Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

29521 Publications
Overexpression of receptor tyrosine kinase EphB4 triggers tumor growth and hypoxia in A375 melanoma xenografts: insights from multitracer small animal imaging experiments
Neuber, C.; Belter, B.; Meister, S.; Hofheinz, F.; Bergmann, R.; Pietzsch, H.-J.; Pietzsch, J.ORC
Experimental evidence has associated receptor tyrosine kinase EphB4 with tumor angiogenesis also in malignant melanoma. Considering the limited in vivo data available, we have conducted a systematic multitracer and multimodal imaging investigation in EphB4-overexpressing and mock-transfected A375 melanoma xenografts. Tumor growth, perfusion, and hypoxia were investigated by positron emission tomography. Vascularization was investigated by fluorescence imaging in vivo and ex vivo. The approach was completed by magnetic resonance imaging, radioluminography ex vivo, and immunohistochemical staining for blood and lymph vessel markers. Results revealed EphB4 to be a positive regulator of A375 melanoma growth, but a negative regulator of tumor vascularization. Resulting in increased hypoxia, this physiological characteristic is considered as highly unfavorable for melanoma prognosis and therapy outcome. Lymphangiogenesis, by contrast, was not influenced by EphB4 overexpression. In order to distinguish between EphB4 forward and EphrinB2, the natural EphB4 ligand, reverse signaling a specific EphB4 kinase inhibitor was applied. Blocking experiments show EphrinB2 reverse signaling rather than EphB4 forward signaling to be responsible for the observed effects. In conclusion, functional expression of EphB4 is considered a promising differentiating characteristic, preferentially determined by non-invasive in vivo imaging, which may improve personalized theranostics of malignant melanoma.
Keywords: Eph receptor tyrosine kinase family; Ephrin ligands; tumor microenvironment; malignant melanoma; small animal positron emission tomography; tumor angiogenesis; tumor hypoxia

Registration No. 27108 - Permalink


Magnetic stirring and sonication of metal melts
Gerbeth, G.
  • Invited lecture (Conferences)
    XVIII International UIE-Congress, 06.-09.06.2017, Hannover, Germany

Registration No. 27103 - Permalink


Experimental Modelling of Metallurgical Processes
Eckert, G.; Gerbeth, S.
  • Invited lecture (Conferences)
    12th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries - SINTEF, 30.05.-01.06.2017, Trondheim, Norway

Registration No. 27102 - Permalink


Interaction of Stem Cell Properties and DNA Repair determine the Radiosensitizing Effect after Inhibition of CHK1, RAD51 and PARP1 in TNBCs
Meyer, F.; Becker, S.; Niecke, A.; Werner, S.; Peitzsch, C.; Hein, L.; Dubrovska, A.; Goy, Y.; Parplys, A.; Petersen, C.; Riepen, B.; Zielinski, A.; Rothkamm, K.; Borgmann, K.

Registration No. 27100 - Permalink


Recent update on the KLOE ISR-measurements
Keshavarzi, A.; Müller, S. E.ORC; Teubner, T.; Venanzoni, G.
Recent updates on KLOE ISR measurements
  • Invited lecture (Conferences)
    Workshop on hadronic vacuum polarization contributions to muon g-2, 12.-14.02.2018, KEK Tsukuba, Japan

Registration No. 27097 - Permalink


Intratumoral heterogeneity and TERT promoter mutations in progressive/higher-grade meningiomas
Juratli, T. A.; Thiede, C.; Koerner, M. V. A.; Tummala, S. S.; Daubner, D.; Shankar, G. M.; Williams, E. A.; Martinez-Lage, M.; Soucek, S.; Robel, K.; Penson, T.; Krause, M.; Appold, S.; Meinhardt, M.; Pinzer, T.; Miller, J. J.; Krex, D.; Ely, H. A.; Silverman, I. M.; Christiansen, J.; Schackert, G.; Wakimoto, H.; Kirsch, M.; Brastianos, P. K.; Cahill, D. P.
Background: Recent studies have reported mutations in the telomerase reverse transcriptase promoter (TERTp) in meningiomas. We sought to determine the frequency, clonality and clinical significance of telomere gene alterations in a cohort of patients with progressive/higher-grade meningiomas.

Methods: We characterized 64 temporally- and regionally-distinct specimens from 26 WHO grade III meningioma patients. On initial diagnoses, the meningiomas spanned all WHO grades (3 grade I, 13 grade II and 10 grade III). The tumor samples were screened for TERTp and ATRX/DAXX mutations, and TERT rearrangements. Additionally, TERTp was sequenced in a separate cohort of 19 patients with radiation-associated meningiomas. We examined the impact of mutational status on patients’ progression and overall survival.

Results: Somatic TERTp mutations were detected in six patients (6/26 = 23%). Regional intratumoral heterogeneity in TERTp mutation status was noted. In 4 patients, TERTp mutations were detected in recurrent specimens but not in the available specimens of the first surgery. Additionally, a TERT gene fusion (LPCAT1-TERT) was found in one sample. In contrary, none of the investigated samples harbored an ATRX or DAXX mutation. In the cohort of radiation-induced meningiomas, TERTp mutation was detected in two patients (10.5%). Importantly, we found that patients with emergence of TERTp mutations had a substantially shorter OS than their TERTp wild-type counterparts (2.7 years, 95% CI 0.9 – 4.5 years versus 10.8 years, 95% CI 7.8 -12.8 years, p=0.003).

Conclusions: In progressive/higher-grade meningiomas,TERTp mutations are associated with poor survival, supporting a model in which selection of this alteration is a harbinger of aggressive tumor development. In addition, we observe spatial intratumoral heterogeneity of TERTp mutation status, consistent with this model of late emergence in tumor evolution. Thus, early detection of TERTp mutations may define patients with more aggressive meningiomas. Stratification for TERT alterations should be adopted in future clinical trials of progressive/higher-grade meningiomas.

Registration No. 27096 - Permalink


Robustness evaluation of single-and multifield optimized proton plans for unilateral head and neck
Cubillos-Mesías, M.; Baumann, M.; Troost, E. G. C.; Appold, S.; Krause, M.; Richter, C.; Stützer, K.

Registration No. 27094 - Permalink


Ein möglicher prognostischer Biomarker für das Therapieansprechen und therapeutisches Zielmolekül zur Strahlensensitivierung in Kopf-Hals-Plattenepithelkarzinomen
Digomann, D.; Kurth, I.; Linge, A.; Hein, L.; Baumann, M.; Dubrovska, A.
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 193(2017), S25-S26

Registration No. 27090 - Permalink


Preparation of small animal irradiation experiments with laser-accelerated protons
Kroll, F.; Beyreuther, E.; Brack, F. E.; Gaus, L.; Karsch, L.; Kraft, S.; Metzkes, J.; Pawelke, J.; Schlenvoigt, H. P.; Schürer, M.; Zeil, K.; Schramm, U.
  • Open Access LogoAbstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 62(2017)Suppl. 1, S239
    DOI: 10.1515/bmt-2017-5044

Registration No. 27087 - Permalink


Origin of field-induced discontinuous phase transitions in Nd2Fe17
Diop, L. V. B.; Kuz'Min, M. D.; Skokov, K. P.; Skourski, Y.; Gutfleisch, O.
Magnetic properties of a trigonal ferromagnet Nd2Fe17 have been studied on single crystals in steady (14 T) and pulsed (32 T) magnetic fields. The easy-magnetization direction lies close to the [120] axis, deviating from the basal plane by 2.9° (at T = 5 K). Of particular interest is the low-temperature magnetization process along the high-symmetry axis [001], which is the hard direction. This process is discontinuous and involves two first-order phase transitions (FOMPs). One of them (at 20 T) is a symmetry FOMP similar to that observed in Sm2Fe17. The second transition (at 10.4 T) is unusual: as the magnetization turns abruptly toward the applied field, it also changes its azimuthal orientation (the angle ϕ) by 60°. Both transitions can be reasonably accounted for by the presence of a significant sixth-order trigonal anisotropy term.

Registration No. 27083 - Permalink


Radiative neutron capture on 242Pu in the resonance region at the CERN n_TOF-EAR1 facility
Lerendegui-Marco, J.; Guerrero, C.; Mendoza, E.; Quesada, J. M.; Eberhardt, K.; Junghans, A. R.; Krtička, M.; Aberle, O.; Andrzejewski, J.; Audouin, L.; Bécares, V.; Bacak, M.; Balibrea, J.; Barbagallo, M.; Barros, S.; Bečvář, F.; Beinrucker, C.; Berthoumieux, E.; Billowes, J.; Bosnar, D.; Brugger, M.; Caamaño, M.; Calviño, F.; Calviani, M.; Cano-Ott, D.; Cardella, R.; Casanovas, A.; Castelluccio, D. M.; Cerutti, F.; Chen, Y. H.; Chiaveri, E.; Colonna, N.; Cortés, G.; Cortés-Giraldo, M. A.; Cosentino, L.; Damone, L. A.; Diakaki, M.; Dietz, M.; Domingo-Pardo, C.; Dressler, R.; Dupont, E.; Durán, I.; Fernández-Domínguez, B.; Ferrari, A.; Ferreira, P.; Finocchiaro, P.; Furman, V.; Göbel, K.; García, A. R.; Gawlik, A.; Glodariu, T.; Gonçalves, I. F.; González-Romero, E.; Goverdovski, A.; Griesmayer, E.; Gunsing, F.; Harada, H.; Heftrich, T.; Heinitz, S.; Heyse, J.; Jenkins, D. G.; Jericha, E.; Käppeler, F.; Kadi, Y.; Katabuchi, T.; Kavrigin, P.; Ketlerov, V.; Khryachkov, V.; Kimura, A.; Kivel, N.; Kokkoris, M.; Leal-Cidoncha, E.; Lederer, C.; Leeb, H.; Lo Meo, S.; Lonsdale, S. J.; Losito, R.; Macina, D.; Marganiec, J.; Martínez, T.; Massimi, C.; Mastinu, P.; Mastromarco, M.; Matteucci, F.; Maugeri, E. A.; Mengoni, A.; Milazzo, P. M.; Mingrone, F.; Mirea, M.; Montesano, S.; Musumarra, A.; Nolte, R.; Oprea, A.; Patronis, N.; Pavlik, A.; Perkowski, J.; Porras, J. I.; Praena, J.; Rajeev, K.; Rauscher, T.; Reifarth, R.; Riego-Perez, A.; Rout, P. C.; Rubbia, C.; Ryan, J. A.; Sabaté-Gilarte, M.; Saxena, A.; Schillebeeckx, P.; Schmidt, S.; Schumann, D.; Sedyshev, P.; Smith, A. G.; Stamatopoulos, A.; Tagliente, G.; Tain, J. L.; Tarifeño-Saldivia, A.; Tassan-Got, L.; Tsinganis, A.; Valenta, S.; Vannini, G.; Variale, V.; Vaz, P.; Ventura, A.; Vlachoudis, V.; Vlastou33, R.; Wallner, A.; Warren, S.; Weigand, M.; Weiss, C.; Wolf, C.; Woods, P. J.; Wright, T.; Žugec, P.
The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with uranium to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. However, an extensive use of MOX fuels, in particular in fast reactors, requires more accurate capture and fission cross sections for some Pu isotopes. In the case of 242Pu there are sizable discrepancies among the existing capture cross-section measurements included in the evaluations (all from the 1970s) resulting in an uncertainty as high as 35% in the fast energy region. Moreover, postirradiation experiments evaluated with JEFF-3.1 indicate an overestimation of 14% in the capture cross section in the fast neutron energy region. In this context, the Nuclear Energy Agency (NEA) requested an accuracy of 8% in this cross section in the energy region between 500 meV and 500 keV. This paper presents a new time-of-flight capture measurement on 242Pu carried out at n_TOF-EAR1 (CERN), focusing on the analysis and statistical properties of the resonance region, below 4 keV. The 242Pu(n,γ) reaction on a sample containing 95(4) mg enriched to 99.959% was measured with an array of four C6D6 detectors and applying the total energy detection technique. The high neutron energy resolution of n_TOF-EAR1 and the good statistics accumulated have allowed us to extend the resonance analysis up to 4 keV, obtaining new individual and average resonance parameters from a capture cross section featuring a systematic uncertainty of 5%, fulfilling the request of the NEA.
Keywords: Neutron physics, nuclear reactions, radiative capture, reactor fuel and coolants, radioactive waste

Registration No. 27080 - Permalink


Electrical properties of surface and interface layers of the N- and In-polar undoped and Mg-doped InN layers grown by PA MBE
Komissarova, T. A.; Kampert, E.; Law, J.; Jmerik, V. N.; Paturi, P.; Wang, X.; Yoshikawa, A.; Ivanov, S. V.
Electrical properties of N-polar undoped and Mg-doped InN layers and In-polar undoped InN layers grown by plasma-assisted molecular beam epitaxy (PA MBE) were studied. Transport parameters of the surface and interface layers were determined from the measurements of the Hall coefficient and resistivity as well as the Shubnikov-de Haas oscillations at magnetic fields up to 60 T. Contributions of the 2D surface, 3D near-interface, and 2D interface layers to the total conductivity of the InN films were defined and discussed to be dependent on InN surface polarity, Mg doping, and PA MBE growth conditions.

Registration No. 27078 - Permalink


ChimeraTK OPC UA Adapter for the Integration of a MicroTCA.4 based digital LLRF
Steinbrück, R.; Kuntzsch, M.; Zenker, K.; Hierholzer, M.; Killenberg, M.; Iatrou, C. P.; Rahm, J.
The superconducting linear accelerator ELBE at Helmholtz-Center Dresden-Rossendorf is a versatile light source operated in continuous wave mode. Currently there is a transition from an analogue low level radio frequency control (LLRF) to a digital MicroTCA.4 based solution developed at DESY, Hamburg. Control system integration is realized collaboratively by DESY, Technische Universität Dresden (TUD) and HZDR with ChimeraTK and the incorporated OPC UA adapter. The poster gives an overview of the variable mapping scheme used to represent LLRF data in the OPC UA server address space, the graphical user interface and first integration test results.
Keywords: ELBE MicroTCA.4 LLRF "OPC UA" ChimeraTK
  • Lecture (others)
    6th MicroTCA Workshop for Industry and Research, 04.-07.12.2017, Hamburg, Deutschland

Registration No. 27072 - Permalink


Control System Integration of a MicroTCA.4 Based Digital LLRF Using the ChimeraTK OPC UA Adapter
Steinbrück, R.; Kuntzsch, M.; Michel, P.; Hierholzer, M.; Killenberg, M.; Schlarb, H.; Iatrou, C. P.; Rahm, J.; Urbas, L.
The superconducting linear electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf is a versatile light source. It operates in continuous wave (CW) mode to provide a high average beam current. In order to meet the requirements for future high resolution experiments the analogue low level radio frequency control (LLRF) is currently replaced by a digital MicroTCA.4 LLRF system based on a development at DESY, Hamburg.
Operation and parametrization is realized by a server application implemented by DESY using the ChimeraTK software framework. To interface the WinCC 7.3 based ELBE control system an OPC UA adapter for ChimeraTK has been developed in cooperation of DESY, Technische Universität Dresden (TUD) and HZDR. The contribution gives an overview of the collaborating parties, the variable
mapping scheme used to represent LLRF data in the OPC UA server address space and integration experiences with different industrial OPC UA Clients like WinCC 7.3 and LabVIEW.
Keywords: MicroTCA.4 LLRF "OPC UA" ChimeraTK
  • Poster
    ICALEPCS2017 - 16th International Conference on Accelerator and Large Experimental Physics Control Systems, 03.-13.10.2017, Barcelona, Spain
    DOI: 10.18429/JACoW-ICALEPCS2017-THPHA166
  • Contribution to proceedings
    ICALEPCS2017 - 16th International Conference on Accelerator and Large Experimental Physics Control Systems, 08.-13.10.2017, Barcelona, Spain
    Proceedings of ICALEPCS2017
    DOI: 10.18429/JACoW-ICALEPCS2017-THPHA166

Registration No. 27070 - Permalink


Vertical Nanowire Based Single Electron Transistor Self-Assembled by Ion Beam Mixing and Phase Separation
Heinig, K.-H.; von Borany, J.; Hlawacak, G.; Hübner, R.; Wolf, D.; Engelmann, H.-J.; Bischoff, L.; Xu, X.; Prüfer, T.; Möller, W.; Facsko, S.
Electronics has been dominated by silicon since half a century. Si will dominate electronics another decade, however its functionality might change from classical field-controlled currents through channels (the Field Effect Transistor FET) to quantum mechanical effects like field-controlled hopping of single electrons to a quantum dot (Single Electron Transistor SET). The SET is the champion of low-power consumption. This is attractive for the Internet of Things: more and more devices need batteries and plugs. Together with improved batteries, advanced computation must be delivered at extremely low-power consumption. At low temperatures, the functionality of SETs has been proven. Large-scale use of SETs requires room temperature operation, which can be achieved with tiny Si dots (<4 nm) in SiO2, exactly located between source and drain with distances of ~1…2 nm. Manufacturability of such nanostructures is the roadblock for large-scale use of SETs. Lithography cannot deliver such feature sizes. Therefore, there are currently intense studies to fulfill these requirements by self-organization processes. The ion beam technique is a well-established technology in microelectronics used for doping and amorphization, and even for ion beam mixing [1]. The parameters of ion beam processing are very well controllable. We searched for a self-organization process in a vertical silicon nanowire with an embedded, very thin (~6nm) SiO2 layer. Ion beam mixing transforms this layer to metastable SiOx. If the nanowire is thin enough, a subsequent thermal treatment leads by phase separation to a single Si nanodot (~3nm) self-aligned to the lower and upper Si at distances of <2nm. Here, we present 3D computer simulations on ion beam mixing (TRI3DYN code [2]) and Si nanodot formation (3D kinetic Monte Carlo code [3]). Such simulations predicted successfully the fabrication of non-volatile memories using ion beam mixing [4]. Experimentally, single Si nanodot formation has been proven by local mixing in a c-Si/SiO2/a-Si layer stack. The nanoscale mixing has been performed with a Helium Ion Microscope using an Argon beam of ~2nm diameter. After Rapid Thermal Annealing, the self-organized single Si nanodot has been imaged by cross-section energy-filtered transmission electron microscopy EFTEM. In a vertical nanowire the very small volume of mixed SiO2 is not due to nanoscale ion beams but due to the small diameter of the wire. It will be shown, how a vertical nanowire gate-all-around SETs operating at room temperature can be CMOS-compatibly fabricated by this method.
This work has been funded by the European Union’s Horizon 2020 research and innovation program under grant
agreement No 688072.
[1] K.H. Heinig, T. Müller, B. Schmidt, M. Strobel, W. Möller, Appl. Phys. A77 (2003) 17.
[2] W. Möller, NIM B322 (2014) 23.
[3] M. Strobel, K.-H. Heinig, W. Möller, Phys. Rev. B64 (2001) 245422.
[4] T. Mueller et al., Appl .Phys. Lett. 81 (2002) 3049; ibid 85 (2004) 2373.
Keywords: ion beam mixing, phase separation, computer simulations, manufacturing, single electron transistor
  • Lecture (Conference)
    Symposium “Progress in Developing and Applications of Functional 1D Nanostructiures”, 2017 Fall Meeting of the Materials Research Society, 26.11.-01.12.2017, Boston, USA

Registration No. 27068 - Permalink


Ion-Beam-Induced Self-Organisation of Nanostructures at Interfaces
Heinig, K.-H.; Prüfer, T.; Möller, W.; Hlawacek, G.; Xu, X.; Bischoff, L.; Hübner, R.; Wolf, D.; Facsko, S.; von Borany, J.
Ion irradiation through an interface between the phases A and B causes atomic displacements which results at low temperatures in a diffusion-like concentration profile. Even if phases A and B are immiscible, a metastable layer of an A/B mixture forms at high ion fluence. A subsequent thermal treatment will activate phase separation in this A/B mixture via nucleation and coarsening. This phase separation process has the potential of self-organisation of nanostructures, where the resulting nanostructure can be tailored by understanding and controlling the reaction pathway.
(i) At first, in this presentation it will be shown how the ion beam mixing of a flat infinite interface can be simulated with the SRIM and TRIDYN programs.
(ii) Then, by means of 3D kinetic lattice Monte-Carlo simulations it will be demonstrated how a thermally activated phase separation of the A/B mixture starts either by formation of nuclei of the minority phase or by spinodal decomposition.
(iii) Simulations for long times show that the subsequent nanostructure evolution is driven by interface minimization, i.e. Ostwald ripening of nanocluster ensembles or coarsening of spinodal structures.
At this stage, a self-organisation process governed by Brailsford's diffusional screening length can evolve, which can be eventually controlled. The A/B interface which re-forms during phase separation plays a central role for self-organisation and self-alignment of nanostructures.
These general mechanisms are effective in ion beam mixing of a thin SiO2 layer buried in Si with the following observations: (i) Zones denuded of Si form during annealing at the upper and lower interface. (ii) Additionally, three, two or one layer of Si nanoclusters form and align with the interface. (iii) If only a tiny volume ~(10nm)^3 of metastable SiOx (such as in an ion beam mixed nanopillar of a Si/SiO2/Si stack) becomes phase separated, the reaction pathway leads always to the existence of a single Si dot for a rather long time period.
This single Si nanodot fabrication becomes even more stable if all boundaries of the tiny SiOx volume are sinks for Si diffusing in SiO2, which can be realized by sideways in-diffusion of oxygen into the nanopillar.
Finally it will be shown, how such a single Si nanodot fabrication process can be used for manufactoring of single electron transisrors working at room temperature.
Keywords: Nanostructure fabrication, ion-beam-mixing, phase separation, silicon nanodot, single electron transistor
  • Invited lecture (Conferences)
    FOR3NANO: Formation of 3D Nanostructures by Ion Beams, 28.-30.06.2017, Helsinki, Finland

Registration No. 27067 - Permalink


Underground Nuclear Astrophysics in 2017 at LUNA, LUNA-MV, and Felsenkeller
Bemmerer, D.
The state of the art of underground nuclear astrophysics is reviewed. Starting from recent progress on hydrogen burning and Big Bang nucleosynthesis at LUNA, the upcoming new underground accelerators LUNA-MV and Felsenkeller are discussed.
Keywords: Nuclear Astrophysics underground; LUNA; Felsenkeller
  • Invited lecture (Conferences)
    Strategietreffen "Astroteilchenphysik in Deutschland", 07.-08.12.2017, Bad Honnef, Deutschland

Registration No. 27062 - Permalink


Strahlenschutzaspekte beim neuen Beschleunigerlabor im Dresdner Felsenkeller
Bemmerer, D.
Strahlenschutzaspekte beim neuen Beschleunigerlabor im Dresdner Felsenkeller. Zusätzlich zum klassischen Strahlenschutz am 5 MV Ionenbeschleuniger im Felsenkeller wird auch die Low-Background-Problematik unter Tage diskutiert.
  • Invited lecture (Conferences)
    TÜV Süd Akademie "Strahlenschutz in Medizin, Forschung und Industrie", 06.-07.12.2017, Marburg/Lahn, Deutschland

Registration No. 27061 - Permalink


Nuclear Astrophysics Basics II
Bemmerer, D.
Carbon-nitrogen-oxygen cycle, nuclear cosmology, Felsenkeller underground accelerator
  • Invited lecture (Conferences)
    Lecture Week on Nuclear Structure and Nuclear Astrophysics, 04.-05.12.2017, Zell / Mosel, Deutschland

Registration No. 27060 - Permalink


Nuclear Astrophysics Basics I
Bemmerer, D.
Nuclear Astrophysics Basics I: Cross Section, Gamow Peak, Thermonuclear Reaction Rate, and the Sun.
  • Invited lecture (Conferences)
    Lecture Week on Nuclear Structure and Nuclear Astrophysics, 04.-05.12.2017, Zell / Mosel, Deutschland

Registration No. 27059 - Permalink


Using XFELs to Probe Kilotesla Magnetic Fields inside Solid Density Plasmas Driven by Optical High Power Lasers
Huang, L. G.; Schlenvoigt, H.-P.; Takebe, H.; Cowan, T. E.
The relativistic laser matter interaction is a complex interplay of ionization, extreme current densities, rapidly evolving strong fields and acceleration processes. Understanding the interaction physics is a challenging but highly rewarding endeavor. The unprecedented brightness of XFELs opens a new window for discovering the interior of solid-density plasmas created by relativistic laser interactions with matter, resolving the relevant femtosecond and sub-micrometer scales experimentally.
Here, we focus on discussing the feasibility of probing the magnetic fields by X-Ray polarimetry via Faraday rotation using XFEls.
Keywords: laser,plasmas, magnetic fields,faraday rotation,xfel
  • Poster
    European XFEL Users' Meeting 2018, 23.-26.01.2018, Hamburg, Germany

Registration No. 27055 - Permalink


Quasifree (p,2p) Reactions on Oxygen Isotopes: Observation of Isospin Independence of the Reduced Single-Particle Strength
Atar, L.; Paschalis, S.; Barbieri, C.; Bertulani, C.  A.; Díaz Fernández, P.; Holl, M.; Najafi, M.  A.; Panin, V.; Alvarez-Pol, H.; Aumann, T.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Boillos, J.  M.; Boretzky, K.; Borge, M.  J.  G.; Caamaño, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Cravo, E.; Crespo, R.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L.  M.; Freer, M.; Galaviz Redondo, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Hufnagel, A.; Ignatov, A.; Johansson, H.  T.; Jonson, B.; Kahlbow, J.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knyazev, A.; Kröll, T.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec-Gałązka, J.; Movsesyan, A.; Nacher, E.; Nikolskii, E.  Y.; Nilsson, T.; Nociforo, C.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Reifarth, R.; Ribeiro, G.; Rigollet, C.; Rossi, D.  M.; Röder, M.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Syndikus, I.; Taylor, J.  T.; Tengblad, O.; Thies, R.; Togano, Y.; Vandebrouck, M.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Wheldon, C.; Wilson, G.  L.; Winfield, J.  S.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.
Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the
R3B/LAND setup with incident beam energies in the range of 300–450 MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type AO(p,2p)A−1N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry

Registration No. 27054 - Permalink


Femtosecond laser-generated high-energydensity states studied by x-ray FELs
Nakatsutsumi, M.; Appel, K.; Baehtz, C.; Chen, B.; Cowan, T. E.; Göde, S.; Konopkova, Z.; Pelka, A.; Priebe, G.; Schmidt, A.; Sukharnikov, K.; Thorpe, I.; Tschentscher, T.; Zastrau, U.
The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behaviour of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump–probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.
Keywords: x-ray free-electron laser, femtosecond dynamics, relativistic plasma, high-energydensity state

Registration No. 27053 - Permalink


Isothermal differential dilatometry based on X-ray analysis applied to stress relaxation in thin ion-beam-sputtered Pt films
Gruber, W.; Baehtz, C.; Geue, T.; Stahn, J.; Schmidt, H.
Relaxation of stress and point defects in ion-beam-sputtered Pt films with a thickness of 20 and 40 nm during isothermal annealing was investigated. First, isothermal differential dilatometry measurements based on X-ray analysis were carried out between 130 and 400 °C. They show that the relaxation of compressive stress is associated with the formation of vacancies at the surface. From the measurements, an activation enthalpy of 0.14 eV was estimated for the stress relaxation process. In addition, self-diffusion experiments of Pt were carried out on the same type of films using stable 194Pt tracer. From secondary ion mass spectrometry on samples annealed for longer times, an activation enthalpy of 0.5 eV for Pt diffusion in grain boundaries was estimated. The influence of vacancy creation at the surface, vacancy transport, and the annihilation of nonequilibrium
bulk interstitials and thermally created vacancies on stress relaxation is discussed.
Keywords: Thin films Synchrotron X-ray diffraction ion-beam-sputtering

Registration No. 27052 - Permalink


Chiral-partner D mesons in a heat bath within QCD sum rules
Buchheim, T.; Hilger, T.; Kämpfer, B.; Leupold, S.
Utilizing QCD sum rules, we extract the temperature dependences of the spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral partners. Besides the masses also decay constants are analyzed as the D meson yields in heavy-ion collisions may be sensitive to their altered decay properties in an ambient strongly interacting medium. Our findings are (i) a decreasing scalar D meson mass for growing temperatures while its pseudo-scalar partner meson seems hardly affected, which is in qualitative agreement with hadronic model calculations; (ii) inferring an equally weak temperature dependence of the pseudo-scalar D meson decay properties the decreasing residua and decay constants of the scalar particle point towards partial chiral restoration. As a bonus of our analysis in the pseudo-scalar sector we determine the pseudo-scalar decay constant at vanishing temperature. Due to the connection to particular leptonic branching fractions this decay constant is of great interest allowing for the determination of the off-diagonal CKM matrix element |Vcd| at zero temperature.

Registration No. 27050 - Permalink


Assisted Vacuum Decay by Time Dependent Electric Fields
Otto, A.; Oppitz, H.; Kämpfer, B.
We consider the vacuum decay by electron-positron pair production in spatially homogeneous, time dependent electric fields by means of quantum kinetic equations. Our focus is on the impact of various pulse shapes as envelopes of oscillating fields and the assistance effects in multi-scale fields, which are also seen in photons accompanying the creation and motion of pairs.

Registration No. 27049 - Permalink


Large scale structures of a turbulent Rayleigh-Bénard convection in a liquid metal layer confined by a moderate aspect ratio box
Akashi, M.; Tasaka, Y.; Yanagisawa, T.; Murai, Y.; Vogt, T.; Eckert, S.
We report laboratory experiments of Rayleigh-Bénard convection with a liquid metal, Prandtl number Pr = 0.03, in a rectangular cell with a moderate aspect ratio. Rayleigh number, Ra, was set at a range from 7.9 × 10^3 to 3.5 × 10^5 at which the thermal turbulence regime is expected. Multiple horizontal velocity profiles in the fluid layer by ultrasonic velocity profiling elucidated formations of several large scale flow structures with periodic oscillations. The flow structure has transitions as increasing Ra from a quasi-two-dimensional roll-like structure to a three-dimensional cell-like structure via unstable intermediate regimes with stepwise increase of its horizontal scale. By using observed Ra dependences of the frequency of oscillation and the velocity of large scale flow, we made up a model to explain the increase of horizontal scale. We evaluated effective viscosities and diffusivities based on the turbulent fluctuations, and found that the morphology of roll-like structure can be understood by using these effective values.
  • Lecture (Conference)
    The 70th Annual Meeting of the American Physical Society Division of Fluid Dynamics, 20.11.2017, Denver, USA

Registration No. 27046 - Permalink


New Heterodinuclear Zn/Ln (Ln = Gd, Tb, Er, Yb) Complexes of Hexadentate N,N'-Bis(3-alkoxy-2-hydroxybenzyl)cyclohexane-1,2-diamines: Synthesis and Structure
Kelly, N.; Schnaars, K.; Gloe, K.; Doert, T.; Weigand, J. J.; Gloe, K.
Two N,N′-bis(3-alkoxy-2-hydroxybenzyl)cyclohexane-1,2-diamine proligands, H₂L¹ (R = OCH₃) and H₂L² (R = OC₂H₅), and five heterodinuclear Znᴵᴵ/Lnᴵᴵᴵ complexes, [Zn(L)(µ-CH₃COO)Ln(NO₃)₂], containing [L¹]²⁻ and Gd³⁺, Tb³⁺, Er³⁺, or Yb³⁺ and [L²]²⁻ and Yb³⁺ have been synthesised and structurally characterised. The complexes are isostructural and crystallise in the P2₁/n monoclinic space group. Zinc(II) is coordinated by the inner N₂O₂ donor set of the ligand and an oxygen of the bridging acetate anion; the lanthanide(III) ions possess an O₉ coordination environment involving the interaction with the ligand’s outer O₄ donor set, two bidentate nitrate ions, and the bridging acetate.

Registration No. 27043 - Permalink


Investigation of heavy metal release at a municipal solid waste incineration facility - an excellent example for the unique potential of intrinsic radiotracer application to the investigation of industrial processes in chemical engineering
Jentsch, T. B. O.
Radiotracers are widespread in use for investigation of material transport processes in industry and environment. Often they are used for the measurement of the residence time distribution in continuously operating chemical engineering facilities and reactors. Mostly intrinsic or physical tracers are used for these purposes.

In case of phase transformation processes are in the focus of interest physical or extrinsic tracers are not the labelling material of choice. Intrinsic or chemical tracers are required in that case.

At example of the heavy metal release investigation at a municipal solid waste incineration facility the unique potential of intrinsic radiotracers will be demonstrated in the given paper.

Goal of the investigation at the municipal solid waste incineration facility reported in this paper was the behaviour study of different heavy metal species at various incineration conditions. With the help of short lived radioisotopes of copper (Cu-64) and zinc (Zn-69m) could be shown at which position of the incinerator and in which amount the heavy metal under investigation was released.

The experimental results of this investigation were an essential contribution for better understanding the processes inside the incinerator and to optimize the processing conditions.
Keywords: heavy metal release, radiotracer, municipal solid waste incineration, copper-64, zinc-69m,
  • Lecture (Conference)
    ICARST 2017 - International Conference on Applications of Radiation Science and Technology, 24.-28.04.2017, Wien, Österreich

Registration No. 27039 - Permalink


PO-0619: Comparison of a nanoString and RNA microarray gene signature predicting LRC after PORT-C in HNSCC
Schmidt, S.; Linge, A.; Zwanenburg, A.; Leger, S.; Lohaus, F.; Gudziol, V.; Nowak, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A. L.; Abdollahi, A.; Debus, J.; Belka, C.; Combs, S. E.; Mönnich, D.; Zips, D.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.; Löck, S.
A gene signature predicting loco-regional control (LRC) of locally advanced head and neck squamous cell carcinoma (HNSCC) after postoperative radiochemotherapy (PORTC) will be evaluated using nanoString and RNA microarray data. The prognostic power of the signature as well as the correlation between both methods is evaluated to underline the robustness of the proposed signature.

Downloads:

Registration No. 27038 - Permalink


Pencil beam scanning treatments in free-breathing lung cancer patients–is 5 mm motion a limit?
Jakobi, A.; Perrin, R.; Knopf, A.; Richter, C.
To evaluate the dose degradation when treating lung cancer patie nts with proton pencil beam scanning during free-breathing. We assess if treatments without rescanning are feasible in order to avoid prolonged treatment time, especially for slow scanning facilities.

Downloads:

Registration No. 27034 - Permalink


High-precision radiotherapy–Do we need better pre-treatment CT imaging?
Greilich, S.; Richter, C.
Computed tomography (CT) images from fan-beam medical grade scanners are the current gold standard for treatment planning in radiation oncology: they provide geometrically correct, reliable, and quantitative measures of photon attenuation in the patient. However, this information is not fully identical with the physical quantities needed for dose calculation and optimization and additional uncertainty is introduced by inferring them from the kV images. Also, the low soft tissue contrast in CT impacts delineation accuracy. While additional Imaging modalities are advocated as complementary – sometimes alternative – techniques to CT imaging, uncertainties in image registration can even deteriorate the quality of treatment planning. Dual-energy CT – i.e. using scans from two X-ray spectra or detection in two separate energy ranges – retains the virtues of computed tomography while it opens at the same time the possibility to overcome the restrictions mentioned. It can improve the accuracy of dose calculation and delineation and enables to abandon the use of a general translation rule (“Hounsfield look-up table”) for the photon attenuation (CT numbers) - replacing it by a patient-specific determination of radiological tissue quantities. DECT-derived quantities might additionally provide opportunities in advanced image analysis methods such as radiomics, i.e. the machine-learning-based approach for the prediction of patient outcome and treatment personalization. CT-based radiomics analyses might even be able to uncover information that can so far only be derived from additional multi-modal imaging. Currently, many applications based on innovations in pre-treatment CT imaging and image analysis are investigated that could have the potential to change clinical practice in future. This presentation is intended to set the stage for the focus session which tries to look into the question, which of These applications can find its way into routine clinical application.
  • Open Access LogoAbstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 62(2017), S292-S297
    DOI: 10.1515/bmt-2017-5057

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Registration No. 27032 - Permalink


PO-0819: Robustness evaluation of single-and multifield optimized proton plans for unilateral head and neck.
Cubillos-Mesías, M.; Baumann, M.; Troost, E. G. C.; Appold, S.; Krause, M.; Richter, C.; Stützer, K.
To compare 4 different proton pencil beam scanning (PBS) treatment approaches for unilateral head and neck cancer (HNC) targets in terms of robustness, including anatomical changes during the treatment course.

Downloads:

Registration No. 27030 - Permalink


Modeling patterns of anatomical deformations in prostate patients undergoing radiation therapy with an endorectal ballon
Brion, E.; Richter, C.; Macq, B.; Stützer, K.; Exner, F.; Troost, E.; Hölscher, T.; Bondar, L.
External beam radiation therapy (EBRT) treats cancer by delivering daily fractions of radiation to a target volume. For prostate cancer, the target undergoes day-to-day variations in position, volume, and shape. For stereotactic photon and for proton EBRT, endorectal balloons (ERBs) can be used to limit variations. To date, patterns of non-rigid variations for patients with ERB have not been modeled. We extracted and modeled the patient-specific patterns of variations, using regularly acquired CT-images, non-rigid point cloud registration, and principal component analysis (PCA). For each patient, a non-rigid point-set registration method, called Coherent Point Drift, (CPD) was used to automatically generate landmark correspondences between all target shapes. To ensure accurate registrations, we tested and validated CPD by identifying parameter values leading to the smallest registration errors (surface matching error 0.13±0.09 mm). PCA demonstrated that 88±3.2% of the target motion could be explained using only 4 principal modes. The most dominant component of target motion is a squeezing and stretching in the anterior-posterior and superior-inferior directions. A PCA model of daily landmark displacements, generated using 6 to 10 CT-scans, could explain well the target motion for the CT-scans not included in the model (modeling error decreased from 1.83±0.8 mm for 6 CT-scans to 1.6±0.7 mm for 10 CT-scans). PCA modeling error was smaller than the naive approximation by the mean shape (approximation error 2.66±0.59 mm). Future work will investigate the use of the PCA-model to improve the accuracy of EBRT techniques that are highly susceptible to anatomical variations such as, proton therapy.
  • Abstract in refereed journal
    Proceedings of SPIE 10135(2017), 1013506
    DOI: 10.1117/12.2251933

Downloads:

Registration No. 27028 - Permalink


Combined PET/MRI: Global Warming-Summary Report of the 6th International Workshop on PET/MRI, March 27-29, 2017, Tübingen,
Bailey, D. L.; Pichler, B. J.; Gückel, B.; Antoch, G.; Barthel, H.; Bhujwalla, Z. M.; Biskup, S.; Biswal, S.; Bitzer, M.; Boellaard, R.; Braren, R. F.; Brendle, C.; Brindle, K.; Chiti, A.; La Fougère, C.; Gillies, R.; Goh, V.; Goyen, M.; Hacker, M.; Heukamp, L.; Knudsen, G. M.; Krackhardt, A. M.; Law, I.; Morris, J. C.; Nikolaou, K.; Nuyts, J.; Ordonez, A. A.; Pantel, K.; Quick, H. H.; Riklund, K.; Sabri, O.; Sattler, B.; Troost, E.; Zaiss, M.; Zender, L.; Beyer, T.
The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in Tübingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient care.

Registration No. 27024 - Permalink


Atomistic Simulation of Interface-Driven Self-Alignment of Si-SiO2 Nanostructures
Prüfer, T.; Heinig, K. H.; Möller, W.; von Borany, J.
Si nanostructures are very promising candidates for optical and electrical applications. Charged nanocluster can be used for data storage [2]; their discrete energy levels can be used for logic operations; sponge nanostructures can be used as the ion conductor in fuel cells. The size-dependency of their energy levels makes them interesting for application in colour displays.
Among a lot of other methods to synthesize nanoclusters or sponges we present an approach which allows a selfalignment of nanostructures at an interface. The basic idea is to bring together Si, SiO2 and SiOx and anneal it to cause phase separation of SiOx. The interfaces between Si/SiOx and SiOx/SiO2 act as driving forces for the selfalignment of the separated Si and SiO2. To create SiOx we consider 2 processes: (i) Deposition of SiOx films by PVD or CVD and (ii) Ion beam Mixing of Si/SiO2 interfaces.
By PVD it’s possible to create arbitrary shapes of Si/SiO2/SiOx layerstacks. The subsequent annealing causes different effects at the interface. Mainly depending on the structure of the layerstack, but also on the annealing time, different reaction pathways can be observed. The system can end up with different numbers of cluster layers or sponge structures, aligned parallel to the interface. Here we show how and why it is possible to control the sizes, densities and distances of these structures.
The ion irradiation through a Si/SiO2 interface causes mixing of both phases and transforms the interface into SiOx.
This method is not that flexible as PVD, but it’s easier to be implemented into common industrial technologies, like the production of CMOS compatible devices. The reformation of the Si/SiO2 interface during heat treatment is again acting as a driving force for the self-alignment and forms a zone between the interface and the resulting nanostructures which is denuded of excess Si. In this case, sizes and density can be controlled by irradiation and annealing parameters.
Earlier studies [1] have proven the reliability of dot formations using ion beam mixing technologies for application as memories [2]. Here, we show simulation results for the formation of Si nanostructures at interfaces in layerstacks of Si, SiOx, SiO2 and basic principles of the driving forces for this kind of self-alignment. Computer simulations using the binary collision approximation (TRIDYN [3]) and the kinetic monte carlo method [4] are employed to subsequently describe the ion irradiation and annealing processes, respectively.
This part of the work is being funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).
[1] T. Müller et al., Appl. Phys. Lett. 81 (2002) 3049; ibid. 85 (2004) 2373.
[2] K.H. Heinig et al., Appl. Phys. A77 (2003)17.
[3] W. Möller, W. Eckstein, Nucl. Instr. and Meth. in Phys. Res. B2 (1984) 814
[4] M. Strobel et al., Phys. Rev. B64 (2001)245422.
  • Lecture (Conference)
    Material Research Society Fall Meeting 2017, 26.11.-01.12.2017, Boston, United States of America

Registration No. 27018 - Permalink


WTZ Russland - Transientenanalysen für schnelle Reaktoren
Kliem, S.ORC; Nikitin, E.; Rachamin, R.; Glivici-Cotruta, V.
Der Reaktordynamikcode DYN3D wird für Kernanalysen von Natrium-gekühlten schnellen Reaktoren (SFR) erweitert. In diesem Bericht werden neu implementierte thermomechanische Modelle für die adäquate Simulation von SFR-Transienten beschrieben, die die Simulation der axialen Wärmeausdehnung von Brennstäben und die radiale Ausdehnung des Reaktorkerns umfassen. Darüber hinaus wurde das Verfahren zur Erstellung von Querschnittsbibliotheken für DYN3D für SFR-Analysen erweitert. Die Verifizierung der neuen Modelle und der Querschnittserstellung erfolgte auf Vollkern-Ebene mit stationären Experimenten von der BFS-Testanlage des IPPE Obninsk und Daten des großen oxidischen Kerns des OECD/NEA-Benchmark und den Experimenten zum Zyklusende des Phenix-Kerns. Die DYN3D-Ergebnisse wurden mit der Monte-Carlo-Referenzlösung verglichen, die durch den SERPENT-Code berechnet wurde. Die Testergebnisse zeigen, dass die neu entwickelten Modelle die Wärmeausdeh-nungseffekte der Kernstruktur genau berücksichtigen können. Das neu entwickelte Verfahren zur Erstellung von Querschnittsbibliotheken wurde ebenfalls auf der Basis von SERPENT-Ergebnissen erfolgreich verifiziert. Zur Validierung wurden mehrere Tests, die sowohl stationäre als auch transiente Fälle aus den Phenix-Experimenten enthalten, mit DYN3D berechnet. Die DYN3D-Lösungen weisen eine gute Übereinstimmung mit den experimentellen Daten auf, was die Anwendbarkeit der Codes für Kernanalysen von Natrium-gekühlten schnellen Reaktoren bestätigt.
Keywords: DYN3D, SERPENT, Natrium gekühlter Reaktor, thermomechanische Modelle, Validierung
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-086 2018
    ISSN: 2191-8708

Registration No. 27016 - Permalink


Process Simulation of Single Si Quantum Dot Formation for Single Electron Transistors
Prüfer, T.; Heinig, K. H.; Möller, W.; Hlawacek, G.; Xu, X.; Friedlund, C.; Djurabekova, F.; von Borany, J.
Conventional Lithography allows the fabrication of structures down to ~10 nm, being still too large for single electron transistors (SET) operating at room temperature (RT), which requires a tiny quantum dot (<5nm) embedded in SiO2, with tunnel distances to the source and drain <2nm. Here, we predict a fully CMOS-compatible method of self-assembly of a single Si quantum dot. We assume that 10…20nm thin nanopillars of a layer stack c-Si/6nm SiO2/30nm a-Si are made by conventional lithography. We predict that such a single dot is self-organized and self-assembled between the top and bottom silicon layer by phase separation of metastable SiOx. The SiOx is made by collisional mixing in the layer stack, which is simulated by TRI3DYN [1]. The phase separation of SiOx is described by 3D kinetic lattice Monte Carlo simulations [2]. Our results predict that a single Si nanodot forms if the volume of SiOx is smaller than (10nm)^3. This work has been funded by the European Union's Horizon 2020 research and innovation program under grant agreement No 688072.
[1] W. Möller; NIM B, 322, 23–33
[2] M. Strobel, K.H. Heinig, W. Möller, PRB 64, 245422
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Registration No. 27014 - Permalink


Influence of resistance and spin-torque bias dependence on the output power of MgO-based nano oscillators
Kowalska, E.; Fukushima, A.; Sluka, V.; Fowley, C.; Kákay, A.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Yuasa, S.; Deac, A. M.
Spin-transfer torques (STTs) can be exploited in order to manipulate magnetic moments of nanomagnets, allowing for new consumer-oriented devices to be designed, such as tuneable radio-frequency spin-torque nano oscillators (STNOs) for wireless communication. Currently, the structure involving an MgO-based magnetic tunnel junction (MTJ) with hybrid geometry combining an IP reference layer and an out-of-plane free layer is the system of choice [1,2]. This configuration, Fig. 1a, maximizes the output power, reduces the critical current [3], and can allow for stable precession regardless of magnetic or applied current history [1,4,5].

Here, we experimentally observe an unusual curvature of the critical lines on the current-field phase diagram enclosing the region of steady-state dynamics (Fig. 2a) which has never been reported in similar metallic- or MTJ-based devices. Theoretically, we incorporate the angular dependence of the TMR (dRAP/dV) [6-8] and bias dependent spin-transfer torques [9-11] into the in-plane and the perpendicular STT and solve LLGS equation [12]. We find that the angular dependence of TMR introduces an asymmetry in the in-plane STT and gives rise to stable precession. Moreover, including the bias dependence of TMR (Fig. 1b) correctly reproduces the curvature of the dynamical region in the experimental phase diagram (Fig. 2b), gradually suppressing the induced asymmetry, and with it the output power. Therefore, the TMR ratio and its bias dependence are both equally crucial factors governing the performance of MTJ-based STNOs.
Keywords: STNO,MTJ,STT
  • Lecture (Conference)
    MMM 2017 - 62nd Annual Conference on Magnetism and Magnetic Materials, 06.-10.11.2017, Pittsburgh, USA

Registration No. 27010 - Permalink


15 years of CW SRF operation at ELBE
Arnold, A.; Büchner, A.; Büttig, H.; Freitag, M.; Lehnert, U.; Michel, P.; Schneider, C.; Teichert, J.
ELBE is a compact, accelerator-driven photon and particle source. The variety of secondary radiation being offered extends from high-energy gamma rays to infrared and THz radiation as well as from neutrons to positrons and electrons. Since 2001 ELBE is operated as a user facility, providing more than 5500 hours of beamtime with an efficiency of more than 90% each year. The electron accelerator is based on four superconducting 9-cell TESLA cavities that are driven in CW operation to accelerate an average current of 1 mA up to beam energies of 40 MeV. Although these cavities performed well in the vertical test, they were limited by field emission from the very beginning to about 10 MV/m each. The reason is still unknown, but several candidates are being discussed. The prime suspect is particle contamination during cleanroom and beamline assembly but also a mechanism that allows particles to migrate from far away towards the cavity over an extended period of time might be possible. And also outgassing EPDM gaskets that are installed in the entire accelerator are a candidate for deterioration. Nevertheless, to ensure a reliable user operation, the performance of the cavities is determined in regular intervals by Q vs. E measurements and by means of high power RF processing and complete thermal cycling the performance could be partially returned to an earlier state. With the contribution we try to summarize our experiences in operating a superconducting CW LINAC over the last 15 years in an unclassified and probably dirty environment.
Keywords: CW, SRF, operation, ELBE, cryomodule
  • Invited lecture (Conferences)
    Operating SRF systems reliably in a "dirty" accelerator, 14.-15.09.2017, Berlin, Deutschland

Registration No. 27009 - Permalink


Cancer stem cells: Radioresistance, prediction of radiotherapy outcome and specific targets for combined treatments.
Krause, M.; Dubrovska, A.; Linge, A.; Baumann, M.
Inactivation of cancer stem cells (CSCs) is of utmost importance for tumor cure after radiotherapy. An increasing body of evidence complies with a higher radioresistance of CSCs compared to the mass of tumor cells, supporting the use of CSC related biomarkers for prediction of radiotherapy outcome. Treatment individualization strategies for patient groups with vastly different risk of recurrence will most likely require application of more than one biomarker. Specifically, inclusion of established biomarkers like tumor size for primary radio(chemo)therapy or human papilloma virus (HPV) infection status in head and neck squamous cell carcinoma seems to be of very high relevance. The high heterogeneity of CSC subclones along with changes of the functional behavior of individual tumors under treatment underlines the importance of the selection of the optimal timepoint(s) of biomarker evaluation, but also provides a potential therapeutic target for combined treatment approaches with irradiation.

Registration No. 27005 - Permalink


PORTAF–postoperative radiotherapy of non-small cell lung cancer: accelerated versus conventional fractionation–study protocol for a randomized controlled trial
Bütof, R.; Simon, M.; Löck, S.; Troost, E.; Appold, S.; Krause, M.; Baumann, M.
BACKGROUND:

In early-stage non-small cell lung cancer (NSCLC) without affected lymph nodes detected at staging, surgical resection is still the mainstay of treatment. However, in patients with metastatic mediastinal lymph nodes (pN2) or non-radically resected primary tumors (R1/R2), postoperative radiotherapy (possibly combined with chemotherapy) is indicated. So far, investigations about time factors affecting postoperative radiotherapy have only examined the waiting time defined as interval between surgery and start of radiotherapy, but not the overall treatment time (OTT) itself. Conversely, results from trials on primary radio(chemo)therapy in NSCLC show that longer OTT correlates with significantly worse local tumor control and overall survival rates. This time factor of primary radio(chemo)therapy is thought to mainly be based on repopulation of surviving tumor cells between irradiation fractions. It remains to be elucidated if such an effect also occurs when patients with NSCLC are treated with postoperative radiotherapy after surgery (and chemotherapy). Our own retrospective data suggest an advantage of shorter OTT also for postoperative radiotherapy in this patient group.
METHODS/DESIGN:

This is a multicenter, prospective randomized trial investigating whether an accelerated course of postoperative radiotherapy with photons or protons (7 fractions per week, 2 Gy fractions) improves locoregional tumor control in NSCLC patients in comparison to conventional fractionation (5 fractions per week, 2 Gy fractions). Target volumes and total radiation doses will be stratified in both treatment arms based on individual risk factors.
DISCUSSION:

For the primary endpoint of the study we postulate an increase in local tumor control from 70% to 85% after 36 months. Secondary endpoints are overall survival of patients; local recurrence-free and distant metastases-free survival after 36 months; acute and late toxicity and quality of life for both treatment methods.

Registration No. 26999 - Permalink


PO-0616: HPV, CSC marker expression and tumor hypoxia as prognosticators for LRC in patients with HNSCC
Linge, A.; Löck, S.; Krenn, C.; Appold, S.; Lohaus, F.; Schneider, M.; Nowak, A.; Gudziol, V.; Baretton, G. B.; Buchholz, F.; Baumann, M.; Krause, M.
PO-0616: HPV, CSC marker expression and tumor hypoxia as prognosticators for LRC in patients with HNSCC

Registration No. 26997 - Permalink


PO-0968: The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC
Kurth, I.; Digomann, M.; Hein, L.; Linge, A.; Koi, L.; Loeck, S.; Maebert, K.; Stephan, H.; Peitzsch, C.; Krause, M.; Baumann, M.; Dubrovska, A.
PO-0968: The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC

Registration No. 26996 - Permalink


Optimisation and stabilisation of cathepsin B-endopeptidase substrates: Towards a Cathepsin B-activated cell-penetrating peptide
Kuhne, K.; Behring, L.; Belter, B.; Neuber, C.; Wodtke, R.; Pietzsch, J.; Löser, R.
Cathepsin B (CTB), whose expression in tumours correlates with increased metastasis, therapy resistance, and generally poor prognosis, represents an excellent target for molecular imaging using radiotracers [1]. It is our aim to develop a CTB-specifc, substrate-based radiotracer based on activatable, poly-D-arginine-derived cell pentrating peptides [2]. Central prerequisite for such a probe is an endopeptidase substrate for CTB used as an activator sequence that shows efficient cleavage kinetics towards CTB and is stable in circulation and against other relevant cathepsins. After newly identifying the P4' position as major determinant of CTB endopeptidase specificity, we determined Val (kcat/KM=245 mM-1s-1, 16xGly) as the ideal amino acid at this position. In terms of stabilisation, we were able to increase serum half-life from 3.6 min to >1440 min by amino acid exchange at P1 and N2-methylation of a secondary cleavage site, while still retaining good cleavability by CTB. Analysis of cleavage by other relevant ctahepsins is currently ongoing.

Literature
[1] Löser & Pietzsch Front. Chem. 2015, 3, 37
[2] Jang et al. PNAS 2004, 101, 17867
  • Poster
    International Sympsosium on Bioorganic Chemistry (ISBOC-11), 27.-29.09.2017, Konstanz, Deutschland

Registration No. 26995 - Permalink


Neutron imaging of particle laden Foam
Heitkam, S.; Lappan, T.; Eckert, S.; Eckert, K.
This presentation reports on the simultaneous measurement of foam structure and attached particles employing neutron imaging. An aqueous foam sample is placed in the NEUTRA beamline at PSI, enables for achieving a spatial resolution of less than 200 μm at a frame rate of more than 1 Hz. A forced drainage setup allows to control the liquid content of the foam. The averaged attenuation of the neutrons is demonstrated to yield the liquid fraction of the foam. Hydrophobized gadolinium particles of 200 μm diameter are added to the foam. Using two surfactants different levels of hydrophobicity are achieved. Depending on the drainage flow and the hydrophobicity, the particles are washed out of the foam with different rates. An avalanche-like motion of particle clusters is observed. The neutron radiography is demonstrated to yield unique insights into the unsteady froth flotation process.
Keywords: Neutron Imaging, Froth, Foam
  • Lecture (others)
    Seminarvortrag, 24.10.2017, Strasbourg, Frankreich

Registration No. 26994 - Permalink


Using Lorentz forces to control the distribution of bubbles in a vertical tube filled with liquid metal
Heitkam, S.; Tschisgale, S.; Krull, B.; Wetzel, T.; Baake, E.; Fröhlich, J.
In this work, a method to increase the residence time of bubbles in tubes or pipes filled with liquid metal is investigated. Imposing a horizontal electric current and a perpendicular horizontal magnetic field generates an upward-directed Lorentz force. This force can counteract gravity and cause floating of bubbles. Even with homogeneous electric fields these float in the mean but fluctuate randomly within the swarm due to mutual interactions.
In the present case the cylindrical shape of the container furthermore creates inhomogeneous electric currents and an inhomogeneous force distribution resulting in a macroscopic convection pattern stirring the bubbles and further homogenising the spatial distribution of the bubbles.
Keywords: Magnetohydrodynamics, Bubbles, Flow

Registration No. 26993 - Permalink


Measurement of foam flow using Ultrasound Doppler Velocimetry + Froth dynamics by Neutron Imaging
Heitkam, S.; Nauber, R.; Büttner, L.; Czarske, J.; Eckert, K.
The flowing behavior of liquid foam and froth is only scarcely investigated. One reason for that is, that no adequate measurement technique exists. Also, industrial flotation applications could be improved by monitoring the froth flow in the process.

In this work, the Ultrasound Doppler Velocimetry has been used to measure the velocity distribution inside liquid foam. To that end, an array of ultrasound transducers sends pulses into the foam and receiving the echoes. Sound pulses are reflected at moving particles and air-liquid interfaces. The echoes reveal the longitudinal velocity distribution on the beam axis. Multiplexing of the array allows for 2D-1C measurement.

Comparing with optical measurement it is demonstrated, that the velocity uncertainty at 2.5 Hz frame rate is below 15 percent and the spatial resolution better than 10 mm. These parameters allow for on-line monitoring of industrial processes as well as scientific investigation of three-dimensional froth and foam flows.
Keywords: Foam, Froth, Flotation, Ultrasound Dopller Velocimetry, Neutron Imaging
  • Lecture (Conference)
    Flotation17, 12.-16.11.2017, Cape Town, South Africa

Registration No. 26982 - Permalink


Profile of European proton and carbon ion therapy centers assessed by the EORTC facility questionnaire.
Weber, D. C.; Abrunhosa-Branquinho, A.; Bolsi, A.; Kacperek, A.; Dendale, R.; Geismar, D.; Bachtiary, B.; Hall, A.; Heufelder, J.; Herfarth, K.; Debus, J.; Amichetti, M.; Krause, M.; Orecchia, R.; Vondracek, V.; Thariat, J.; Kajdrowicz, T.; Nilsson, K.; Grau, C.
BACKGROUND:

We performed a survey using the modified EORTC Facility questionnaire (pFQ) to evaluate the human, technical and organizational resources of particle centers in Europe.
MATERIAL AND METHODS:

The modified pFQ consisted of 235 questions distributed in 11 sections accessible on line on an EORTC server. Fifteen centers from 8 countries completed the pFQ between May 2015 and December 2015.
RESULTS:

The average number of patients treated per year and per particle center was 221 (range, 40-557). The majority (66.7%) of centers had pencil beam or raster scanning capability. Four (27%) centers were dedicated to eye treatment only. An increase in the patients-health professional FTE ratio was observed for eye tumor only centers when compared to other centers. All centers treated routinely chordomas/chondrosarcomas, brain tumors and sarcomas but rarely breast cancer. The majority of centers treated pediatric cases with particles. Only a minority of the queried institutions treated non-static targets.
CONCLUSIONS:

As the number of particle centers coming online will increase, the experience with this treatment modality will rise in Europe. Children can currently be treated in these facilities in a majority of cases. The majority of these centers provide state of the art particle beam therapy.

Registration No. 26981 - Permalink


Radiation Resistance in KRAS-Mutated Lung Cancer Is Enabled by Stem-like Properties Mediated by an Osteopontin-EGFR Pathway.
Wang, M.; Han, J.; Marcar, L.; Black, J.; Liu, Q.; Li, X.; Nagulapalli, K.; Sequist, L. V.; Mak, R. H.; Benes, C. H.; Hong, T. S.; Gurtner, K.; Krause, M.; Baumann, M.; Kang, J. X.; Whetstine, J. R.; Willers, H.
Lung cancers with activating KRAS mutations are characterized by treatment resistance and poor prognosis. In particular, the basis for their resistance to radiation therapy is poorly understood. Here, we describe a radiation resistance phenotype conferred by a stem-like subpopulation characterized by mitosis-like condensed chromatin (MLCC), high CD133 expression, invasive potential, and tumor-initiating properties. Mechanistic investigations defined a pathway involving osteopontin and the EGFR in promoting this phenotype. Osteopontin/EGFR-dependent MLCC protected cells against radiation-induced DNA double-strand breaks and repressed putative negative regulators of stem-like properties, such as CRMP1 and BIM. The MLCC-positive phenotype defined a subset of KRAS-mutated lung cancers that were enriched for co-occurring genomic alterations in TP53 and CDKN2A. Our results illuminate the basis for the radiation resistance of KRAS-mutated lung cancers, with possible implications for prognostic and therapeutic strategies. Cancer Res; 77(8); 2018-28. ©2017 AACR.

Registration No. 26980 - Permalink


Heat shock protein 70 and tumor-infiltrating NK cells as prognostic indicators for patients with squamous cell carcinoma of the head and neck after radiochemotherapy: A multicentre retrospective study of the German Cancer Consortium
Stangl, S.; Tontcheva, N.; Sievert, W.; Shevtsov, M.; Niu, M.; Schmid, T.; Pigorsch, S.; Combs, S.; Haller, B.; Balermpas, P.; Rödel, F.; Rödel, C.; Fokas, E.; Krause, M.; Linge, A.; Lohaus, F.; Baumann, M.; Tinhofer, I.; Budach, V.; Stuschke, M.; Grosu, A.; Abdollahi, A.; Debus, J.; Belka, C.; Maihöfer, C.; Mönnich, D.; Zips, D.; Multhoff, G.
Tumor cells frequently overexpress heat shock protein 70 (Hsp70) and present it on their cell surface, where it can be recognized by pre-activated NK cells. In our retrospective study the expression of Hsp70 was determined in relation to tumor-infiltrating CD56+ NK cells in formalin-fixed paraffin embedded (FFPE) tumor specimens of patients with SCCHN (N = 145) as potential indicators for survival and disease recurrence. All patients received radical surgery and postoperative cisplatin-based radiochemotherapy (RCT). In general, Hsp70 expression was stronger, but with variable intensities, in tumor compared to normal tissues. Patients with high Hsp70 expressing tumors (scores 3-4) showed significantly decreased overall survival (OS; p = 0.008), local progression-free survival (LPFS; p = 0.034) and distant metastases-free survival (DMFS; p = 0.044), compared to those with low Hsp70 expression (scores 0-2), which remained significant after adjustment for relevant prognostic variables. The adverse prognostic value of a high Hsp70 expression for OS was also observed in patient cohorts with p16- (p = 0.001), p53- (p = 0.0003) and HPV16 DNA-negative (p = 0.001) tumors. The absence or low numbers of tumor-infiltrating CD56+ NK cells also correlated with significantly decreased OS (p = 0.0001), LPFS (p = 0.0009) and DMFS (p = 0.0001). A high Hsp70 expression and low numbers of tumor-infiltrating NK cells have the highest negative predictive value (p = 0.00004). In summary, a strong Hsp70 expression and low numbers of tumor-infiltrating NK cells correlate with unfavorable outcome following surgery and RCT in patients with SCCHN, and thus serve as negative prognostic markers.
Keywords: Hsp70; IHC; NK cells; SCCHN; prognostic biomarker; retrospective trial

Registration No. 26978 - Permalink


Tumor heterogeneity determined with a γH2AX foci assay: A study in human head and neck squamous cell carcinoma (hHNSCC) models
Rassamegevanon, T.; Löck, S.; Range, U.; Krause, M.; Baumann, M.; von Neubeck, C.
PURPOSE:

This study aimed to analyze the intra-tumoral heterogeneity of γH2AX foci in tumor specimens following ex vivo radiation to evaluate the potential of γH2AX foci as predictors for radiosensitivity.
MATERIAL AND METHODS:

γH2AX foci were quantified in tumor specimens of 3hHNSCC tumor models with known differences in radiosensitivity after reoxygenation in culture medium (10h, 24h), single dose exposure (0Gy, 4Gy), and fixation 24h post-irradiation. Multiple, equally treated samples of the same tumor were analyzed for foci, normalized and fitted in a linear mixed-effects model.
RESULTS:

The ex vivo reoxygenation time had no significant effect on γH2AX foci counts. A significant intra model heterogeneity could be shown for FaDu (p=0.033) but not for SKX (p=0.167) and UT-SCC-5 (p=0.082) tumors, respectively. All tumor models showed a significant intra-tumoral heterogeneity between specimens of the same tumor (p<0.01) or among microscopic fields of a particular tumor specimen (p<0.0001).
CONCLUSION:

Similar results for ex vivo γH2AX foci between 10h and 24h reoxygenation time support the applicability of the assay in a clinical setting. The high intra-tumoral heterogeneity underlines the necessity of multiple analyzable samples per patient and therewith the need for an automated foci analysis.

Copyright © 2017 Elsevier B.V. All rights reserved.
Keywords: Biomarker; Radiosensitivity; Tumor heterogeneity; γH2AX foci

Registration No. 26977 - Permalink


Development of a genetic sensor that eliminates p53 deficient cells
Mircetic, J.; Dietrich, A.; Paszkowski-Rogacz, M.; Krause, M.; Buchholz, F.
The TP53 gene fulfills a central role in protecting cells from genetic insult. Given this crucial role it might be surprising that p53 itself is not essential for cell survival. Indeed, TP53 is the single most mutated gene across different cancer types. Thus, both a theoretical and a question of significant practical applicability arise: can cells be programmed to make TP53 an essential gene? Here we present a genetic p53 sensor, in which the loss of p53 is coupled to the rise of HSV-TK expression. We show that the sensor can distinguish both p53 knockout and cells expressing a common TP53 cancer mutation from otherwise isogenic TP53 wild-type cells. Importantly, the system is sensitive enough to specifically target TP53 loss-of-function cells with the HSV-TK pro-drug Ganciclovir both in vitro and in vivo. Our work opens new ways to programming cell intrinsic transformation protection systems that rely on endogenous components.

Registration No. 26974 - Permalink


Comparison of detection methods for HPV status as a prognostic marker for loco-regional control after radiochemotherapy in patients with HNSCC.
Linge, A.; Schötz, U.; Löck, S.; Lohaus, F.; von Neubeck, C.; Gudziol, V.; Nowak, A.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Bunea, H.; Grosu, A.; Abdollahi, A.; Debus, J.; Ganswindt, U.; Lauber, K.; Pigorsch, S.; Combs, S.; Mönnich, D.; Zips, D.; Baretton, G.; Buchholz, F.; Krause, M.; Belka, C.; Baumann, M.
OBJECTIVE:

To compare six HPV detection methods in pre-treatment FFPE tumour samples from patients with locally advanced head and neck squamous cell carcinoma (HNSCC) who received postoperative (N = 175) or primary (N = 90) radiochemotherapy.
MATERIALS AND METHODS:

HPV analyses included detection of (i) HPV16 E6/E7 RNA, (ii) HPV16 DNA (PCR-based arrays, A-PCR), (iii) HPV DNA (GP5+/GP6+ qPCR, (GP-PCR)), (iv) p16 (immunohistochemistry, p16 IHC), (v) combining p16 IHC and the A-PCR result and (vi) combining p16 IHC and the GP-PCR result. Differences between HPV positive and negative subgroups were evaluated for the primary endpoint loco-regional control (LRC) using Cox regression.
RESULTS:

Correlation between the HPV detection methods was high (chi-squared test, p < 0.001). While p16 IHC analysis resulted in several false positive classifications, A-PCR, GP-PCR and the combination of p16 IHC and A-PCR or GP-PCR led to results comparable to RNA analysis. In both cohorts, Cox regression analyses revealed significantly prolonged LRC for patients with HPV positive tumours irrespective of the detection method.
CONCLUSIONS:

The most stringent classification was obtained by detection of HPV16 RNA, or combining p16 IHC with A-PCR or GP-PCR. This approach revealed the lowest rate of recurrence in patients with tumours classified as HPV positive and therefore appears most suited for patient stratification in HPV-based clinical studies.
Keywords: DKTK-ROG; HNSCC; HPV; Loco-regional control; Radiochemotherapy; p16

Registration No. 26970 - Permalink


Thionine-graphene oxide covalent hybrid and its interaction with light.
Krzyszkowska, E.; Walkowiak-Kulikowska, J.; Stienen, S.; Wojcik, A.
Graphene oxide sheets (GO) were covalently functionalized with thionine molecules. The obtained hybrid material, Th-GO, was characterized by means of scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Subsequently, the interaction of light with the free dye molecules and with dye molecules bound to the graphene oxide sheets was probed via UV-Vis spectroscopy, fluorescence spectroscopy and femtosecond pump-probe spectroscopy. The experimental results proved that thionine was successfully grafted onto the GO sheets, however, only one of the two amino groups of thionine was always involved in the amide bond formation. The Th-GO hybrid suspended in N,N-dimethylformamide (DMF) exhibited suppressed fluorescence as compared to the free dye in the same solvent, pointing to an efficient interaction between the photoexcited dye and the graphene sheets. Yet, no electron transfer products were detected by transient absorption measurements, even though there was a shortening of the singlet excited state lifetime of thionine (from the 567 ps for the free dye to the 313 ps for the dye in Th-GO). These results can be rationalized in terms of a fast back electron transfer process or possibly an energy transfer process.

Downloads:

Registration No. 26965 - Permalink


Synchrotron X-ray Imaging and Numerical Modelling of Dendritic Sidebranch Evolution during Coarsening
Neumann-Heyme, H.; Shevchenko, N.; Eckert, K.; Grenzer, J.; Beckermann, C.; Eckert, S.
We study the local dynamics of dendritic side arms during coarsening by combining in-situ radiography observations with numerical and analytical models. A flat sample of a Ga-In alloy is partially solidified and then held isothermally in a vertical temperature gradient. The evolving dendritic microstructure is visualized by synchrotron X-ray imaging at the BM20 beamline (ESRF, France). The resulting 2D images provide a high resolution in space and time at low noise levels, enabling accurate dynamical measurements. Throughout the initial growth stage there is evidence of solutal natural convection, which however vanishes towards the subsequent coarsening processes. During the coarsening stage, the time evolution of essential geometrical features of side branches was captured by automated image processing. This data is used to quantify the dynamics of three basic evolution scenarios for side branches: retraction, pinch-off and coalescence. We exploit the universal dynamics of sidearm necks during pinch-off to determine the product of liquid diffusivity and capillarity length, 𝐷𝑑0, as a parameter that is crucial in the calibration of quantitative reference models. By employing an idealized phase-field model for the evolution of a single side branch, we are able to predict the behaviour of selected side branches from the experiment in a consistent way.
Keywords: Dendritic Solidification, Coarsening Dynamics, Material Properties
  • Contribution to proceedings
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK, 978-1-908549-29-7, 214-217
  • Lecture (Conference)
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK

Registration No. 26964 - Permalink


Laboratory experiments on dynamo action and magnetorotational instability
Stefani, F.
Magnetic fields of planets, stars and galaxies are produced by the homogeneous dynamo effect in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can foster cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), Keplerian flows that would be otherwise hydrodynamically stable.
For a long time, both effects had been the subject of purely theoretical and numerical research. This changed in 1999 when the threshold of magnetic-field self-excitation was crossed in the two liquid sodium experiments in Riga and Karlsruhe [1]. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest, such as field reversals and excursions. Liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, and Socorro have contributed further important findings. MRI-related research was partly successful with the observation of the helical MRI [2] and the azimuthal MRI [3] at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). First evidence of the current-driven Tayler instability (TI) in a liquid metal was obtained here, too [4].
The lecture gives a cursory account of the recent laboratory experiments on dynamo action and magnetically triggered flow instabilities. It concludes with an overview about future experiments, with special focus on the precession-driven liquid sodium experiment and the large-scale MRI experiment that are under construction in the framework of the DRESDYN project at HZDR [5].

[1] Gailitis, A. et al., Rev. Mod. Phys. 74 (2002), 973-990
[2] Stefani, F. et al., Phys. Rev. Lett. 97 (2006), 184502
[3] Seilmayer, M. et al., Phys. Rev. Lett. 113 (2014), 024505
[4] Seilmayer, M. et al., Phys. Rev. Lett. 108 (2012), 244501
[5] Stefani, F. et al., IOP Conf. Ser.: Mater. Sci. Eng. 228 (2017), 012002
  • Invited lecture (Conferences)
    Séminaires de l'IRAP, 18.01.2018, Toulouse, France

Registration No. 26962 - Permalink


Tidally synchronized Tayler-Spruit and Babcock-Leighton type dynamos
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.
The usual explanation of the Hale cycle of the solar magnetic field builds on intrinsic features of the solar dynamo, comprising the turbulent resistivity and the intensities of the alpha effect, the Omega effect and the meridional circulation. However, the dissimilarity of the sequence of solar cycles with a random walk in phase, and their remarkable synchronization with the 11.07 years period of the alignment of the tidally dominant planets Venus, Earth and Jupiter has not remained unobserved.
Asking for a viable physical mechanism that could link the very weak planetary forces with solar dynamo action, we focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability that is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantly excited by m=2 perturbations that reflect tidal oscillations. Specifically, we speculate that the 11.07 years tidal oscillation may lead to a 1:1 resonant excitation of the oscillation of the associated alpha effect. In the framework of simple dynamo model of the Tayler-Spruit type, we recover the 22.14-year cycle of the solar dynamo. Interestingly, slight parameter changes of this model lead to transitions between oscillatory and pulsatory behaviour with maintained phase coherence, which might serve as an analogue of the behaviour during grand minima.
We have also tested similar dynamo models of the Babcock-Leighton type, for which we have pursued two ideas on how such a synchronization could work. The first one bears on the concept of a sensitive flux storage capacity of the tachocline, which might be easily influenced by minor perturbations as provoked by tidal forces, the second one on periodic changes of the Omega effect. In either case, and in contrast to this easy and robust synchronizability of Tayler-Spruit type dynamos, the model proved rather rather stubborn to synchronization.
  • Lecture (others)
    GDRI Dynamo Meeting, 27.-29.11.2017, Paris, France

Registration No. 26961 - Permalink


Dynamos, instabilities, inverse problems: Paul Roberts' legacy for experimental MHD
Stefani, F.
Retracing Paul Roberts' footsteps, I survey the recent experimental activities related to dynamo action, magnetically triggered flow instabilities, Alfvén waves, and magnetic flow tomography. I'm certain he will be most pleased by those developments that have superseded some of the pessimistic prognoses made in his seminal 1967 book: "Since processes of self-excitation are out of the question..." (p. 172), is just a case in point.
  • Invited lecture (Conferences)
    Fifty years after Roberts’ MHD: Dynamos and planetary flows today (PHR2017), 16.-17.11.2017, London, UK

Registration No. 26960 - Permalink


Of Mikes and butterflies
Stefani, F.
More often than not, after having worked for some time on a problem related to dynamos or magnetic instabilities, I said to myself: "I should have read Michael Proctor before!" Actually, not many scientists have influenced magnetohydrodynamics so profoundly as he did. In a personally biased selection, I discuss some experimental and theoretical MHD topics which were strongly influenced by Michael Proctor's ideas. Those include: 1) The distinction between convective and absolute instabilities, which turned out to be essential for the experimental demonstration of the dynamo effect in Riga and the helical magnetorotational instability (MRI) in Dresden, 2) the Malkus-Proctor effect, as nicely illustrated by the saturation mechanism of the Riga dynamo, 3) double-diffusive magnetic instabilities, such as buoyancy instabilities, but also helical and azimuthal MRI and Super-AMRI, 3) spectral degeneracies of dynamo operators in diabolic or exceptional points, and their (putative) role for reversals of the geodynamo, 4) highly nonlinear dynamo mechanisms, such as MRI dynamos and Tayler-Spruit dynamos.
  • Lecture (others)
    MREP 2017, 11.-12.09.2017, Cambridge, UK

Registration No. 26959 - Permalink


Laboratory experiments and numerical simulations on magnetic instabilities.
Stefani, F.; Gellert, M.; Kasprzyk, C.; Paredes, A.; Rüdiger, G.; Seilmayer, M.
Magnetic fields of planets, stars, and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both hydromagnetic dynamo action and magnetically triggered flow instabilities had been the subject of purely theoretical research. Meanwhile, however, the dynamo effect has been observed in large-scale liquid sodium experiments in Riga, Karlsruhe, and Cadarache. In this chapter, we summarize the results of some smaller liquid metal experiments devoted to various magnetic instabilities, such as the helical and the azimuthal magnetorotational instability, the Tayler instability, and the different instabilities that appear in a magnetized spherical Couette flow. We conclude with an outlook on a large scale Tayler-Couette experiment using liquid sodium, and on the prospects to observe magnetically triggered instabilities of flows with positive shear.
Keywords: Dynamo, Magnetorotational instability
  • Book chapter
    Lühr H., Wicht J., Gilder S., Holschneider M.: Magnetic fields in the solar system. Astrophysics and Space Science Library, vol. 448, Cham: Springer, 2018, 978-3-319-64291-8, 125-152
    DOI: 10.1007/978-3-319-64292-5_5

Registration No. 26958 - Permalink


Evaporation-assisted magnetic separation of rare earth ions in aqueous solutions
Lei, Z.; Fritzsche, B.; Eckert, K.ORC
This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient [1] despite the presence of a counteracting Brownian motion. For that purpose, we study a rare earth chloride (DyCl3) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure in a specially developed cell, see Fig. 1.
The temporal evolution of the refractive index field of this solution, as a result of heat and mass transfer, is measured by means of a Mach-Zehnder interferometer. We develop a numerical algorithm which splits the refractive index field into two parts, one space-dependent and conservative and the other time-dependent and transient. By using this algorithm in conjunction with a numerical simulation of the temperature and concentration field, we are able to show that 90% of the refractive index in the evaporation-driven boundary layer is caused by an increase in the concentration of Dy(III) ions. A simplified analysis of the gravitational and magnetic forces, entering the Rayleigh number, leads to a diagram of the system's instability. Accordingly, the enrichment layer of elevated Dy(III) concentration is placed in a spatial zone dominated by a field gradient force. This leads to the unconditional stability of this layer in the present field. The underlying mechanism is the levitation and reshaping of the evaporation-driven boundary layer by the magnetic field gradient [2].

[1] X. Yang, K. Tschulik, M. Uhlemann, S. Odenbach, K. Eckert, J. Phys. Chem. Lett. 3 (2012), 3559–3564.
[2] Z. Lei, B. Fritzsche, K. Eckert, submitted to J. Phys. Chem. C (2017).
Keywords: magnetic separation, rare earth, interferometry
  • Lecture (Conference)
    International Conference on Magneto-Science 2017 (ICMS 2017), 23.-27.10.2017, Reims, Frankreich

Registration No. 26957 - Permalink


Laser ion acceleration using the Draco Petawatt facility at HZDR
Zeil, K.; Obst, L.; Rehwald, M.; Brack, F.; Metzkes, J.; Kraft, S.; Schlenvoigt, H.-P.; Ziegler, T.; Jahn, A.; Kroll, F.; Kluge, T.; Schramm, U.
Demanding applications like radiation therapy of cancer are pushing the frontier of laser driven proton accelerators with controlled and well-defined proton beam properties. This talk will give an overview of recent achievements at the high-contrast high power laser source DRACO at the HZDR in Dresden (Germany). The laser system was recently upgraded by an additional Petawatt (PW) amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. In first experiments the delivery of these pulses on target was demonstrated and the feasibility of worldwide first controlled volumetric irradiation of a specifically developed tumor model, grown on the ears of nude mice with laser-accelerated protons was investigated. In order to efficiently capture and shape the divergent TNSA proton beam, a setup of two pulsed high-field solenoid magnets will be presented to reliably generate homogeneous dose distributions in lateral direction and in depth.
The performance of laser based proton and ion acceleration and the scaling of the laser energy to achieve increased ion energies strongly depend on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse. Re-collimating single plasma mirror devices have been implemented into the Draco laser beam lines and the talk will summarize on measurements of the resulting contrast enhancement comparing different techniques. With the achieved contrast enhancement, laser proton acceleration and proton energy scaling were investigated within the TNSA regime using ultra-thin foil targets and implications for the radiobiological experiments will be discussed.
  • Lecture (Conference)
    Laser and Plasma Acceleration Workshop, 28.08.2017, Jeju Island, South Korea

Registration No. 26956 - Permalink


Laser ion acceleration using the Draco Petawatt facility at HZDR - experiments and radio-biological application
Zeil, K.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Brack, F.; Kroll, F.; Metzkes, J.; Prencipe, I.; Huebl, A.; Kluge, T.; Bussmann, M.; Kraft, S.; Ziegler, T.; Bernert, C.; Jahn, A.; Gaus, L.; Schramm, U.
Demanding applications like radiation therapy of cancer are pushing the frontier of laser driven proton accelerators with controlled and well-defined proton beam properties. This talk will give an overview of recent achievements at the high-contrast high power laser source DRACO at HZDR. The laser system was recently upgraded by an additional Petawatt (PW) amplifier stage and new front end components finally providing high contrast pulses of >500 TW on target at 1 Hz pulse repetition rate. In first experiments with the new PW beam line of Draco the feasibility of worldwide first controlled volumetric irradiation of a specifically developed tumor model, grown on the ears of nude mice with laser-accelerated protons was investigated. In order to efficiently capture and shape the divergent TNSA proton beam, a setup of two pulsed high-field solenoid magnets was used. In the talk the reliable generation of homogeneous dose distributions lateral and in depth will be discussed.

The performance of laser based ion acceleration and the scaling of the laser energy to achieve increased ion energies strongly depend on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse. With such contrast enhancement techniques laser proton acceleration using ultra-thin foil targets as well as a renewable debris-free hydrogen jet (in collaboration with SLAC and European XFEL) target was investigated with a laser pulse energy of 3 J and duration of 30 fs and show robust TNSA proton pulses with energies of up to 25 MeV. An important implication of this is the demonstration of a credible path toward high repetition rate laser-based ion acceleration applications.
  • Invited lecture (Conferences)
    International Conference on High Energy Density Sciences, 21.4.2017, Tokio-Yokohama, Japan

Registration No. 26955 - Permalink


Evolution of the Interfacial Area in Dendritic Solidification
Neumann-Heyme, H.; Eckert, K.; Beckermann, C.
The specific area of the solid-liquid interface is an important integral measure for the morphological evolution during solidification. It represents not only the inverse of a characteristic length scale of the microstructure, but it is also a key ingredient in volume-averaged models of alloy solidification. Analytical descriptions exist for either pure coarsening or pure growth processes. However, all alloy solidification processes involve concurrent growth and coarsening. In the present study, the kinetics of the solid-liquid interface of a dendrite are studied using a 3D phase-field model. The simulation results are combined with data from recent synchrotron tomography experiments to study the influence of the cooling rate and alloy composition on the evolution of the interfacial area. A general relation for the specific interfacial area of dendrites is presented that is valid over the entire range of cooling rates, including isothermal coarsening.
Keywords: Dendritic Solidification, Interfacial Area, Phase-Field Simulation
  • Contribution to proceedings
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK
    Evolution of the Interfacial Area in Dendritic Solidification, 978-1-908549-29-7, 193-196
  • Lecture (Conference)
    International Conference on Solidification Processing, SP17, 25.-28.07.2017, Old Windsor, UK

Registration No. 26954 - Permalink


Research at the Dresden High Magnetic Field Laboratory
Wosnitza, J.
  • Invited lecture (Conferences)
    Seminar at the Department of Chemistry, Graduate School of Science, Osaka University, 22.09.2017, Osaka, Japan

Registration No. 26953 - Permalink


The FFLO state in layered organic superconductors
Wosnitza, J.
  • Invited lecture (Conferences)
    International Conference on Electron Correlation in Superconductors and Nanostructures, 17.-20.08.2017, Odessa, Ukraine

Registration No. 26951 - Permalink


FFLO states in layered organic superconductors
Wosnitza, J.
  • Invited lecture (Conferences)
    QCNP 2017 Quantum Criticality & Novel Phases, 26.02.-01.03.2017, Berlin, Deutschland

Registration No. 26950 - Permalink


Stereotactic radiosurgery for brainstem metastases : In experienced hands a good treatment option with excellent risk-benefit ratio
Khademalhosseini, Z.; Khademolhosseini, M.; Kummer, B.; Krause, M.

Registration No. 26949 - Permalink


SDF-1/CXCR4 expression in head and neck cancer and outcome after postoperative radiochemotherapy
De-Colle, C.; Mönnich, D.; Welz, S.; Boeke, S.; Sipos, B.; Fend, F.; Mauz, P.-S.; Tinhofer, I.; Budach, V.; Jawad, J. A.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Bayer, C.; Belka, C.; Pigorsch, S.; Combs, S. E.; Lohaus, F.; Linge, A.; Krause, M.; Baumann, M.; Zips, D.; Menegakis, A.
Introduction

Outcome after postoperative radiochemotherapy (RT-CT) for patients with advanced head and neck squamous cell carcinomas (HNSCC) remains unsatisfactory, especially among those with HPV negative tumours. Therefore, new biomarkers are needed to further define subgroups for individualised therapeutic approaches. Preclinical and first clinical observations showed that the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12) play an important role in tumour cell proliferation, survival, cancer progression, metastasis and treatment resistance. However, the data on the prognostic value of SDF-1/CXCR4 expression for HNSCC are conflicting. The aim of our hypothesis-generating study was to retrospectively explore the prognostic potential of SDF-1/CXCR4 in a well-defined cohort of HNSCC patients collected within the multicenter biomarker study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG).
Material and methods

Patients with stage III and IVA HNSCC of the oral cavity, oropharynx and hypopharynx were treated with resection and adjuvant radiotherapy (RT) with ≥60 Gy and concurrent cisplatin-based chemotherapy (CT). Tissue micro-arrays (TMAs) from a total of 221 patients were generated from surgical specimens, 201 evaluated for the SDF-1 and CXCR4 expression by immunofluorescence and correlated with clinico-pathological and outcome data.
Results

In univariate and multivariate analyses intracellular SDF-1 expression was associated with lower loco-regional control (LRC) in the entire patient group as well as in the HPV16 DNA negative subgroup. CXCR4 expression showed a trend for lower LRC in the univariate analysis which was not confirmed in the multivariate analysis. Neither for SDF-1 nor CXCR4 expression associations with distant metastasis free or overall survival were found.
Conclusions

Our exploratory data support the hypothesis that overexpression of intracellular SDF-1 is an independent negative prognostic biomarker for LRC after postoperative RT-CT in high-risk HNSCC. Prospective validation is warranted and further exploration of SDF-1/CXCR4 as a potential therapeutic target to overcome treatment resistance in HNSCC appears promising.

Registration No. 26947 - Permalink


The PD-1/PD-L1 axis and human papilloma virus in patients with head and neck cancer after adjuvant chemoradiotherapy: A multicentre study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG).
Balermpas, P.; Rödel, F.; Krause, M.; Linge, A.; Lohaus, F.; Baumann, M.; Tinhofer, I.; Budach, V.; Sak, A.; Stuschke, M.; Gkika, E.; Grosu, A.-L.; Abdollahi, A.; Debus, J.; Stangl, S.; Ganswindt, U.; Belka, C.; Pigorsch, S.; Multhoff, G.; Combs, S. E.; Welz, S.; Zips, D.; Lim, S. Y.; Rödel, C.; Fokas, E.
We examined the prognostic role of PD-1+ and CD8+ tumor infiltrating lymphocytes (TILs), and PD-L1+ cells in patients with squamous cell carcinoma of the head and neck (SCCHN) treated with surgery and postoperative chemoradiotherapy (CRT). FFPE samples from 161 patients were immunohistochemically stained for PD-1, CD8 and PD-L1. The immune marker expression was correlated with clinicopathologic characteristics, and overall survival (OS), local progression-free survival (LPFS) and distant metastases free-survival (DMFS), also in the context of HPV16 DNA/p16 status. The median follow-up was 48 months (range: 4-100). The 2-year-OS was 84.1% for the entire cohort. High PD-1 and PD-L1 expression were more common in patients with positive HPV16 DNA (p < 0.001 and p = 0.008, respectively) and high infiltration by CD8+ TILs (p < 0.001 for both markers). High PD-L1 expression correlated with superior OS (p = 0.025), LPFS (p = 0.047) and DMFS (p = 0.048) in multivariable analysis, whereas no significance could be demonstrated for PD-1. Patients with CD8high /PD-L1high expression had favorable outcome (p < 0.001 for all endpoints) compared to other groups. We validated the superior OS data on CD8high /PD-L1high using the Cancer Genome Atlas TCGA dataset (n = 518; p = 0.032). High PD-L1 expression was a favorable prognostic marker in HPV16-negative but not HPV16-positive patients. In conclusion, HPV-positive tumors showed higher expression of immune markers. PD-L1 expression constitutes an independent prognostic marker in SCCHN patients post-adjuvant CRT. In conjunction with CD8 status, these data provide an important insight on the immune contexture of SCCHN and are directly relevant for future treatment stratification with PD-1/PD-L1 immune checkpoint inhibitors to complement CRT.
Keywords: CD8; HPV; PD-1/PD-L1; SCCHN; chemoradiotherapy; prognostic

Registration No. 26945 - Permalink


Prompt gamma spectroscopy for range control with CeBr3.
Martins, P. M.; Bello, R. D.; Rinscheid, A.; Roemer, K.; Werner, T.; Enghardt, W.; Pausch, G.; Seco, J.
Prompt gamma spectroscopy for range control with CeBr3.

Registration No. 26944 - Permalink


Magnetically induced cavitation for the dispersion of nanoparticles in liquid metals
Sarma, M.; Gerbeth, G.; Grants, I.; Kaldre, I.; Bojarevics, A.
Dispersion of particles to produce metal matrix nanocomposites (MMNC) can be achieved by means of ultrasonic vibration of the melt using ultrasound transducers. However direct transfer of this method to produce steel composites is not feasible because of the much higher working temperature. Therefore, an inductive technology for contactless treatment by acoustic cavitation was developed. This report describes the samples produced to assess the feasibility of the proposed method for nano-particle separation in steel. Stainless steel samples with inclusions of TiB2, TiO2, Y2O3, CeO2, Al2O3 and TiN have been created and analyzed. Additional experiments have been performed using light metals with an increased value of the steady magnetic field using a superconducting magnet with a field strength up to 5 T.
Keywords: MMC production, Steel composites, Cavitation treatment
  • Contribution to proceedings
    XVIII International UIE-Congress Electrotechnologies for Material Processing, 06.-09.06.2017, Hannover, Deutschland: Vulkan-Verlag GmbH, 978-3-8027-3095-5

Registration No. 26938 - Permalink


Azimuthal magnetorotational instability with super-rotation
Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.
It is demonstrated that the azimuthal magnetorotational instability (AMRI) also works with radially increasing rotation rates contrary to the standard magnetorotational instability for axial fields which requires negative shear. The stability against non-axisymmetric perturbations of a conducting Taylor–Couette flow with positive shear under the influence of a toroidal magnetic field is considered if the background field between the cylinders is current free. For small magnetic Prandtl number Pm->0 the curves of neutral stability converge in the (Hartmann number, Reynolds number) plane approximating the stability curve obtained in the inductionless limit Pm=0. The numerical solutions for Pm=0 indicate the existence of a lower limit of the shear rate. For large Pm the curves scale with the magnetic Reynolds number of the outer cylinder but the flow is always stable for magnetic Prandtl number unity as is typical for double-diffusive instabilities. We are particularly interested to know the minimum Hartmann number for neutral stability. For models with resting or almost resting inner cylinder and with perfectly conducting cylinder material the minimum Hartmann number occurs for a radius ratio of 0.9. The corresponding critical Reynolds numbers are smaller than 10000.

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  • Secondary publication expected from 25.07.2018

Registration No. 26936 - Permalink


Quasi-free (p,pN) scattering of light neutron-rich nuclei around N = 14
Diaz Fernandez, P.; Alvarez-Pol, H.; Crespo, R.; Cravo, E.; Atar, L.; Deltuva, A.; Aumann, T.; Avdeichikov, V.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boillos, J. M.; Boretzky, K.; Borge, M. J. G.; Caamano, M.; Cabanelas, P.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chartier, M.; Chulkov, L. V.; Cortina-Gil, D.; Datta Pramanik, U.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fernandez-Dominguez, B.; Fraile, L. M.; Freer, M.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Golubev, P.; Göbel, K.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Hufnagel, A.; Ignatov, A.; Johansson, H. T.; Jonson, B.; Jurciukonis, D.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knyazev, A.; Kröll, T.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lindberg, S.; Machado, J.; Marganiec, J.; Moro, A. M.; Movsesyan, A.; Nacher, E.; Najafi, A.; Nikolskii, E.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietras, B.; Pietri, S.; Plag, R.; Reifarth, R.; Ribeiro, G.; Rigollet, C.; Rossi, D.; Röder, M.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Syndikus, I.; Taylor, J. T.; Tengblad, O.; Thies, R.; Togano, Y.; Vandebrouck, M.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Wheldon, C.; Wilson, G.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.
In this work we investigate for the first time the quasi-free scattering reactions (p,pn) and (p,2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15.
Keywords: quasi-free scattering reactions radioactive beams single-particle

Registration No. 26935 - Permalink


Single molecule level measurements: salen molecule
Kilibarda, F.; Sendler, T.; Mortensen, M.; Gothelf, K.; Erbe, A.
The research presents novel ideas and directions which are supposed to overcome the obstacles conditioned by larger and larger deviations from the Moor's law. One of the possible solutions of the problem lies in the field of Molecular Electronics. We attempt to reduce the size and power needed to operate the device by using single molecules as building blocks in our circuits. This not only offers new features but also self-organizing properties. In order to choose the correct building blocks for our future circuits, we first characterize them. One of the prominent techniques is the Mechanically Controllable Break Junction (MCBJ). With this method we can examine properties of electron transport through single molecules, and determine parameters such as molecular energy level and metal-molecule coupling strength. The technique is demonstrated on salen and salen derivatives. The research shows that we can successfully tune molecular energy levels by the use of chemical doping.
Keywords: Scaling, molecular electronics, single molecule, self-organizing, MCBJ, break junction, characterization, electron transport, energy level, salen, energy level tuning, chemical doping
  • Poster
    Trends in Nanoscience 2017, 27.-30.03.2017, Kloster Irsee, Bavaria, Deutschland

Registration No. 26932 - Permalink


Design rules for molecular electronics: Theoretical and experimental approach
Lokamani, L.; Kilibarda, F.; Wolf, J.; Zahn, P.; Huhn, T.; Gemming, S.; Erbe, A.
Diarylethenes, a class of photosensitive molecules which exhibit photochromism, can be switched between open- and closed-ring isomers. In break-junction experiments diarylethene derivatives in open and closed-ring forms can be distinguished by a low and high conductance state respectively with a difference in current levels of about one order of magnitude.

Here, we explore the underlying design rules for modulating electronic transport in derivatives of diarylethene. In particular, we analyze the effect on molecular orbitals due to various electron accepting and donating groups and in turn the modulation of the conductance properties of single molecules attached to gold electrodes.

We have demonstrated that the mechanically controllable break junction (MCBJ) technique can be used to classify and determine the properties of electronic transport through single organic molecules. We present an outlook on experimental methods for exploring the underlying design rules for diarylethene molecules and derivatives. As a result, we show how the addition of different side groups modifies electronic behavior of the molecules.
Keywords: Diarylethenes, photosensitive molecules, photochromism, molecular switch, break junction, MCBJ, conductance modulation, conductance, molecular design rules, single molecule, side group
  • Poster
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26930 - Permalink


Constructing nanoelectronic circuits by top-down and bottom-up strategies
Kilibarda, F.; Sendler, T.; Deb, D.; Khan, B. M.; Teschome, B.; Erbe, A.
The construction of nanoelectronic circuits requires the development of bottom-up strategies, which can be combined with top-down structuring. We show how reconfigurable silicon nanowires are produced using electron-beam lithography and reactive ion etching. Such structures can be used as large-scale electrodes to networks of self-assembled electronics on the nanoscale. As a first step towards the development of nanoscale circuits by self-organization, we demonstrate the construction of nanoscale metallic wires based on metallized DNA origamis. Active building blocks with smallest dimensions on the molecular scale are developed in single molecule contacts. The properties of those junctions need to be characterized. We have demonstrated that the mechanically controllable break junction (MCBJ) technique can be successfully used to determine the properties of electronic transport through single organic molecules and that the participating molecular energy levels and the metal-molecule coupling can be characterized using this technique. Further developments are based on the use of more complex molecules, which can, for example, be used as single molecule switches. We present the first demonstration of a single molecule junction, in which the molecule is switched in situ from the non-conducting off-state to the conducting on-state.
Keywords: silicon nanowire, e-beam lithography, lithography, self-assembled electronics, DNA origami, single molecule, MCBJ, electron transport, molecular switch
  • Poster
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26929 - Permalink


Experimental study of accretion processes in X-ray binary stars using an external magnetic field
Kroll, F.; Pelka, A.; Albertazzi, B.; Brack, F.; Brambrink, E.; Cowan, T.; Drake, P.; Falize, E.; Filipov, E.; Kuramitsu, Y.; Kuranz, C.; Lamb, D.; Levesque, J.; Li, C.; Manuel, M.; Michel, T.; Morita, T.; Ozaki, N.; Pikuz, S.; Rigon, G.; Rödel, M.; Sakawa, Y.; Schramm, U.; Shimogawara, H.; van Box Som, L.; Koenig, M.
Here we report on recent results from an experiments carried out at LULI2000 using the nanosecond beam to generate a high-density plasma flow by laser-driven rear-side shock breakout. The sample was positioned inside a pulsed coil generating a magnet field of ~15T in order to study the influence of the magnetic field on the plasma flow. In addition, an obstacle was placed behind the sample to investigate the formation of a return shock. As diagnostics we used laser-driven X-ray point projection radioscopy driven by the pico2000 beam and optical Schlieren Imaging, shadowgraphy, and Streaked Optical Pyrometry from two sides.

Accretion processes are among the most important phenomena in high-energy astrophysics since they are widely believed to provide the power supply in various astrophysical objects and they are the main source of radiation in several binary systems [1]. Understanding the complex physical processes that allow releasing gravitational energy in form of radiation is fundamental to interpret the high-energy astronomical observations [2]. Among the different X-ray binary systems are cataclysmic variable stars, close binary systems containing a white dwarf that accretes matter from a late type Roche-lobe filling secondary star [3]. They provide unique insight on accretion processes in extreme astrophysical regimes since sources of luminosity other than the accretion region itself are relatively weak.

In some cataclysmic variable stars, the magnetic field is strong enough (B>10MG) to prevent the formation of an accretion disk and to channel the accreting plasmas onto the compact object magnetic poles, leading to the formation of an accretion column and impacts the white dwarf atmosphere. By fulfilling similarity properties and scaling laws these processes can be scaled to laboratory length and time scales und thus can be studied using high energy laser-matter interactions. [4] Up to now experiments used a tube in order to collimate the plasma flow generated [5]. This induced spurious effects such as wall shocks and tube explosion that are necessary to avoid. Here we instead applied a pulsed high-field magnetic coil in order to study the coupling of radiative processes in a supersonic plasma flow with magnetic effects. Both the dynamics of high-density and low-density regions of the flow were investigated by utilizing a combination of X-ray radiography and optical Schlieren imaging.
  • Invited lecture (Conferences)
    International Symposium on Topical Problems of Nonlinear Wave Physics (NWP-2017) - LaB Workshop, 22.-28.07.2017, Moscow - St.-Petersburg, Russia

Registration No. 26926 - Permalink


Formation of orthorhombic (Zr,Ta)O₂ in thin Zr-Ta-O films
Lehninger, D.; Rafaja, D.; Wünsche, J.; Schneider, F.; von Borany, J.; Heitmann, J.
The formation of orthorhombic (Zr,Ta)O2 was found in annealed thin Zr-Ta-O films with various tantalum concentrations deposited by co-sputtering a ZrO2 target and a mixed ZrO2/Ta2O5 target. In the as-deposited state, all films were amorphous. After annealing, tetragonal (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) < 0.19 and orthorhombic (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) > 0.19 were formed. Thin films with excess of tantalum ([Ta]/([Ta]+[Zr])> 0.5) decomposed into two orthorhombic phases upon crystallization: (Zr,Ta)O2 and tantalum-rich (Ta,Zr)2O5. The Rietveld analysis of Xray diffraction patterns revealed that the crystal structure of (Zr,Ta)O2 can be described with the non-centrosymmetric space group Pbc21. The broad range of tantalum concentrations, in which orthorhombic (Zr,Ta)O2 is formed as a single crystalline phase, is promising for the use of this
compound in ferroelectric field effect transistors.
Keywords: Zr-Ta-O thin films, Orthorhombic (Zr,Ta)O2, ferroelectric field effect transistors

Downloads:

  • Secondary publication expected from 30.06.2018

Registration No. 26925 - Permalink


Evolutionary Algorithm for Automated IBA Spectra Fitting
Heller, R.
In order to extract chemical compositions and layer thicknesses of layered samples from IBA spectra (RBS, ERD, etc.) experimentalists usually have to take the following approach: Simulation of a theoretical spectrum for an initial target configuration and comparison to the measured data followed by the successive adjustment of the target model iteratively until simulation result and experimental spectrum fit together. For multi-layer samples this procedure can get rather time consuming, especially when a series of similar samples with varying layer thickness and/or stoichiometry has to be analyzed.
Although modern IBA spectrum simulation software like SimNRA[1] or WINDF[2] have become quite powerful and handy tools, the analysis of IBA spectra consumes still a significant fraction of an IBA scientist’s working time. SimNRA offers therefore the opportunity to partially fit layer thicknesses and/or elemental ratios for a given layer within a certain region of a spectrum. WINDF goes a step further and has an automated spectrum fitting included which is based on a simulated annealing algorithm. However, it takes the user quite some time to set up the boundary conditions and fit parameters until the actual fit procedure can be initiated. Furthermore, the outcome of the fit procedure in some cases requires multiple re-adjustments of the boundary conditions / fit parameters.
In the present contribution, we present a new approach for automated IBA spectra fitting by implementing an evolutionary algorithm. We will show that this powerful algorithm is very well suited and robust for complete and fast IBA spectrum fitting with minimum input of boundary conditions. Furthermore, the benefits of this algorithm over other ones and the particular differences to simulated annealing are pointed out.
Based on this algorithm a software package has been developed, written in the programming language Java that is platform independent and comprises a clean and easy-to-use graphical user interface. We will introduce this software in a basic overview.
Keywords: IBA Fit routine evolutionary algorithm
  • Poster
    Ion Beam Analysis, 08.-13.10.2017, Shanghai, China

Registration No. 26924 - Permalink


Preparation of small animal irradiation experiemnts with laser-accelerated protons
Kroll, F.; Beyreuther, E.; Brack, F.-E.; Gaus, L.; Karsch, L.; Kraft, S.; Metzkes, J.; Pawelke, J.; Schlenvoigt, H.-P.; Schürer, M.; Zeil, K.; Schramm, U.
Laser-driven ion acceleration has been considered a potential alternative for conventional accelerators that may provide for a more compact and cost-efficient particle therapy solution in the future. The beam properties of laser-accelerated beams strongly differ from quasi-continuous beams from synchrotrons or cyclotrons. Laser-driven ion bunches are typically picoseconds short, yet carry up to 10^13 particles with a broad energy spectrum and high divergence.

A current driving question is whether the highly intense pulsed ion beams obtain an equivalent biological effectiveness compared to quasi-continuous beams in the case that a living organism is irradiated. Therefore, a controlled small animal irradiation (LN229 glioblastoma cells on nude mouse ear) will be performed at the Dresden laser acceleration source Draco using an intense proton beam.

The talk gives a general overview on laser-acceleration efforts in the context of translational medical research at HZDR and focuses on the experimental preparation and characterization of a proton beamline based on two pulsed high-field (20 T) solenoid magnets. The magnets match the pulsed nature of the particle source and provide for efficient beam capture, transport and field formation. Two challenging experimental tasks will be critically discussed: First, 25 MeV proton beam production at mean dose rates of the order of Gy/min with a high degree of reproducibility. And second, the generation of homogeneous lateral and depth dose distributions by means of the beam transport system.
  • Lecture (Conference)
    BMTMedPhys 2017 - Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5044

Registration No. 26923 - Permalink


Tunneling Magnetoresistance in MnRuGa based Magnetic Tunnel Junctions
Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y. C.; Thiyagarajah, N.; Atcheson, G.; Coey, M.; Stamenov, P.; Rode, K.; Lindner, J.; Faßbender, J.; Deac, A.
Some intermetallic Heusler compounds display high spin polarization and low magnetic moment. Thin-film samples can possess huge uniaxial anisotropy fields, exceeding tens of teslas. This, combined with their tuneable properties, make these materials very attractive for THz based spin-transfer-torque oscillators. Recently new material from this family was discovered - MnRuGa (MRG) - the first experimentally achieved fully-compensated half-metallic ferrimagnet. Here we show that MRG can be integrated in perpendicular anisotropy magnetic tunnel junctions stacks. Tunneling magnetoresistance (TMR) ratios up to 40% are observed. We also demonstrate that the TMR exists even when the net magnetization of MRG is strictly zero, implying that, at compensation, MRG exhibits a sizable spin polarization. The role of different diffusion barrier layers between MRG and the tunneling barrier as well as annealing temperature was investigated.

This work is supported by the Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.
Keywords: Ferrimagnetism, Half-metals, Magnetic Tunnel Junctions, Heusler Alloy
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany

Registration No. 26922 - Permalink


Tunneling magnetoresistance with zero-moment half-metallic Mn2RuXGa
Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y.-C.; Thiyagarajah, N.; Atcheson, G.; Coey, J. M. D.; Stamenov, P. S.; Rode, K.; Lindner, J.; Faßbender, J.; Deac, A. M.
Intermetallic Heusler compounds can possess high spin polarization, low magnetic moment, low Gilbert damping constant α, and huge uniaxial anisotropy fields, of the order of tens of tesla. Such a wide range of properties, most of them tunable, make these materials very attractive for spin-transfer-torque oscillators in the (sub-) THz range. A particularly suitable candidate is the near-cubic Heusler alloy of Mn, Ru, and Ga (MRG) [1]. Here, we show that tunneling magnetoresistance (TMR) of about ten percent can be achieved in MRG-based magnetic tunnel junctions (MTJs), and that the TMR can be improved by integrating different insertion layers acting as diffusion barriers between the half-metallic electrode and the tunnel barrier.

MRG-based stacks were deposited using a “Shamrock” fully automated sputter deposition tool by co-sputtering from a Mn2Ga and a Ru target. Changing the Ru concentration allows tuning the compensation temperature Tcomp between 2 and 450 K. The thin-film stacks were subsequently patterned into 20 × 20 μm2 junctions using standard UV lithography, prior to annealing in temperatures ranging from 250 °C to 350 °C. Selected samples were investigated by transmission electron microscopy (TEM).

The magnetic properties of the MTJs were analyzed by magnetotransport measurements as a function of applied bias voltage at room temperature. We found that 0.6 nm of Al acts as good diffusion barrier in Mn2RuXGa / MgO / CoFeB MTJs. Low-temperature measurements on the same device show TMR in excess of 40% close to zero bias [2]. In addition, we demonstrate non-zero TMR while cooling through the compensation temperature (where the magnetic moment is zero), indicating that magnetotransport in MRG is governed by one Mn sublattice only. This hypothesis is further supported by the fact that samples with Tcomp above room temperature exhibit inverted TMR as compared to samples that compensated below. The precise value of Tcomp is the result of a delicate balance between the moments carried by Mn ions on the 4c and 4a sites. Upon thermal annealing, this balance is slightly shifted due to partial annihilation of Mn anti-sites, and Tcomp may pass from above room temperature to below, giving rise to an inverted TMR response. The next step is to fabricate sub-µm devices based on MRG for detecting spin-transfer induced dynamics, which should occur at frequencies of several hundred GHz, given the ultra-high anisotropy of these.

This work is supported by the Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.
Keywords: Ferrimagnetism, Half-metals, Magnetic Tunnel Junctions, Heusler Alloy
  • Lecture (Conference)
    Moscow International Symposium on Magnetism, 01.-05.07.2017, Moscow, Russia

Registration No. 26921 - Permalink


Tunneling magnetoresistance in MnRuGa based Magnetic Tunnel Junctions
Titova, A.; Fowley, C.; Borisov, K.; Betto, D.; Lau, Y. C.; Thiyagarajah, N.; Atcheson, G.; Coey, M.; Stamenov, P.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.
Nowadays great attention has been paid to the research of intermetallic Heusler compounds. These materials have widely tunable properties. They display high spin polarisation [1], low magnetic moment [2] and low Gilbert damping α [3]. Furthermore, these thin-film samples can possess huge uniaxial anisotropy fields, exceeding tens of Teslas [4]. Such a wide range of almost completely tunable properties make these materials very attractive for THz based spin-transfer-torque oscillators [6]. Here we have successfully integrated a compensated half-metallic ferrimagnet as a fixed layer in magnetic tunnel junctions (MTJ). Theoretically, this class of materials was predicted in 1995 by van Leuken and de Groot [7], but experimentally the zero-moment half-metal was realized only in 2014 [8] for a near-cubic Heusler alloy of Mn, Ru, and Ga (MRG). We showed that Tunneling Magnetoresistance (TMR) ratio reaches 40% in our stacks. We also demonstrate that the TMR exists even when the net magnetization of MRG is strictly zero, implying that, at compensation, MRG exhibits a sizable spin polarization [9]. We investigated the role of different diffusion barrier layers between MRG and the tunneling barrier as well as annealing temperature.
Keywords: Ferrimagnetism, Half-metals, Magnetic Tunnel Junctions, Heusler Alloy
  • Poster
    IEEE Magnetics Society Summer School, 18.-23.06.2017, Santander, Spain

Registration No. 26919 - Permalink


Structural disorder induced magnetization in FeAl and FeRh: The perspectives for laterally patterned magnetic metamaterials
Semisalova, A. S.; Bali, R.; Wintz, S.; Barton, C.; Thomson, T.; Hlawacek, G.; Fowley, C.; Ehrler, J.; Bottger, R.; Potzger, K.; Lindner, J.; Fassbender, J.
The possibilities of fabrication of magnetic nanostructures using ion irradiation will be exampled with the recent achievements in FeAl and FeRh. Magnetization of both alloys at room temperature is highly sensitive to the structural state (ordered or disordered). This opens a way for lateral patterning of nanoscale ferromagnets embedded in paramagnetic (FeAl) or antiferromagnetic (FeRh) ordered matrix and studying the effect of planar geometry of magnetic interfaces.
  • Invited lecture (Conferences)
    META'17, The 8th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 25.-28.07.2017, Incheon - Seoul, Korea

Registration No. 26918 - Permalink


Multifrequency ferromagnetic resonance study of the antiferromagnetic-ferromagnetic phase transition in FeRh
Semisalova, A.; Ehrler, J.; Barton, C.; Thomson, T.; Lenz, K.; Fassbender, J.; Potzger, K.; Lindner, J.
The first order phase transition of an equiatomic FeRh thin film from the antiferromagnetic (AFM) to the ferromagnetic (FM) state was studied using broadband ferromagnetic resonance (FMR). The films were deposited on MgO(001) substrates by means of magnetron sputtering of an alloy target. The position and linewidth of the FMR signal have been investigated in the frequency range up to 50 GHz. Conclusions on the temperature dependence of the magnetic damping are presented. The linewidth was found to be strongly affected by the exchange coupling due to reversible nucleation of AFM and FM domains in FeRh within the temperature range of the phase transformation.
  • Poster
    DPG Spring Meeting 2017, 19.-25.03.2017, Dresden, Germany

Registration No. 26917 - Permalink


Vortex dynamics in disks with tailored magnetisations
Ramasubramanian, L.; Fowley, C.; Kákay, A.; Yildirim, O.; Matthes, P.; Böttger, R.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.
The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design [2, 3].

Using micromagnetic simulations, [4] we show that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. Experimentally we employ ion implantation as a promising method to fabricate such devices [5].

Disks with different radii- 0.5 µm to 4 µm, thicknesses- 25 nm and 30 nm and lateral electrical contacts were prepared using electron beam lithography followed by electron beam evaporation to study the formation of magnetic vortices with respect to size and thickness.

Magnetotransport measurements (Fig. 1(a)) show the presence of anisotropic magnetoresistance (AMR. The resonance frequencies measured using a lock-in technique on 25 nm thick permalloy disks are shown in Fig. 1(b). The disks were subsequently subjected to partial ion irradiation and the induced modification of the resonance frequency will be presented.

The Nanofabrication Facilities Rossendorf at the IBC is gratefully acknowledged.
Funding : Helmholtz Young Investigator Initiative Grant No. VH-N6-1048.
Keywords: frequency tunability, chromium implantation in permalloy, electrically detected dynamics
  • Poster
    MMM 2017 - 62nd Annual Conference on Magnetism and Magnetic Materials, 06.-10.11.2017, Pittsburgh, USA

Registration No. 26916 - Permalink


Vortex dynamics in disks with tailored magnetisations
Ramasubramanian, L.; Fowley, C.; Kákay, A.; Yildirim, O.; Matthes, P.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.
The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design [2, 3]. Micromagnetic simulations [4] have shown that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. Ion implantation is a promising method to fabricate such devices [5].

Disks with different radii- 0.5 µm to 4 µm and thicknesses- 25 nm and 30 nm were prepared using electron beam lithography followed by electron beam evaporation to study the formation of magnetic vortices with respect to size and thickness. The single disks were contacted by gold leads to study the interaction of spin polarized current on the magnetic vortex. The presence of vortex is verified by magneto optic Kerr effect (MOKE) and X-ray magnetic circular dichroism (XMCD).

Magnetotransport measurements on electrically contacted disks (Figure 1 (a)) show the presence of anisotropic magnetoresistance (AMR) in different disks with varying thickness (Figure 1 (b)). The resonance frequencies measured using a lock-in technique on 3 µm and 4 µm radii disks with 25 nm permalloy are 40.9 MHz and 29.5 MHz respectively. Modification of the resonance frequency by ion irradiation will be presented.
Keywords: frequency tunability, magnetic vortex
  • Poster
    The Moscow International Symposium on Magnetism (MISM), 01.-05.07.2017, Moscow, Russia

Registration No. 26915 - Permalink


Application of an immersed boundary method with analytical interface approximation to a bubble chain in liquid metal
Krull, B.; Schwarz, S.; Fröhlich, J.; Strumpf, E.; Shevchenko, N.; Roshchupkina, O.; Eckert, S.
Bubble-laden liquid metal flows are an important topic in metallurgy, where bubbles are used for stirring, to remove inclusions, to control chemical reactions, etc. The bubbles encountered in this flows are generally too large to remain spherical, but deform. Deformation can enhance separation of the wake behind the bubble noticeably increasing drag [1]. Furthermore, deformable bubbles lead to an increase of turbulent kinetic energy while having almost no impact on the mean flow, which is a significant difference to flows with spherical bubbles. Furthermore, the near-wall behavior of spherical and non-spherical bubbles differs [2,3]. The deformation of a stationary rising single bubble is well-understood [4]. However, for unsteady flows containing larger numbers of interacting bubbles the deformation and its impact on the flow is not known and therefore investigated in this work.
Keywords: bubbly flow, immersed boundary method, bubble deformation, bubble chain, liquid metal
  • Lecture (Conference)
    The 3rd International Conference on Numerical Methods in Multiphase Flows ICNMMF-III, 26.-29.06.2017, Tokyo, Japan

Registration No. 26914 - Permalink


Investigations of fluid flow effects on dendritic solidification: Consequences on fragmentation, macrosegregation and the influence of electromagnetic stirring
Shevchenko, N.; Neumann-Heyme, H.; Pickmann, C.; Schaberger-Zimmermann, E.; Zimmermann, G.; Eckert, K.; Eckert, S.
Solidification experiments and numerical simulations have been performed to improve the understanding of the complex interrelation between melt flow and the formation of dendritic structures during solidification of Al-Cu and Ga-In alloys. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Within this project special interest was focused on fragmentation and segregation phenomena. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. X-ray radioscopy was applied as a powerful tool for the visualization of dendritic growth and coarsening.
Keywords: Fluid flow, dendritic solidification, fragmentation, macrosegregation, electromagnetic stirring

Registration No. 26913 - Permalink


Realizing the insulator-to-metal transition in Se-hyperdoped Si via non-equilibrium material processing
Liu, F.; Prucnal, S.; Berencén, Y.; Zhang, Z.; Yuan, Y.; Liu, Y.; Heller, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.
We report on the insulator-to-metal transition in Se-hyperdoped Si layers driven by manipulating the Se concentration via non-equilibrium material processing, i.e. ion implantation followed by millisecond-flash lamp annealing. Electrical transport measurements reveal an increase of the carrier concentration and conductivity with the increasing Se concentration. For the semi-insulating sample with Se concentrations below the Mott limit, quantitative analysis of the temperature dependence of the conductivity indicates a variable-range hopping mechanism with an exponent of s  =  1/2 rather than 1/4, which implies a Coulomb gap at the Fermi level. The observed insulator-to-metal transition is attributed to the formation of an intermediate band in the Se-hyperdoped Si layers.

Downloads:

  • Secondary publication expected from 15.09.2018

Registration No. 26911 - Permalink


PT-symmetry and related geometrical structures
Günther, U.
In non-relativistic quantum mechanics, the dynamics of closed quantum systems is described by Hamiltonians which are self-adjoint in appropriately chosen Hilbert spaces. For PT-symmetric quantum systems, the Hamiltonians are in general no longer self-adjoint in standard Hilbert spaces, but rather they are self-adjoint in Krein spaces, Hilbert spaces endowed with indefinite metric structures. Moreover, the spectra of PT-symmetric Hamiltonians are symmetric with regard to the real axis in the spectral plane. Apart from Hamiltonians with purely real spectra this includes also Hamiltonians whose spectra may contain sectors of pairwise complex-conjugate eigenvalues. Considering families of parameter-dependent Hamiltonians one can arrange for parameter-induced passages from sectors of purely real spectra to sectors of complex-conjugate spectral branches. Corresponding passages can be regarded as PT-phase transitions from sectors of exact PT-symmetry to sectors of spontaneously broken PT-symmetry. Approaching a PT-phase transition point, the eigenvectors of the Hamiltonian tend toward their isotropic limit --- an, in general, infinite-dimensional (Krein-space) generalization of the light-cone limit in Minkowski space. At a phase transition, the Hamiltonian is no longer diagonalizable, but similar to an arrangement of nontrivial Jordan-blocks. The interplay of these structures is briefly reviewed with special emphasis on the related Lie-algebraic and Lie-group aspects. With the help of Cartan-decompositions associated hyperbolic structures and Lie-triple-systems are discussed for finite-dimensional setups as well as for their infinite-dimensional generalizations (Hilbert-Schmidt (HS) Lie groups, HS Lie algebras, HS Grassmannians). The interconnection of Krein-space structures and PT-phase transitions is demonstrated on two exactly solvable models: PT-symmetric Bose-Hubbard models and PT-symmetric plaquette arrangements.
Keywords: PT symmetry, PT phase transitions, Krein spaces, Jordan blocks, Lie algebras, Lie triple systems, Hilbert-Schmidt Lie groups, HS Lie algebras, HS Grassmannians, PT-symmetric Bose-Hubbard models, plaquette arrangements
  • Invited lecture (Conferences)
    Symmetry 2017 - The First International Conference on Symmetry, 16.-18.10.2017, Barcelona, Spain
  • Open Access LogoAbstract in refereed journal
    Proceedings / MDPI AG 2(2018), 25
    DOI: 10.3390/proceedings2010025

Registration No. 26910 - Permalink


PT quantum mechanics: finite-dimensional and infinite-dimensional matrix models and their Lie group structures
Günther, U.
Structural features of PT-symmetric quantum mechanical matrix models are discussed: hidden group theoretical aspects, Lie triple systems following from Cartan decompositions of the corresponding Lie algebras, projectivization embeddings to resolve singularities at PT phase transitions. Starting from these structural findings for finite-dimensional PT-symmetric matrix setups, possible technically feasible extensions toward infinite-dimensional Hilbert-Schmidt Lie groups, Fredholm groups and PT-symmetry related Hilbert-Schmidt Grassmannians are sketched. Concrete physical setups where these features show up are briefly discussed.
Keywords: PT symmetry, phase transitions, Lie algebras, Lie triple systems, PT phase transitions, Hilbert-Schmidt Lie groups, Fredholm groups, Hilbert-Schmidt Grassmannians
  • Invited lecture (Conferences)
    15th Conference “Mathematics in Technical and Natural Sciences”, 17.-22.09.2017, Zakopane, Poland

Registration No. 26909 - Permalink


ESUO activities: an update
Froideval, A.
The European Synchrotron and free-electron laser (FEL) User Organisation (ESUO) established in 2010, is now representing about 30.000 users of the European synchrotron and FEL radiation facilities. This user community is distributed over 30 European countries and is represented within the ESUO board by 1 up to 4 national delegate(s) per country, depending on the size of the user community in that country. In the present talk, the past, recent and future ESUO activities are presented.
Keywords: European synchrotron and FEL user organisation (ESUO), European projects, scientific collaborations, European synchrotron and FEL radiation facilities
  • Lecture (others)
    3rd Meeting of the European User Offices, 23.-24.10.2017, Lund, Sweden

Registration No. 26908 - Permalink


Unusual Coulomb effects in graphene
Winnerl S.
In many semiconductors Coulomb scattering plays an essential role in the thermalization process of a non-equilibrium carrier distribution. Here we discuss three surprising and fascinating manifestations of Coulomb scattering in graphene.
The first observation concerns a double-bended saturation behavior of bleaching induced by near-infrared radiation. The complete bleaching at high fluences is related to Pauli blocking. At much lower fluences, however, the balance between scattering into or out of the optically probed regions in k-space via Coulomb interaction results in a qualitatively similar behavior [1].
The second phenomenon is the optically induced anisotropy in k-space for excitation with linearly polarized radiation and its relaxation to a Fermi-Dirac distribution. Polarization resolved pump-probe experiments at different photon energies provide strikingly direct insights into role of individual processes: Carrier-phonon scattering rapidly transforms the initial anisotropic non-equilibrium distribution into an isotropic one [2]. When carrier-phonon scattering is quenched by applying photon energies below the optical phonon energy, however, Coulomb interaction is the only strong source of scattering [3]. As Coulomb scattering in graphene is predominantly collinear, the anisotropy persists for fairly long times (a few ps).
The third set of experiments tackles the dynamics of graphene in a magnetic field perpendicular to the graphene layer. In this case, the band structure beaks up into a series of non-equidistant Landau levels (LLs). We study in detail the population and polarization dynamics of the levels with index -1, 0 and 1. Applying circularly polarized radiation allows one to selectively excite the energetically degenerate transitions LL-1  LL0 and LL0  LL1, respectively. Applying all four combinations of pumping and probing with left and right circularly polarized radiation reveals a surprising behavior: The possibility to deplete the zeroth Landau level while it is optically pumped at the same time [4]. This is caused by strong Auger scattering, the Coulomb process that thermalizes the carrier distribution in Landau quantized graphene. It also causes a fast dephasing of the microscopic polarization, as evidenced in four-wave-mixing experiments [5]. We discuss the possibility to apply Landau quantized graphene as a gain medium in a tunable laser and as a tunable nonlinear optical material.
We are grateful to a number of people, most importantly, from the experimental side, to M. Mittendorff, J. C. König-Otto, H. Schneider and M. Helm. Furthermore to E. Malic, A. Knorr and A. Belyanin for microscopic theory, and to C. Berger and W. A. de Heer for sample growth.
[1] T. Winzer, M. Mittendorff, S. Winnerl, H. Mittenzwey, R. Jago, M. Helm, E. Malic, and A. Knorr, Nature Commun. 8, 15042 (2017).
[2] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, Manfred Helm, and S. Winnerl, Nano Lett. 14, 1504 (2014).
[3] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).
[4] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Physics 11, 75 (2015).
[5] J. C. König-Otto, Yongrui Wang, Alexey Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H. Schneider, M. Helm, S. Winnerl, Nano Lett. 17, 2184 (2017).
Keywords: graphene, ultrafast dynamics, Coulomb scattering
  • Invited lecture (Conferences)
    Finite Systems in Nonequilibrium: From Quantum Quench to the Formation of Strong Correlations, 10.-30.09.2017, Natal, Brasil

Registration No. 26907 - Permalink


Landau-quantized graphene as a nonlinear THz material
König-Otto, J. C.; Wang, Y.; Belyanin, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Graphene, a gapless two-dimensional semiconductor, features constant optical absorption in a wide spectral range. In presence of a magnetic field, the linear band structure of graphene at low energies splits up into a series of non-equidistant Landau levels (LLs). Consequently, the optical absorption is redistributed into Landau-level resonances. Population inversion [1, 2] and strong optical nonlinearities [3] have been predicted for Landau-quantized graphene. Experimentally the population dynamics has been studied and direct evidence for strong Auger scattering in the time domain has been found [4]. In this presentation we show first experiments on the polarization dynamics and the scaling behavior of the four-wave mixing (FWM) signal.
The experiments were performed on almost intrinsic layers of epitaxial multilayer graphene grown on the C-terminated side of SiC. The sample was kept at 10 K in a split coil magnet with optical access. Using linearly polarized radiation at a frequency of 19 THz we investigated the LL-1 → LL0 and LL0 → LL1 transition, which were tuned into resonance by a magnetic field of 4.5 T. Employing radiation pulses with a duration of 4 ps from the free-electron laser FELBE, the degenerate FWM signals were recorded and compared to pump-probe signals. The FWM signal is essentially symmetric and reflects the pulse duration of radiation pulses. This indicates that the dephasing time of the microscopic polarization is faster than the pulse duration. The excited population, on the other hand, is present on much longer timescales. At low intensities, the FWM scales quadratically with the power of the incident beam, that delivers two photons for the FWM process. At incident fields above ~10 kV/cm saturation is observed. Furthermore, the magnetic field was tuned while keeping the photon energy fixed. This reveals a considerably smaller linewidth of the third-order susceptibility resonance as compared to the linewidth of the linear absorption measured by Fourier transform spectroscopy. This is consistent with the nonlinear scaling of the FWM signal. Our experimental results, in particular also the deduced value for the surface susceptibility of the order of 10-19 m3/V2, are in accord with theoretical predictions based on the density matrix formalism.
In summary, Landau-quantized graphene represents a strong nonlinear medium with a resonance tunable by the magnetic field. This may be interesting for nonlinear THz applications, such as frequency mixing and parametric generation.
We are grateful to C. Berger and W. A. de Heer from Georgia Tech and M. Orlita from LNCMI-CNRS in Grenoble for sample growth and linear magneto-spectroscopy measurements, respectively.

References
[1] F. Wendler and E. Malic, Sci. Rep. 5, 12646, 2015.
[2] Y. Wang, M. Tokman, and A. Belyanin Phys. Rev. Lett. 91, 033821 (2015).
[3] X. Yao and A. Belyanin, Phys. Rev. Lett. 108, 255503 (2012).
[4] M. Mittendorff, F. Wendler, E. Malic, E. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Phys. 11, 75 (2015).
Keywords: graphene, nonlinear optics, Landau quantization
  • Lecture (Conference)
    Optical Terahertz Science and Technology, 02.-07.04.2017, London, UK

Registration No. 26906 - Permalink


Teilchenphysik in Bleistiftstaub: das Wundermaterial Graphen
Winnerl, S.
Kohlenstoff ist in Form von Graphit und Diamant den Menschen seit Jahrtausenden bekannt. Die erste Kohlenstoff Nanostruktur wurde in Form von Fullerenen („Fußballmoleküle“) in den 1980er Jahren entdeckt, es folgten Kohlenstoff-Nanoröhren in den 1990er Jahren. Im Jahr 2004 wurde schließlich Graphen, eine einzelne Schicht aus bienenwabenförmig angeordneten Kohlenstoffatomen, von Geim und Novoselov entdeckt und untersucht. Für diese Forschung wurden die beiden im Jahr 2010 mit dem Physik-Nobelpreis ausgezeichnet.
Graphen besitzt faszinierende grundlegende physikalische Eigenschaften. Insbesondere weisen Elektronen in Graphen eine Energie-Impuls Beziehung auf, wie man sie von Teilchen aus der Hochenergiephysik kennt. Wir werden diskutieren, wie sich dies auf weitere physikalische Eigenschaften auswirkt und einen kurzen Überblick geben, wie sich die mechanischen, optischen und elektrischen Eigenschaften von Graphen von anderen Materialien unterscheiden. Daraus lassen sich Schlüsse ziehen, für welche Anwendungen Graphen interessant ist.
Schließlich geben wir einen kurzen Einblick in unsere eigene Forschung an Graphen, die sich besonders mit der Dynamik von Graphen-Elektronen auf ultrakurzen Zeitskalen beschäftigt und dafür das Großgerät FELBE (Freie-Elektronen Laser am HZDR) verwendet.
  • Lecture (others)
    Seniorenakademie Dresden, 26.11.2017, Dresden, Deutschland

Registration No. 26905 - Permalink


Magneto-structural correlations in Fe60Al40 thin films
Ehrler, J.; Potzger, K.; Grenzer, J.; Zhou, S.; Böttger, R.; Bali, R.
Magnetic materials become more significant for future data storage devices and spintronic applications. In certain alloy thin films like Fe60Al40, nano-sized ferromagnetic structures can be created by means of focused ion irradiation.[1,2,3] Fe60Al40 shows a disorder induced phase transition from the thermodynamically stable, chemically ordered B2 to the metastable A2 phase going along with an evolution of ferromagnetism and an increase of the lattice parameter (Figure 1). This can be explained with the higher local number of Fe-Fe nearest neighbors in the disordered state. The correlation between structural and magnetic properties in the phase transition regime, consisting of A2 and B2 phases, is uncertain as well as the influence of the ion type or the temperature treatment.
The effects of ion implantation on the structural and magnetic properties of 250 nm thick Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction (XRD) and Vibrating sample magnetometry. From XRD measurements, the order parameter S and the peak shift due to the change of the lattice parameter have been derived and correlated with the magnetization. The irradiation of paramagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of the saturation magnetization (MS) which was expected to be directly related to the number of displacements per atom (dpa) by using the simulation program TRIM [4], independent on the ion species. However, unlike than expected, the induced magnetization differed but correlated directly with the measured lattice parameter. A significant change of lattice parameter and MS did not appear for proton irradiation at elevated temperatures (250 °C) where the ordered B2 phase was retained. Upon low temperature (LN2) hydrogen implantation of disordered A2 Fe60Al40 films, on the other hand, unlike for helium or neon irradiation, the lattice parameter and the saturation magnetization decreased indicating a little ordering. This might offer the possibility of H+ irradiation induced ordering of chemically disordered alloy thin films well below the ordering temperature.
Furthermore, the studies show that the structural and magnetic properties of 250 nm thick Fe60Al40 films are directly linked with each other (Figure 2) and do not depend on the type of treatment. The chemical disorder induced evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak represented by the order parameter dropping to 0. Nevertheless, the role of defects remains uncertain since ion irradiation leads besides the structural disordering also to an increase of the defect concentration and a temperature treatment to structural ordering and an annealing of defects. However, as described beforehand, H+ implantation causes little ordering but also an increase of the open volume defect concentration, which was characterized by means of Positron annihilation spectroscopy. This offers the opportunity to differentiate between structural disorder and defect concentration.
Given the fact that the proton implanted films follow the shown general behavior a dependence on the structural order only can be assumed.
  • Lecture (Conference)
    Seminar der Professur Werkstofftechnik, 12.-13.01.2018, Meißen, Germany

Registration No. 26904 - Permalink


Tuning the magnetic and structural properties of Fe60Al40 thin films by ion irradiation
Ehrler, J.; Bali, R.; Böttger, R.; Zhou, S.; Grenzer, J.; Potzger, K.
Magnetic materials become more significant for future data storage devices and spintronic applications. In certain alloy thin films like Fe60Al40, nano-sized ferromagnetic structures can be created by means of focused ion irradiation.[1,2,3] Fe60Al40 shows a disorder induced phase transition from the thermodynamically stable, chemically ordered B2 to the metastable A2 phase going along with an evolution of ferromagnetism and an increase of the lattice parameter (Figure 1). This can be explained with the higher local number of Fe-Fe nearest neighbors in the disordered state. The correlation between structural and magnetic properties in the phase transition regime, consisting of A2 and B2 phases, is uncertain as well as the influence of the ion type or the temperature treatment.
The effects of ion implantation on the structural and magnetic properties of 250 nm thick Fe60Al40 films, possessing A2 and B2 structure respectively, have been investigated by means of X-ray diffraction (XRD) and Vibrating sample magnetometry. From XRD measurements, the order parameter S and the peak shift due to the change of the lattice parameter have been derived and correlated with the magnetization. The irradiation of paramagnetic B2 Fe60Al40 with H+, He+ or Ne+ ions with different fluences at low temperatures led to an increase of the saturation magnetization (MS) which was expected to be directly related to the number of displacements per atom (dpa) by using the simulation program TRIM [4], independent on the ion species. However, unlike than expected, the induced magnetization differed but correlated directly with the measured lattice parameter. A significant change of lattice parameter and MS did not appear for proton irradiation at elevated temperatures (250 °C) where the ordered B2 phase was retained. Upon low temperature (LN2) hydrogen implantation of disordered A2 Fe60Al40 films, on the other hand, unlike for helium or neon irradiation, the lattice parameter and the saturation magnetization decreased indicating a little ordering. This might offer the possibility of H+ irradiation induced ordering of chemically disordered alloy thin films well below the ordering temperature.
Furthermore, the studies show that the structural and magnetic properties of 250 nm thick Fe60Al40 films are directly linked with each other (Figure 2) and do not depend on the type of treatment. The chemical disorder induced evolution of ferromagnetism comes along with an abrupt disappearance of the (100)-superlattice peak represented by the order parameter dropping to 0. Nevertheless, the role of defects remains uncertain since ion irradiation leads besides the structural disordering also to an increase of the defect concentration and a temperature treatment to structural ordering and an annealing of defects. However, as described beforehand, H+ implantation causes little ordering but also an increase of the open volume defect concentration, which was characterized by means of Positron annihilation spectroscopy. This offers the opportunity to differentiate between structural disorder and defect concentration.
Given the fact that the proton implanted films follow the shown general behavior a dependence on the structural order only can be assumed.
  • Poster
    HZDR PhD Seminar, 16.-18.10.2017, Seiffen, Germany

Registration No. 26903 - Permalink


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