models from hydrodynamic simulations and experiments of precession driven flows
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.
We used a model water experiment and hydrodynamic simulations to estimate the flow in a precessing cylinder. The resulting velocity fields are dominated by standing inertial waves which makes them appropriate for the application in a kinematic dynamo model based on the time-averaged flow. We found dynamo action at magnetic Reynolds numbers of the order of Rm~500.
Essential for the dynamo is the coupling of the primary (directly forced) flow with azimuthal wave number m = 1 and a non-geostrophic axisymmetric mode which at Re = 10000 emerges in a narrow regime around Po = 0.10.

Our results point out a first promising – but narrow – regime
where we may expect dynamo action in the large scale dynamo
experiment currently under construction at HZDR.
Keywords: Dynamo Dresdyn
  • Lecture (Conference)
    GDRI DYNAMO Meeting, 27.-29.11.2017, Paris, France

Registration No. 26270 - Permalink


Magnetic and acoustic properties of CoCr2S4
Felea, V.; Cong, P. T.; Prodan, L.; Gritsenko, Y.; Wosnitza, J.; Zherlitsyn, S.; Tsurkan, V.
We report results of magnetic and ultrasound studies of the sulfide spinel CoCr2S4, for which the multiferroicity has recently been suggested. Clear anomalies in the magnetic and acoustic properties have been observed at TN = 222 K and in applied magnetic fields evidencing the important role of magnetoelastic interac-tions in this material. In contrast, no anomalies have been detected at TC = 28 K, where a spontaneous electric polarization and isostructural distortions have been reported. We have extracted the H–T phase diagram of CoCr2S4 from our experiments for magnetic fields applied along the <111> direction. We discuss our observa-tions in relation to our earlier results obtained for the oxide multiferroic spinel CoCr2O4.
  • Low Temperature Physics 43(2017), 1618-1621

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  • Secondary publication expected from 25.09.2018

Registration No. 26269 - Permalink


Bulk Fermi surface of the Weyl type-II semimetallic candidate γ -MoTe2
Rhodes, D.; Schönemann, R.; Aryal, N.; Zhou, Q.; Zhang, Q. R.; Kampert, E.; Chiu, Y.-C.; Lai, Y.; Shimura, Y.; Mccandless, G. T.; Chan, J. Y.; Paley, D. W.; Lee, J.; Finke, A. D.; Ruff, J. P. C.; Das, S.; Manousakis, E.; Balicas, L.
Corresponding author: Balicas, L. National High Magnetic Field Laboratory, Florida State University, Tallahassee & Department of Physics, Florida State University, Tallahassee, Florida, USA
The electronic structure of semimetallic transition-metal dichalcogenides, such as WTe2 and orthorhombic γ-MoTe2, are claimed to contain pairs of Weyl points or linearly touching electron and hole pockets associated with a nontrivial Chern number. For this reason, these compounds were recently claimed to conform to a new class, deemed type-II, of Weyl semimetallic systems. A series of angle-resolved photoemission experiments (ARPES) claim a broad agreem nt with these predictions detecting, for example, Fermi arcs at the surface of these crystals. We synthesized single crystals of semimetallic MoTe2 through a Te flux method to validate these predictions through measurements of its bulk Fermi surface (FS) via quantum oscillatory phenomena.We find that the superconducting transition temperature of γ-MoTe2 depends on disorder as quantified by the ratio between the room- and low-temperature resistivities, suggesting the possibility of an unconventional superconducting pairing symmetry. Similarly to WTe2, the magnetoresistivity of γ-MoTe2 does not saturate at high magnetic fields and can easily surpass 106%. Remarkably, the analysis of the de Haas–van Alphen (dHvA) signal superimposed onto the magnetic torque indicates that the geometry of its FS is markedly distinct from the calculated one. The dHvA signal also reveals that the FS is affected by the Zeeman effect precluding the extraction of the Berry phase. A direct comparison between the previous ARPES studies and density-functional-theory (DFT) calculations reveals a disagreement in the position of the valence bands relative to the Fermi level εF . Here, we show that a shift of the DFT valence bands relative to εF , in order to match the ARPES observations, and of the DFT electron bands to explain some of the observed dHvA frequencies, leads to a good agreement between the calculations and the angular dependence of the FS cross-sectional areas observed experimentally. However, this relative displacement between electron and hole bands eliminates their crossings and, therefore, the Weyl type-II points predicted for γ-MoTe2.

Registration No. 26268 - Permalink


Methods of dilatometric investigations under extreme conditions and the case of spin-ice compounds
Doerr, M.; Granovsky, S.; Rotter, M.; Stöter, T.; Wang, Z.-S.; Zherlitsyn, S.; Wosnitza, J.
Corresponding author: Doerr, M. Technische Universität Dresden, Institut für Festkörperphysik, Dresden, Germany
We give an overview on how dilatometric methods have been developed in the last decade. The concept of capacitive dilatometry was successfully adapted to dilution refrigerators with a resolution of 10-9. Miniaturized dilatometers with an overall diameter of 18 mm or less are optimally suited for measuring longitudinal and transversal components of the striction tensor. Going to another extreme, to the highest (pulsed) fields, optical methods, such as the FBG technology, were developed for investigations up to 100 T.
As examples for utilizing dilatometry at low temperatures we show results for the spin-ice materials Dy2Ti2O7 and Ho2Ti2O7. To characterise the magneto-elastic coupling in these materials, we investigated the thermal expansion and magnetostriction between 80 mK and 15 K and in magnetic fields aligned along the [111] direction and found field-induced phases and strong correlations below 500 mK. Our data demonstrate, that the formation of the field-induced phase is strongly influenced by lattice distortions: any change in interatomic distances will result in a variation of the exchange couplings.

Registration No. 26267 - Permalink


Biomarkers in Malignant Melanoma: Recent Trends and Critical Perspective
Belter, B.; Haase-Kohn, C.; Pietzsch, J.ORC
The worldwide incidence of malignant melanoma is steadily increasing, suggesting a probable melanoma “epidemic.” From a clinical point of view, malignant melanoma still is an unpredictable disease and, once in the advanced stage, allows only scarce therapeutic options. There is an urgent need to identify, characterize, and validate informative biomarkers, biomarker patterns, or surrogate markers in order to not only improve early diagnosis of melanoma but also for differential diagnosis, staging, prognosis, therapy selection, and therapy monitoring.
In this chapter, an update on the ongoing debate on serologic and histologic markers such as lactate dehydrogenase, tyrosinase, S100 family of calcium-binding proteins, cyclooxygenase-2, matrix metalloproteinases, and stem and/or progenitor cell markers are presented, and novel, innovative, and promising trends currently being explored are discussed.
Keywords: Cyclooxygenase-2; Lactate dehydrogenase; Malignant melanoma; Matrix metalloproteinases; S100 proteins; Tyrosinase
  • Open Access LogoBook chapter
    William H. Ward; Jeffrey M. Farma: Cutaneous Melanoma: Etiology and Therapy, Brisbane, Australia: Codon Publications, 2017, 978-0-9944381-4-0, 39-56
    DOI: 10.15586/codon.cutaneousmelanoma.2017

Registration No. 26263 - Permalink


High Temperature Stability of BaZrO3: An Ab Initio Thermodynamic Study
Raja, N.; Murali, D.; Posselt, M.; Satyanarayana, S. V. M.
Corresponding author: Raja, Nadarajan Department of Physics, Pondicherry University, Puducherry 605 014, India
BaZrO3 exhibits excellent proton conductivity and good high-temperature stability. It is therefore a promising electrolyte material for solid oxide fuel cells. The stability of BaZrO3 at high temperatures is generally explained by the low diffusivity of O vacancy. Present first principle density functional theory calculations show that the slow migration of the doubly charged O vacancy at high temperature cannot be solely caused by the ground-state migration energy but by the contribution of phonon excitations to the free migration energy. With increasing temperature, the effective barrier for oxygen vacancy migration increases. At about 1000 K, which is the operating temperature of fuel cells, the calculated O vacancy diffusivity is more than one order of magnitude lower than that determined using ground-state migration barrier. The calculated diffusivity data agree well with experimental results from literature. The present work reveals that the high-temperature stability of BaZrO3 is mainly due to the phonon contribution to the free migration energy of the O vacancy.
Keywords: perovskite, high-temperature stability, ab-initio calculation, O vacancy

Registration No. 26262 - Permalink


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