Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Approved and published publications
Only approved publications

39129 Publications

Update on the FLUKA geometry modeling

Müller, S.

Update on FLUKA geometry modeling

Keywords: FLUKA; Mu2e

  • Lecture (others)
    Mu2e Simulation Workinggroup Meeting, 18.07.2019, Batavia, USA

Publ.-Id: 29516

Update on FLUKA simulation activities for the Mu2e experiment

Müller, S.

Update on the FLUKA simulation for the Mu2e experiment

Keywords: FLUKA; Mu2e

  • Lecture (others)
    Mu2e collaboration meeting, 26.06.2019, Minneapolis, USA

Publ.-Id: 29515

Electrovortex liquid metal flows in cells with localized current supply

Kolesnichenko, I.; Frick, P.; Stefani, F.; Eltischev, V.; Weber, N.; Mandrykin, S.; Ozernykh, V.; Khalilov, R.

The paper studies the flow of a liquid metal in a cylindrical cell caused by the action of electromagnetic force. An electric current passes through the metal. The current is locally supplied to the area at the bottom of the cell and discharged at the top. Force generates from the joint action of an electric current and its own magnetic field. The vorticity of the force is nonzero and an electro-vortex flow (EVF) arises. The characteristics of the intensity and oscillations of EVF are studied numerically and experimentally. Methods for contactless determination of the position of the liquid metal boundary have been developed. The possibility of manipulation of the intensity and shape of EVF was studied.

  • Lecture (Conference)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.07.2019, Reims, Frankreich
  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.07.2019, Reims, Frankreich

Publ.-Id: 29514

Electro-vortex flow in a cylindrical container

Liu, K.; Li, B. W.; Stefani, F.; Weber, N.; Weier, T.

In a cylindrical container filled with the eutectic alloy GaInSn, an electro-vortex flow (EVF) is caused by the interaction of a non-uniform current with the magnetic field that it generates. In this paper, we investigate the EVF numerically and experimentally. First, based on a solver by Weber, we develop a more advanced one, in which the effect of Joule heating is considered. The magnetic field, which is the combination of the current induced magnetic field and the external geomagnetic field, is also taken into account. For getting a higher computational efficiency, the so-called parent-child mesh technique is applied in OpenFOAM. Second, we conduct an experiment corresponding to the numerical simulation, in which Ultrasound Doppler Velocimetry (UDV) is applied for flow measurements. The results of the experiment are in good agreement with those of the simulation.

Keywords: electro-vortex flow; Joule heating; parent-child mesh; OpenFOAM

  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich
  • Poster
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, Frankreich

Publ.-Id: 29513

Novel Thyristor-Based Pulsed Current Converter for a Medical Application - a Conceptual Introduction

Wettengel, S.; Lindenmueller, L.; Bernet, S.; Schramm, U.; Kroll, F.; Brack, F.-E.; Pawelke, J.

A novel ion beam radiation therapy apparatus employing pulsed high magnetic field coils for transporting the ion beam has been proposed. In this paper a new pulsed current converter topology is introduced, which can be used as a pulsed power supply for the therapy apparatus. Thyristors are selected as the semiconductors used in the pulsed current converter. Since the planned operating point is outside of the typical range of the semiconductors, research has been done to predict their behavior during turn-off (the most critical phase of the pulse). A behavioral model has been derived and experimentally parametrized to predict the turn-off behavior and to optimize snubber design.

  • Contribution to proceedings
    PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 05.-07.06.2018, Nuremberg, Germany
    PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 978-3-8007-4646-0

Publ.-Id: 29512

A Statistical Approach for Analysis of Dissolution Rates Including Surface Morphology

Pedrosa, E. P.; Kurganskaya, I.; Fischer, C.; Luttge, A.

Understanding mineral dissolution is relevant for natural and industrial processes that involve the interaction of crystalline solids and fluids. The dissolution of slow dissolving minerals is typically surface controlled as opposed to diffusion/transport controlled. At these conditions, the dissolution rate is no longer constant in time or space, an outcome observed in rate maps and correspondent rate spectra. The contribution and statistical prevalence of different dissolution mechanisms is not known. Aiming to contribute to close this gap, we present a statistical analysis of the variability of calcite dissolution rates at the nano- to micrometer scale. A calcite-cemented sandstone was used to perform flow experiments. Dissolution of the calcite-filled rock pores was measured using vertical scanning interferometry. The resultant types of surface morphologies influenced the outcome of dissolution. We provide a statistical description of these morphologies and show their temporal evolution as an alternative to the lack of rate spatial variability in rate constants. Crystal size impacts dissolution rates most probably due to the contribution of the crystal edges. We propose a new methodology to analyze the highest rates (tales of rate spectra) that represent the formation of deeper etch pits. These results have application to the parametrization and upscaling of geochemical kinetic models, the characterization of industrial solid materials and the fundamental understanding of crystal dissolution.

Keywords: dissolution kinetics; calcite; surface morphology

Publ.-Id: 29511

Numerical simulation of electrovortex flows in cylindrical fluid layers and liquid metal batteries

Herreman, W.; Nore, C.; Ziebell Ramos, P.; Cappanera, L.; Guermond, J.-L.; Weber, N.

We use the multiphase magnetohydrodynamic code SFEMaNS to study the generation of electrovortex flows in liquid metal batteries. We first reproduce some well known results in a single-phase liquid metal column and then we characterize the electrovortex flow in layered multiphase fluid systems. A simple energy density balance argument accurately estimates the typical interface deformation caused by the electrovortex flow. When applied to Mg-Sb liquid metal batteries, we find that the electrovortex flows may have the capacity to cause short-circuits even in moderate size batteries with radii in the range [10, 20] cm.


Publ.-Id: 29510

Exploring new materials for optical thermometric sensing

Sharma, S.; Beyer, J.; Fuchs, M.; Gloaguen, R.; Heitmann, J.

The luminescence intensity ratio (LIR) of emission from two thermally coupled excited states is one of the most popular temperature sensing schemes, which has proven to be reliable due to its non-invasive nature, minimal dependence on the measurement conditions, and high temperature-spatial resolution. However, it requires a special design effort to obtain stable luminescence emission, which can be used for any practical application, for example, optical thermometric sensing. In this work, we present our results on the influence of excitation-emission processes on the dynamical behaviour of charges, and their temperature dependence in a wide temperature range (300-870 K), on a single crystal of EuPO4. The EuPO4 host which previously did not appear suitable for temperature sensing, was successfully converted to a highly sensitive optical temperature sensor, by following appropriate experimental strategy. The coupling of two excited states of Eu3+ showed a relative sensitivity of 2.00 %K-1, while, the coupling between two ground states of Eu3+ showed a relative sensitivity of 0.34 %K-1. The results suggest that by optimizing experimental parameters, highly sensitive optical thermometric sensors can be prepared, with ease.

  • Lecture (Conference)
    2019 Spring Meeting of the European Materials Research Society (E-MRS), 27.-31.05.2019, Nice, France


Publ.-Id: 29509

A Machine Learning Framework for Drill-Core Mineral Mapping Using Hyperspectral and High-Resolution Mineralogical Data Fusion

Contreras Acosta, I. C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.

Mining companies heavily rely on drill-core samples during exploration campaigns as they provide valuable geological information to target important ore accumulations. Traditional core logging techniques are time-consuming and subjective. Hyperspectral (HS) imaging, an emerging technique in the mining industry, is used to complement the analysis by rapidly characterizing large amounts of drill-cores in a nondestructive and noninvasive manner. As the accurate analysis of drill-core HS data is becoming more and more important, we explore the use of machine learning techniques to improve speed and accuracy, and help to discover underlying relations within large datasets. The use of supervised techniques for drill-core HS data represents a challenge since quantitative reference data is frequently not available. Hence, we propose an innovative procedure to fuse high-resolution mineralogical analysis and HS data. We use an automatic high-resolution mineralogical imaging system (i.e., scanning electron microscopy-mineral liberation analysis) for generating training labels. We then resample the MLA image to the resolution of the HS data and adopt a soft labeling strategy for mineral mapping. We define the labels for the classes as mixtures of geological interest and use the classifiers (random forest and support vector machines) to map the entire drill-core. We validate our framework qualitatively and quantitatively. Thus, we demonstrate the ability of the proposed technique to fuse and up-scale high-resolution mineralogical analysis with drill-core HS data.

Keywords: Data fusion; drill-cores; hyperspectral (HS) data; machine learning; mineral liberation analysis (MLA); random forest (RF); support vector machine (SVM)


Publ.-Id: 29508

Characterization of the rotenone mouse model of Parkinson’s disease using radioligands for the adenosine A2A receptor ([18F]FESCH) and the nicotinic α4β2 receptor ((‐)‐[18F]Flubatine)

Toussaint, M.; Kranz, M.; Schröder, S.; Lai, T. H.; Deuther-Conrad, W.; Dukic‐Stefanovic, S.; Shang, Q.; Patt, M.; Reichmann, H.; Funk, R.; Sabri, O.; Pan‐Montojo, F.; Brust, P.

Rotenone-treated mice are regarded as a model for Parkinson´s disease (PD). Increased availability of the adenosine A2A receptor (A2AR) and decreased availability of the α4β2 nicotinic acetylcholine receptor (nAChR) have been found in the striatum and thalamus, respectively, of patients with PD [1,2]. Therefore, we evaluated the potential of [18F]FESCH (for A2AR) and (-)-[18F]Flubatine (for α4β2nAChR) to characterize similar receptor changes in the mouse model of PD with small animal PET/MR imaging.
Two groups of 18-months-old male C57BL/6JRj mice (28-35 g) (Janvier labs, France) were investigated: a control group (n=5) treated with a vehicle solution (2% carboxymethyl cellulose, 1.25% chloroform) and a PD group (n=7) treated with rotenone (Sigma-Aldrich, Germany) during 4 months (5 days/week, 5 mg/kg p.o.). [18F]FESCH (5.0±1.8 MBq; Am: 116±19 GBq/µmol, EOS) or (-)-[18F]Flubatine (6.5±2.4 MBq; Am: 1080±2156 GBq/µmol, EOS) were injected intravenously followed by 60 min dynamic PET scans (Mediso nanoScan®, PET/MRI 1T, Hungary). Time-activity curves from the striatum, cerebellum, and thalamus were analyzed (PMOD v3.9, PMOD Technologies LLC, Switzerland). The cerebellum was used as a reference tissue.
PET scans revealed high uptake of (-)-[18F]Flubatine in thalamus (SUV ~3.5 at 40 min p.i.) and considerably lower uptake in cerebellum (SUV ~1.2 at 40 min p.i.). The SUV ratio (SUVR) thalamus/cerebellum, indicating specific radiotracer binding, is significantly decreased in the rotenone-treated group compared to the control (Figure 1A).
Also for [18F]FESCH much higher uptake was observed in striatum (SUV ~0.9 at 5 min p.i.) compared to cerebellum (SUV ~0.2 at 5 min p.i.). Although not significant for this rather small and highly variable data set, the SUVR striatum/cerebellum is increased in the rotenone-treated group compared to the control suggesting a higher specific binding in striatum (Figure 1B). These findings are in accordance with a recent publication [3].
We have established a concordance between clinical imaging findings in PD and small animal PET/MR in rotenone-treated mice. Thus, we assume the rotenone mouse model to be suitable for further investigation of molecular aspects of PD in particular related to A2AR and α4β2nAChR.
The European Regional Development Fund and Sächsische Aufbaubank are acknowledged for financial support (Project No. 100226753).
[1] Vuorimaa et al. Contrast Media Mol Imaging 2017; 6975841. [2] Meyer et al., Arch Gen Psych 2009, 66: 866-877. [3] Khanapur et al., J Nucl Med 2017; 58: 466–472.

Keywords: Parkinson disease; adenosine A2A receptor; α4β2 nicotinic acetylcholin receptor; [18F]FESCH; [18F]Flubatine; rotenone model

  • Poster
    23rd International Symposium on Radiopharmaceutical Sciences (ISRS 2019), 26.-31.05.2019, Beijing, China

Publ.-Id: 29507

Landscape dynamics and human-environment interactions in the northern foothills of Cho Oyu and Mount Everest (southern Tibet) during the Late Pleistocene and Holocene

Meyer, M.; Gliganic, L. A.; May, J.-H.; Merchel, S.; Rugel, G.; Schlütz, F.; Aldenderfer, M.; Krainer, K.

Here we present an integrated earth surface process and paleoenvironmental study from the Tingri graben and the archaeological site of Su-re, located on the southern rim of the Tibetan plateau, spanning the past ca. 30 ka. The study area is characterized by cold climate earth surface processes and aridity due to its altitude and location in the rain shadow of the Mount Everest–Cho Oyu massif and is thus sensitive to climatic and anthropogenic perturbations. During the global last glacial maximum (gLGM) glaciers from the main Himalaya range advanced into the Tingri graben and deposited massive hummocky moraines, while the zone of discontinuous permafrost was depressed by ~450 m relative to today, greatly intensifying permafrost and periglacial hillslope processes and leading to fluvial aggradation of the valley floors of ≥12 m. We observe formation of a thick (≥50 cm) pedo-complex starting at ca. 6.7 ka before present (BP) and erosional truncation at ca. 3.9 ka BP. Widespread landscape instability and erosion characterize the region subsequent to 3.9 ka and intensifies in the 15th century AD. Several lines of (geo)archaeological evidence, including the presence of pottery sherds, sling-shot projectiles and hammer stones within the sedimentary record, indicate human presence at Su-re since ca. 3.9 ka BP. Our data suggest that in the Su-re-Tingri area climatic conditions were warm and moist enough to allow vegetation expansion and soil formation only from ca. 6.7-3.9 ka, followed by weakening of the Indian summer monsoon (ISM) strength between ca. 3.9 and 4.2 ka, which is a prominent climatic event in the wider Asian monsoon region, and reflected in the investigation area by the 3.9 ka erosional boundary. Merging our Holocene landscape reconstruction with the geoarchaeological evidence, we speculate that the combined effect of Little Ice Age (LIA) cooling and an anthropogenic overuse of the landscape led to climatically induced landscape degradation and ultimately to an anthropogenically triggered ecological collapse in the 15th century. Such a scenario is in-line with regional historical data on declining monastery construction and migration of the ethnic group of the Sherpas. From an earth surface dynamics perspective, we find that short-term transient landscape processes on the southern rim of the Tibetan plateau are strongly linked to millennial scale changes in the ISM intensity and duration. We identify three types of unidirectional non-linear ISM-landscape interactions. Given that the Tibetan plateau is the largest high-altitude landmass on our planet and our limited understanding of several of the key earth surface processes on the plateau, we pinpoint the need for more long-term (Quaternary scale) empirical data particularly on permafrost and periglacial processes and human-environment interactions.

Keywords: Tibet; monsoon; periglacial; permafrost; optical methods; cosmogenic isotopes; landscape degradation; Holocene; Pleistocene

Related publications

Publ.-Id: 29506

Numerical modelling of horizontal oil-water pipe flow

Höhne, T.; Rayya, A.; Montoya, G.

The purpose of this work is the validation of ANSYS Fluent and ANSYS CFX with the Algebraic Interfacial Area Density (AIAD) model for a horizontal oil-water flow. Software and hardware developments in the last years have significantly increased and improved the accuracy, flexibility and performance of simulations. At HZDR, the Euler-Euler approach for multiphase flow modeling with free surfaces is used. Therefore, the AIAD (Algebraic Interfacial Area Density) model was developed at HZDR in close cooperation with ANSYS. In this work the applicability of the AIAD model for an oil-water flow is investigated. The validation of various multiphase flow models in ANSYS Fluent and the AIAD model in ANSYS CFX for the oil-water flow was performed by calculations with different oil and water inlet velocities and various boundary conditions. Thereafter, the achieved results of the appropriate models for the modeling of the oil-water flow in the two solvers were used with existing experimental results for validation. The results of the simulations show, that horizontal oil-water flow can be modelled with rather good accuracy.

Keywords: AIAD; Oil; Water; CFD; pipeline

Publ.-Id: 29505

Predicting in Vitro Cancer Cell Survival Based on Measurable Cell Characteristics

Oesten, H.; Neubeck, C. V.; Jakob, A.; Enghardt, W.; Krause, M.; Mcmahon, S. J.; Grassberger, C.; Paganetti, H.; Lühr, A.

Variation in cellular characteristics may determine tumor response and, consequently, patient survival in radiation therapy. However, patient-specific prediction of cellular radiation response is currently unavailable for treatment planning. Thus, the importance of developing a novel approach based on clinically accessible parameters prior to treatment (e.g., by biopsy) is high. The goal of this study was to predict in vitro cancer cell survival through the p53mutation status and the number of chromosomes (NoC). To predict cell survival, we modified a mechanistic radiation response model incorporating DNA repair and cell death, originally designed for normal human cells. Cell-specific parameters of 24 cell lines originating from two laboratories (OncoRay, Dresden, Germany and HIMAC, Chiba, Japan) were considered for modeling. In a first step, we obtained estimates of the only unknown model input parameter genome size (GS) by fitting cell survival simulations onto experimental data. We then analyzed measured and published input model parameters (NoC, p53-mutation status and cell-cycle distribution) to assess their impact on measured and simulated parameters (modeled GS, and measured α, β, SF2 and H2AX). The resulting data suggested a linear correlation between NoC and modeled GS (R2 > 0.93) allowing for estimating GS based on NoC. Applying the estimated GS resulted in predicted cell survival that matched measured data mostly within the experimental uncertainty. The measured radiobiological value β increased quadratically with the cell's modeled GS irrespective of other cell-specific parameters. The measured α and SF2 split into two groups, depending on the cells' p53-mutation status, both linearly increasing and decreasing, respectively, with modeled GS. Model predictions of foci numbers were, on average, in agreement with published H2AX measurement data. In conclusion, knowledge of clinically accessible parameters (p53-mutation status and NoC) may support patient stratification in radiotherapy based on cell-specific survival prediction testable in prospective clinical trials. © 2019 by Radiation Research Society. All rights of reproduction in any form reserved.

Publ.-Id: 29504

Challenges and caveats of a multi-center retrospective radiomics study: An example of early treatment response assessment for NSCLC patients using FDG-PET/CT radiomics

van Timmeren, J.-E.; Carvalho, S.; Leijenaar, R. T. H.; Troost, E. G. C.; van Elmpt, W.; de Ruysscher, D.; Muratet, J. P.; Denis, F.; Schimek-Jasch, T.; Nestle, U.; Jochems, A.; Woodruff, H. C.; Oberije, C.; Lambin, P.

Background Prognostic models based on individual patient characteristics can improve treatment decisions and outcome in the future. In many (radiomic) studies, small size and heterogeneity of datasets is a challenge that often limits performance and potential clinical applicability of these models. The current study is example of a retrospective multi-centric study with challenges and caveats. To highlight common issues and emphasize potential pitfalls, we aimed for an extensive analysis of these multi-center pre-treatment datasets, with an additional 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/ CT) scan acquired during treatment. Methods The dataset consisted of 138 stage II-IV non-small cell lung cancer (NSCLC) patients from four different cohorts acquired from three different institutes. The differences between the cohorts were compared in terms of clinical characteristics and using the so-called ‘cohort differences model’ approach. Moreover, the potential prognostic performances for overall survival of radiomic features extracted from CT or FDG-PET, or relative or absolute differences between the scans at the two time points, were assessed using the LASSO regression method. Furthermore, the performances of five different classifiers were evaluated for all image sets. Results The individual cohorts substantially differed in terms of patient characteristics. Moreover, the cohort differences model indicated statistically significant differences between the cohorts. Neither LASSO nor any of the tested classifiers resulted in a clinical relevant prognostic model that could be validated on the available datasets. Conclusion The results imply that the study might have been influenced by a limited sample size, heterogeneous patient characteristics, and inconsistent imaging parameters. No prognostic performance of FDG-PET or CT based radiomics models can be reported. This study highlights the necessity of extensive evaluations of cohorts and of validation datasets, especially in retrospective multi-centric datasets.

Publ.-Id: 29503

Magnetoelastic coupling across the field-induced transition of uranium mononitride

Gorbunov, D.; Nomura, T.; Zvyagin, A. A.; Henriques, M. S.; Andreev, A. V.; Skourski, Y.; Zvyagina, G. A.; Troc, R.; Zherlitsyn, S.; Wosnitza, J.

Uranium mononitride (UN) displays a spin-flop-like transition for magnetic field applied along all principal crystallographic directions just below 60 T. Here, we report on ultrasound and magnetocaloric-effect results for UN in pulsed magnetic fields up to 65 T. The field-induced phase transition causes a discontinuous temperature decrease, indicating a larger magnetic entropy above the transition. Furthermore, we find pronounced anomalies in the acoustic properties, which signals strong spin-lattice interactions. A further anomaly observed at fields slightly above the transition is likely related to the formation of magnetic domains. A model based on the exchange-striction coupling mechanism well reproduces the strong renormalization of the acoustic properties.


Publ.-Id: 29502

Early and late side effects, dosimetric parameters and quality of life after proton beam therapy and IMRT for prostate cancer: a matched-pair analysis

Dutz, A.; Agolli, L.; Baumann, M.; Troost, E. G. C.; Krause, M.; Hölscher, T.; Löck, S.

Purpose: To compare early and late toxicities, dosimetric parameters and quality of life (QoL) between conventionally fractionated proton beam therapy (PBT) and intensity-modulated radiation therapy (IMRT) in prostate cancer (PCA) patients. Methods: Eighty-eight patients with localized PCA treated between 2013 and 2017 with either definitive PBT (31) or IMRT (57) were matched using propensity score matching on PCA risk group, transurethral resection of the prostate, prostate volume, diabetes mellitus and administration of anticoagulants resulting in 29 matched pairs. Early and late genitourinary (GU) and gastrointestinal (GI) toxicities according to Common Terminology Criteria for Adverse Events (CTCAE) and QoL based on EORTC-QLQ-C30/PR25 questionnaires were collected prospectively until 12 months after radiotherapy (RT). Associations between toxicities and dose–volume parameters in corresponding organs at risk (OARs) were modeled by logistic regression. Results: There were no significant differences in GI and GU toxicities between both treatment groups except for late urinary urgency, which was significantly lower after PBT (IMRT: 25.0%, PBT: 0%, p =.047). Late GU toxicities and obstruction grade ≥2 were significantly associated with the relative volume of the anterior bladder wall receiving 70 Gy and the entire bladder receiving 60 Gy, respectively. The majority of patients in both groups reported high functioning and low symptom scores for the QoL questionnaires before and after RT. No or little changes were observed for most items between baseline and 3 or 12 months after RT, respectively. Global health status increased more at 12 months after IMRT (p =.040) compared to PBT, while the change of constipation was significantly better at 3 months after PBT compared to IMRT (p =.034). Conclusions: Overall, IMRT and PBT were well tolerated. Despite the superiority of PBT in early constipation and IMRT in late global health status compared to baseline, overall QoL and the risks of early and late GU and GI toxicities were similar for conventionally fractionated IMRT and PBT.

Publ.-Id: 29501

Successive Trimming of a Permalloy Stripe to enhance the localized Edge Mode Spectrum probed by Ferromagnetic Resonance

Lenz, K.; Schneider, T.; Hlawacek, G.; Narkowicz, R.; Stienen, S.; Lenz, M.; Lindner, J.

Finite-size effects in ultrathin magnetic films are a well-known feature. They usually play a role, when the surface and interface layers dominate over the volume contribution of the sample and have different properties, due to roughness, texture, hybridization, modified magnetic moment, or dipolar fields. For micro- and especially nanostructures these effects might be there as well—but at the side walls. Regarding the magnetization dynamics these effects lead to additional spin wave modes, e.g. localized spin wave modes (edge modes). It has been shown that these edge modes are influenced by the quality of the side walls, namely by angled side walls, edge roughness, beveled edges, or even magnetic dilution [1]. As these structures have to be prepared by means of lithography involving masks a certain edge roughness or even side wall slope are inevitable. Nevertheless, when it comes to micromagnetic simulations to corroborate or explain measurements these contributions are usually excluded from the model. Here we show, how successive trimming the sides of a 5 µm x 1 µm Permalloy stripe by a focused Ne ion beam improves the spin wave spectrum and enhances the edge mode spectrum as probed by ferromagnetic resonance (FMR). To achieve the sensitivity to detect the FMR of the weak edge modes of a single Permalloy stripe we use planar microresonator FMR [2,3]. The experimental results are corroborated by micromagnetic simulations. Including just edge roughness of ~4 nm (rms) in the simulations is enough to perfectly match the FMR experimental data. The residual edge roughness is in the order of the grain size of the polycrystalline permalloy. Although the focused ion beam and its motion are able to cut the side walls perfectly straight and vertical with sub-nm precision, the Ne ions penetrate the side wall up to 15 nm (called straggling). This is due to the collision cascade with the Ni and Fe atoms of the Permalloy causing possible lateral damage of the Permalloy lattice. Hence, we attribute the residual roughness to the ion induced damage by the lateral penetration during trimming of the side walls, and a small remaining edge roughness due to changes in sputter yield for differently oriented Permalloy grains.

[1] R.D. McMichael, B.B. Maranville, Phys. Rev. B 74,024424 (2006).
[2] A. Banholzer et al., Nanotechnology 22, 295713 (2011).
[3] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).

Keywords: Magnetic nanostructures; ferromagnetic resonance; spin waves; edge modes; HIM

Related publications

  • Poster
    International Conference on Magnetism ICM 2018, 15.-20.07.2018, San Francisco, United States of America
  • Poster
    9th Joint European Magnetic Symposia, JEMS 2018, 03.-07.09.2018, Mainz, Deutschland

Publ.-Id: 29500

Turbulent Multiphase CFD Modelling: State-of-the-art applications in Nuclear Engineering

Höhne, T.

Two-phase flows occur in many industrial-relevant processes in power plants, chemical engineering, oil and gas industries and others.
Reliable predictions of the flow characteristics are important for the design of the facilities, the optimization of processes and safety analyses.
Experimental results are often hardly transferable to modified geometries, flow condition or scales.

Keywords: CFD; AIAD; GENTOP; Multiphase

  • Lecture (Conference)
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA

Publ.-Id: 29499

Colloidal Mercury-Doped CdSe Nanoplatelets with Dual Fluorescence

Galle, T.; Kazes, M.; Hübner, R.; Lox, J.; Khoshkhoo, M. S.; Sonntag, L.; Tietze, R.; Sayevich, V.; Oron, D.; Koitzsch, A.; Lesnyak, V.; Eychmüller, A.

Quasi-two-dimensional (2D) CdSe nanoplatelets (NPLs) are distinguished by their unique optical properties in comparison to classical semiconductor nanocrystals, such as extremely narrow emission line widths, reduced Auger recombination, and relatively high absorption cross sections. Inherent to their anisotropic 2D structure, however, is the loss of continuous tunability of their photoluminescence (PL) properties due to stepwise growth. On top of that, limited experimental availability of NPLs of different thicknesses and ultimately the bulk band gap of CdSe constrain the achievable PL wavelengths. Here, we report on the doping of CdSe NPLs with mercury, which gives rise to additional PL in the red region of the visible spectrum and in the near-infrared region. We employ a seeded-growth method with injection solutions containing cadmium, selenium, and mercury. The resulting NPLs retain their anisotropic structure, are uniform in size and shape, and present significantly altered spectroscopic characteristics due to the existence of additional energetic states. We conclude that doping takes place by employing elemental analysis in combination with PL excitation spectroscopy, X-ray photoelectron spectroscopy, and single-particle fluorescence spectroscopy, confirming single emitters being responsible for multiple distinct emission signals.

Related publications

Publ.-Id: 29498

Trimming of permalloy stripes to enhance the localized edge mode spectrum probed by ferromagnetic resonance

Lenz, K.; Schneider, T.; Hlawacek, G.; Narkowicz, R.; Stienen, S.; Kákay, A.; Lenz, M.; Fassbender, J.; Lindner, J.

Finite-size effects in ultrathin magnetic films are a well-known feature, i.e., when the surface or interfaces dominate the volume of the sample due to different roughness, texture, hybridization, modified magnetic moment, or dipolar fields. For nanostructures these effects could arise at the side walls as well. This leads to localized spin wave modes (edge modes).
It has been shown that the quality of the side walls (angled side walls or roughness) influence these modes [1]. During preparation of samples by lithography a certain edge roughness and side wall slope are sometimes inevitable. Nevertheless, in micromagnetic simulations these contributions are usually excluded from the model. We show, how successive trimming the sides of a 5 μm x 1 μm Permalloy stripe by a focused Ne ion beam improves the spin wave spectrum and enhances the edge mode spectrum as probed by planar microresonator ferromagnetic resonance (FMR) [2,3] as depicted in Figure 1. Including an rms edge roughness of ~2 nm (within the order of the permalloy grain size) in the simulations is enough to match the FMR data. Hence, we attribute the residual roughness to the ion induced damage by the lateral penetration during trimming of the side walls, and a small remaining edge roughness due to changes in the sputter yield for differently oriented Permalloy grains.

Keywords: ferromagnetic resonance; nanostructures; trimming; HIM; FMR; edge modes; spin waves

Related publications

  • Poster
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italy

Publ.-Id: 29497

Direct measurements of the magneto-caloric effect of MnFe4Si3 in pulsed magnetic fields

Maraytta, N.; Skourski, Y.; Voigt, J.; Friese, K.; Herrmann, M. G.; Perßon, J.; Wosnitza, J.; Salman, S. M.; Brückel, T.

We have studied the magnetic and magnetocaloric response of MnFe4Si3 to pulsed and static magnetic fields up to 50 T. We determine the adiabatic temperature change ΔTad directly in pulsed fields and compare to the results of magnetization and specific heat measurements in static magnetic fields. The high ability of cycling even in fields μ0H = 50 T confirms the high structural stability of MnFe4Si3 against field changes, an important property for applications. The magnetic response to magnetic fields up to μ0H = 35 T shows that the anisotropy can be overcome by fields of approx. 4 T.

Publ.-Id: 29496

Magnetic structure and spin waves in the frustrated ferro-antiferromagnet Pb2VO(PO4)2

Bettler, S.; Landolt, F.; Aksoy, Ö. M.; Yan, Z.; Gvasaliya, S.; Qiu, Y.; Ressouche, E.; Beauvois, K.; Raymond, S.; Ponomaryov, A. N.; Zvyagin, S. A.; Zheludev, A.

Single crystal neutron diffraction, inelastic neutron scattering, and electron spin resonance experiments are used to study the magnetic structure and spin waves in Pb2VO(PO4)2, a prototypical layered S = 1/2 ferromagnet with frustrating next-nearest neighbor antiferromagnetic interactions. The observed excitation spectrum is found to be inconsistent with a simple square lattice model previously proposed for this material. At least four distinct exchange coupling constants are required to reproduce the measured spin wave dispersion. The degree of magnetic frustration is correspondingly revised and found to be substantially smaller than in all previous estimates.

Publ.-Id: 29495

Numerical study of simultaneous heat and mass transfer in Liquid Metal Batteries

Personnettaz, P.; Weber, N.; Weier, T.

Liquid metal batteries (LMBs) are promising candidates for electrical energy storage. An LMB is a concentration cell made of three liquid layers, stably stratified by density. A molten salt acts as an electrolyte between two liquid metal electrodes. The simple chemistry and geometry, the liquid nature of the active layers and the presence of multi-physics phenomena have made the LMB an intriguing candidate for continuum mechanics investigations. Simultaneous transport of charge, heat, mass and momentum takes place in each liquid layer together with chemical reactions. The interfaces between layers are the places in which electrochemical reactions occur along with interfacial transport phenomena.
In our work we investigate heat and mass transport in LMBs with openFOAM libraries using a multi-region approach. We assign to each layer a numerical region and we design a procedure able to ensure the physical coupling between the different transport mechanisms through an iterative procedure. The heat and mass transfer equations are solved on a global mesh and in the positive electrode region respectively. Then we solve the Navier-Stokes equations in each fluid region. Appropriate boundary conditions were designed to ensure a consistent transport at the interfaces between different regions. Thanks to this procedure we can compute temperature and concentration distributions and the corresponding thermal and compositional convection. Therefore, we can investigate the interaction of different mechanisms and can give a prediction of the fluid flow in the interior of an LMB. The numerical procedure is introduced as well as the first results. Furthermore, the modeling limitations and the future developments are discussed.

Keywords: Liquid metal battery; openFOAM; mass transport; heat transfer; transport phenomena

  • Poster
    OpenFOAM Workshop 2019, 23.-26.07.2019, Duisburg, Deutschland

Publ.-Id: 29494

A semiconducting layered metal-organic framework magnet

Yang, C.; Dong, R.; Wang, M.; Petkov, P. S.; Zhang, Z.; Wang, M.; Han, P.; Ballabio, M.; Bräuninger, S. A.; Liao, Z.; Zhang, J.; Schwotzer, F.; Zschech, E.; Klauss, H.-H.; Cánovas, E.; Kaskel, S.; Bonn, M.; Zhou, S.; Heine, T.; Feng, X.

The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), namely K3Fe2[(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe] (K3Fe2[PcFe-O8]) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm2 V−1 s−1 as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and 57Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K3Fe2[PcFe-O8] arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.


Publ.-Id: 29493

Strain-induced perpendicular magnetic anisotropy and Gilbert damping of Tm3Fe5O12 thin films

Ciubotariu, O.; Semisalova, A.; Lenz, K.; Albrecht, M.

In the attempt of implementing iron garnets with perpendicular magnetic anisotropy (PMA) in spintronics, the attention turned towards strain-grown iron garnets. One candidate is Tm3Fe5O12 (TmIG) which possesses an out-of-plane magnetic easy axis when grown under tensile strain. In this study, the effect of film thickness on the structural and magnetic properties of TmIG films including magnetic anisotropy, saturation magnetization, and Gilbert damping is investigated. TmIG films with thicknesses between 20 and 300 nm are epitaxially grown by pulsed laser deposition on substituted-Gd3Ga5O12(111) substrates. Structural characterization shows that films thinner than 200 nm show in-plane tensile strain, thus exhibiting PMA due to strain-induced magnetoelastic anisotropy. However, with increasing film thickness a relaxation of the unit cell is observed resulting in the rotation of the magnetic easy axis towards the sample plane due to the dominant shape anisotropy. Furthermore, the Gilbert damping parameter is found to be in the range of 0.02 ± 0.005.

Keywords: Thulium iron garnet; magnetic anisotropy; Gilbert damping

  • Open Access Logo Scientific Reports 9(2019), 17474
    DOI: 10.1038/s41598-019-53255-6
    Cited 20 times in Scopus
  • Poster
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italy
  • Poster
    MMM 2019 - Annual Conference on Magnetism and Magnetic Materials, 04.-08.11.2019, Las Vegas, United States of America

Publ.-Id: 29492

A measurement of the equation of state of carbon envelopes of white dwarfs

Kritcher, A. L.; Swift, D.; Doppner, T.; Nilsen, J.; Bachmann, B.; Benedict, L.; Collins, G.; Dubois, J.; Elsner, F.; Fontaine, G.; Gaffney, J.; Hamel, S.; Macdonald, M.; Lazicki, A.; Johnson, W.; Kostinski, N.; Kraus, D.; Maddox, B.; Martin, M.; Neumayer, P.; Nikroo, A.; Remington, B.; Saumon, D.; Sterne, P.; Sweet, W.; Correa Tedesco, A.; Whitley, H.; Falcone, R.; Glenzer, S.

White dwarfs represent the final state of evolution for most stars. Certain classes of white dwarfs pulsate, leading to observable brightness variations, and analysis of these variations with theoretical stellar models probes their internal structure. Modelling of these pulsating stars provides stringent tests of white dwarf models and a detailed picture of the outcome of the late stages of stellar evolution6. However, the high-energy-density states that exist in white dwarfs are extremely difficult to reach and to measure in the laboratory, so theoretical predictions are largely untested at these conditions. Here we report measurements of the relationship between pressure and density along the principal shock Hugoniot (equations describing the state of the sample material before and after the passage of the shock derived from conservation laws) of hydrocarbon to within five per cent. The observed maximum compressibility is consistent with theoretical models that include detailed electronic structure. This is relevant for the equation of state of matter at pressures ranging from 100 million to 450 million atmospheres, where the understanding of white dwarf physics is sensitive to the equation of state and where models differ considerably. The measurements test these equation-of-state relations that are used in the modelling of white dwarfs and inertial confinement fusion experiments7,8, and we predict an increase in compressibility due to ionization of the inner-core orbitals of carbon. We also find that a detailed treatment of the electronic structure and the electron degeneracy pressure is required to capture the measured shape of the pressure–density evolution for hydrocarbon before peak compression. Our results illuminate the equation of state of the white dwarf envelope (the region surrounding the stellar core that contains partially ionized and partially degenerate non-ideal plasmas), which is a weak link in the constitutive physics informing the structure and evolution of white dwarf stars.

Publ.-Id: 29491

Theranostic CAR T cell targeting: A brief review

Arndt, C.; Bachmann, M.; Bergmann, R.; Berndt, N.; Feldmann, A.; Koristka, S.

More than 100 years ago Paul Ehrlich postulated that our immun system should be able to eliminate tumor cells. Just recently, the development of check point inhibitors, bispecific antibodies, and T cells genetically modified to express chimeric antigen receptors (CARs) underlines the true power of our immune system. T cells genetically modified with CARs can lead to complete remission of malignant hematologic diseases. However, they can also cause life-threatening side effects. In case of cytokine release syndrome, tumor lysis syndrome, or deadly side effects on the central nervous system, an emergency shut down of CAR T cells is needed. Targeting of tumor-associated antigens that are also expressed on vital tissues require a possibility to repeatedly switch the activity of CAR T cells on and off on demand and to follow the treatment by imaging. Theranostic, modular CARs such as the UniCAR system may help to overcome these problems.

Keywords: bispecific antibody; BiTE; chimeric antigen receptor; immunotherapy; T cells; UniCAR

Publ.-Id: 29490

Electronic Properties of a New Family of Layered Materials from Groups 14-15: First-Principles Simulations

Ramzan, M. S.; Bacic, V.; Jing, Y.; Kuc, A.

Variaty of 2D layered materials has gain tremendous focus of materials scientists, physics, chemistry, and other fields of science. This is due to the fact that thin films of layered materials often exhibit superior (for a given application) properties than the parental bulk materials. Thus, in this work, we studied a new family of layered materials with a general composition of XY3 (where X and Y are elements from Group-14 and 15, respectively). Among the proposed materials, 3D bulk structures of layered GeP3 and SnP3 are stable, metallic, and already synthesized in the 1970s. We calculated cleavage energies of mono- and bilayers to be less than 1 J m-2, what indicates possibility of exfoliation from the bulk materials. Many of the investigated monolayers are mechanically and thermally stable. Electronic structure calculations indicate strong interlayer quantum confinement and consequently a metal-to-semiconductor transition when going from bulk to a mono- or bilayer. These electronic properties promise interesting applications in nanoelectronic devices.


Publ.-Id: 29488

Structural modifications and thermal stability of Cd2+ -exchanged stellerite, a zeolite with STI framework-type

Cametti, G.; Scheinost, A. C.; Churakov, S. V.

The structure and thermal stability of a Cd2+-exchanged zeolite with STI framework type was investigated by combining single crystal X-ray diffraction (SCXRD), ab initio molecular dynamic (MD) simulations and X-ray absorption fine structure spectroscopy (XAFS). The room temperature structure was found to be monoclinic, space group F2/m. The Cd2+ ions were disordered at partially occupied sites with maximum occupancy of 0.38(2). MD simulations and XAFS spectroscopy indicated that Cd forms Cd(H2O) 2+6 complexes distributed within the t-sti-1* cage running parallel to [100]. The dehydration was monitored in situ by SCXRD. Upon heating a new contracted phase was observed at 225 C. Compared to the pristine material, the Cd2+-exchanged
structure started collapsing already at 325 C, pointing out a reduced thermal stability.

Keywords: zeolite; molecular dynamics; EXAFS; stellerite

Related publications


Publ.-Id: 29487

Spatial solitons in KTaxNb1-xO3 waveguides produced by swift carbon ion irradiation and femtosecond laser ablation

He, S.; Zhang, Z.; Liu, H.; Akhmadaliev, S.; Zhou, S.; Wang, X.; Wu, P.

We report on the fabrication of planar waveguide and ridge waveguides in a KTN crystal by using swift heavy C5+ ions irradiation and femtosecond laser ablation. The reconstructed refractive index profile of the irradiated KTN waveguide illustrates an optical well and barrier distribution. The confocal Raman spectra suggest that the enhanced tetragonality and the lattice damage occurs in the waveguide region and the optical barrier area, respectively. The optical spatial solitons at 632.8 nm are observed from the planar waveguide and the ridge waveguides with a width of 60 μm and 20 μm, respectively, at room temperature.

Related publications

Publ.-Id: 29486

Defect-induced magnetism in SiC

Zhou, S.; Chen, X.

Defect-induced magnetism describes a magnetic phenomenon in materials containing neither unpaired 3d nor 4f  electrons. Therefore, it presents a challenge to the conventional understanding of magnetism and has remained under debate for over a decade. Different from graphite and oxides which are common research venues in defect-induced magnetism, SiC is commercially available at large scale and with high quality at the microelectronic grade. Therefore, SiC presents a suitable model system for studying defect-induced ferromagnetism and exploring possible applications. Understanding and controlling defect-induced magnetism in a semiconductor like SiC opens up the possibility for producing spintronic devices based on classical semiconductor technologies. Here, we review recent studies on defect-induced magnetism in SiC. We start with a brief description about defects in SiC. Then we summarize the experimental results on defect-induced magnetism in SiC, the microscopic origin of the magnetism and the magnetic coupling mechanism. We also propose several potential applications, particularly using magnetometry as a complementary method for quantitative characterization of defects in SiC. At the end, we list the challenges from our point of view, such as controlling defects in SiC regarding their charge states, distribution and local environment, and understanding defect-induced magnetism by local and elemental selective probe techniques.

Related publications


Publ.-Id: 29485

Spectroscopic insights into U(IV) speciation in aqueous solution

Lehmann, S.; Steudtner, R.; Gerber, U.; Zimmermann, T.; Brendler, V.

This work is focused on uranium as the major component of the nuclear fuel cycle. It is important to predict its environmental behavior for, e.g., the safety assessment of a future repository or the remediation of the various legacies of uranium mining and milling. Typically, diluted to highly saline aquifer systems under reducing conditions with carbonates, silicates, phosphates, chlorides and sulfates as important complexing agents are to be considered. However, predictions for U(IV) speciation often suffer from a sparsely populated thermodynamic data base [1], often due to a missing spectroscopic evaluation of species stoichiometry and structure.
This work combines absorption and fluorescence spectroscopies to reveal the speciation of U(IV) in solution in concentrations down to 10⁻⁶ M uranium. The set-up for time-resolved laser-induced fluorescence was optimized to allow the determination of fluorescence decay times of U(IV) in perchloric as well as in chloric acid with 2.5 ± 0.4 ns at room temperature and 152 ± 8.3 ns at liquid nitrogen temperature. By decreasing the temperature we gained an improved fine structure with a band splitting of the main peak at 410 nm and a redshift could be observed.
By evaluation of UV-vis based titration series (pH = 0 2, [U] = 10⁻⁴-10⁻⁵ M, [SO4] from 0 to 1.9·10⁻⁵ M) in the U(IV) sulfate system, complex formation constants for USO₄²⁺ and U(SO₄)₂(aq) could be derived, yielding 6.9 ± 0.3 and 11.8 ± 0.5, respectively, when extrapolated to infinite dilution. This log K values for the 1:1 complex is close to the NEA recommendation of 6.58 whereas our value for the 1:2 complex is about one order of magnitude higher than that selected in [1]. The NEA recommendations are exclusively based on liquid-liquid extraction experiments, with higher ionic strengths (up to 2 M) and U(IV) concentrations (up to 0.1 M) as applied in this work.
The potential of direct U(IV) spectroscopy for speciation analysis at environmentally relevant uranium concentrations was proven in this study. Eventually, all acquired information will increase confidence in respective U(IV) reactive transport modelling.
The authors gratefully acknowledge funding by the German Federal Ministry of Economic Affairs and Energy under the grant 02E11334B.
[1] R. Guillaumont et al. (2003). "Update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technetium., vol. 5 of Chemical Thermodynamics." Elsevier: 960 pp.

Keywords: tetravalent uranium; photometry; thermodynamics

  • Poster
    EGU General Assembly 2019, 07.-12.04.2019, Wien, Österreich

Publ.-Id: 29484

Formation of structured membranes by coacervation of xanthan gum with CnTAB surfactants

Keshavarzi, B.; Schwarzenberger, K.; Huang, M.; Javadi, A.; Eckert, K.

We present a novel approach for studying membrane formation by interaction of polymers and surfactants with opposite charge using a Hele-Shaw experimental setup. A solution of the anionic biopolymer xanthan gum is placed in direct contact with a CnTAB surfactant solution (n=10, 12, 14 and 16). Thereby, a polymer-surfactant membrane spontaneously forms between the two solutions due to the precipitation of polymer-surfactant complexes, which grows afterwards in direction of the polymer solution. The dynamics of the growth of the membrane thickness and the mass transfer of polymer are evaluated for different surfactant types and concentrations.
The experiments and supporting numerical calculations indicate that polymer mass transfer is driven by diffusion of the charged macromolecules along the concentration gradient which is coupled to the electric field induced by the faster diffusion of the more mobile counterions. The properties and structure of the formed membrane significantly depend on surfactant hydrophobicity and concentration. In addition, in a wide range of experiments, the formation of a porous structure in the membrane is observed whose characteristics can be tuned by the process parameters. A mechanism is proposed for the pore formation explaining it as an instability of the growing membrane surface in interaction with the supply of polymer across the depleted zone in the vicinity of the membrane front.

Keywords: Polymer-surfactant interaction; structure formation; Hele-Shaw; membrane


Publ.-Id: 29483

Annual Report 2018 - Institute of Ion Beam Physics and Materials Research

Faßbender, J.; Helm, M.; Zahn, P.

The Institute of Ion Beam Physics and Materials Research conducts materials research for future applications in, e.g., information technology. To this end, we make use of the various possibilities offered by our Ion Beam Center (IBC) for synthesis, modification, and analysis of thin films and nanostructures, as well as of the free-electron laser FELBE at HZDR for THz spectroscopy. The analyzed materials range from semiconductors and oxides to metals and magnetic materials. They are investigated with the goal to optimize their electronic, magnetic, optical as well as structural functionality. This research is embedded in the Helmholtz Association’s programme “From Matter to Materials and Life”. Six publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute.

Related publications

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-097 2019
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 29482

Progress in the second-moment closure for bubbly flow based on direct numerical simulation data

Ma, T.; Lucas, D.; Jakirlić, S.; Fröhlich, J.

Data from direct numerical simulations (DNS) of disperse bubbly flow in an upward vertical channel are used to develop a new second-moment closure for bubble-induced turbulence (BIT) in the Euler–Euler framework. The closure is an extension of a BIT model originally proposed by Ma et al. (Phys. Rev. Fluids, vol. 2, 2017, 034301) for two-equation eddy-viscosity models and focuses on the core region of the channel, where the interfacial term and dissipation term are in balance. Particular attention in this study is given to the treatment of the pressure–strain term for bubbly flows and the form of the interfacial term to account for BIT. For the latter, the concept of an effective BIT source is proposed, which leads to a significant simplification of the modelling work for both the pressure–strain correlation and the interfacial term itself. The anisotropy of bubbly flow is analysed with the aid of the anisotropy-invariant map obtained from the DNS data, and a parameter governing this issue is established. The complete second-moment closure is tested against reference data for different bubbly channel flows and a case of a bubble column. The agreement achieved with the DNS data is very good and the performance of the new model is better than obtained with the standard procedure. Furthermore, the model is shown to be robust and to fulfil the requirements of realizability.

Keywords: turbulence modelling; multiphase flow; Direct Numerical Simulation

Publ.-Id: 29481

Multi-photon regime of non-linear Breit-Wheeler and Compton processes in short linearly and circularly polarized laser pulses

Titov, A. I.; Otto, A.; Kämpfer, B.

Non-linear Breit-Wheeler e+e− pair production and its crossing channel - the non-linear Compton process - in the multi-photon regime are analyzed for linearly and circularly polarized short laser pulses. We show that (i) the azimuthal angular distributions of outgoing electrons in these processes differ on a qualitative level, and (ii) they depend on the polarization properties of the pulses. A finite carrier envelope phase (CEP) leads to a non-trivial non-monotonic behavior ofthe azimuthal angle distributions of the considered processes. That effect can be used for the (CEP) determination.


Publ.-Id: 29480

Lokale Effekte im DWR-Kern infolge von Zinkborat-Ablagerungen nach KMV (Projekt-Abschlussbericht BMWi-Vorhaben "Zinkborat")

Hampel, U.; Harm, U.; Kryk, H.; Ding, W.; Wiezorek, M.; Unger, S.

Im Falle eines Kühlmittelverluststörfalles (KMV) im Primärkühlkreislauf von DWR hat durch Korrosion im Kühlmittel (KM) freigesetztes Zink das Potenzial, in den Reaktorkern zu gelangen und sich bei Erwärmung (z. B. in Heißkanälen) in feste Korrosionsprodukte (Zinkborate) umzuwandeln.
Aus den Ergebnissen generischer Experimente im Rahmen der vorangegangenen BMWi-Vorhaben 1501467 und 1501430 ging hervor, dass für eine genaue Analyse und Bewertung von Zinkborat-Anlagerungen, speziell des zeitlichen Verlaufs während der Notkühlphase infolge eines KMV, die realen Randbedingungen nachgebildet werden müssen. Dies betrifft die thermohydraulischen Parameter sowohl bei der Zinkfreisetzung im Sumpf (Zinkquelle) als auch im Reaktorkern als mögliche Zinkborat-Senke. Diese Nachbildung ermöglicht eine Zuordnung der parallel ablaufenden Quelle-Senke-Mechanismen zueinander und einen Vergleich möglicher Abläufe für unterschiedliche KMV-Szenarien.
Mittels der experimentellen Umsetzung von Randbedingungen (KM-Chemie, Termperaturverläufe im Sumpf und im Kern) ausgewählter KMV-Szenarien in Laborexperimenten wurden die Zinkfreisetzung im Sumpf sowie mögliche Ausfällungen und Ablagerungen von Zinkborat im Kern (Schichtbildung auf BE-Oberflächen / mobile Partikel im KM) untersucht und charakterisiert. Die erzielten Ergebnisse eröffnen die Möglichkeit einer vergleichenden Bewertung unterschiedlicher KMV-Szenarien im Hinblick auf mögliche thermohydraulische Folgen im DWR-Kern.

Keywords: Kühlmittelverluststörfall; KMV; DWR; Korrosion; Zinkfreisetzung; Zinkborat; Experiment; Modellierung

Publ.-Id: 29479

LOCA scenario-related zinc borate precipitation studies at lab scale

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

During the sump recirculation operation after a postulated loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR), coolant spilling out of the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps. The long-term contact of the boric acid containing coolant with hot-dip galvanized containment internals (e.g. grating treads, strainers, support grids) may cause corrosion of the corresponding materials forming zinc borates (ZnB) dissolved in the cooling water.
Investigations regarding such zinc corrosion processes, changes of the coolant chemistry and possible resulting in-core effects are subject of joint research projects of the Helmholtz-Zentrum Dresden - Rossendorf (HZDR), TU Dresden (TUD) and Zittau/Görlitz University of Applied Sciences (HSZG). Lab-scale experiments at HZDR and TUD are focused on elucidation of physico-chemical corrosion and precipitation processes as well as resulting fouling effects at hot surfaces.
Long-term experiments of up to three weeks in a lab scale facility were conducted to simulate the simultaneous zinc dissolution (in sump) and ZnB precipitation (in hot core regions) during sump recirculation operation under boundary conditions of selected PWR LOCA scenarios. This includes LOCA-related zinc dissolution (corrosion) rates as well as experimental simulation of previously calculated scenario-related temperature courses of the coolant in the sump and area-related decay heat power courses of the reactor core. Results indicate significant precipitations of different solid ZnB products during the experiments. It turned out that the period between the start of the sump recirculation operation and the start of the ZnB precipitation as well as the precipitation rate essentially depend on the specific LOCA scenario (e.g. leak size). The ZnB precipitates usually formed dense layers on hot surfaces of electrically heated PWR cladding tubes of the lab scale facility. Additionally, flocculation or formation of solid ZnB particles inside the fluid has been observed. In most experiments, the different types of precipitates (layers, flocs or particles) were quantified and in certain cases the chemical compositions of the solid ZnB species were determined using different chemical analysis methods.
Since an influence of the ZnB precipitates on the thermal hydraulics inside the core cannot be ruled out, the results obtained at lab-scale were complemented by corresponding experiments in semi-technical test facilities of the project partner HSZG.
The investigations are supported by the German Federal Ministry for Economic Affairs and Energy under contract nos. 1501491 and 1501496.

Keywords: LOCA; Loss of coolant accident; corrosion; zinc release; experiments; Nuclear energy; corrosion; zinc borate; PWR; loss-of-coolant accident

  • Lecture (Conference)
    50th Annual Meeting on Nuclear Technology (AMNT 2019), 07.-08.05.2019, Berlin, Deutschland
  • Contribution to proceedings
    50th Annual Meeting on Nuclear Technology (AMNT 2019), 07.-08.05.2019, Berlin, Deutschland
    Proceedings of the 50th Annual Meeting on Nuclear Technology (AMNT 2019), Berlin: INFORUM Verlags- und Verwaltungsgesellschaft mbH, 978-3-926956-95-8

Publ.-Id: 29478

Qualification of a Photometer Probe for Local Concentration Measurement in Dense Bubbly Flows

Hampel, U.; Kryk, H.; Kipping, R.

Topics of current research activities within the DFG priority program SPP 1740 “Reactive Bubbly Flows” are studies on local mass transfer and reaction processes in order to gain a deeper understanding about the coupling of hydrodynamics, mass transfer and reaction kinetics in reactive bubbly flows as well as its influence on yield and selectivity in case of complex chemical reactions. Precondition for experimental investigations is the availability of sensors for local concentration measurements of components in the liquid phase. Due to limitations of currently available non-invasive measuring techniques, local concentration measurements in dense bubbly flows at technical scale pose technological challenges. Therefore, a minimal-invasive photometer probe have been qualified to measure concentrations of intermediates and products within the liquid phase of dense bubbly flows with high temporal and spatial resolution.
This work was supported by the German Research Foundation (DFG), reactive bubbly flows (SPP 1740).

Keywords: PAT; photometer; multiphase flow; hydrodynamics; mass transfer; bubbly flow; chemical reaction; concentration measurement

  • Poster
    Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland
  • Contribution to proceedings
    Jahrestreffen Reaktionstechnik 2019 gemeinsam mit der Fachgruppe Mehrphasenströmungen, 27.-29.05.2019, Würzburg, Deutschland
    Book of Abstracts, Frankfurt: DECHEMA e.V.

Publ.-Id: 29477

Twist-angle-dependent interlayer exciton diffusion in WS2–WSe2 heterobilayers

Yuan, L.; Zheng, B.; Kunstmann, J.; Brumme, T.; Kuc, A. B.; Ma, C.; Deng, S.; Blach, D.; Pan, A.; Huang, L.

The nanoscale periodic potentials introduced by moiré patterns in semiconducting van der Waals heterostructures have emerged as a platform for designing exciton superlattices. However, our understanding of the motion of excitons in moiré potentials is still limited. Here we investigated interlayer exciton dynamics and transport in WS2–WSe2 heterobilayers in time, space and momentum domains using transient absorption microscopy combined with first-principles calculations. We found that the exciton motion is modulated by twist-angle-dependent moiré potentials around 100 meV and deviates from normal diffusion due to the interplay between the moiré potentials and strong exciton–exciton interactions. Our experimental results verified the theoretical prediction of energetically favourable K–Q interlayer excitons and showed exciton-population dynamics that are controlled by the twist-angle-dependent energy difference between the K–Q and K–K excitons. These results form a basis to investigate exciton and spin transport in van der Waals heterostructures, with implications for the design of quantum communication devices.


Publ.-Id: 29476


Frust, T.; Starke, S.

Testabstract Testabstract Testabstract Testabstract Testabstract Testabstract..

  • Test

Publ.-Id: 29475

Improvement of TOPFLOW void fraction data using potential field simulations of the wire-mesh sensor response

Prasser, H.-M.; Beyer, M.; Lucas, D.

At the TOPFLOW test facility of the HZDR, gas-liquid two-phase flow experiments were conducted in a vertical DN200 pipe aimed at the creation of a high-quality database. A quality check of the measurement results obtained for 48 different combinations of superficial air and water velocities (water: 0.04 -1.6 m/s, air: 0.0025 - 3.2 m/s) has shown that an overestimation of the cross-section averaged void fraction by the wire-mesh sensor is evident. This finding is supported by the analysis of drift fluxes calculated from the measured void fraction and the injected flow rates of liquid and gas, which are too low, often even negative, to be physically plausible. Another indication of the overestimation is the miss of the reproduction of the gas flow rate from a multiplication of void fraction and gas velocity profiles obtained from signals of a pair of successive sensors. Reconstructed superficial gas velocities tend to exceed significantly the values known from the injected gas flow rates in the bubbly flow region. Prasser & Häfeli (2018) showed that a linear dependency between conductance and liquid holdup at a crossing point of wires delivers too high void fraction values. The application of Maxwell’s equation for the conductivity of an emulsion was instead proposed to improve results. Furthermore, the nature of frequently observed overshoots of the conductance above the calibration values was found to correspond to a real physical phenomenon. During the previous evaluation of the TOPFLOW data, these overshoots were eliminated by setting the gas fraction to zero when they occur. The paper presents the results of a reevaluation of the TOPFLOW data using an approach based on Maxwell’s equation and a correction of the overshoots instead of truncating them. It is shown that the problem of negative drift velocities is now eliminated; the match of reconstructed and injected gas velocities considerably improved.

Keywords: Gas-liquid two-phase flow; vertical pipe; wire-mesh sensor; signal processing; measuring uncertainty

  • Contribution to proceedings
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Experiments related to Nuclear Reactor Thermal Hydraulics and Severe Accidents, 22.-25.10.2019, Livorno, Italy
  • Lecture (Conference)
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Experiments related to Nuclear Reactor Thermal Hydraulics and Severe Accidents, 22.-25.10.2019, Livorno, Italy

Publ.-Id: 29472

Multi-fluid models for gas-liquid flows: innovative concepts

Lucas, D.

This lecture presents innovative concepts to extent the applicability of CFD-methods in the multi-fluid framework. The GENTOP-concepts allows to consider different flow morphologies including transitions between them.

Keywords: CFD; multi-fluid; Euler-Euler; GENTOP; flow pattern transition

  • Invited lecture (Conferences)
    XIII Workshop & Summer School „Modelling of Multiphase Flows in Thermo-Chemical Systems”, 13.-15.06.2019, Wieżyca, near Gdańsk, Poland

Publ.-Id: 29470

Multi-fluid models for gas-liquid flows: consolidation of CFD modelling

Lucas, D.

This lecture presents the status and strategies for the consolidation of CFD-modelling in the multi-fluid framework. This is illustrated by the example of recent research on the further qualification of the baseline model for poly-disperse bubbly flows.

Keywords: CFD; multi-fluid; Euler-Euler; baseline model; bubbly flow

  • Invited lecture (Conferences)
    XIII Workshop & Summer School „Modelling of Multiphase Flows in Thermo-Chemical Systems”, 13.-15.06.2019, Wieżyca, near Gdańsk, Poland

Publ.-Id: 29469

Status and perspectives of CFD modelling of gas-liquid flows in the multi-fluid framework

Lucas, D.

There is an increasing request to use CFD-methods for simulations on medium and large scale industrial applications, e.g. in chemical engineering, energy techniques and nuclear safety. For most of such applications the Euler-Euler two or multi-fluid approach is the only feasible one. Gas and liquid phases are represented by interpenetrating fields and the information on the interface gets lost during the averaging process which is applied to obtain the balance equations. To close these equations the corresponding local phenomena at the gas-liquid interfaces have to be considered by closure models. As recently discussed by Lucas et al. (2016) there is not yet consensus achieved in the community regarding the most appropriate closures which limits the reliability of CFD-simulations using the Euler-Euler approach. A so-called baseline model concept was proposed in that paper. Since the closure models have to reflect the local phenomena a case by case tuning is not meaningful and instead a fixed set of closure models should be defined for certain flow conditions and applied to different cases without any modification.

Different flow morphologies as bubbly flows, droplet flows and segregated flows with large interfaces have to be distinguished. These different approaches require different closure models. In addition for poly-disperse bubbly flows it may be necessary to divide the gas phase into sub-phases reflecting bubbles of different size respectively. At HZDR a baseline model for poly-disperse bubbly flows basing on the inhomogeneous MUSIG (iMUSIG) approach (Rzehak and Krepper, 2016) and a model for segregated flows basing on the AIAD model (Porombka and Höhne, 2016) have been established. Especially the baseline model for poly-disperse flows with fixed model formulations and model parameters was validated on a large number of experiments (more than 150) for different flow geometries, flow rates and material systems. There is already an acceptable agreement for many cases, but for some also clear deviations occur. It is the scientific challenge to identify the main reasons for these deviations and figure out a better model for the corresponding phenomenon. The baseline model strategy will be illustrated by the recent developments to improve the modelling of bubbly flows and a general strategy how to develop better models will be presented.

In many flow situations interfaces may vary over a large range of scales combining dispersed and segregated morphologies. To handle such flows the innovative GENTOP concept was developed (Hänsch et al., 2012). It combines the iMUSIG and AIAD approaches and allows also simulating transitions between the different morphologies. The well validated baseline models are thus part of GENTOP. Recently the concept was applied for a simulation of a boiling pipe which includes flow pattern transitions (Höhne et al., 2017). The second part of the lecture will report about these developments which aim to extend the range of applicability of CFD simulations.

The above mentioned approaches were first implemented and tested in the commercial CFD-code ANSYS-CFX. Presently a similar framework is established for the OpenSource code OpenFOAM. A GitLab based version control system allows a high level quality assurance and has a high potential for international co-operation. Joint efforts can be done to qualify the code system.

Keywords: CFD; multi-fluid; gas-liquid; bubbly flow; segregated flow

  • Invited lecture (Conferences)
    10th International Conference on Multiphase Flow, 19.-24.05.2019, Rio de Janeiro, Brazil
  • Contribution to proceedings
    10th International Conference on Multiphase Flow, 19.-24.05.2019, Rio de Janeiro, Brazil

Publ.-Id: 29468

Heterogeneous adsorption of actinides on host rocks at the pore scale: Application of an improved surface complexation model

Yuan, T.; Bollermann, T.; Fischer, C.

In Germany, Opalinus clay strata are considered as a potential host rock for the storage of high-level nuclear waste. The adsorption efficiency of actinides in the host rock at the pore scale is essential for better understanding and prediction of actinide retention at the continuum scale, i.e., core scale and above. Surface complexation models (SCM) are a powerful tool for describing adsorption processes of actinides onto mineral surfaces. At the pore scale, the surface energy is a key constraint, which is modified by multiple parameters, e.g., crystallographic orientation, crystal defects, and nanotopography [1, 2]. Current studies on SCM [3] utilize simple retention coefficients to characterize the fluid-solid interactions without considering the effect of surface energy.

In this study, calcite and phyllosilicates are considered as two important mineral types in the Opalinus clay rock. We propose an improved SCM that implements crystal surface energy to simulate Eu (III) and U(IV) adsorption processes onto the surfaces of reference crystals. The reactions and parameters describing adsorption are modified based on the experimental results, which focus on the adsorption efficiency and its dependence on surface energy at the pore scale. The preliminary results provide the quantitative insights into the actinide retention variability in the host rock at the pore scale, which contribute to a comprehensive understanding at the core scale and above.

  • Open Access Logo Invited lecture (Conferences)
    Annual Meeting of the Nuclear Chemistry Section of GDCh 2019, 25.-27.09.2019, Dresden, Germany

Publ.-Id: 29467

Message from the Guest Editor of the 16th Multiphase Flow Conference Special Issue

Lucas, D.

Selected contributions of the 16th Multiphase Flow Conference at HZDR were published in a special issue of the Open Access Journal Experimental and Computational Multiphase Flow. In this contribution an overview on the conference and a short introduction to the single papers is given.

Keywords: multiphase flow; conference

  • Open Access Logo Abstract in refereed journal
    Experimental and Computational Multiphase Flow 1(2019), 231-232
    DOI: 10.1007/s42757-019-0037-7

Publ.-Id: 29466

Multiphase numerical modeling of a pilot-scale bubble column with a fixed poly-dispersity approach

Hosseini, A.; Mereu, R.; Canu, S.; Ziegenhein, T.; Lucas, D.; Inzoli, F.

A three-dimensional numerical study of air/water bubbly flow in a cylindrical large-scale bubble column is performed using Euler-Euler approach. The main objective is to investigate the influence of different boundary conditions such as bubble size distribution, polydispersity effects (mono and bi-dispersed approach) and mass flow rate distribution at sparger. In bi-dispersed approach the population of bubbles are divided into two groups of small and large bubbles and a mean diameter is considered for each group. The division is based on the critical bubble diameter, for which the lift coefficient changes its sign from positive to negative. For air/water system Tomiyama lift coefficient model is widely used and the critical bubble diameter is equal to 5.8 mm. A new critical bubble diameter and lift force coefficient model is introduced in this study and compared with well-known Tomiyama model. The numerical predictions are compared against the experimental data and the effect of different conditions is assessed on basis of comparison of axial gas fraction (local holdup) and global holdup. Better predictions are obtained by taking into account poly dispersity of the flow with new critical bubble diameter and new lift coefficient model. Also, it was found that mass flow-rate distribution at the sparger does not affect numerical results for global and local holdup, however a different flow pattern is observed near the sparger region.

Keywords: Computational Fluid Dynamics (CFD); bubble column; critical bubble diameter; lift force coefficient

Publ.-Id: 29465

High-speed X-ray tomography of silo discharge

Stannarius, R.; Sancho Martinez, D.; Boerzsoenyi, T.; Bieberle, M.; Barthel, F.; Hampel, U.

The outflow of granular materials from storage containers with narrow outlets is studied by means of ultrafast X-ray computed tomography (UFXCT). The used acquisition speed of this tomograph (1000 fps) is high enough to allow high-speed recording of horizontal cross sections of the container during the discharge of material. Analyzing space-time plots that were generated from the tomograms, we retrieve velocity profiles and packing structures in the container. We compare hard spherical grains with soft, low-frictional hydrogel spheres. Their flow profiles are qualitatively different. While the hard spheres form stagnant zones at the container side walls, the hydrogel spheres flow in all regions of the container. Moreover, a shell-like positional arrangement of the soft spheres induced by the container walls is revealed. The results obtained for the flow field structure confirm earlier conclusions drawn from sequences of X-ray tomograms of clogged states.

Keywords: Ultrafast X-ray CT; silo flow

Publ.-Id: 29464

Fundamentals in GPU programming

Bieberle, A.

For the 2nd TOMOCON Summer School “Process Tomography & Data Processing”, that is conducted this time in Delft, a lecture will be given about parallel data processing programming using suitable architechtures, such as graphic processing units (GPU).

Keywords: Parallelism; GPU programming; CUDA

  • Lecture (Conference)
    2nd TOMOCON Summer School “Process Tomography & Data Processing, 01.-03.07.2019, Delft, Niederlande

Publ.-Id: 29463

Nonlinear Optical Control of Chiral Charge Pumping in a Topological Weyl Semimetal

Jadidi, M. M.; Kargarian, M.; Mittendorff, M.; Aytac, Y.; Shen, B.; König-Otto, J.; Winnerl, S.; Ni, N.; Gaeta, A. L.; Murphy, T. E.; Drew, H. D.

Solids with topologically robust electronic states exhibit unusual electronic and optical transport properties that do not exist in other materials. A particularly interesting example is chiral charge pumping, the so-called chiral anomaly, in recently discovered topological Weyl semimetals, where simultaneous application of parallel DC electric and magnetic fields creates an imbalance in the number of carriers of opposite topological charge (chirality). Here, using timeresolved terahertz measurements on the Weyl semimetal TaAs in a magnetic field, we optically interrogate the chiral anomaly by dynamically pumping the chiral charges and monitoring their subsequent relaxation. Theory based on Boltzmann transport shows that the observed effects originate from an optical nonlinearity in the chiral charge pumping process. Our measurements reveal that the chiral population relaxation time is much greater than 1 ns.
The observation of terahertz-controlled chiral carriers with long coherence times and topological protection suggests the application of Weyl semimetals for quantum optoelectronic technology.

Keywords: Wyle semimetal; TaAs; chiral charge pumpping

Related publications


Publ.-Id: 29462

Direct nanoscopic observation of plasma waves in the channel of a graphene feld-effect transistor

Soltani, A.; Kuschewski, F.; Bonmann, M.; Generalov, A.; Vorobiev, A.; Ludwig, F.; Wiecha, M. M.; Cibaraite, D.; Walla, F.; Winnerl, S.; Kehr, S. C.; Eng, L. M.; Stake, J.; Roskos, H. G.

Plasma waves play an important role in many solid-state phenomena and devices. They emerge as signifcant also in electronic device structures as the operation frequencies of these devices increase. A prominent example are feld-effect transistors which are increasingly being used as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies, where they exhibit very good sensitivity even high above the cut-off frequencies which limit their application in amplifers and switches. Transport theory predicts that coupling of radiation at THz frequencies into the channel of a feld-effect transistor leads to the development of a gated plasma wave collectively involving the charge carriers of both the two-dimensional electron gas and of the gate electrode. Because of the small spatial separation of the channel from the gate, such a wave propagates with a speed much lower than the vacuum speed of light. In this paper, we present the first direct visualization of such waves. Employing graphene FETs with a buried gate electrode, we utilize near-field THz nanoscopy at room temperature to probe the electric field amplitude of the propagating wave directly on the exposed graphene sheet. Mapping of the feld distribution allows us to determine the decay length and the gate-voltage-dependent propagation speed of the plasma waves which is found to lie in the range of 3.5-7 x 10^6 m/s, in good agreement with theory.

Keywords: graphene field-effect transistor; plasma waves; near-field microscopy

Related publications

Publ.-Id: 29461

Suppressed Auger scattering and tunable light emission of Landau-quantized massless Kane electrons

But, D. B.; Mittendorff, M.; Consejo, C.; Teppe, F.; Mikhailov, N. N.; Dvoretskii, S. A.; Faugeras, C.; Winnerl, S.; Helm, M.; Knap, W.; Potemski, M.; Orlita, M.

The Landau level laser has been proposed a long time ago as a unique source of monochromatic radiation, widely tunable in the THz and infrared spectral ranges using an externally applied magnetic field. In spite of decades of efforts, this appealing concept never resulted in the design of a reliable device. This is due to effcient Auger scattering of Landau-quantized electrons, which is an intrinsic non-radiative recombination channel that eventually gains over cyclotron emission in all materials studied so far: in conventional semiconductors with parabolic bands, but also in graphene with massless electrons. The Auger processes are favored in these systems by Landau levels (or their subsets) equally spaced in energy. Here we show that this scheme does not apply to massless Kane electrons in gapless HgCdTe alloy, in which undesirable Auger scattering is strongly suppressed and the sizeable cyclotron emission observed, for the first time in the case of massless particles. The gapless HgCdTe thus appears as a material of choice for future technology of Landau level lasers.

Keywords: Kane electrons; Landau quantization; Auger scattering; cyclotron emission

Related publications


Publ.-Id: 29460

Holistic Data Management as a Key Towards Reproducible Science in a Diverse and Dynamic Ecosystem

Juckeland, G.

Eingeladener Vortrag an der RWTH Aachen

  • Open Access Logo Lecture (others)
    IT Seminar der RWTH Aachen, 12.07.2019, Aachen, Deutschland

Publ.-Id: 29459

High-gain quantum free-electron laser: Emergence and exponential gain

Kling, P.; Giese, E.; Carmesin, C. M.; Sauerbrey, R.; Schleich, W. P.

We derive an effective Dicke model in momentum space to describe collective effects in the quantum regime of a free-electron laser (FEL). The resulting exponential gain from a single passage of electrons allows the operation of a Quantum FEL in the high-gain mode and avoids the experimental challenges of an x-ray FEL oscillator. Moreover, we study the intensity fluctuations of the emitted radiation, which turn out to be super-Poissonian.

Keywords: Quantum Free Electron Laser; Quantum FEL; Free Electron Laser; QFEL; FEL; Dicke model

Publ.-Id: 29457

Experimental and numerical studies on high-pressure Steam Condensation in a horizontal condenser tube

Bieberle, A.; Moonesi Shabestary, A.; Boden, S.; Beyer, M.; Unger, S.; Lucas, D.; Hampel, U.

We introduce results of an experimental and numerical study on condensation steam heat transfer in a near horizontal tube at pressure up to 65 bar. Experiments have been performed at the COSMEA test facility at HZDR, which is part of the TOPFLOW Two-Phase Flow facility. Objective of the experimental study was a detailed analysis of the interplay between two-phase flow and heat transfer during steam condensation in an emergency condenser tube. The experimental results are part of a system and CFD code qualification project for passive heat removal systems. The condenser tube resembles a section of a single tube in the KERENA emergency condenser for which integral tests have been performed at Framatome’s INKA test facility in Karlstein, Germany. Beside integral heat flux and condensation rates the experiments at COSMEA deliver high-resolution cross-sectional flow images obtained by X-ray tomography and angularly resolved heat flux through the condenser tube wall. Accompanying CFD simulations have been carried out with ANSYS CFX and a new consistent model for wall and direct contact condensation.

Keywords: KERENA; passive decay heat removal; high-pressure steam condensation; computed tomography; heat flux measurement; CFD modeling

  • Contribution to proceedings
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Experiments related to Nuclear Reactor Thermal Hydraulics and Severe Accidents, 22.-25.10.2019, Livorno, Italien
  • Lecture (Conference)
    Specialists Workshop on Advanced Instrumentation and Measurement Techniques for Experiments related to Nuclear Reactor Thermal Hydraulics and Severe Accidents, 22.-25.10.2019, Italien, Livorno

Publ.-Id: 29456

Ultrafast X-ray CT imaging for hydrodynamic investigations of gas-liquid two-phase flow in centrifugal pumps

Schäfer, T.; Neumann-Kipping, M.; Bieberle, A.; Bieberle, M.; Hampel, U.

Gas entrainment into centrifugal pumps decreases pump performance and may raise safety issues, e.g. through insufficient cooling. Although there is some phenomenological knowledge in form of correlations between operating parameters and pump performance a further understanding via direct observation of the gas-liquid mixture was so far not possible. In this paper, we demonstrate the capability of ultrafast X-ray computed tomography (UFXCT) to disclose gas-liquid two-phase flow dynamics in the impeller region of a centrifugal pump mockup. Experiments were performed for gas injection at impeller speeds between 1300 rpm and 1600 rpm. We analyzed the time-resolved X-ray images with respect to the gas distribution and compared them with time-averaged image data of a real pump obtained earlier with gamma-ray tomography.

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast X-ray computed tomography


Publ.-Id: 29455

Flow morphology and heat transfer analysis for high-pressure steam condensation in an inclined tube part II: Numerical investigations

Moonesi Shabestary, A.; Bieberle, A.; von der Cron, D.; Ding, W.; Krepper, E.; Lucas, D.; Hampel, U.

In this part of the paper, we introduce and discuss the numerical investigation of two-phase flow and heat transfer during steam condensation inside an inclined tube. For that we developed and employed a three-dimensional two-phase computational fluid dynamics model in ANSYS CFX which comprises a consistent heat transfer model that considers wall condensation and direct contact condensation. Wall condensation is covered by a new subgrid model for the thin liquid film. For modelling of the heat transfer on the steam-liquid interface, three different heat transfer correlations have been implemented to check their performance. Simulation results were compared with experimental data of the COSMEA facility, which has been documented in part I of this paper. Particular focus was given to the development of the liquid film inside the tube and its effects on the wall heat transfer. Moreover, we compared the CFD simulations with system code simulations performed with the ATHLET submodule of AC².

Keywords: wall condensation; direct contact condensation; wall heat flux; liquid film thickness; CFD modelling; AC²; ATHLET


Publ.-Id: 29454

Thermodynamic and structural aspects of the aqueous uranium(IV) system – hydrolysis vs. sulfate complexation

Lehmann, S.; Foerstendorf, H.; Zimmermann, T.; Patzschke, M.; Bok, F.; Brendler, V.; Stumpf, T.; Steudtner, R.

The aquatic species of U(IV) in acidic aqueous solution in the presence of sulfate was studied in the micromolar range by a combined approach of optical spectroscopies (UV/vis and mid-IR), quantum-chemical calculations (QCC), and thermodynamic modelling. The number of species occurring in solution within the pH range 0–2 was assessed by decomposition and fitting of photometric spectra using HypSpec and Geochemist’s Workbench software. Single component spectra of U⁴⁺, UOH³⁺, USO₄²⁺ and U(SO₄)₂ were obtained and extinction coefficients ελ have been calculated to be 58.8, 19.2, 47.6 and 40.3 L mol ⁻ ¹ cm ⁻ ¹, respectively. Complex formation constants of two U(IV) sulfate species and the first hydrolysis species UOH³⁺ in infinite diluted solution were determined by thermodynamic modelling to be log β⁰₁₀₁ = 6.9 ± 0.3, log β⁰₁₀₂ = 11.8 ± 0.5 and log β⁰₁₁₀ = − (0.36 ± 0.1), respectively. No further U(IV) sulfate and hydrolysis species were observed under the prevailing conditions. Molecular structural information of the sulfate species was derived from vibrational spectra and QCC exhibiting a predominant monodentate coordination of the sulfate ions.

Keywords: speciation; absorption; photometry; vibrational spectroscopy; complex formation constant; DFT


Publ.-Id: 29453

Flow morphology and heat transfer analysis during high-pressure steam condensation in an inclined tube part I: Experimental investigations

Bieberle, A.; Moonesi Shabestary, A.; Geißler, T.; Boden, S.; Beyer, M.; Hampel, U.

In this paper, experimental investigations on the flow morphology and heat transfer in a single steam condenser tube are presented, which were performed at the thermal hydraulic test facility COSMEA (COndensation test rig for flow Morphology and hEAt transfer studies). This facility has been setup to study the interrelation of condensation heat transfer with two- phase flow in an isolated single condenser tube that is cooled by forced convection. Studies have been performed for elevated pressures up to 65 bar at saturation conditions and for inlet steam mass flow of up to 1 kg/s and different inlet steam qualities. The wall heat flux is measured with distributed heat flux probe and global condensation rates have been obtained from integral heat and mass balances. As a unique feature the cross-sectional phase distribution has been studied via X-ray computed tomography. The data is going to be used for the validation of numerical simulations with 1D ATHLET and 3D CFD codes as presented in the second part of this paper.

Keywords: condensation heat transfer; heat exchangers; two-phase flow; heat flux; X-ray tomography; passive safety systems


Publ.-Id: 29452

Modeling of passive heat removal systems: A review with reference to the Framatome BWR reactor KERENA : Part II

Manthey, R.; Viereckl, F.; Moonesi Shabestary, A.; Zhang, Y.; Ding, W.; Lucas, D.; Schuster, C.; Leyer, S.; Hurtado, A.; Hampel, U.

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modelling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modelling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities.

Keywords: Passive heat removal systems; Condensation; System codes; CFD; Emergency condensers; Containment cooling condensers; Two-phase flow instabilities


Publ.-Id: 29451

Modelling of passive heat removal systems: A review with reference to the Framatome BWR reactor KERENA :Part I

Moonesi Shabestary, A.; Viereckl, F.; Zhang, Y.; Manthey, R.; Lucas, D.; Schuster, C.; Leyer, S.; Hurtado, A.; Hampel, U.

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modelling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I deals with numerical and experimental methods for modelling of condensation inside the emergency condensers and on the containment cooling condenser while part II deals with boiling and two-phase flow instabilities.

Keywords: Passive heat removal systems; condensation; 1D Codes; CFD; emergency condensers; containment cooling condensers

Publ.-Id: 29450

Polarization-dependent near-field phonon nanoscopy of oxides: SrTiO₃, LiNbO₃, and PbZr₀.₂Ti₀.₈O₃

Wehmeier, L.; Lang, D.; Liu, Y.; Zhang, X.; Winnerl, S.; Eng, L. M.; Kehr, S. C.

Resonant infrared near-field optical spectroscopy provides a highly material-specific response with sub-wavelength lateral resolution of about 10 nm. Here, we provide the near-field response of selected paraelectric and ferroelectric materials, i.e. SrTiO3, LiNbO3, and PbZr0:2Ti0:8O3, showing resonances in the wavelength range from 13.0 to 15.8 µm. We investigate these materials using scattering scanning near-field optical microscopy (s-SNOM) in combination with a tunable midinfrared free-electron laser (FEL). Fundamentally, we demonstrate that phonon-induced resonant near-field excitation surprisingly is possible for both p- and s-polarized incident light, a fact that is of particular interest for the nanoscopic investigation of anisotropic and hyperbolic materials. Moreover, we show that near-field spectroscopy, as compared to far-field techniques, bears substantial advantages such as lower penetration depths, stronger confinement, and a high spatial resolution. The latter permits the investigation of minute material volumes, e.g. with nanoscale changes in crystallographic structure, which we prove here via near-field imaging of ferroelectric domain structures in PbZr0.2Ti0.8O3 thin film.

Keywords: Near-field microscopy; ferroelectrica

Related publications


Publ.-Id: 29449

Direct Correction of Residual Symmetric Aberrations in Electron Holograms of Weak Phase Objects

Kern, F.; Linck, M.; Wolf, D.; Niermann, T.; Arora, H.; Alem, N.; Erbe, A.; Gemming, S.; Lubk, A.

Thin TEM specimen are regarded as weak objects (WPO), if the amplitude variation of the electron wave by the specimen can be neglected and the phase modulation is very small (≪π). Large classes of topical materials can be described in this approximation, such as most 2D materials, organic semiconductor materials or biological specimen. Due to the lack of amplitude (and hence intensity) contrast, conventional TEM (CTEM) investigations on WPOs are commonly performed under a certain defocus, which transfers part of the phase information to the recorded intensity. This intermixing contrast transfer from amplitude to phase and vice versa is commonly described by the phase contrast transfer function (PCTF), while the non-mixing contrast transfer for amplitude and phase is referred to as amplitude contrast transfer function (ACTF). Due to the transfer gap in the PCTF, the CTEM contrast transfer at low spatial frequencies is degraded in defocused images of WPOs (Fig. 1). By employing electron holography, however, both amplitude and phase of the electron wave can be reconstructed without a transfer gap. Having the whole wave information also enables the a-posteriori correction of geometric aberrations as it was already proposed in D. Gabor’s seminal paper from 1948 [1]. The realization of his idea, however, remains challenging in the absence of additional knowledge about the sample, due to the lack of a criterion for a successful aberration correction.

Keywords: electron holography; ERC; density-functional calculations; all-electron; 2D materials

Related publications

  • Lecture (Conference)
    Microscopy Conference 2019, 01.-06.09.2019, Berlin, Deutschland
  • Microscopy and Microanalysis 25(2019)S2, 98-99
    DOI: 10.1017/S1431927619001223

Publ.-Id: 29448

Simulation of STM images and spectroscopy of single nitrogen-doped molecules with 5-7 membered rings on Au(111) surfaces

Nikipar, S.; Ryndyk, D. A.; Gemming, S.; Moresco, F.; Cuniberti, G.; Frauenheim, T.

We consider STM images and spectroscopy (STS) of molecules on metal surfaces. We combine DFT based atomistic tight-binding model (DFTB approach) with Green function technique, which offers a framework to consider tip, molecule and surface as one integrated system and taking into account the tip geometry. Besides, it captures the interference and interaction effects. This approach can be applied for the investigation of finite-voltage effects and describe the high-energy molecular transport states. It allows to simulate quantitatively the I(V) current-voltage spectroscopy curves and dI/dV maps in both constant current and constant height modes. We applied our methods to nitrogen-doped molecules with 5-7 membered rings on Au(111) surface and showed that the electronic properties of molecules are strongly influenced by formation of azulene-motifs. We developed the integrated open software suite for quantum nanoscale modeling (TraNaS OpenSuite, for convenient calculations of large-scale molecular nanosystems on metal surfaces.

Keywords: molecular electronics; STM; conductance calculations; density-functional tight binding

  • Poster
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29447

Electron Transport through single Mn-salen molecule: Theoretical Study

Lokamani, M.; Kilibarda, F.; Sendler, T.; Zahn, P.; Mortensen, M.; Gothelf, K. V.; Erbe, A.; Gemming, S.

Metal-salen complexes, formed by the coordination of a metal cation and a N,N’-bis(salicylidene)ethylenediamine-based ligand, are promising candidates for molecular electronics, because of possible modulations of transport channels using different metal cations. One such candidate is Mn-salen complex.

Here, we first explore the electronic structure of single molecules using wave function (MS-CASSCF) and density-functional (DFT+U) methods. We then employ the non-equilibrium Green’s function (NEGF) technique to study electron transport through single molecules attached to gold electrodes under finite bias. We explore various docking configurations for the single molecule between the gold electrodes.

A comparison with experimental coupling constants and energy levels, obtained using mechanically controllable break junction (MCBJ) technique is also presented.

Keywords: molecular electronics; NEGF; density-functional theory; Hartree-Fock; ab-initio; complete active space; multiconfigurational approach; transport calculation

  • Lecture (Conference)
    DPG Frühjahrstagung, 31.03.-04.05.2019, Regensburg, Deutschland

Publ.-Id: 29446

Statistical studies of random silicon-germanium alloys using electronic structure calculations

Roscher, W.; Fuchs, F.; Wagner, C.; Schuster, J.; Gemming, S.

Random alloys are relevant for many applications. One example is silicon-germanium which is used for high frequency devices like heterojunction-bipolar transistors. We therefore investigate the electronic structure of Si1−xGex alloys in the entire composition range 0≤ x≤ 1. For our study we use density functional theory in combination with bulk models of the alloys. To describe the band gap precisely we use the pseudopotential projector shift method as implemented in QuantumATK 18.06.

We perform a random generation of Si1−xGex structures to get statistical distributions of the electronic properties. After optimizing the structure we evaluate the band structure by averaging equivalent directions in the Brillouin zone.

The mean of the band gap is in good agreement with experimental reference data. We also demonstrate wide variations of the band gap, which are in the range of about 10 %. Further properties, such as the lattice constant and the formation energy are studied as well. Finally, we investigated also the impact of additional carbon dopants in the silicon-germanium alloy.

Keywords: Silicon nanowires; germanium nanowires; random alloys; Monte-Carlo; grand canonical potential simulations; entropy corrections; density functional calculations; mixing enthalpy; mixing entropy

  • Poster
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29445

Understanding the formation of interlayer excitons in the case of MoS2 on GaSe.

Wagner, C.; Rahaman, M.; Zahn, D. R. T.; Gemming, S.

The fabrication of hybrid van-der-Waals heterostructures of two-dimensional nano materials is an emerging field of study: The (weak) electronic interaction between two layers is often reasonably described by a perturbation of the physical effects of the isolated layers, such as electrostatic doping and screening of intralayer excitons. However, it turns out that this picture of the weak interaction is not exhaustive in terms of optical properties: the formation of bound excitons from electrons of one layer and the holes from another layer yields the formation of interlayer excitons. These states are measured experimentally by photoluminescence and photocurrents, e.g. in the case of MoS2 on GaSe due to type-II band alignment.

This contribution elucidates the conditions for the formation of interlayer excitons from a first-principles point of view. For this, first-principles studies of a minimal test system are conducted. One perspective is then to predict these states as a function of the heterostack in order to specifically taylor efficient solar cells.

Keywords: densit-function calculations; 2D materials; interlayer exciton; exciton; Bethe-Salpeter; two-particle excitations; 2D heterostructure

  • Lecture (Conference)
    DPG Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29444

Understanding the electron transport through NiSi2-Si interfaces

Fuchs, F.; Gemming, S.; Schuster, J.

Metal-semiconductor interfaces are of huge importance for applications and can be found in various field-effect transistors. We study the interface between NiSi2 and silicon on the basis of density functional theory and the NEGF formalism. Different crystal orientations and strain states are investigated systematically.

We focus on the tunneling phenomena of carriers through the Schottky contact at the interface, which are crucial for the on-current in transistors. The on-current is found to be strongly dependent on strain and orientation. It will be shown that the height of the Schottky barrier determines the tunneling current. However, not all changes in the current can be traced back to the barrier height. The modification of the electronic structure matter as well, which can be modeled based on the effective mass of the tunneling carriers. We have also extracted work functions of the isolated materials which we relate to the extracted Schottky barrier heights. It will be shown that the Schottky-Mott model fails for this material system. Better approaches will be discussed in our contribution.

Keywords: one-dimensional transport; density-functional theory; electronic structure; reconfigurable electronics; RFET; silicon nanowires; nickel silicides; 1D contacts

Related publications

  • Invited lecture (Conferences)
    International Workshop "Correlations and Transport in one-dimensional structures", 04.-07.07.2019, Dresden, Deutschland
  • Lecture (Conference)
    DPG-Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland
  • Invited lecture (Conferences)
    Seminar Series on Topical Problems in Theoretical Physics, 20.03.2019, London, U.K.

Publ.-Id: 29443

Modeling the interaction of magnetically capped colloidal particles

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

Colloidal self-assembly bears significant potential for the bottom-up fabrication of advanced materials and micromechanical structures. A wide range of particles with different types of anisotropy have been recognized as promising precursors for controlled structure engineering. Here, we concentrate on particles that interact via polar fields, which are intrinsically anisotropic. More specifically, we focus on the assembly of micron-sized silica spheres which are partly covered by a thin ferromagnetic layer with an out-of-plane magnetic anisotropy. To study assemblies of such magnetic particles, we introduce a simple two-parameter model: The extended magnetization distribution is approximated by a current-carrying coil enclosed inside a hard sphere. The far field of that current reproduces the stray field of a point dipole model, the near field reflects an extended magnetization. Such a model employs only two parameters to describe the shape of the magnetization distribution: The radius and the position of the coil inside the sphere. We present stable assemblies as a function of both parameters. In the limit of very small coils the analytical solution for two particles with shifted point dipoles is correctly reproduced. By increasing the radius of the coil, we reproduce experimentally observed particle arrangements not covered by models based on single shifted dipoles.

Keywords: colloid; Janus particle; self-assembly; model potential; soft matter

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 31.03.-05.04.2019, Regensburg, Deutschland

Publ.-Id: 29442

Characterization of irradiation-induced microstructure in reactor pressure vessel steels

Ulbricht, A.; Bergner, F.; Keiderling, U.

SANS contributed significantly to the understanding of the behaviour of reactor pressure vessel (RPV) steels exposed to irradiation with fast neutrons. It allows macroscopically representative, statistically reliable and robust measures of size, volume fraction and number density of nmsized solute clusters to be obtained. In particular, the use of the ferromagnetic properties of the matrix allows, under certain assumptions, the exact determination of the scattering contrast and thus the absolute volume fraction. The lower detection limit in terms of volume fraction is typically about 0.005%. The A-ratio, that is the total-to-nuclear scattering ratio, can be used as one-parameter signature of the mean composition of irradiation-induced clusters. Major limitations of SANS are related to the uncertainty of the scattering contrast (cluster composition, magnetism) and to the lower detection limit. Especially because of the incoherent scattering contribution of different iron isotopes, the lower detection limit is approximately 0.5 nm in terms of radius. The unirradiated reference condition of a RPV steel exhibits a high scattering background essentially caused by different sizes of carbides and should be carefully subtracted from the investigated neutron-damaged condition.
In the present work we give an overview about major influence factors on irradiation-induced microstructural changes. Increase of neutron exposure gives rise to an increase of the volume fraction of solute clusters. This susceptibility is essentially determined by the existing alloying elements and impurities. Cu-rich precipitates are the dominant type of nanofeatures in Cubearing steels (Cu> 0.1wt%) and Mn-Ni-(Si) precipitates or their nonequilibrium precursors are the dominant type of nanofeatures in low-Cu, Mn-Ni-alloyed ferritic materials. The size of clusters remains small and does not exceed a radius of 4 nm. In recent years, research was focussed on the transferability from accelerated irradiations to real operation conditions of materials in a power reactor, for instance the effect of neutron flux on irradiation-induced damage. Here, SANS results show a clear trend. The size distribution of low flux condition is shifted towards larger radii. The effect of neutron flux on the volume fraction of irradiationinduced clusters is not so obvious. There seems to be a trend that the cluster volume fraction decreases at increasing flux. Here, the detection limits of SANS (very small clusters and/or reduced scattering contrast) and the uncertainties of the irradiation conditions possibly hide an explicit flux dependence. Differences in the A-ratio were not observed for flux pairs of one and the same material. Thus, no significant changes of cluster composition appear at different fluxes.
Strong and robust correlations between SANS-based characteristics of irradiation-induced clusters, such as (the square-root of) volume fraction and irradiation-induced changes of mechanical properties, such as Vickers hardness, yield stress or brittle/ductile transition temperature are confirmed.

Keywords: small-angle neutron scattering; irradiation-induced clusters; reactor pressure vessel steel

  • Poster
    canSAS XI workshop, 08.-11.07.2019, Freising, Deutschland

Publ.-Id: 29440

Flux effect on RPV materials

Ulbricht, A.

The effect of neutron flux on the irradiation-induced microstructure and mechanical behaviour is one of the still open issues for the scientific community both for RPV steels and internals. In the case of RPV steels, more and statistically more reliable microstructural data are needed, in particular for low-Cu RPV steels irradiated up to high fluence. Within SOTERIA, suitable pairs of low-Cu RPV steels irradiated at different flux up to the same levels of fluence were identified.
This deliverable D2.1 reports about the effect of neutron flux on the neutron-irradiation-induced microstructure of RPV base and weld materials. The main methods applied are small-angle neutron scattering (SANS), positron lifetime spectroscopy (PAS), transmission electron microscopy (TEM) and atom probe tomography (APT).
Using these methods, a number of different kinds of irradiation-induced nanofeatures were detected. These comprise dislocation loops, vacancies, sub-nm vacancy clusters, solute atom clusters and segregated dislocations. Loops are insufficient in number density and vacancy clusters are too small to contribute significantly to the irradiation-induced changes of the mechanical properties, but play a role in the overall evolution of the irradiated microstructures. Solute atom clusters are decisive for irradiation hardening.
SANS and APT indicate a common trend that an increasing flux gives rise to smaller sizes and higher number densities of solute atom clusters. APT additionally shows that the clusters are more dilute at higher flux. The counteracting effects of flux on size and number density of solute atom clusters partly compensate each other and, therefore, rationalize the relative insensitivity of the mechanical properties to the neutron flux.

Keywords: reactor pressure vessel steel; low Cu; microstructure; neutron irradiation; flux effect; vacancy/solute cluster

Related publications

  • Lecture (others)
    SOTERIA Final Workshop, 25.-27.06.2019, Miraflores de la Sierra, Spain

Publ.-Id: 29439

Eulerian-Eulerian two-fluid model for laminar bubbly pipe flows: validation of the baseline model

Liao, Y.; Upadhyay, K.; Schlegel, F.

In the present paper, an Euler-Euler two-fluid model combined with the baseline model, which is a set of closures for the interfacial momentum and turbulence transfer, is validated against experimental data for low Reynolds number bubbly flows in vertical pipes. The model has already been validated for high Reynolds number pipe flows and bubble columns in the previous work (Liao et al., 2019, Chem. Eng. Sci. 202, 55-69). To further substantiate the k-omega SST model with consideration of bubble-induced source included in the baseline model, it is of interest to examine it for low Reynolds number pipe flows, where the bulk is laminar and the transition to turbulence is induced sorely by the agitation of bubbles. Simulations are configured and carried out in the open source CFD code OpenFOAM for eight test cases. Each of them has a different combination of gas and liquid volumetric flow rates. The numerical results are then compared with the experimental data taken from the literature. The comparison is based on different parameters including air void fraction, mean bubble velocity, mean liquid velocity, turbulent kinetic energy and Reynolds shear stress.
Although, mostly, confirming results with the experimental data are presented but further improvement of the model for turbulent transition as well as inter-phase momentum transfer is necessary. Reliable prediction of velocity profile in single-phase and extremely sparse bubbly flow cases is shown, and the phase distribution in fully-developed cases is well captured. In addition to the bulk Reynolds and void fraction, the pipe-to-bubble size ratio is found to have definite influence on the laminar-turbulent transition.

Keywords: Baseline model; Bubbly flows; Bubble-induced turbulence; Low-Re (Reynolds) flows; OpenFOAM


Publ.-Id: 29438

Benchmarking of CFD modelling closures for two-phase turbulent bubbly flows

Colombo, M.; Rzehak, R.; Fairweather, M.; Liao, Y.; Lucas, D.

Eulerian-Eulerian computational fluid dynamic models are used in the prediction of multiphase gas-liquid flows in nuclear reactor thermal hydraulics and in many other chemical and process engineering applications. The modelling approach, based on the concept of interpenetrating continua, allows the calculation of complex and large-scale industrial flows with a relatively limited computational load. However, interfacial transfer processes need to be entirely modelled through numerous closure relations. A large number of different optimized closure sets are available, each often showing remarkable accuracy, but generally only over a few experimental data sets. This specificity makes it difficult to compare the overall accuracy of the models and obstructs the development of more general and robust approaches. In this paper, the bubbly flow models developed at the University of Leeds and the Helmholtz-Zentrum Dresden - Rossendorf are benchmarked against relevant experiments. These two research groups follow a similar modelling approach, aimed at identifying a single universal set of widely applicable closures. The models, implemented respectively in Star-CCM+ and CFX, are applied to a large selection of bubbly flows in different geometries. The main focus is on the momentum transfer, mainly responsible for the lateral bubble distribution in any flow, and on turbulence closures. Therefore, monodispersed bubbly flows that can be effectively characterized with a single average bubble diameter are selected. Overall, the models are found to be generally reliable and robust, and additional developments towards further improved accuracy, increased generality and the definition of a common unified set of model closures are identified. In future, additional benchmark exercises of this kind will be performed, and potentially the definition of proven sets of reference experiments will be recommended.

Keywords: CFD; bubbly flows; two-fluid model; baseline closure; void distribution; two-phase turbulence

  • Contribution to proceedings
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, Oregon, USA

Publ.-Id: 29437

ATM controls improved DNA repair and mitochondria transfer between neighboring cells

Jin, S.; Cordes, N.


In multicellular tissue, the cells communicate constantly with their environment including neighboring cells as well the extracellular matrix by giving and receiving signals for their vitality and homeostasis. Accumulated evidence has shown the exposure to genotoxic agents such as ionizing radiation can be detrimental in non–target bystander cell, however, little is known mechanistically about the prosurvival impact of unexposed neighboring cells on genotoxically injured cells. In this study, we explored how feedback signals from non–target cells facilitate the dynamic of mitochondrial fusion and fission and modify DNA damage repair in genotoxically damaged target cells.


We performed super resolution 3D imaging in combination with cell biological, biochemical and biophysical methods in a coculture model system deployed of different cell types (MiaPaCa 2 human pancreatic cancer cells; ATM wildtype (wt) and ATM knockout fibroblasts, as well ATM and DNA-PK inhibitor treated ATM wt). We tracked fluorescently labeled mitochondria in living cells and analyzed their morphology upon irradiation with or without combination of pharmaceutical compounds treatment. We further measured the foci resolution dynamics in cells exposed to x-rays (i.e. target cells), which were cultured in the presence or absence of undamaged cells using different markers (53BP1, phospho–Histone H2A.X S193 (γ–H2AX), phospho–ATM S1981 and phospho–DNA PKcs S2056).


Our data show that (i) bilateral transfer of mitochondria between target (irradiated) and non-target cells occurs in a ATM-dependently manner; (ii) DNA damage repair in target (irradiated) cells is accelerated through the presence of non-target cells in both not only in ATM wt and cells but also in ATM deficient fibroblastscells; (iii) cell cycle distribution in target cells is substantially different in co–cultured target cells as compared to mono-cultures of target cells; and (iv)a functional microtubules system is required for this intercellular signaling through direct cell–to–cell contact.


Our data suggest that ATM is be a key determinant transducer for DNA damage repair in in cell–to–cell communication. ATM provides yet to be identified cues that signaling regulates radiogenic DNA damage repair in neighboring target cells, and intercellular mitochondria transfer in a manner dependent on the microtubules system. and It benefits the fusion between radiation damaged and healthy mitochondria restoring a healthy mitochondria system, which originated from different cell populations. from non-target to target cells in a manner dependent on the microtubule system. Consequently, normal cells support each other in surviving radiogenic DNA damage, while cancer cells might be prone to develop resistances to current radiochemotherapies – all of which are critical for general survival of multicellular organs including tumors.

Keywords: ATM; Cell-cell communication

  • Lecture (Conference)
    DeGBS, 23.09.2019, Mannheim, Deutschland

Publ.-Id: 29436

The intermediate filament synemin regulates non-homologous end joining DNA repair upon genotoxic damage in an ATM dependent manner

Deville, S. S.; Vehlow, A.; Förster, S.; Dickreuter, E.; Borgmann, K.; Cordes, N.

Background: Therapy resistance is a great challenge during cancer treatment. A well-known determinant of radiochemoresistance is cell adhesion to extracellular matrix. Targeting focal adhesion proteins (FAPs) has been shown to enhance cancer radiochemosensitivity in various tumor entities. Previous studies demonstrated a functional crosstalk between specific FAPs and DNA repair processes; however, the molecular mechanism remains unsolved. This study aimed to identify alternative FAPs associated with DNA damage repair mechanisms and radioresistance in head and neck squamous cell carcinomas (HNSCC).
Materials and Methods: A novel 3D High Throughput RNAi Screen (3DHT-RNAi-S) using laminin-rich extracellular matrix was established to determine radiation-induced residual DNA double strand breaks (DSBs) and clonogenic radiation survival using UTSCC15 cells expressing pEGFP-53BP1. Validations were performed in 10 3D grown HNSCC cell lines. DNA repair mechanisms, protein expression and kinetics post irradiation were investigated using immuno-fluorescence/-blotting, reporter assays for DSB repair activity and kinase activity profiling (PamGene) upon protein knockdown with/-out X-ray exposure. Protein-protein interactions were determined using immunoprecipitation (IP) and proximity ligation assay.
Results: In the 3DHT-RNAi-S, Synemin emerged as resulted one of the most promising candidates to determine HNSCC cell radiosensitivitysurvival and DNA damage repair. Synemin silencing radiosensitized HNSCC cells, while its exogenous overexpression induced radioprotection. Synemin depletion elicited a 40% reduction in non-homologous end joining activity without affecting other DNA DSB repair mechanisms. In line, ATM, DNA-PKcs and c-Abl phosphorylation as well as Ku70 expression strongly declined in synemin depleted and irradiated cells relative to controls. In kinome analysis, tyrosine kinases showed significantly reduced activity after synemin silencing relative to controls. Furthermore, IP revealed a protein complex formed between synemin, DNA-PKcs and c-Abl. This protein complex dispersed when ATM was pharmacologically inhibited. Using different protein constructs of synemin (ΔLink-Tail, ΔHead-Link, Synemin_301-961, Synemin_962-1565, S1114A and S1159A), the phosphorylation site at the serine 1114 located on the distal portion of synemin´s tail was identified as essential protein-protein interaction site involved in synemin´s function in DNA repair. Using different protein constructs with domain deletions of synemin, the distal portion of synemin´s tail was identified as essential protein site regulating synemin´s function in DNA repair processes.
Conclusions: The 3DHT-RNAi-S provides a robust screening platform for identifying novel targets involved in therapy resistance. Based on this screen and detailed mechanistic analyses, the intermediate filament synemin was discovered as a novel important determinant of DNA repair, tyrosine kinase activity and radioresistance of HNSCC cells. These results fundamentally support the concept of cytoarchitectural elements as co-regulators of nuclear events.further support the concept that DNA repair is regulated by cooperative interactions between nuclear and cytoplasmic proteins.

Keywords: Radioresistance; HNSCC; Synemin

  • Lecture (Conference)
    DeGBS, 23.09.2019, Mannheim, Deutschland

Publ.-Id: 29435

Inhibition of β1 Integrins Increases Radiosensitivity in Therapy-Naïve and –Resistant Pancreatic Cancer Cell Lines

Görte, J.; Cordes, N.

Introduction: Despite some therapeutic progress, pancreatic ductal adenocarcinoma (PDAC) remains hard to treat. Disruption of cell adhesion to extracellular matrix (ECM) in this tumor entity with an ECM-rich microenvironment and an overexpression of integrin cell adhesion molecules, including β1 integrins, seems promising. As the efficacy of β1 integrin targeting and its underlying mechanisms remain elusive, this study aims to decipher the potential of β1 integrin inhibition in therapy-naïve and -radioresistant PDAC cells.
Methods: We investigated the effect of the β1 integrin inhibitory antibody AIIB2 on cell survival after irradiation, chemotherapy or their combination in six therapy-naïve and one therapy-resistant pancreatic cancer cell lines using 3D, matrix-based colony formation assays. In addition to TCGA transcriptome data sets (Oncomine, OncoLnc, COSMIC), siRNA-mediated knockdown and stable overexpression of Itgb1, protein expression and phosphorylation (Western blot, immunofluorescence staining) were employed. A broad-spectrum kinase activity profiling of phosphotyrosine kinases (PTKs) and serine/threonine kinases (STKs) by PAMgene technology was conducted to characterize therapy-naïve and -resistant PDAC cells.
Results: TCGA mRNA data analysis showed a strong correlation of high β1 integrin expression with shorter survival of PDAC patients. AIIB2, similar to knockdown, significantly enhanced the radiosensitivity of all tested cell lines differing in β1 integrin expression levels. We observed a cell line-dependent reduction of the SF6 by 2- to more than 7-fold. Likewise, sensitization to radiochemotherapy as well as sensitization of the radioresistant cell line down to the level of the therapy-naïve cell line is accomplished by AIIB2. Kinase activity profiles demonstrated a higher degree of deactivation in PTKs than STKs after AIIB2 in therapy-naïve cells; a finding similarly found in resistant cells. However, comparison of naïve and -resistant cell populations showed different kinases to be altered specifically. Validation experiments are on-going.
Conclusion: Our results reveal, like in other tumor types, β1 integrins as potential targets in per se therapy-sensitive and -resistant PDAC cells. We demonstrate that different molecular mechanisms and signaling proteins associated with β1 integrins elicit therapy-resistance, thus, providing multiple options for therapeutic multi-targeting intervention.

Keywords: beta1 Integrin; Radiotherapy; pancreatic cancer

  • Poster
    DeGBS, 23.09.2019, Mannheim, Deuntschland

Publ.-Id: 29434

Das Adapterprotein Lamellipodin ist involviert in die Strahlenresistenz und Invasion von Glioblastomzellen

Moritz, S.; Cordes, N.; Krause, M.; Vehlow, A.

Fragestellung: Die Prognose von Patienten mit einem Glioblastom (GBM) ist trotz eines multimodalen Therapieansatzes sehr schlecht, weshalb die zugrundeliegenden . Zur Entwicklung effizienterer Therapien ist das Verständnis komplexer molekularer Resistenzmechanismen besser aufgeklärt werden müssen bedeutend. Es ist bekannt, dass Interaktionen von GBM Zellen mit zellulären und nicht-zellulären Faktoren im Tumormikromilieu entscheidend zu Invasion und Therapieresistenzen von GBM-Zellen beitragen. Die Kommunikation zwischen Zellen und dem Tumormikromilieu führen zu Adaptionen intrazellulärer Signalkaskaden, welche unter anderem von dem Signaladapterp-Protein Lamellipodin (Lpd), dessen Funktion in GBM-Zellen unklar ist, vermittelt werden. Die Funktion von Lpd in GBM ist bisher nicht erforscht. In der vorliegenden Studie evaluieren wir die Rolle von Lpd für die GBM Invasion und Radioresistenz und charakterisieren den zugrundeliegenden molekularen Mechanismus.
Methodik: Die Invasionsfähigkeit acht verschiedener GBM Zellen wurde in einer dreidimensionalen Kollagen Typ-1 Matrix nach siRNA-vermittelten Lamellipodin oder Kontroll Knockdown analysiert. Das klonogene Überleben und residuale DNA Doppelstrangbrüche (γH2AX/53BP1) wurden nach Lpd Depletion und Röntgenbestrahlung (2, 4, 6 Gy) evaluiert. Die Lpd Expression und Phosphorylierungsstatus (Y426, Y1226) wurden mittels Western Blot in acht GBM Zelllinien zu verschiedenen Zeitpunkten (0,5 24 h) nach Röntgenbestrahlung mit 6 Gy analysiert. Direkte Lpd Interaktionspartner wurden mittels Massenspektrometrie von Lpd Immunpräzipitataten nach Röntgenbestrahlung ermittelt und mittels Datenbankanalyse ausgewertet (Reactome, Gene Ontology).
Ergebnisse: Lpd Knockdown reduzierte in allen getesteten, untershiedliche PLpd-Level aufweisende GBM Zellkulturen die Invasionskapazität und führte zu einer signifikanten Strahlensensibilisierungtivierung in vier von acht GBM Zelllinien. Dieser Effekt ging mit einer erhöhten Anzahl von γH2AX/53BP1-positiven residualen DNA-Doppelstrangbrüchen nach Bestrahlung und Lpd Depletion einher. Die basale Expression und Phosphorylierung von Lpd variierte in den verschiedenen GBM Zelllinien. Eine Bestrahlung mit 6 Gy Röntgen führte zu einem Anstieg in der Lpd Phosphorylierung Y1226 nach 1 h bis zu 24 h, wohingegen die Lpd Expression unverändert blieb. Nach Bestrahlung wurden mittels Immunpräzipitation und anschließender massenspektrometrische Analyse 56 potentielle Lpd Interaktionspartner identifiziert. Die funktionelle Datenbankanalyse der Interaktoren ergab einen hohen Anteil an Interaktionspartnern, die in den vesikulären Transport, Metabolismus und Signaltransduktion involviert sind.
Schlussfolgerung: Zusammenfassend zeigen die Ergebnisse eine bedeutende Funktion von Lpd bei der Invasion und Radioresistenz von Glioblastomen. Nachfolgende Untersuchungen fokussieren sich auf die Evaluierung und Charakterisierung des zugrunde liegenden molekularen Signalweges.

Keywords: Gliom; Radiotherapie

  • Poster
    DEGRO, 14.06.2019, Münster, Deutschland

Publ.-Id: 29433

Die Hemmung von beta1 Integrinen führt zu einer gesteigerten Strahlenempfindlichkeit in therapie-naiven und -resistenten Pankreaskarzinomzelllinien

Görte, J.; Cordes, N.

Fragestellung: Trotz großer Fortschritte in der Therapie des Adenokarzinoms des Pankreas (PDAC) ist die Prognose schlecht. Obwohl das therapiesensibilisierende Potenzial einer Hemmung von β1 Integrinen in diversen Malignomen bekannt ist, unterscheiden sich die zugrundeliegenden Mechanismen zwischen den Tumortypen teilweise beträchtlich. Sie sind jedoch sowohl für Patientenstratifizierung als auch Entwicklung von Multi-Targeting Therapien in Kombination mit konventioneller Radiochemotherapie entscheidend. In der vorliegenden Studie widmen wir uns der Sensibilisierung von therapie-naiven und therapieresistenten Pankreaskarzinomzellen durch Antikörper-basierte β1 Integrin Hemmung und beleuchten, einerseits, die sich überlappenden und, andererseits, die sich unterscheidenden Mechanismen.
Methodik: In physiologischeren Matrix-basierten 3D-Zellkulturen wird der Effekt des β1 Integrin blockierenden Antikörpers AIIB2 auf das Überleben nach Bestrahlung, Chemotherapie oder die Kombination mit Koloniebildungsassays in sechs therapienaiven Pankreaskarzinomzelllinien sowie einer radioresistenten Zelllinie untersucht. Proteinexpression und Signaltransduktion werden mittels Western Blot und Immunfluoreszenz analysiert. Zur molekularen Charakterisierung von therapie-naiven und therapieresistenten Pankreaszellen wird eine Kinomanalyse durchgeführt.
Ergebnis: Die Analyse von TCGA Daten zeigt eine starke Korrelation zwischen hoher Expression des β1 Integrins auf mRNA-Ebene mit kürzerem Überleben von PDAC Patienten. Passend zu diesen Daten reagieren alle untersuchten Zelllinien, die unterschiedliche β1 Integrin Expressionslevel aufweisen, auf AIIB2 mit hoch signifikanter Steigerung der Strahlenempfindlichkeit. Zelllinien-abhängig wird die SF6 um das 2- bis 7-fache gesenkt. Interessanterweise wird auch die signifikant radioresistentere Zelllinie durch AIIB2 erneut auf das Niveau der therapie-naiven sensibilisiert. Je nach untersuchter Zelllinie führt die AIIB2-Gabe zudem zu einer Radiochemosensibilisierung. FAK, eine für das zelluläre Überleben bedeutende Kinase, die nach Bestrahlung stärker aktiviert vorliegt, zeigt nach β1 Integrin Hemmung eine deutliche Dephosphorylierung. Die Kinomanalyse von über 150 Tyrosin- und über 150 Serin/Threoninkinasen inklusive biostatistischer Auswertung befindet sich in der Finalisierung.
Schlussfolgerung: Unsere Ergebnisse zeigen auch im Pankreaskarzinom eine besondere Rolle des β1 Integrins für Therapiesensibilisierung und Resistenz, die wir uns zu Nutze machen wollen. Interessant ist die Beobachtung, dass Tumorzellen keine Resistenz für eine β1 Integrin Hemmung entwickeln und therapieresistente Zellen effektiv radiochemosensibilisert werden können. Erste Einblicke in die molekularen Mechanismen dieser potenziellen und potenten molekularen Targetingstrategie für das PDAC werden präsentiert.

Keywords: beta1 Integrin; Radiotherapie; Pankreaskarzinom

  • Poster
    DEGRO, 14.06.2019, Münster, Deutschland

Publ.-Id: 29432

Emerging Noble Metal Aerogels: State of the Art and a Look Forward

Du, R.; Fan, X.; Jin, X.; Hübner, R.; Hu, Y.; Eychmüller, A.

Noble metal aerogels (NMAs), as the most important class of noble metal foams (NMFs), appear as emerging functional porous materials in the field of materials science. Combining the irreplaceable roles of noble metals in certain scenarios, as well as monolithic and porous features of aerogels, NMAs can potentially revolutionize diverse fields, such as catalysis, plasmonics, and biology. Despite profound progress, grand challenges remain in their fabrication process, including the efficient structure control, the comprehensive understanding of the formation mechanisms, and the generality of the fabrication strategies, thus inevitably retarding the material design and optimization. This Perspective focuses on the key progress, especially of the fabrication strategies for NMAs during the last two decades, while other NMFs are also succinctly introduced. Challenges and opportunities are summarized to highlight the unexploited space and future directions in expectation of stimulating the broad interest of interdisciplinary scientists.

Related publications

Publ.-Id: 29431

Extending the temperature sensing range using Eu3+ luminescence up to 865 K in a single crystal of EuPO4

Sharma, S.; Köhler, T.; Beyer, J.; Fuchs, M.; Gloaguen, R.; Heitmann, J.

The temperature evaluation through the measurement of emission intensities (intensity ratio method) require two distinct bands; one of which is used as a reference, and the emission intensity of other is monitored as a function of a change in temperature. Herein, we report the influence of excitation wavelengths, and a coupling scheme between lanthanoid and defect emission from the host lattice, to extend the temperature sensing range by using a single crystal of europium (III) phosphate. The temperature dependence of emission intensity was studied for different excitation wavelengths: 365 (intraconfigurational 4f2 excitation), 338 (defect excitation), and 254 nm (O2- →Eu3+ charge-transfer excitation), in the temperature range, 293--865 K. We determined the Boltzmann equilibrium among different coupling schemes using a linear regression model to infer that for an excitation at 338 nm wavelength, and evaluating the intensity ratio between defect emission and the Eu3+ 5D0,1 → 7FJ transitions, the temperature sensing range can be extended upto at least 865 K, with relative sensitivity in the range, 0.33-1.94%K-1 (at 750 K). The results showed resolution of < 1 K with an excellent reproducibility, suggesting that the thermometers can be used with high reliability.

Keywords: photoluminescence; Eu3+ doping; temperature sensing; relative sensitivity

Publ.-Id: 29430

Achieving optimal laser-proton acceleration through multi-parameter interaction control

Obst-Hübl, L.

Relativistic laser-driven plasmas can be the source of energetic proton beams and have received increasing attention due to their high potential as compact and cost-efficient medical particle accelerators for radiation therapy. As such, exploring viable routes to scale the maximum proton energy to the medically relevant regime remains the subject of ongoing efforts in the Field. This endeavor is inherently linked to the discernment and control of seminal aspects of the acceleration process, ranging on vast temporal and spatial ranges due to highly variable plasma densities and laser intensities within one single interaction. This thesis investigates laser-proton acceleration on various physical scales and the influence of realistic laser pulse parameters, to ultimately find an optimum regime for stable proton beam production with highest particle energies. Experimental studies following this objective were primarily conducted at the high-power titanium:sapphire laser system Draco 150 TW at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Efficient on-demand control of the temporal laser pulse history was established in the form of a plasma mirror filter combined with on-shot temporal pulse contrast characterization based on an advanced spectral interferometry diagnostic. This allowed for experiments with variable pulse contrast, thus providing additional handles for proton source optimization and additionally, extending the selection of applicable interaction targets to lower thicknesses and densities. Studies with novel target technologies such as ultra-thin liquid crystal films and solid hydrogen jets were performed, each at optimized acceleration conditions, resulting in excellent proton beams with high energies and particle numbers that promise to be highly scalable with increasing laser intensities. Elaborate diagnostic suites in combination with numerical simulations delivered an improved picture of the acceleration process, which generally remains difficult to assess experimentally on the microscopic spatial and ultrafast temporal scale. As an important result, the onset of relativistic target transparency was observed for ultra-thin liquid crystal films, an operation regime that may deliver increased proton energies when optimized. Proton acceleration results from the hydrogen jet agreed well with predictive particle-in-cell simulations, thus establishing a test bed for closely linked experimental and numerical studies into advanced acceleration mechanisms, as are for example associated with target transparency. Furthermore, an unexpected proton beam structuring effect was discovered that can play a significant role in experiments with transparent or very small targets. Formerly unrecognized by the community, this effect leads to the extension of spatial and temporal interaction scales beyond the initial proton acceleration in the laser focus, that need to be considered for appropriate interpretation of proton profile signatures.

  • Doctoral thesis
    TU Dresden, 2019
    Mentor: Dr. Karl Zeil
    150 Seiten
    DOI: 10.5281/zenodo.3252952
  • Lecture (others)
    Verteidigungsvortrag, 18.06.2019, Dresden, Deutschland

Publ.-Id: 29429

Investigation of Bubble Plume Oscillations by Euler-Euler Simulation

Fleck, S.; Rzehak, R.

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. An ongoing effort at HZDR has led to a validated set of closures for adiabatic bubbly flows that is applicable under a rather broad range of conditions including flows in pipes and bubble columns. Up to now, however, only flows with stationary mean values have been considered. The present contribution extends the model validation to dynamic flow phenomena by considering a periodically oscillating bubble plume. Consequently, the turbulence model then runs in URANS mode. Literature data for a partially aerated flat rectangular bubble column are used for comparison. In particular, results for the plume oscillation period show good agreement between simulation and experiment.

Keywords: bubble columns; dispersed gas liquid multiphase flow; Euler-Euler two fluid model; closure relations; CFD simulation; model validation

  • Open Access Logo Chemical Engineering Science 207(2019), 853-861
    DOI: 10.1016/j.ces.2019.07.011
    Cited 13 times in Scopus
  • Lecture (Conference)
    Jahrestreffen der ProcessNet-Fachgruppe „Computational Fluid Dynamics“, 19.-20.03.2019, Frankfirt/Main, Deutschland


Publ.-Id: 29428

Electron transport through NiSi2-Si contacts and their role in reconfigurable field-effect transistors

Fuchs, F.; Gemming, S.; Schuster, J.

A model is presented which describes reconfigurable field-effect transistors (RFETs) with metal contacts, whose switching is controlled by manipulating the Schottky barriers at the contacts. The proposed modeling approach is able to bridge the gap between quantum effects on the atomic scale and the transistor switching. We apply the model to transistors with a silicon channel and NiSi2 contacts. All relevant crystal orientations are compared, focusing on the differences between electron and hole current, which can be as large as four orders of magnitude. Best symmetry is found for the < 110 > orientation, which makes this orientation most advantageous for RFETs. The observed differences are analyzed in terms of the Schottky barrier height at the interface. Our study indicates that the precise orientation of the interface relative to a given transport direction, perpendicular or tilted, is an important technology parameter, which has been underestimated during the previous development of RFETs. Most of the conclusions regarding the studied metal-semiconductor interface are also valid for other device architectures.

Keywords: density functional; nanowire; nanoelectronics; NanoNet; device modeling; interface; silicide; silicon


Publ.-Id: 29427

Organic Iron Complexes Enhance Iron Transport Capacity along Estuarine Salinity Gradients

Herzog, S. D.; Kvashnina, K.; Persson, P.; Kritzberg, E.

Rivers discharge a notable amount of Fe (1.5 x 109 mol yr−1) to coastal waters, but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently however, several studies demonstrate relatively high stability of riverine Fe to salinity induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can “survive” the salinity gradient, while Fe (oxy)hydroxides are prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn, and that Fe-OM was more dominant in low-order streams in a catchment than at the river mouth. The stability of Fe to increasing salinity correlated well to the relative contribution of Fe-OM, i.e. confirming that organic complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amounts of potentially bioavailable Fe to marine waters beyond the estuary, due to organic matter complexes

Publ.-Id: 29426

Dual-time-point 64Cu-PSMA-617-PET/CT in patients suffering from prostate cancer

Hoberück, S.; Wunderlich, G.; Michler, E.; Hölscher, T.; Walther, M.; Seppelt, D.; Platzek, I.; Zöphel, K.; Kotzerke, J.

Regardless of its high positron energy, 68Ga-labeled PSMA ligands have become standard of care in metabolic prostate cancer imaging. 64Cu, a radionuclide with a much longer half-life (12.7 h), is available for PSMA labeling allowing imaging much later than 68Ga. In this study, the diagnostic performance of 64Cu-labeled PSMA was compared between early and late scans. Sixteen men (median age: 70 y) with prostate cancer in different stages underwent 64Cu-PSMA-617-PET/CT 2 and 22 hours post tracer injection. Pathologic and physiologic uptakes were analyzed for both points of time. Pathologic tracer accumulations occurred in 12 patients. Five patients presented with pathologic uptake in 17 different lymph nodes, two patients showed pathologic bone uptake in nine lesions, and seven patients had pathologic PSMA uptake in eight prostatic lesions. Physiologic uptake of the renal parenchyma, urine bladder, and salivary glands decreased over time, while the physiologic uptake of liver and bowel increased. In the present study, 64Cu-PSMA-617-PET demonstrated to be feasible for imaging prostate cancer for both the primary tumor site and metastases. Later imaging showed no additional, clinically relevant benefit compared with the early scans. At least the investigated time points we chose did not vindicate the additional expenditure.

Keywords: 64Cu; dual time; PET; prostate cancer; PSMA


Publ.-Id: 29425

Spin textures and spin waves as seen by x-ray microscopy

Wintz, S.

The investigation of spin-wave phenomena, also referred to as magnonics, plays an important role in present condensed matter research. This holds true, in particular, as spin waves are seen as signal carriers for future spintronic information processing devices, with a high potential to outperform present charge-based technologies in terms of energy efficiency and device miniaturization. Yet a successful implementation of magnonic technology will require the usage and control of spin waves with nanoscale wavelengths. Here, I will show that ferromagnetic spin textures in metallic systems can be used as nanoscale spin-wave emitters and wave guides. In particular, topological spin vortex cores prove to act as efficient and tunable generators for sub-100 nm waves, while domain walls can be utilized as quasi one-dimensional channels for spin-wave propagation and routing. The underlying spin dynamic processes were directly imaged by using time-resolved x-ray microscopy.

Related publications

  • Invited lecture (Conferences)
    NAP 2019, 15.-20.09.2019, Odessa, Ukraine
  • Invited lecture (Conferences)
    Challenges & Opportunities in X-Ray Microscopy, 11.-15.02.2019, Kreuth (Schloss Ringberg), Deutschland
  • Invited lecture (Conferences)
    SpinS-2019, 02.-04.10.2019, Duisburg, Deutschland

Publ.-Id: 29424

Decoherence of collective motion in warm nuclei

Frauendorf, S.; Petrache, C.; Schwengner, R.; Wimmer, K.

Collective states in cold nuclei are represented by a wave function that assigns coherent phases to the participating nucleons. The degree of coherence decreases with excitation energy above the yrast line because of coupling to the increasingly dense background of quasiparticle excitations. The consequences of decoherence are discussed, starting with the well studied case of rotational damping. In addition to superdeformed bands, a highly excited oblate band is presented a new example of screening from rotational damping. Suppression of pair correlation leads to incoherent thermal M1 radiation, which appears as an exponential spike (LEMAR) at zero energy in the gamma strength function of spherical nuclei. In deformed nuclei a Scissors Resonance appears and LEMAR changes to damped magnetic rotation, which is interpreted as partial restoration of coherence.

Keywords: Collective motion in atomic nuclei; quantal coherence; collective bands; rotational damping; magnetic rotation; thermal M1 radiation; Scissors resonance

Publ.-Id: 29423

ExploreASL: a collaborative effort to process and explore multi-center ASL data

Mutsaerts, H. J.; Petr, J.; Groot, P.; Ingala, S.; Robertson, A.; Vaclavu, L.; Groote, I.; Kuijf, H.; O'Daly, O.; Zelaya, F.; Vandemaele, P.; Wink, A. M.; Kant, I.; Caan, M.; Morgan, C.; de Bresser, J.; Lysvik, E.; Schrantee, A.; Shirzadi, Z.; Kuijer, J. P. A.; Anazodo, U.; Richard, E.; Bokkers, R.; Reneman, L.; Masellis, M.; Achten, E.; Günther, M.; Macintosh, B.; Golay, X.; Hendrikse, J.; Chapell, M.; van Osch, M.; Thomas, D.; de Vita, E.; Bjornerud, A.; Nederveen, A.; Asllani, I.; Barkhof, F.

Arterial spin labeling (ASL) has undergone significant development since its inception; yet, standardized images processing procedures remain elusive. We present ExploreASL, a robust open source ASL image processing pipeline for clinical studies. Initiated through the European COST action ASL network, this joint effort provides integration and analysis of both single- and multi-center datasets across different operating systems. ExploreASL is optimized for both native- and standard-space analyses, and provides visual and automatic quality control on all intermediate and final images, allowing exploration of ASL datasets from multiple perspectives.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2705
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29422

Hemodynamic impairments in asymptomatic unilateral carotid artery stenosis are increased within individual watershed areas

Kaczmarz, S.; Goettler, J.; Petr, J.; Hansen, M. B.; Kufer, J.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.

Internal carotid-artery stenosis (ICAS) causes complex and not yet well understood physiological impairments, which currently limits treatment decisions. We present multimodal perfusion and oxygenation-related MRI-data from unilateral asymptomatic ICAS-patients and age-matched healthy controls. The major aim was to investigate hemodynamic impairments in ICAS within individually defined watershed areas (iWSA’s) to account for individual vascular configurations. We found statistically significant lateralization of hemodynamic parameters within iWSA’s - strongest in WM of iWSA’s. Therefore, our iWSA-based approach facilitates detection of even subtle hemodynamic changes in ICAS. Furthermore, we detected spatially widespread capillary flow heterogeneity increases which are promising future treatment indicators.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 3246
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29421

Recovery of cerebrovascular reactivity after asymptomatic carotid artery stenosis treatment is assessable by Breathhold-fMRI within global watershed areas

Kaczmarz, S.; Goettler, J.; Sollmann, N.; Kufer, J.; Hansen, M. B.; Hock, A.; Sorg, C.; Zimmer, C.; Mouridsen, K.; Hyder, F.; Preibisch, C.; Petr, J.

Asymptomatic unilateral internal carotid-artery stenosis (ICAS) causes complex and currently poorly understood hemodynamic impairments which could possibly improve treatment decisions. Cerebrovascular reactivity (CVR) is an important biomarker of vascular health and can potentially serve to evaluate ICAS-treatment efficacy. We present perfusion MRI-data from a longitudinal study in 16 asymptomatic ICAS-patients before and after treatment plus 17 age-matched healthy controls. We hypothesize that CVR impairments in ICAS and their recovery after treatment can be assessed by Breathhold-fMRI analyzed by a data-driven approach. Our results demonstrate statistically significant CVR impairments within global watershed areas before treatment and significant CVR recovery after treatment.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0739
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29420

Cerebral hypometabolism measured with intravascular T2-prepared tissue relaxation with inversion recovery (T2-TRIR) and pCASL in adults with sickle cell disease

Vaclavu, L.; Petersen, E. T.; Mutsaerts, H. J.; Petr, J.; Majoie, C. B.; Wood, J. C.; Vanbavel, E. T.; Biemond, B. J.; Nederveen, A. J.

Cerebral metabolic rate of oxygen (CMRO2) quantifies the amount of oxygen consumed by the brain, and relies on continuous delivery of nutrients and oxygen via cerebral blood flow (CBF). In sickle cell disease (SCD), CBF is elevated to compensate for chronic anaemia. This study investigates CMRO2 in adults with SCD using T2-prepared tissue relaxation with inversion recovery (T2-TRIR). CBF increased after acetazolamide-induced vasodilation in both groups but CMRO2 reduced even further in SCD patients while it remained stable in controls. Our results suggest that cerebral shunting is exacerbated by high flow conditions.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 0291
  • Lecture (Conference)
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29419

A multi-site round robin assessment of ASL using a perfusion phantom

Oliver-Taylor, A.; Hampshire, T.; Mutsaerts, H.-J.; Clement, P.; Warnert, E.; Kuijer, J. P. A.; Baas, K.; Petr, J.; Siero, J. C. W.; Marques, J. P.; Sunaert, S.; Borra, R. J. H.; van Osch, M. J. P.; Golay, X.; Achten, E.

Arterial Spin Labelling shows great promise for perfusion measurements; however, despite numerous volunteer reproducibility studies, comparisons have not been made using a phantom to establish differences due to the acquisition hardware and pulse sequences. We present data from a multi-site study using a perfusion phantom, targeting 3T MRI systems from a single vendor running the same software version.

  • Contribution to proceedings
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada
    Proceedings of the ISMRM 27th Annual Meeting & Exhibition, 2653
  • Poster
    ISMRM 27th Annual Meeting & Exhibition, 11.06.2019, Montreal, Canada

Publ.-Id: 29418

Extra-neurite Perfusion Measurement with Combined Arterial Spin Labeling and Diffusion Weighted MRI

Asllani, I.; Petr, J.; Mutsaerts, H.-J.; Bozzali, M.; Cercignani, M.


Arterial Spin Labeling (ASL) is an MRI method that uses magnetically labeled endogenous water as a tracer for measuring cerebral perfusion in vivo1. The arterial water that is usually 'labeled' at a plane positioned at the base of the brain, perpendicular to the carotids. A post-labeling delay (PLD) is introduced prior to acquisition to allow labeled water to cross the vasculature and perfuse into the tissue1. Because of signal decay due to T1 relaxation, fast acquisition schemes are employed to ensure optimal SNR. Consequently, the spatial resolution of ASL is relatively low (~ 3 x 3 x 6 mm3). As such, the measured blood flow from a given voxel reflects a mixture of signals from gray matter (GM), white matter (WM), and CSF, a phenomenon known as partial voluming (PV)2. To correct for the confounding effects of PV in ASL imaging, an algorithm (PVC) has been developed and already used by several studies2,3. The algorithm is based on GM and WM volume data obtained from the segmentation of the T1w image2, and makes no further distinction between different compartments within the same tissue type. Here, we investigated the potential of PVC ASL to map blood perfusion in the extra-neurite compartment (e.g., soma, glial cells4) and the intra-neurite (comprised of axons and axon terminals4) within the same tissue, independently. We applied the PVC algorithm using compartmental data from a diffusion weighted imaging (DWI) model, referred to as NODDI4. The underlying hypothesis was that the blood flow in the extra- and intra-neurite compartments would vary with the PLD; a short PLD acquisition would increase the flow in the extra-neurite compartment compared to the long PLD for which there should be an increased flow in the intra-neurite compartment instead.
At any given voxel, the blood flow (fT) is given as:
where, VFIn, VFEn, VFIso represent respectively: the intra-neurite, extra-neurite, and non-tissue compartments obtained from NODDI4. By assuming that for each compartment blood flow is constant over a 'kernel', the equation can be re-written in vectorial form to reflect the flow at the voxel in the center of the kernel2, from which then each compartmental flow can be computed using linear regression as detailed in Asllani et al.2..

MRI protocol & image analysis
T1w (MPRAGE), NODDI, and ASL MRI images were obtained on 4 healthy participants (mean age = 44.5 ± 7.4 y, 2 men) a Siemens 3T system. To test the hypothesis that a shorter PLD would increase the signal in the extra-neurite GM compartment, ASL was acquired with a short (200ms) and long PLD (1800ms). Only results from voxels with GM content > 80% are presented.
Fig.1 shows the raw images that were used by the PVC algorithm to extract the flow from each compartment within the GM. For the long-PLD acquisition, average CBF in the extra- and intra-neurite compartments was 76 ± 10 mL/100g*min and 59 ± 8 mL/100g*min, respectively. As hypothesized, for the short-PLD, the CBF signal was contained primarily in the extra-neurite department (118 ± 17 mL/100g*min) with the intra-neurite compartment flow being essentially zero (-0.9 ± 0.6 mL/100g*min). Results from one participant are shown in Fig.2.
Supporting Image: Fig1.jpg
·Fig.1: ‘Raw’ NODDI and ASL images used by the PVC algorithm from one subject. Top row: MPRAGE and VFIn images; middle row: VFEn and VFISO; bottom row: CBF for short PLD (left) and long PLD (right).
Supporting Image: Fig2.jpg
·Fig.2: Top: Extra-neurite GM CBF from short (left) & long (right) PLD acquisitions. Bottom: axial and sagittal views of Intra-neurite CBF for long PLD with areas in blue indicating ~zero signal.

We combined NODDI with PVC ASL MRI to distinguish between blood flow in the extra- and intra-neurite compartments within GM. While these initial results look promising, more work is needed to test the sensitivity of this method and its feasibility for clinical applications. For example, a larger PLD range is needed to test whether the method can be used to detect inter-neurite subcortical flow. If successful, this method could prove invaluable in mapping blood flow with high spatial specificity.

Keywords: Cerebral Blood Flow; Data analysis; fMRI CONTRAST MECHANISMS; MRI

  • Open Access Logo Contribution to proceedings
    Organization for Human Brain Mapping Annual Meeting 2019, 09.-13.06.2019, Rome, Italy
  • Open Access Logo Poster
    Organization for Human Brain Mapping Annual Meeting 2019, 13.06.2019, Rome, Italy


Publ.-Id: 29417

Photoelectrocatalytic degradation of emerging contaminants at WO₃/BiVO₄ photoanodes in aqueous solution

Cristino, V.; Pasti, L.; Marchetti, N.; Berardi, S.; Bignozzi, C. A.; Molinari, A.; Passabi, F.; Caramori, S.; Amidani, L.; Orlandi, M.; Bazzanella, N.; Piccioni, A.; Kesavan, J. K.; Boscherini, F.; Pasquini, L.

WO3/BiVO4 films obtained by electrochemical deposition of BiVO4 over mesoporous WO3 were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO3/BiVO4 films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na2SO4 electrolytes.
Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO3/BiVO4 junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO3/BiVO4 interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO4 and a different water oxidation mechanism, the employment of WO3/BiVO4 in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO2 and WO3.

Publ.-Id: 29416

NH₃‑SCR over V−W/TiO₂ Investigated by Operando X‑ray Absorption and Emission Spectroscopy

Doronkin, D. E.; Benzi, F.; Zheng, L.; Sharapa, D. I.; Amidani, L.; Studt, F.; Roesky, P. W.; Casapu, M.; Deutschmann, O.; Grunwaldt, J.-D.

V−W/TiO2-based catalysts, which are used for the removal of NOx from the exhaust of diesel engines and stationary sources via selective catalytic reduction with NH3 (NH3-SCR), were studied by operando X-ray absorption spectroscopy (XAS) and emerging photon-in/photon-out techniques. In order to minimize the influence of highly X-ray absorbing tungsten and the fluorescence of titanium, we used a high-energyresolution fluorescence setup that is able to separate efficiently the V Kβ1,3 emission lines and additionally allows to record valence-to-core (vtc) X-ray emission lines. High-energy resolution fluorescence-detected XAS (HERFD-XAS) and vtc X-ray emission spectroscopy (vtc-XES) proved to be the only way to perform an operando V K edge X-ray spectroscopic study on industrially relevant V−W/TiO2 catalysts so far. The V−W/TiO2 and V/TiO2 samples synthesized by incipient wetness impregnation and grafting exhibited high activity toward NH3-SCR. Raman spectroscopy showed that they mainly contained highly dispersed, isolated, and polymeric V-oxo species. HERFD-XAS and XES identified redox cycling of vanadium species between V4+ and V5+. With respect to most of the potential NH3 adsorption complexes, density functional theory calculations further showed that vtc-XES is more limited than surface-sensitive techniques such as infrared spectroscopy; hence, a combination of X-ray techniques with IR or similar spectroscopies is required to unequivocally identify the mechanism of NH3-SCR over vanadia-based catalysts.


Publ.-Id: 29415

Synthesis and Characterization of an Epidermal Growth Factor Receptor selective Ru(II) Polypyridyl-Nanobody Conjugate as a Photosensitizer for Photodynamic Therapy

Karges, J.; Jakubaszek, M.; Mari, C.; Zarschler, K.; Goud, B.; Stephan, H.; Gasser, G.

There is currently a surge for the development of novel photosensitizers (PSs) for photodynamic therapy (PDT) since those currently approved are not completely ideal. Among the tested compounds, we have previously investigated the use of Ru(II) polypyridyl complexes with a [Ru(bipy)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ scaffold (bipy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2′,3′-c]-phenazine, phen = 1,10-phenanthroline). These complexes selectively target DNA. However, since DNA is ubiquitous, it would be of great interest to increase the selectivity of our PDT PSs by linking them to a targeting vector in view of targeted PDT. Herein, we present the synthesis, characterization and in-depth photophysical evaluation of a nanobody containing Ru(II) polypyridyl conjugate selective for the epidermal growth factor receptor (EGFR) in view of targeted PDT. Using ICP-MS and confocal microscopy, we could demonstrate that our conjugate had a high selectivity for the EGFR receptor, which is a crucial oncological target as it is overexpressed and/or deregulated in a variety of solid tumors. However, contrary to expectations, this conjugate was found to not produce reactive oxygen species (ROS) in cancer cells and to be therefore not phototoxic.

Keywords: Bioinorganic Chemistry; Medicinal Inorganic Chemistry; Metal-based drugs; Metals in Medicine; Photodynamic Therapy

Publ.-Id: 29412

Carrier Flotation: State of the Art and its Potential for the Separation of Fine and Ultrafine Mineral Particles

Eckert, K.; Schach, E.; Gerbeth, G.; Rudolph, M.

Critical raw materials (CRMs) are of primary importance for energy storage systems as needed for electromobility. Many mineral deposits which contain CRMs are low-grade ores. To liberate the CRMs, a grinding of the mineral ores to very fine sizes below 20 µm particle size is necessary. However, the present class of industrial flotation plants fail to extract such fine and ultrafine particles. To improve the recovery in fine particle flotation, techniques have been developed which attempt to agglomerate the fine valuable particles into larger aggregates which subsequently can be separated by established technologies such as froth flotation. Carrier flotation is one of these techniques. The present work reviews the state of the art of this technique for the recovery of fines and ultrafines.

Keywords: Flotation; Fine particles; Carrier Flotation


  • Secondary publication expected

Publ.-Id: 29411

Multidimensional characterization of separation processes – Part 1: Introducing kernel methods and entropy in the context of mineral processing using SEM-based image analysis

Schach, E.; Buchmann, M.; Tolosana Delgado, R.; Leißner, T.; Kern, M.; van den Boogaart, K. G.; Rudolph, M.; Peuker, U. A.

An alternative method for the particle tracking approach for scanning electron microscopy-based image analysis is introduced, using kernel density estimates instead of discrete bins. This allows for information that is more robust. Uncertainties of the data are assessed using the bootstrap resampling method. The presented methodology enables the calculation of multidimensional partition curves, which can be used for a detailed analysis of separation processes. It has been found that the statistical entropy is a helpful tool to evaluate the separation efficiency of these partition maps. The methodology was applied to a density separation process of a cassiteritebearing skarn ore from the Hämmerlein deposit in the Erzgebirge region in Germany, which serves as a case study. A Sepro™ Falcon concentrator was utilized for the density separation.

Keywords: Multidimensional characterization; Partition curve; Separation process; Mineral processing; Kernel density estimation; Entropy; Bootstrap resampling

Publ.-Id: 29410

Uncertainty assessment in particle tracking processing models of cassiterite in complex skarn ores

Schach, E.; Buchmann, M.; Tolosana Delgado, R.; Kern, M.; Leißner, T.; Möckel, R.; van den Boogaart, K. G.; Rudolph, M.; Peuker, U. A.

An alternative method for the particle tracking approach for SEM-based image analysis is introduced, using kernel density estimates instead of discrete bins. This allows to obtain more robust information. Therefore, the bandwidth adjustment for the kernels is of special importance. Uncertainties of the data are assessed using the bootstrap resampling method. The mentioned methodology enables for the calculation of multidimensional partition curves, which can be used for a detailed analysis of separation processes. The measure of the entropy is used to evaluate the separation efficiency of the partition maps. A density separation process, using a falcon separator and a dry magnetic separation process, using a drum type separator serve as case studies for the described methodology. As feed material for the separation processes a cassiterite bearing skarn ore from the Pöhla deposit in the Erzgebirge region in Germany is used.

  • Lecture (Conference)
    Procemin-Geomet 2018, 28.-30.11.2018, Santiago, Chile

Publ.-Id: 29409

Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.] [329.]