Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

32228 Publications
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

Publ.-Id: 27059 - Permalink

Attempts to understand potential deficiencies in chemical procedures for AMS
Merchel, S.ORC; Gurlit, S.; Opel, T.; Rugel, G.; Scharf, A.; Tiessen, C.; Weiß, S.; Wetterich, S.
A major research focus of the DREsden Accelerator Mass Spectrometry (DREAMS) facility is sample preparation: in-house and at cooperating laboratories. Besides routine applications, developments are mainly driven by the users' demands such as "new" radionuclides (e.g. short-lived 7Be), radionuclides from new matrices or in larger sample amounts and at lower concentrations. Within the chemical preparation of BeO for 7,10Be, Al2O3 for 26Al, AgCl for 36Cl, and Fe2O3 for 60Fe and actinide AMS targets, we investigated and improved mostly particular steps: For oxide preparation alteration for several hours and two-times rinsing of hydroxides is recommended, especially for Be(OH)2 and Al(OH)3, to prevent losses in the final preparation steps. Rinsing of freshly precipitated hydroxides can yield to losses as high as 31%. For Al(OH)3 rinsing with H2O (pH5) instead of pH8-9 is recommended for further reducing redissolving. For 60Fe and coprecipitated actinides (the latter tested by U6+ and Er3+), rinsing of overnight-altered Fe(OH)3, yield to 2.6-3.5% losses. The depletion of the isobar 7Li for (7)BeO is easily gained by hydroxide precipitation and rinsing. The quality of BeO and Al2O3 AMS targets can be monitored and improved (e.g. by using larger ion exchanger columns) by using the so-called "quality factor", which is the current of the stable nuclide (9Be or 27Al), normalised to the current of the standard of the same batch. Finally, there is a high potential for ion exchange as a pre-enrichment tool for Cl for large ice samples containing low natCl concentrations and low absolute amounts of natCl.
Keywords: accelerator mass spectrometry, 10Be, 26Al, 36Cl, 60Fe, cosmogenic nuclides

Publ.-Id: 27058 - Permalink

Invenio-Uploadbyurl - background uploads via SFTP and HTTP protocol for Invenio
Frust, T.;
A lot of HZDR research data is already located on one of the storage systems in a data center. For those data there are better ways transfering them to Rodare than using an HTTP web upload. This module for Invenio allows you to browse all the files that reside on registered storage systems accessible via the SFTP protocol. They are transferred to the Invenio using SFTP in a background job.
Keywords: SFTP; Invenio; RODARE; Background upload
  • Software in external data repository
    Publication year 2018
    Programming language: Python 3
    System requirements: Python 3, SFTP, Paramiko, Celery, Invenio
    License: GPLv3 (Link to license text)
    Hosted on HZDR GitLab: Link to location

Publ.-Id: 27057 - Permalink

Gold transport in hydrothermal chloride-bearing fluids: Insights from in situ x-ray absorption spectroscopy and ab initio molecular dynamics
Tagirov, B. R.; Trigub, A. L.; Filimonova, O. N.; Kvashnina, K. O.; Nickolsky, M. S.; Lafuerza, S.; Chareev, D. A.;
Chloride-bearing fluids are widespread in the Earth's interior from low-temperature subsurface conditions to deep lithosphere. The concentration of chloride salts varies from diluted aqueous solutions to concentrated brines and anhydrous (dry) chloride melts beneath volcanoes. Here we report an investigation of the state of Au in hydrothermal chloride fluids and anhydrous melts by means of in situ X-ray absorption spectroscopy combined with ab initio molecular dynamics simulations and thermodynamic modeling. The experiments included registration of Au L 3 -edge X-ray absorption near edge structure/extended X-ray absorption fine structure spectra of Au-bearing fluids in the temperature range from 350 to 575 °C at pressures of 150-4500 bar. Spectra of Au dissolved in dry CsCl/NaCl/KCl + K 2 S 2 O 8 melt were recorded at 650 °C. It was found that Au is coordinated by two Cl atoms (R Au-Cl = 2.25-2.28 Å). The alkali metal atoms (Me) were detected in the distant coordination sphere of Au at R Au-Me = 3.3-4.1 Å. The alkali metal cations in the vicinity of Au-Cl complex partly compensate the positive charge located on Au and, by this way, affect the Au-Cl distance. An increase of the fluid pressure causes expansion of the second coordination sphere composed of the alkali metal cations, which leads to the increase of the positive Au charge and results in slight contraction of the first coordination sphere of Au. Accordingly, the transport of Au in high-temperature chloride-bearing natural ore-forming fluids of moderate to high densities (>0.3 g·cm -3 ) can be explicitly described by the formation of the AuCl 2 - at any salt concentration from low-salinity fluids to hydrosaline liquids and anhydrous melts. In general, this means that the hydrothermal fluid chemistry simplifies with increasing temperature.


  • Secondary publication expected from 26.12.2019

Publ.-Id: 27056 - 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 27052 - Permalink

Non-Reciprocal Spin-Wave Emission from Topological Spin Textures
Schneider, T.; Sluka, V.; Kakay, A.; Weigand, M.; Warnatz, T.; Mattheis, R.; Gallardo, R. A.; Roldan-Molina, A.; Landeros, P.; Tiberkevich, V.; Slavin, A.; Erbe, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.;
Investigations of spin waves are of great interest for both fundamental science and applications. For the excitation of spin waves with short wavelengths, it was typically necessary to either use patterned transducers with sizes on the order of the desired wavelengths or to generate such spin waves parametrically.
Here, we will show a combined experimental and theoretical study of spin waves in a stacked vortex pair system formed in a NiFe/Ru/CoFeB trilayer. The magnetization dynamics was imaged by means of time-resolved scanning transmission x-ray microscopy (STXM). Thereby, two different spin wave regimes were identified. For excitation frequencies above 500 MHz, mainly 2D plane waves within the magnetic domains were observed. However, a transition from 2D to 1D wave transport occurs for excitation frequencies below 500 MHz. In this case almost no spin waves were detected within the domains but high amplitudes were found within the 180° domain walls. An analytic and numerical analysis was done for both regimes, resulting in both a qualitative and quantitative understanding of the finite frequency gap in the spin wave dispersion relation for the ferromagnetic domains. Moreover, the dispersion relation was found to exhibit a strong non-reciprocity.
Keywords: Spin-wave, non-reciprocity, spin textures
  • Lecture (Conference)
    APS March Meeting 2018, 05.-09.03.2018, Los Angeles, USA

Publ.-Id: 27051 - 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.


  • Secondary publication expected

Publ.-Id: 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.


Publ.-Id: 27049 - Permalink

Characteristics of large-scale structures in turbulent Rayleigh-Benard convection in a liquid metal layer
Yanagisawa, T.; Akashi, M.; Tasaka, Y.; Murai, Y.; Vogt, T.; Eckert, S.;
We performed laboratory experiments on Rayleigh-Benard convection with a liquid metal in a square box geometry having an aspect ratio five. Horizontal velocity profiles of convective flow were measured at several lines by using ultrasonic velocity profiling. By combining the information from profiles, we can reconstruct organized large-scale flow structures with turbulent fluctuations. Systematic variation of the structure was detected with increasing the Rayleigh number (Ra) from 10^4 to 10^5; a quasi-two-dimensional roll changes to a cell having a relatively larger horizontal scale. In addition, we found that the large-scale structure, whether it is roll or cell, show quasi-periodic oscillation whose representative period is approximately same as the circulation time of the large-scale flow. We also performed numerical simulations of convection with the same geometry as our experiments by setting a small Prandtl number (Pr=0.025) like a liquid metal. Quantitative comparison on the velocity profiles between experiments and simulations provided quite satisfactory agreement, and we analyzed the whole structure of the flow and the style of oscillation in detail based on the result of simulation. By integrating results from experiments and simulations, we propose a scaling low on the Ra dependence of horizontal size of large-scale flow structure, and estimate an enlarged value of effective momentum diffusivity by turbulence in a low Pr convection.
  • Lecture (Conference)
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 11), 05.-07.09.2018, Berlin, Germany

Publ.-Id: 27047 - 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

Publ.-Id: 27046 - Permalink

High-resolution patterning of germanium for nanoelectronics applications
Gangnaik, A. S.; Khan, M. B.; Ghamsari, S. J.; Rebohle, L.; Erbe, A.; Holmes, J. D.; Georgiev, Y. M.ORC
Ge is among the most attractive alternative channel materials for the next-generation nanoelectronics. However, Ge patterning with electron beam lithography (EBL) using the negative resist HSQ is challenging. The complex native oxide GeOx is soluble in the HSQ aqueous developers. As a result, lift-off of sub-20 nm features written by EBL occurs during development. In the presentation, it will be shown that this issue can be solved by: (i) removal of GeOx and passivation of Ge surface prior to HSQ deposition or (ii) application of a buffer layer between GeOx and HSQ. Arrays of sub-20 nm HSQ lines were successfully fabricated on Ge with both approaches. Moreover, a significantly simplified process for removal of GeOx and passivation of Ge surface will also be presented, which allows patterning of 6-7 nm Ge NWs, the smallest Ge nanostructures reported to date.

Finally, different applications of the above mentioned patterning processes will be discussed.
Keywords: Germanium, nanowires, nanoelectronics, electron beam lithography
  • Lecture (Conference)
    DPG Spring Meeting 2018 in Berlin, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 27045 - Permalink

Technology for fabrication of suspended sub-5 nm silicon nanowires and applications thereafter
Petkov, N.; Georgiev, Y. M.ORC
Si nanowires (Si NWs) are very promising as channels for field effect transistors (FETs) and also as sensing devices. When the NW diameter is in the sub-10 nm range, quantum confinement of carriers is observed at room temperature, which is very appealing from scientific and application point of view.

This paper will present a technology for fabrication of sub-5 nm suspended Si NWs on silicon-on-insulator wafers. News of 20 nm width are first defined in the top Si layer by electron beam lithography and reactive ion etching. Then the NWs are subjected to three consecutive cycles of rapid thermal oxidation in oxygen atmosphere and wet etching in hydrofluoric acid. The resulting suspended Si NWs have high-quality crystalline structure and sub-5 nm size.

The possible applications of such NWs will be discussed, including FET-based Si NW chemo-/biosensors as well as gate all around (GAA) FETs. Additionally, the development of self-aligned nickel silicide NW contacts will be presented. The formation mechanism was examined by in-situ electron microscopy as a function of NW diameter and surface oxide.
Keywords: Silicon nanowires, field effect transistors (FETs), nanowire sensors, silicon-on-insulator, nickel silicide, electron beam lithography
  • Lecture (Conference)
    DPG Spring Meeting 2018 in Berlin, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 27044 - 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.

Publ.-Id: 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

Publ.-Id: 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.


Publ.-Id: 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.


Publ.-Id: 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


Publ.-Id: 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.


Publ.-Id: 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


Publ.-Id: 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.

Publ.-Id: 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

Publ.-Id: 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


Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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
  • Invited lecture (Conferences)
    TESLA Technology Collaboration Meeting, 06.-09.02.2018, Mailand, Italien

Publ.-Id: 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.

Publ.-Id: 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.;

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.

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.

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.

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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.

[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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 26993 - Permalink

The Role of epithelial to mesenchymal transition (EMT) as Biomarker for Radioresistance in HNSCC
Kurth, I.; Digomann, D.; Hein, L.; Linge, A.; Koi, L.; Loeck, S.; Maebert, K.; Stephan, H.; Peitzsch, C.; Krause, M.; Baumann, M.; Dubrovska, A.;
Purpose or Objective
It is described that epithelial – to -mesenchymal transition (EMT) plays an important role in head and neck squamous carcinomas (HNSCC) progression and resistance to therapy. Recent studies suggest that for instance the expression of EMT related microRNAs may cause intrinsic radioresistance in HNSCC. During the process of EMT epithelial cancer cells obtain a more mesenchymal –like motile and invasive phenotype, which has been argued to sustain survival and therapy resistance of those tumor cells and facilitate cancer progression. Radiotherapy is one of the main approaches to treat HNSCC. However, tumor radioresistance often impedes the success of radiotherapy and has been found to drive tumor aggressiveness and expansion. In this study we asked the question, if radioresistant HNSCC populations display EMT features on a molecular as well as on a functional level and whether we can correlate those characteristics to treatment outcome.
Material and Methods
We used multiple irradiated HNSCC lines (IR) as an established model to investigate the traits of radioresistance. Global gene expression analysis in vitro and on xenograft models and functional radiobiological analyis was applied.
Interestingly, global gene expression analysis revealed a negative correlation of genes associated with cell motility and migration in the IR derivatives of two HNSCC cell lines, namely Cal33, FaDu. We functionally validated those findings and screened for known EMT marks from literature by functional migration assays and EMT-related protein expression in several HNSCC model cell lines and established xenografts as well as in their IR derivatives in order to correlate the acquired findings to radiotherapy outcome. The only positive correlation was found for the initial before therapy protein expression in vitro and in vivo for Slug, a zinc - finger protein encoded by the SNAI2 gene and c-Met, a receptor tyrosine kinase encoded by the MET gene. Functional knockdown of Slug or c-Met expression let to radiosensitization in 3-D clonogenic survival assays of several HNSCC cell lines.
Currently the expression of these molecules is scored for clinical outcome to better understand the context of EMT biomarkers for HNSCC progression and the development of a potential well-directed combinational radiochemotherapy.
Keywords: EMT, radiotherapy, HNSCC, migration

Publ.-Id: 26992 - Permalink

Cytokine-dependent regulation of prostate cancer stem cells maintenance in response to radiotherapy
Peitzsch, C.; Baumbach, M.; Cojoc, M.; Hein, L.; Kurth, I.; Baumann, M.; Krause, M.; Dubrovska, A.;
Purpose: According to the cancer stem cell hypothesis prostate cancer is driven by a malignant subpopulation with stem-like properties. These cancer stem cells (CSC) contribute to tumor-initiation, metastasis, therapy-resistance and tumor relapse. In parallel, genetic mutations accumulate over time and CSC subclones evolve. Therapeutic interventions like radiotherapy provide selective pressure for the expansion of resistant subclones with genetic diversification. We hypothesize that the determination of CSC-related biomarker in prostate cancer biopsies is correlating with clinical parameter and can be used for patient stratification and treatment selection to improve personalized radiotherapy.
Methodology: We generated isogenic radioresistant prostate cancer cell lines with a high expression of CSC marker, a epithelial-to-mesenchymal transition (EMT) phenotype, higher self-renewal properties, higher tumorigenicity and enhanced DNA repair capacity. We applied comparative genomic, proteomic, metabolomic, epigenomic and secretome analysis to identify novel biomarker for prostate cancer radioresistance and to unravel contributing molecular mechanisms.
Results: Within our first proof-of-principle study, we could show that ALDH-positive CSCs are radioresistant and maintained directly by the Wnt/β-catenin signaling pathway (1). In addition, we found that irradiation is inducing CSC marker and CSC properties in a dose- and time-dependent manner. This irradiation-induced CSC-plasticity was attributed to the modulation of the histone methylation code (2). Within the present study we analyzed a panel of secreted cytokines and their corresponding cytokine receptors in the radioresistant prostate cancer sublines, in a s.c. xenotransplantation model, in ex vivo irradiated primary prostate cancer biopsies and in blood samples of prostate cancer patients during the course of radiotherapy and found, for example, the CXCR4-CXCL12 signaling to be involved in the CSC maintenance and the induction of prostate cancer radioresistance.


(1) Peitzsch C, Cojoc M, Hein L, Kurth I, Mäbert K, Trautmann F, Klink B, Schrock E, Wirth MP, Krause M et al: An epigenetic reprogramming strategy to re-sensitize radioresistant prostate cancer cells. Cancer research 2016, 76; 2637.

(2) Cojoc M*, Peitzsch C*, Kurth I, Trautmann F, Kunz-Schughart LA, Telegeev GD, Stakhovsky EA, Walker JR, Simin K, Lyle S et al: Aldehyde Dehydrogenase Is Regulated by beta-Catenin/TCF and Promotes Radioresistance in Prostate Cancer Progenitor Cells. Cancer research 2015, 75(7):1482-1494.
Keywords: Cytokines, prostate cancer, radioresistance

Publ.-Id: 26991 - Permalink

Synthesis and 18F-Radiolabelling of Novel Benzoimidazotriazines for Imaging of Phosphodiesterase 2A (PDE2A)
Ritawidya, R.; Wenzel, B.; Teodoro, R.; Scheunemann, M.; Deuther-Conrad, W.; Brust, P.;
1. Introduction
Cyclic nucleotide phosphodiesterases (PDEs) are a class of intracellular enzymes that inactivate the secondary messenger molecules cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Thus, PDEs regulate the signaling cascades mediated by these cyclic nucleotides and affect fundamental cellular processes, such as proliferation, differentiation, migration, survival, and apoptosis. Accordingly, they are promising therapeutic targets. Since PDE2A was found to be related to a variety of tumors, it is our aim to synthesize novel PDE2A inhibitors based on the benzoimidazotriazine (BIT) moiety that might be a prospective lead compound for the development of an F-18 labelled ligand for PDE2A imaging with PET.

Fig A. BIT key intermediates, B. Radiosynthesis of [18F]BIT1

2. Materials & Methods
Based on BIT key intermediates (Fig. A), a small series of novel fluorinated BIT derivatives was successfully prepared (overall in 7-10 steps) and the affinities towards PDE2A and other PDE subtypes were estimated. The most promising compound, BIT1, was radiolabelled by using the corresponding nitro precursor. The reaction was optimized by choosing different solvents, amounts of precursor, modes of heating (conventional or microwave), temperatures, and reaction times. Afterwards, best conditions (Fig. B) were transferred to an automated synthesis module (TracerLab FX2 N, GE Healthcare). The radiotracer was isolated by semi-preparative HPLC (Reprosil-Pur AQ column, 25010mm, 46 % ACN/aqu. 20 mM NH4OAc, flow 5.5 ml/min) followed by purification with a Sep-Pak C18 Plus light cartridge and formulation in isotonic saline containing 10% ethanol.

3. Results
BIT1 showed a high affinity towards PDE2A (IC50 PDE2A3 = 3.33 nM) and selectivity over other PDE subtypes. [18F]BIT1 was successfully synthesized with a radiochemical yield of 51.9 ± 1.3 % (n=3), molar activities between 46 – 100 GBq/µmol and radiochemical purities of ≥ 99%.

4. Discussion & Conclusion
Radiofluorination of a novel PDE2A ligand [18F]BIT1 was obtained with appropriate radiochemical yield and molar activity. First biological investigations are planned to estimate the potential of [18F]BIT1 as imaging agent for PDE2A.

1. Deutsche Forschungsgemeinschaft (German Research Foundation, Project Number: SCHE 1825/3-1).
2. Scholarship Program for Research and Innovation in Science and Technology Project (RISET-PRO)-Indonesia Ministry of Research, Technology and Higher Education.
Keywords: benzoimidazotriazines, PDE2A, radiolabelling, imaging
  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals, 05.-08.04.2018, Groningen, Netherlands

Publ.-Id: 26990 - Permalink

High temperature reactions of UO2, ZrO2, B4C, CaO, and SiO2 under reducing and oxidizing atmospheres
Uehara, A.; Akiyama, D.; Numako, C.; Takeda-Homma, S.; Ikeda-Ohno, A.ORC; Terada, Y.; Ina, T.; Nitta, K.; Kirishima, A.; Sato, N.
Uranium and several other radioactive materials reacted with zircaloy (Zry) and/or its oxide, ZrO2, presented in the fuel cladding, to form fuel debris at the Fukushima Daiichi Nuclear Power Station in 2011. Under very high temperature conditions, the melt core, mainly consisting of the control rods (stainless steel rod filled with B4C) and fuel assembly (UO2 and Zry) materials, was solidified at the lower head of the pressure vessel. In addition, the melt core was also solidified at the lower head of the pedestal reacted with cement materials (CaO and SiO2). In order to forward a safe and controlled decommissioning process, structural and thermodynamic estimations of the fuel debris under various atmospheric conditions such as reducing and oxidizing atmospheres have been conducted. In the present study, the local structure of basic uranium/zirconium compounds has been characterized under different treatment conditions in the presence of B4C, CaO and SiO2 in atmospheric conditions with different temperatures ranging from 1473 to 1873 K. These reactions are of specific interest to the interaction between nuclear fuel and cladding tube materials.
Keywords: Nuclear debris, uranium, zirconium, solid-solution, synchrotron, X-ray absorption spectroscopy, powder X-ray diffraction
  • Lecture (Conference)
    17th international conference on X-ray absorption fine structure (XAFS 2018), 22.-27.07.2018, Krakow, Poland

Publ.-Id: 26989 - Permalink

Epigenetic and metabolic reprogramming as a target for prostate tumor radiosensitization
Dubrovska, A.; Peitzsch, C.; Tyutyunnykova, A.; Cojoc, M.;
Purpose or Objective
Radiotherapy remains one of the main modalities to treat solid cancers and is one of the mainstays of curative prostate cancer treatment. Nevertheless, the risk of recurrence after radiotherapy still remains substantial in locally advanced disease. Tumor relapse after radiotherapy is attributed to the population of cancer stem cells (CSCs) which survived the treatment. Therefore, analysis of the CSC populations might be an important predictive tool of radiotherapy outcome and individualized treatment selection. However, compelling evidence suggests a high plasticity of CSCs imposed by tumor treatment. This study is aiming to investigate the interconnection of the glutamine metabolism and cancer cell plasticity in the development of tumor radioresistance for the development of new biomarkers to predict radiation treatment outcome.
Material and Methods
The employed methodological approaches include gene expression analysis, comparative genomic hybridization array, proteomic analysis, metabolic profiling, in vitro radiobiological clonogenic survival assays, assessment of the histone methylation marks and CSC marker expression, analysis of DNA damage repair and oxidative stress response. This study is based on the different models including tumor cell lines and their radioresistant derivatives, prostate cancer xenografts, ex vivo treated tissues and analysis of the publicly available TCGA prostate cancer datasets.
Our study revealed that irradiation causes long-term upregulation in the expression of stem cell markers and induces tumor cell reprogramming. Furthermore, radioresistant and tumorigenic cell populations undergo a phenotypic switch during the course of radiotherapy. This phenotypic plasticity is associated with genetic, epigenetic and metabolic changes induced by irradiation. Expression of CSC markers and proteins involved in glutamine metabolism can be used to predict clinical outcome of prostate cancer patients.
Our studies suggest that radioresistant properties of prostate cancer cells are dynamic in nature and that combination of irradiation with therapeutic agents which prevent tumor cell reprogramming and metabolic switch may restore the cytotoxic effects of irradiation in radioresistant CSC populations.
Cojoc M et al. Cancer Res. 2015; 75(7):1482-94;
Peitzsch C et al. Cancer Res. 2016; 76(9):2637-51;
Kurth I et al. Oncotarget 2015; 6(33):34494-509;
Krause M et al. Advanced Drug Delivery Reviews, 2016, pii: S0169-409X(16)30052-7.
Keywords: Metabolism, radioresistance, prostate cancer
  • Contribution to proceedings
    ESTRO36, 05.-09.05.2017, Vienna, Austria
  • Open Access LogoAbstract in refereed journal
    Radiotherapy and Oncology 123(2017), S201
    DOI: 10.1016/S0167-8140(17)30815-0

Publ.-Id: 26986 - 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

Publ.-Id: 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.;

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

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.

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.

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.

Publ.-Id: 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.

Publ.-Id: 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

Publ.-Id: 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.;

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.

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.

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).

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

Publ.-Id: 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.

Publ.-Id: 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.;

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.

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.

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.

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

Publ.-Id: 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.


Publ.-Id: 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

Publ.-Id: 26964 - Permalink

Neoadjuvant radiochemotherapy decreases the total amount of tumor infiltrating lymphocytes, but increases the number of CD8+/Granzyme B plus (GrzB) cytotoxic T-cells in rectal cancer
Jarosch, A.; Sommer, U.; Bogner, A.; Reißfelder, C.; Weitz, J.; Krause, M.; Folprecht, G.; Baretton, G. B.; Aust, D. E.;
Although neoadjuvant radiochemotherapy (nRCTx) is an established oncological treatment in patients with advanced rectal cancer, little is known about its effects on the tumor microenvironment. Quantity and composition of tumor infiltrating lymphocytes (TILs) are known to influence patients’ prognosis but nRCTx-induced modifications are still unclear. We determined the composition of the immune cell infiltrate in rectal cancer after nRCTx and its influence on tumor regression, local recurrence rate and survival. We investigated density and composition of tumor infiltrating CD3C and CD8C T-cells and the quantity and ratio of CD8C/GrzBC T-cells to CD8C T-cells in 130 rectal cancers after nRCTx compared to a cohort of 30 primarily resected rectal cancers. Furthermore, we analyzed 22 pretherapeutic rectal cancer biopsies, later
treated with nRCTx and surgery to evaluate nRCTx-inducedmodifications of the tumor microenvironment.
The total numbers of CD3C and CD8C T-cells in tumor stroma (p < 0.001) and tumor Epithelium (p < 0.001 CD3; 0.002 CD8) were significantly lower in rectal cancers after nRCTx compared to primarily resected cases, while the ratio of CD8C/GrzBC T-cells to CD8C T-cells was significantly increased in the nRCTx cohort (p < 0.001). In multivariate analyses, CD8C/GrzBC T-cells in the tumor stroma were significantly associated with high regression grade and a lower likelihood of local recurrence (p D 0.029).
nRCTx modifies the tumor microenvironment of rectal cancer leading to a total decrease of TILs, but a relative increase in CD8C/GrzBC T-cells in the tumor stroma. CD8C/GrzBC T-cells may contribute to local tumor control and the better outcome.
Keywords: rectal cancer; histological tumor regression; granzyme B (GrzB); neoadjuvant radiochemotherapy; Tumor microenvironment


Publ.-Id: 26963 - 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 26953 - Permalink

Therapie des kleinzelligen Lungenkarzinoms im Stadium „limited disease“. RCT normo- oder hyperfraktioniert?
Frosch, S.; Troost, E. G. C.;
Die simultane Radiochemotherapie (RCT) ist beim kleinzelligen Lungenkarzinom der Therapiestandard im Stadium „limited disease“. Aktuell besteht allerdings noch eine Kontroverse über den Bestrahlungsablauf und die optimale Bestrahlungsdosis. Bisherige Daten zeigten die Überlegenheit einer akzeleriert-hyperfraktionierten Bestrahlung mit täglich zwei Fraktionen im Vergleich zur konventionell fraktionierten Bestrahlung mit täglich einer Fraktion, jedoch auf Kosten von mehr Toxizität [1]. Allerdings war in dieser Studie die Gesamtdosis in beiden Gruppen gleich; Kritiker postulieren, dass eine höhere Gesamtdosis – einmal pro Tag appliziert – im konventionellen Therapiearm die Ergebnisse hätte verbessern können.
  • InFo Onkologie 21(2018)1, 27-28

Publ.-Id: 26952 - 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

Publ.-Id: 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

Publ.-Id: 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.;

Publ.-Id: 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.;

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.

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.

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.

Publ.-Id: 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

Publ.-Id: 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.

Publ.-Id: 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

Publ.-Id: 26938 - Permalink

Prospective data registration and clinical trials for particle therapy in Europe
Langendijk, J.; Orrechhia, R.; Haustermans, K.; Zips, D.; Balosso, J.; Lievens, Y.; Weber, D.; Grau, C.; Troost, E.;
To enhance evidence-based introduction of particle therapy in Europe, one of the work packages within the European Proton Therapy network (EPTN) will focus on uniform data registration and defining methodological criteria for phase I, II and III clinical trials. The main objective of EPTN WP1 is to establish a uniform prospective data registration program for all patients treated with particle therapy in Europe. This will be supported by EORTC through existing and new additional QA-platforms and IT-infrastructures for data collection with different formats. In addition, EPTN WP1, to enhance high quality clinical trials, EPTN-WP1 will define the requirements for high quality clinical trials and set up an infrastructure for methodological support.
Keywords: Particle therapy, PROMs, registry

Publ.-Id: 26937 - 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.


Publ.-Id: 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

Publ.-Id: 26935 - Permalink

Comparing the outcome of proton beam irradiation with experimental x-ray and clinical photons in a sophisticated 3-D assay setup
Sorour, N.; Hussein, R.; von Neubeck, C.; Lühr, A.; Schölch, S.; Beyreuther, E.; Pawelke, J.; Kunz-Schughart, L. A.;
Background and Aim:
Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer with a median survival of <6 months. The role of radiotherapy in PDAC treatment is consistently under debate. Recent studies imply the superiority of proton versus photon irradiation and propose a benefit for pancreatic cancer patients. We therefore aimed at a systematical comparison of the treatment outcome of PDAC cells when exposed to different beams (photons, protons). Our study included the technical setup, establishment, and application of a multicellular 3-D assay to assess the putatively „curative“ biological endpoint of spheroid control probabilities (SCP).

Materials and Methods:
Four PDAC cell line models were applied in 96-well liquid-overlay spheroid culture. A clinical LINAC (6 MV) at a dose rate of 3 Gy/min and an experimental X-ray tube (220 kV) at a dose rate of 1.3 Gy/min were used for photon irradiation. For proton exposure, spheroids were placed within a spread-out Bragg peak (SOBP) of a double scattered proton beam (150 MeV) and irradiated with a dose rate of 3, 6 and 10 Gy/min. After single-dose irradiation (0-30 Gy), radioresponse was evaluated by a 60-day post-treatment monitoring of spheroid integrity, recovery, and volume growth.

Results and Conclusions:
For proton irradiation, variations in the dose rate were proven to neither alter the SCP nor the spheroid volume growth behavior. SCP and SCD50 (spheroid control dose 50%) turned out to be reproducible read-outs for 3-D culture treatment outcome. Experimental and clinical photon beams led to similar response of PDAC 3-D models. However, all spheroids showed a higher sensitivity to protons reflected by a significant reduction in the SCD50 values and an RBE of 1.2-1.5. New combinatorial treatment strategies with protons are now under evaluation.
  • Lecture (Conference)
    DEGRO 2018, 21.06.2018, Leipzig, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S29-S30


Publ.-Id: 26934 - Permalink

Sensitization of pancreatic cancer cells to photons and protons via enzymotherapeutic metabolic targeting of arginine
Sorour, N.; Hussein, R.; von Neubeck, C.; Lühr, A.; Stasyk, O.; Kunz-Schughart, L. A.;
Background and Aim:
The abnormal metabolism of pancreatic ductal adenocarcinoma (PDAC) cells offers some interesting points of attack. About 20-30% of PDACs are described to be auxotrophic for arginine because of a reduced or complete loss of anabolic protein expression and/or activity. New strategies for the treatment of this deadly disease should consider the combination of radiotherapy with novel metabolic targeting modalities. We found various arginine deprivation therapy (ADT) approaches to radiosensitize several non-auxotrophic cancer cell types. Hence, we hypothesized that enzymotherapeutic ADT should be particularly efficient in radiosensitizing auxotrophic PDACs to both photons and protons.

Materials and Methods:
Human and murine cell lines reflecting auxotrophic PDACs in patients were studied. ADT was achieved with 2 U/ml of recombinant human arginase in the presence and absence of citrulline. Single dose irradiation of 0-30 Gy was applied with a 200kV X-ray tube and a 150 MeV double-scattered proton beam. Treatment response was assessed by 2-D clonogenic survival and/or 3-D spheroid control probability (SCP) assays. Our specifically designed setup allowed the testing of innovative treatment regimens including proton therapy with/without ADT and Gemcitabine (Gem).

Results and Conclusions:
ADT led to a massive sensitization to X-ray in all PDAC models. Sensitization in 3-D culture was reflected by a significantly reduced SCP and spheroid control dose 50% (SCD50) with an RBE of 2.0. Cells showed a higher sensitivity in the 3-D assay to protons than photons but ADT still further improved the radioresponse. As an example, the RBE of protons plus ADT versus photons alone in one human PDAC spheroid typel was 3.9. In the same model, proton therapy outcome was hardly affected by Gem; however, the combination of ADT with Gem and proton therapy was particularly effective with an exceptional RBE compared to photons of 5.0. Extended mechanistic studies are ongoing; transfer in vivo is envisioned.
  • Lecture (Conference)
    DEGRO 2018, 21.06.2018, Leipzig, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 194(2018), S96

Publ.-Id: 26933 - 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

Publ.-Id: 26932 - Permalink

Molecular characterization in liquid and cryogenic environments
Kilibarda, F.; Strobel, A.; Lokamani, M.; Sendler, T.; Mortensen, M.; Gothelf, K.; Erbe, A.;
Current industrial scaling processes are reaching limits. We see not only diminishing returns with further scaling attempts, but also physical limitations that come more and more into play. In our research we offer a novel approach, to use single molecules as electronic components.
This approach offers not only size improvements, but also a reduction in power consumption and costs. Our research focuses on classifying different molecules with the help of Mechanically Controlled Break Junction (MCBJ). Here we present two different kinds of measurements.
One is performed in liquid solution and under ambient conditions, and the other one in a cryogenic environment, under vacuum.
As a test bed for these measurements we use salen and 𝐶₆₀ molecules, respectively. In the case of salen molecules, we show, how chemical doping influences energy levels and affects electron transport through the molecule. The experimental results are supported by quantum chemical calculations. The 𝐶₆₀ measurements demonstrate that we can remove the influence of the solvent by in situ molecular evaporation into the nanoscopic junction. Additionally, operation under vacuum allows us to use more reactive metals for the nano-junction, and thus vary metal-molecule orbital overlap, where in traditional approach contacts are made out of noble metals like gold.
Keywords: Scaling, single molecule, molecular electronics, MCBJ, break junction, electron transport, energy level, quantum chemical calculation, cryogenic, solvent, chemical doping, salen, 𝐶₆₀
  • Poster
    DPG-Frühjahrstagung, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 26931 - 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

Publ.-Id: 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

Publ.-Id: 26929 - Permalink

Investigation of fluids in macrocrystalline and microcrystalline quartz in agate using Thermogravimetry-Mass-Spectrometry
Richter-Feig, J.; Möckel, R.; Götze, J.; Heide, G.;
Gaseous and liquid fluids in agates (banded chalcedony – SiO2) of different localities were investigated systematically by thermogravimetry-mass-spectrometry in a temperature range between 25°C and 1450°C for the first time. Chalcedony and macrocrystalline quartz from twelve agate samples have been investigated: Germany (Schlottwitz, St. Egidien, Chemnitz and Zwickau), Brazil (Rio Grande do Sul), Scotland (Ayrshire) and the USA (Montana). They originate from mafic and felsic volcanic rocks as well as hydrothermal and sedimentary environments.
The results were evaluated concerning compounds of hydrogen with fluorine, chlorine, nitrogen, carbon and sulfur. Additionally, oxygen compounds were recognized with hydrogen, fluorine, nitrogen, sulfur and carbon. The nature of the compounds was identified based on their mass-charge-ratio and the intensity ratios of the associated fragments. Due to interferences of different compounds with the same mass-charge-ratio, only H2O, HF, NO, S, SO, CO3 as well as several hydrocarbon compounds (for example CO32- or CO) could be properly identified. The main degassing temperatures were detected around 500 °C and 1000 °C. Generally, a difference between quartz and chalcedony concerning the composition of their fluids could not be found. The results indicate a silica source for the agate formation from aqueous solutions, but also the possible role of fluorine compounds. Additionally, CO2 and other fluids were involved in the alteration of volcanic rocks and the mobilization and transport of SiO2.
Keywords: agate; quartz, chalcedony, thermogravimetry-mass-spectrometry, fluids

Publ.-Id: 26928 - Permalink

Modified Calix[4]crowns as Molecular Receptors for Barium
Steinberg, J.; Bauer, D.; Reissig, F.; Köckerling, M.; Pietzsch, H.-J.; Mamat, C.ORC
A series of modified calix[4]crown-6 derivatives was synthesized to chelate the heavy group 2 metal barium, which serves as non-radioactive surrogate for radium-223/-224; radionuclides with promising properties for radiopharmaceutical use. These calixcrowns were functionalized either with cyclic amide moieties or proton-ionizable groups and the corresponding barium complexes were synthesized. Stability constants of these complexes were measured using NMR and UV/Vis titration techniques to determine logK values between 4.1 and 6.4. Further extraction studies were performed to characterize the binding affinity of calixcrowns to radioactive barium-133. Additionally, the ligands containing cyclic amides were investigated regarding their barriers for rotation using temperature dependent NMR measurements.
Keywords: Calix-crown, radiolabeling, barium-133, radium, extraction

Publ.-Id: 26927 - 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

Publ.-Id: 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


Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 26921 - Permalink

Computer simulation of the ternary problem – technical aspects and possibilities
Zedek, L.; Lippold, H.; Sembera, J.;
Interaction between groundwater contaminants (e.g. radioactive elements), soil and humic matter plays a crucial role in transport prognoses. This type of interaction, denoted as the ternary problem, may speed up propagation of a contaminant in comparison with the case in the absence of humic compounds. It is very difficult (almost impossible) to find a simple description of the ternary problem in the form of chemical equations. This difficulty is caused by the complex nature of humic substances. Rather than with particular chemical equations, the ternary problem is commonly described by schematic expressions which consider groups of species. The usual approach for the problem formulation is grouping of species resulting in a system of differential and algebraic equations (DAE). This article introduces a different approach allowing a semi-automatic formulation of a system of ordinary differential equations (ODE) for the same problem. The proposed method enables to avoid an operator-splitting already during the model formulation process. The approach for the model formulation and its solution has been implemented using two different open-source software packages. The results have been compared with reference results of a traditional solution approach using DAE systems. The implementation in Python verified the possibility of automation of the formulation and solution. A sensitivity analysis has been performed to evaluate the behaviour of the system with respect to parameter variation.
Keywords: Chemical reaction simulation; Semi-analytical model; Semi-automatic formulation

Publ.-Id: 26920 - 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 26913 - Permalink

Practice patterns of image guided particle therapy in Europe: a 2016 survey of the European Particle Therapy Network (EPTN)
Bolsi, A.; Peroni, M.; Amelio, D.; Dasu, A.; Stock, M.; Toma-Dasu, I.; Witt Nyström, P.; Hoffmann, A. L.;
Background and Purpose: Image guidance is critical in achieving accurate and precise radiation delivery in particle therapy, even more than in photon therapy. However, equipment, quality assurance procedures and clinical workflows for image-guided particle therapy (IGPT) may vary substantially between centres due to a lack of standardization. A survey was conducted to evaluate the current practice of IGPT in European particle therapy centres.

Material and Methods: In 2016, a questionnaire was distributed among 19 particle therapy centres in 12 European countries. The questionnaire consisted of 30 open and 37 closed questions related to image guidance in the general clinical workflow, for moving targets, current research activities and future perspectives of IGPT.

Results: All centres completed the questionnaire. The IGPT methods used by the 10 treating centres varied substantially. The 9 non-treating centres were in the process to introduce IGPT. Most centres have developed their own IGPT strategies, being tightly connected to their specific technical implementation and dose delivery methods.

Conclusions: Insight into the current clinical practice of IGPT in European particle therapy centres was obtained. A variety in IGPT practices and procedures was confirmed, which underlines the need for harmonisation of practice parameters and consensus guidelines.
Keywords: Particle therapy, image guidance, survey

Publ.-Id: 26912 - 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.


Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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

Publ.-Id: 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.

[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

Publ.-Id: 26906 - Permalink

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