Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The charge-exchange break-up of polarised deuterons pol{d}p -> {pp}n, where the final {pp} diproton system has a very low excitation energy and hence is mainly in the 1S0 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Delta(1232) isobar in the pol{d}p -> {pp}X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A_{xx} and A_{yy}, have been extracted in terms of the momentum transfer to the diproton or the invariant mass Mx of the unobserved system X. The unpolarised cross section in the high Mx region is well described in a model that includes only direct excitation of the Delta isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low Mx, even when Delta excitation in the projectile deuteron is included in the calculation. Furthermore, direct Delta production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related pp-> d pi^+ reaction, though the present results cover also the small-angle region, which was largely absent from these data.

According to the proceedings of the first conference on intersubband transitions in quantum wells (ITQW), which took place in 1991 in Cargèse [1], research on this topic in the early 90s concentrated mostly on mid-infrared detectors (quantum well infrared photodetectors, QWIPs) for applications in thermal imaging. The following reasons make ITQW quite interesting for infrared optoelectronics: (a) III-V semiconductor technology supply a mature technological basis, (b) spectral properties of ITQW are determined basically by layer thicknesses and not by material bandgaps, and (c) theoretically engineered layer structures enable novel device concepts and huge resonant optical nonlinearities [2]. In 1994, the invention of the quantum cascade laser (QCL) [3] has marked the birth of another exciting research field and paved the way for a wide range of new applications for ITQW. Later on, both the QWIP and QCL concepts have been applied to longer wavelengths beyond the Reststrahlen band [4,5], thus giving rise to important devices in the emerging field of terahertz (THz) technology.
Going from the 2D quantum well (QW) system to 1D quantum wires, and even 0D quantum dots (QD), there has been a long debate whether device performance, in particular at high operation temperatures, will become superior due to the restricted phase space for electron scattering. Most importantly, a phonon bottleneck has been predicted [6], which gave rise to the expectation that quantum dot infrared photodetectors (QDIP) [7] and QD-based QCLs could exhibit improved device properties. Even though the formation of a "true" phonon bottleneck is prevented by polaron effects, very long relaxation times up to ~ 1 ns have in fact been observed for intersublevel transitions in n-type QD systems at appropriate transition energies [8]. Nevertheless, the performance of QD-based infrared devices is limited as yet mainly by technological difficulties to realize QD ensembles with sufficient homogeneity, spatial density, and, in particular, optimized QD shape.
Besides QD and QW, yet another interesting system is the quantum well exciton (QWE), which is caused by the Coulomb attraction between a – usually photogenerated – electron and hole inside a QW. This results in a hydrogen-like quasi atom with discrete bound states. In contrast to ITQW, interlevel transitions in QWEs have their dipole matrix elements in the QW plane, such that optical transitions between QWE levels occur under normal incidence. Since QWE can move freely in the QW, the center-of-mass momentum gives rise to a 2D continuum, which is in close analogy to the in-plane dispersion of QW subbands. Being a two-particle molecule, the QWE exhibits more complex physics than an electron in a QW or QD, including angular momentum as a new degree of freedom, finite recombination lifetime, and various optically active (bright) or inactive (dark) exciton states. For possible applications, an intriguing property of QWE is the opportunity of controlling near-infrared (NIR) interband processes (eV range) via intra-exciton transitions (few meV range) between bright and dark exciton states [9-11].
This talk will focus on the internal dynamics of quantum well excitons, which are excited into higher levels using a THz free-electron laser, by monitoring intra-exciton relaxation via time-resolved interband photoluminescence.
Acknowledgements – The authors thank E. Rosencher for initiating the ITQW conference series. We are also indebted to L. Schneebeli, C. N. Böttge, B. Breddermann, S. Chatterjee, M. Kira, and S. W. Koch (U. Marburg, Germany) for fruitful discussions and collaboration, to A.M. Andrews and G. Strasser (TU Vienna) for sample growth, and to P. Michel, W. Seidel (HZDR Dresden) and the ELBE team for their dedicated support.
References
[1] E. Rosencher, B. Vinter, B. F. Levine, Eds., "Intersubband Transitions in Quantum Wells", NATO ASI, Series B: Physics, Vol. 188 (Plenum Press, New York, 1992).
[2] E. Rosencher, A. Fiore, B. Vinter, V. Berger, Ph. Bois, J. Nagle, "Quantum Engineering of Optical Nonlinearities ", Science 271, 168 (1995).
[3] J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, A. Y. Cho, "Quantum Cascade Laser", Science 264, 553 (1994).
[4] H. C. Liu, C. Y. Song, A. J. SpringThorpe, J. C. Cao, "Terahertz quantum-well photodetector", Appl. Phys. Lett. 84, 4068 (2004).
[5] R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, F. Rossi, "Terahertz semiconductor heterostructure laser", Nature 417, 156 (2002).
[6] U. Bockelmann and G. Bastard, "Phonon scattering and energy relaxation in two-, one-, and zero-dimensional electron gases" Phys. Rev. B 42, 8947 (1990).
[7] H. C. Liu, M. Gao, J. McCaffrey, Z. R. Wasilewski, S. Fafard, "Quantum dot infrared photodetectors", Appl. Phys. Lett. 78, 79 (2001).
[8] E. A. Zibik, T. Grange, B. A. Carpenter, N. E. Porter, R. Ferreira, G. Bastard, D. Stehr, S.Winnerl, M. Helm, H. Y. Liu, M. S. Skolnick, L. R. Wilson, "Long lifetimes of quantum-dot intersublevel transitions in the terahertz range", Nature Mat. 8, 803 - 807 (2009).
[9] M. Kira and S. W. Koch, "Exciton-Population Inversion and Terahertz Gain in Semiconductors Excited to Resonance", Phys. Rev. Lett. 93, 076402 (2004).
[10] W. D. Rice, J. Kono, S. Zybell, S. Winnerl, J. Bhattacharyya, H. Schneider, M. Helm, B. Ewers, A. Chernikov, M. Koch, S. Chatterjee, G. Khitrova, H. M. Gibbs, L. Schneebeli, B. Breddermann, M. Kira, S. W. Koch, "Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells", Phys. Rev. Lett. 110, 137404 (2013).
[11] J. Bhattacharyya, M. Wagner, S. Zybell, S. Winnerl, D. Stehr, M. Helm, H. Schneider, "Simultaneous time and wavelength resolved spectroscopy under two-color near infrared and terahertz excitation", Rev. Sci. Instr. 82, 103107 (2011).

Transitions between the 1s and 2p levels of the fundamental heavy-hole exciton in GaAs quantum wells, followed by scattering into the 2s state, are investigated by resonant THz excitations using a free-electron laser. We report on the external control of this intra-excitonic population transfer by an external magnetic field.

This talk reviews recent experimental studies which we carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning the FEL in resonance with the transtion between the excitonic 2s and 2p states (at about 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where far-infrared absorption by single electrons produces sufficient contrast to map individual quantum dots. In graphene, FEL-based pump-probe spectroscopy reveals different relaxation times for excitation energies above and below the optical phonons. At even smaller photon energies, this two-dimensional semiconductor material exhibits a transition from induced transmission to induced absorption, which is indicative for possible applications as an optical modulator.

Bone metastases are a class of cancerous metastases that result from the invasion of a tumor into bone. The solid mass which forms inside the bone is often associated with a constant dull ache and severe spikes in pain, which greatly reduce the quality of life of the patient. Numerous ⁹⁹mTc-labeled bisphosphonate functionalised complexes are well established tracers for bone metastases imaging. The objective of this research was to evaluate the pharmacokinetics and behaviour of three DOTA based bisphosphonate functionalised ligands (BPAMD, BPAPD and BPPED), using both ⁶⁸Ga μ-PET in vivo imaging and ex vivo biodistribution studies in healthy Wistar rats. The compounds were labelled with ⁶⁸Ga in high yields using an ammonium acetate buffer, and subsequently purified using a cation exchange resin. High bone uptake values were observed for all ⁶⁸Ga-labelled bisphosphonates at 60 minutes p.i. The highest uptake was observed for [⁶⁸Ga]BPPED (2.6 ± 0.3% ID/g) which compares favourably with that of [^99mTc]MDP (2.7 ± 0.1 ID/g) and [¹⁸F]fluoride (2.4 ± 0.2% ID/g). The ⁶⁸Ga-labelled DOTA-bisphosphonates showed rapid clearance from the blood and renal system, as well as low binding to soft tissue, resulting in a high bone to blood ratio (9.9 at 60 minutes p.i. for [⁶⁸Ga]BPPED, for example). Although further studies are required to assess their performance in tumor models, the results obtained suggest that these ligands could be useful both in imaging (⁶⁸Ga) and therapeutic treatment (¹⁷⁷Lu) of bone metastases.

Introduction: Bombesin (BBN) and BBN analogues have attracted much attention as high-affinity ligands for selective targeting of the gastrin-releasing peptide (GRP) receptor. GRP receptors are overexpressed in a variety of human cancers including prostate cancer. Radiolabeled BBN derivatives are promising diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of various metabolically stabilized fluorobenzoylated bombesin analogues (BBN-1, BBN-2, BBN-3).

Methods: Three fluorobenzoylated BBN analogues containing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against ¹²⁵I-[Tyr⁴]-BBN for their binding potency to the GRP receptor. Intracellular calcium release in human prostate cancer cells (PC3) was measured to determine agonistic or antagonistic profiles of fluorobenzoylated BBN derivatives. Bombesin derivative BBN-2 displayed the highest inhibitory potency toward GRP receptor (IC₅₀ = 8.7 ± 2.2 nM) and was subsequently selected for radiolabeling with fluorine-18 (¹⁸F) through acylation with N-succinimidyl-4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB). The radiopharmacological profile of ¹⁸F-labeled bombesin [¹⁸F]BBN-2 was evaluated in PC3 tumor-bearing NMRI nude mice involving metabolic stability studies, biodistribution experiments and dynamic small-animal PET studies.

Results: All fluorobenzoylated BBN derivatives displayed high inhibitory potency toward the GRP receptor (IC₅₀ = 8.7–16.7 nM), and all compounds exhibited antagonistic profiles as determined in an intracellular calcium release assay. The ¹⁸F-labeled BBN analogue [¹⁸F]BBN-2 was obtained in 30% decay-corrected radiochemical yield with high radiochemical purity N95% after semi-preparative HPLC purification. [¹⁸F]BBN-2 showed high metabolic stability in vivo with 65% of the radiolabeled peptide remaining intact after 60 min p.i. in mouse plasma. Biodistribution experiments and dynamic small-animal PET studies demonstrated high
tumor uptake of [¹⁸F]BBN-2 in PC3 xenografts (2.75 ± 1.82 %ID/g after 5 min and 2.45 ± 1.25 %ID/g after 60 min p.i.). Specificity of radiotracer uptake in PC3 tumors was confirmed by blocking experiments.

Conclusion: The present study demonstrates that ¹⁸F-labeled BBN analogue [¹⁸F]BBN-2 is a suitable PET radiotracer with favorable metabolic stability in vivo for molecular imaging of GRP receptor-positive
prostate cancer.

We have developed a novel molecular modelling technique for radiopharmaceutical Tc and Re complexes combined with molecular mechanics (MM) and molecular dynamics (MD) for estimating the partition coefficient of these complexes between water and l-octanol (logP). The field force parameters developed with a MM program, "MOMEC" were fitted to all relevant X-ray crystal structures of [^99mTcO(DMSA)₂]^- and [¹⁸⁸ReO(DMSA)₂]^- (DMSA: dimercaptosuccinic acid). The force field parameters were transferred to those in a MD program, "Material Explorer". The MD simulations also indicate that a quantitative structure property relationship (QSPR) was optained, which relates the internal energy difference between the Tc/Re-DMSA derivatives in the water phase and that in l-octanol phase with the experimental logP value.

Ge films with a mean Ga content of about 8 at.% and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change of the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters up to 10,000 atoms. Since no percolating Ga cluster exists, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.

Das 1-(2-Fluorethylindol-6-yl)-oxadiazolylamin NS14490 ist ein hoch affiner α7-Subtyp-spezifischer Ligand für den nikotinischen Acetylcholinrezeptor (nAChR, Ki,α7 = 2,5 nM), für dessen ¹⁸F-markierte Form wir ein Syntheseverfahren entwickelt haben [1]. Das Potential dieses neuen Radiotracers für die molekulare PET-Bildgebung von α7 nAChR bei neurodegenerativen und Tumorerkrankungen wird gegenwärtig von uns untersucht.
Da die Herstellung des zur Radiosynthese von [¹⁸F]NS14490 benötigten Tosylates 1 nach einer ursprünglich verfolgten Methode [1], ausgehend vom N-unsubstituierten NS14490-Derivat unbefriedigende Ergebnisse erbrachte, wurde ein verbessertes Syntheseverfahren aus dem Ester 3 über eine 6-stufige Sequenz, mit BOP-Kupplung zu 7 als Schlüsselschritt [2] entwickelt, das eine Gesamtausbeute von 32% ermöglichte. Die Darstellung von [¹⁸F]NS14490 erfolgt mit [¹⁸F]Fluorid [¹⁸O(p,n)¹⁸F-Reaktion am Cyclone 18/9, Leipzig] in Gegenwart von Kryptofix K2.2.2 in einem Schritt aus 1. Die Isolierung und Reinigung des Radiotracers (radiochemisch ≥95%) ist umfassend optimiert und erfolgt durch semipräparative RP-HPLC mit anschließender Festphasenextraktion (RCA: 36%, spezifische Aktivität: 150 GBq/μmol, Synthesedauer: 2-2,5 h).
Weiterführende In-vitro- und In-vivo-Studien, insbesondere zur Hirn-Aufnahme und zur Selektivität der Bindung von [¹⁸F]NS14490 an α7 nAChR im Gehirn belegen die potentielle Eignung des Radioliganden für die molekularen Bildgebung [1].
(Unterstützt durch die Deutsche Forschungsgemeinschaft, Ref. DE1165/2-1)
Literatur:
[1] S. Rötering et al. Bioorg. Med. Chem. (im Druck). [2] C. G. Levins et al. Org. Lett. 2008, 10, 1755.

The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film.

Se, Pu in the context of radioactive waste disposal
FeII-driven interfacial redox reactions
Se interfacial redox reactions
Pu interfacial redox reactions

Positron emission tomography/computer tomography (PET/CT) is an established method in the preclinical research of small animal disease models and in the clinical diagnosis of cancer. It combines the functional information of the positron-emitting biomarker with the anatomical data from the CT image, thereby allowing for the 4D in vivo investigation of biological processes of interest. Recently, the bone growth of chicken embryos was monitored using [¹⁸F]fluoride as a bone-seeking tracer. We are interested to investigate additional PET/CT tracers in embryonated chicken eggs as in vivo model system. The properties of ¹⁸F-, ⁶⁸Ga-labelled tracers and ⁶⁴Cu-chloride were studied in catheterised eggs via small animal microPET/CT. [¹⁸F]FDG was primarily absorbed at sites of bone growth. ⁶⁴Cu chloride and a ⁶⁸Ga-labelled amyloid-fibril-binding antibody accumulated in the liver, while ⁶⁸Ga-albumin desferrioxamine conjugate was rapidly cleared. The method potentially can be utilised to monitor biological processes in chicken eggs.

In this work, the effect of 180 keV proton radiation in lateral 4H-SiC nMOSFETs with rapid thermally processed (RTP) gate oxides is investigated before and after radiation. Comparison with non-irradiated (NI) samples allows the study of hole trap effects in the oxide and of generated interface traps. It has been observed that for the two lower fluences, the threshold voltage (VTH) shifts toward lower values, reaching a minimum for a fluence of 5x1012 cm-2. The effective channel mobility (µEFF) and the maximum drain current (IDSAT_MAX) reach maximum values for 5x1012 cm-2 as well; the µEFF gets 6 times superior, while the IDSAT_MAX doubles in accordance with the NI sample values.

The impact of proton and electron irradiation on the electrical parameters of 4H-SiC nMOSFETs has been
investigated by using time bias stress instability method. This study has allowed observing the effect of holes trapped in the
oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage,
the effective mobility and the maximum drain current were observed. These amendments could be connected with the
Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These
atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of
passivated Carbon atoms is increasing, hence the interface quality getting improved.

This work presents the 10 MeV proton irradiation effects on 4H-SiC MOSFETs at different fluences. MOSFETs main electrical parameters, such as the channel mobility (µEFF), threshold voltage (VTH), transconductance (gm) and subthreshold current, were analyzed using the time bias stress instability (BSI) technique. Applying this method allowed us to study the effect of carrier interaction with proton induced defects (traps), whether in the bulk or at the interface. Improvements, such as VTH stabilization in time and a significant increase of the µEFF at high fluencies, have been noticed. We assume that this behavior is connected with the atomic diffusion from the SiO2/SiC interface, towards the epilayer during proton irradiation. These atoms, mainly Nitrogen, may create other bonds by occupying various vacancies coming from Silicon and Carbon’s dangling bond. Therefore, by increasing the number of passivated Carbon atoms, we show that high irradiation proton could be a way to improve the SiO2/SiC interface quality.

We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. In the experiments we have chosen an incident ion energy of q x 8.5 keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7 kV. Hence, the ion beam was decelerated and compressed to a diameter of 150 µm without using any additional decelerating lens systems.

Regarding magnetic nanostructures, dipolar stray fields start to evolve with ongoing miniaturization, that grossly alter the magnetic properties. Besides, these fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals.
Hence, a detailed knowledge of the magnetic configuration under geometric confinements on the nanoscale is mandatory.
We present a study of the magnetic fields arising from thin Permalloy films deposited on periodically modulated surfaces (ripples).
These ripples were prepared using a self-organized ion beam erosion process generating modulations on the nanoscale.
Cross-sectional transmission electron holography nowadays offers the necessary sensitivity and nanoscale lateral resolution to probe the magnetic configuration of such rippled films quantitatively.
The imaging allows for an absolute analysis of the local magnetization inside the film as well as the accompanying stray fields outside.
In addition, the evolving stray fields above the sample's surface were investigated by magnetic force microscopy.

Two-magnon scattering is a well-known effect e.g. in ferromagnetic resonance (FMR) experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in periodically perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the resonance response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments [2,3]. The scattering potential of the defects builds up due to the dipolar stray fields at the edges of the defects. Within the perturbation theory this leads on the one hand to a shift of the resonance peak and on the other hand also to a splitting of the uniform resonance mode. Both effects are clearly visible in the FMR experiments. The mode splitting due to the two-magnon scattering finally is also responsible for the opening of magnonic band gaps in the dispersion relation of magnonic crystals. The splitting can be tailored by the geometric and magnetic sample parameters. Experimental data for magnetically patterned stripe samples as well as for ripple samples [3] is presented and compared to calculations by the analytical model (see e.g. Fig. 1).
This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, K. Lenz, A. Banholzer, M. Körner, J. Lindner, J. Fassbender, P. Landeros, Phys Rev. B (2013) submitted
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner, P. Landeros, J. Fassbender, Phys. Rev. B (2013) submitted

Background: The long-term aim of developing a laser based acceleration of protons and ions towards clinical application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short pulsed particle beams. Recent in-vitro data showed similar effects of laser-accelerated versus “conventional” protons on clonogenic cell survival. As the proton energies currently achieved by laser driven acceleration are too low to penetrate standard tumour models on mice legs, the aim of the present work was to establish a tumour model allowing for the penetration of low energy protons (~ 20 MeV) to further verify their effects in vivo.
Methods: KHT mouse sarcoma cells were injected subcutaneously in the right ear of NMRI (nu/nu) mice and the growing tumours were characterized with respect to growth parameters, histology and radiation response. In parallel, the laser system JETI was prepared for animal experimentation, i.e. a new irradiation setup was implemented and the laser parameters were carefully adjusted. Finally, a proof-of-principle experiment with laser accelerated electrons was performed to validate the tumour model under realistic conditions, i.e. altered environment and horizontal beam delivery.
Results: KHT sarcoma on mice ears expressed a high take rate and showed continuous tumour growth after reaching a volume of ~ 5 mm³. The first irradiation experiment using laser accelerated electrons versus 200 kV X-rays was successfully performed and tumour growth delay was evaluated. Comparable tumour growth delay was found between X-ray and laser accelerated electron irradiation. Moreover, experimental influences, like anaesthesia and positioning at JETI, were found to be negligible.
Conclusion: A small animal tumour model suitable for the irradiation with low energy protons was established and validated at a laser based particle accelerator. For this reason, the translation from in vitro to in vivo experimentation was for the first time realized and an important milestone towards the clinical application of laser driven particle accelerators was achieved.

We show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3^rd generation thin-film solar cells. Well passivated by the SiO₂ dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar⁺ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon.

The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P3 (or SP3) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP3 transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance.
The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP3 and diffusion equations, which guarantees high accuracy.
The SP3 equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP3 transport problem.
The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP3 transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.

DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of light-water reactors with square and hexagonal fuel assembly geometries as well as of innovative reactor concepts, which is undergoing continuous development.
In this work, the trigonal-geometry DYN3D diffusion model is verified by means of the AER-FCM-101 benchmark. With increasing trigonal mesh refinement, both effective multiplication factor and power distribution converge well to the extrapolated finite-element reference solution. In addition, a comparison to the hexagonal DYN3D diffusion models HEXNEM1 and HEXNEM2 is given.

We investigate spin-wave propagation in a microstructured magnonic-crystal waveguide fabricated by localized ion implantation. The irradiation caused a periodic variation in the saturation magnetization along the waveguide. As a consequence, the spin-wave transmission spectrum exhibits a set of frequency bands, where spin-wave propagation is suppressed. A weak modification of the saturation magnetization by 7% is sufficient to decrease the spin-wave transmission in the band gaps by a factor of 10. These results evidence the applicability of localized ion implantation for the fabrication of efficient micron- and nano-sized magnonic crystals for magnon spintronic applications.

New results obtained by applying positron annihilation spectroscopy to the investigation of zirconia-based nanomaterials doped with metal cations of different valence are reported. The slow-positron implantation spectroscopy combined with Doppler broadening measurements was employed to study the sintering of pressure-compacted nanopowders of tetragonal yttria-stabilised zirconia (t-YSZ) and t-YSZ with chromia additive. Positronium (Ps) formation in t-YSZ was proven by detecting 3γ-annihilations of ortho-Ps and was found to gradually decrease with increasing sintering temperature. A subsurface layer with enhanced 3γ-annihilations, compared to the deeper regions, could be identified. Addition of chromia was found to inhibit Ps formation. In addition, first results of positron lifetime measurements on nanopowders of zirconia phase-stabilised with MgO and CeO2 are presented.

Super-SIMS - also called Accelerator-SIMS - is an ultrasensitive analytical method (Döbeli et al., 2013; Renno et al., 2013). A Super-SIMS-Set-up is now under installation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) by connecting a conventional SIMS-source (Cameca 7f-Auto) to a 6 MV tandem accelerator (Akhmadaliev et al., 2013). The operation of a classical SIMS demands strong structural and building technological efforts [Cameca, 2012]. The requirements for the 6 MV tandem accelerator at the HZDR are of the same complexity.

Requirements # Cameca 7f-Auto # 6 MV tandem accelerator
vibrations # very strict # -
temperature | fluctuation # 19°C < T < 23°C|< 1°C•h-1 # max. 25°C
relative humidity | fluctuation # 30% < RH < 75% | < 10%•h-1 # 30%< RH < 75%
spurious magnetic field # < 3•10-7 Tesla # < 10-4 Tesla
vacuum # 10-9 mbar # 10-6 mbar
cooling | fluctuation # 17°C – 19°C | < 1°C•h-1 # 20°C – 25°C
nitrogen # N4.8 # N4.8
compressed air # dry | 5 – 7 bar | 35 – 50 L•min-1 # dry | 5 – 7 bar
uninterruptible power supply # 10 min # only for PC
radiation safety # - # very strict

The original specifications to optimally run both machines are in many cases incompatible. An additional challenge originates from the fact that a pre-acceleration voltage of 30 kV to inject negative secondary ions into the accelerator is needed. To guarantee the compliance with all specifications and safety regulations a specific concept for the housing of the Cameca 7f-Auto following a house-in-house-principle was developed. This concept guarantees the following operational options:

• independent operation of the 6 MV tandem accelerator
• independent operation of the Cameca 7f-Auto
• combined operation as a Super-SIMS by remote control
• operation of the Super-SIMS by remote control from outside the HZDR in the framework of the planned Helmholtz-SIMS network SIGMA

New results of a generalized concept developed for the simulation of two-phase flows with multi-scale interfacial structures are presented in this paper. By extending the inhomogeneus Multiple Size Group-model, the concept enables transitions between dispersed and continuous gas morphologies, including the appearance and evanescence of one of these particular gas phases. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for interfacial area density and drag. A new drag-formulation considers shear stresses occurring within the free surface area.
The application of the concept to a collapsing water column demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The simulations have been performed with the CFD-code CFX 14.0 and will be compared with experimental images.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.

Plasma and ion beam technologies have been proven to be effective approaches for modification of surface properties of different materials. In the present work, structure, phase composition, hydrophilicity and microhardness of titanium oxynitride TiNxOy, and pure and phosphorus ions implanted TiO2 coatings produced by metal plasma immersion ion implantation and deposition were investigated. The mixed, highly amorphous TiN0.4O1.6 surface has maximal hydrophilicity and microhardness. P implantation in a TiO2 layer consisting mainly of rutile phase leads to disorder in the crystal lattice, slight amorphisation, and increasing hydrophilicity as well as microhardness of the surface. To evaluate the correlation between the structure of the layers and their cytocompatibility, the influence of the surfaces on the behavior of osteoblast-like SaOS-2 cells was studied in vitro. The cells were cultured on the three Ti-based coatings, both on the bare surfaces as well as on the surfaces biomineralised from simulated body fluid. No statistically significant differences were observed for cell adhesion to all bare Ti-based surfaces. Cell proliferation and osteogenic differentiation were surface sensitive and showed an opposite effect:

osteogenic differentiation, indicated by an increase of alkaline phosphatase (ALP) activity, on the P-implanted TiO2 and TiNxOy surfaces was reduced whereas the proliferation increased in comparison to TiO2.
Attachment and proliferation of cells were significantly lower on biomineralised surfaces.

Equiatomic FeRh thin films with varying thickness have been prepared on MgO (100) substrates via molecular beam epitaxy (MBE). The optimization of the stoichiometry was monitored using XRD, RBS and AES while the magnetic properties were probed using SQUID magnetometry. XRD results evidence a well ordered CsCl-type crystal structure. By increasing the annealing temperature of the films, the structural quality of the films also increases. Moreover, the known first order phase transition at ~350 K from an antiferromagnetic (AF) to a ferromagnetic (FM) state slightly shifts towards higher temperatures. M-H loops of films annealed at 800 ∘C or 850 ∘C recorded at 300 K show an opening, which is likely related to the magnetic field-induced AFM-FM phase transition. Residual low-temperature ferromagnetic moments are of unknown origin, but likely related to strain or diffusion effects at the surface or interface.

Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400°C) leads to the formation of a modified surface layer which shows increased hardness and induced magnetism, without compromising the corrosion resistance. The exact nature of this layer is still a matter of debate.

In this study, ASS 316L has been plasma nitrided with a mixture of 14N and 15N for 30 min at 400°C. Only a single phase, usually called the S phase or expanded austenite, is detected by X-ray diffraction. Transmission electron microscopy shows a high density of stacking faults and lattice distortions in this S phase, but does not provide any direct information regarding its composition, in particular regarding nitrogen and chromium distributions at the nanometer scale. Atom probe tomography and field ion microscopy reveal the presence of nanometric chromium nitride precipitates, with irregular oblate-spheroid-like shape. The preferential precipitation of chromium nitride at grain boundaries and/or stacking faults is investigated. These observations suggest that incorporation of large amounts of N provides strong driving force for chromium nitride formation, even at such a short nitriding time and rather low temperature.

Because of the presence of silicon and obviously iron in this industrial stainless steel, direct composition measurement of these chromium nitrides, in particular their nitrogen content, is not possible. In order to solve this classical analytical issue, specimens were nitrided using different 14N/15N ratios. Possible N+/Si2+ and N2+/Fe2+ overlaps at 14 and 28 Da respectively are investigated in order to estimate the actual chromium nitride composition. Results will be compared with the one obtained with the newly developed high mass resolution Flextap, potentially allowing N+/Si2+ and N2+/Fe2+ peak discrimination.

Magnetic dipole strength functions have been deduced from averages of a large number of M1 transition strengths calculated within the shell model for the nuclides 94Mo, 95Mo, and 90Zr. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M1 strength function deduced from the calculated M1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents for the first time an explanation of the experimental findings.

The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is its questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile. This way we further show how the formerly known lower Liu limit of the critical Rossby number connects naturally with the upper Liu limit.

The development of general models closer to physics and including less empiricism is a long-term objective of the activities of the HZDR research programs. Such models are an essential precondition for the application of CFD codes to the modelling of flow related phenomena in the chemical and nuclear industries. The Algebraic Interfacial Area Density (AIAD) approach allows the use of different physical models depending on the local morphology inside a macroscale multi-fluid framework. A further step of improvement of modelling the turbulence at the free surface is the consideration of sub-grid wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. In fact, the influence on the turbulence kinetic energy of the liquid side can be significantly large. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth and wavy stratified flow experiments of a different rectangular channel. The results approve the ability of the AIAD model to predict key flow features like liquid hold-up and free surface waviness. Furthermore an evaluation of the velocity and turbulence fields predicted by the AIAD model against experimental data was done. The results are promising and show potential for further model improvement.

Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe-9at%Cr and Fe-12.5at%Cr irradiated at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles and exploitation of the full load dependence of hardness. The effects of Cr content, fluence and irradiation temperature are discussed. Hardening features were characterized by means of transmission electron microscopy. A tentative multi-feature hardening model was applied, to this end APT data published for the same alloys ion-irradiated under the same nominal conditions are taken into account.

The structural materials of particular components in nuclear applications like fission or fusion reactors are exposed to high neutron fluxes giving rise to the formation of irradiation-induced defects and subsequent changes of the mechanical properties. Ion-irradiation is a well-recognized tool to simulate damage caused by fast neutron irradiation in a wide range of irradiation temperature and fluence and allows for an efficient screening of potential structural materials for nuclear application due to short irradiation times. The limited depth of penetration of the ions into the material (up to few µm) demands characterization methods suitable for thin layers. In the present work, nanoindentation is applied to deduce the irradiation-induced hardness changes. The approach is based on the generation of an approximately rectangular dpa-profile by means of multi-step irradiations with ions of different energies and the exploitation of the depth dependence of the hardness. Results will be reported for ferritic/martensitic Cr-steels considered as candidate structural materials for future application in Generation IV fission reactors and for Fe-Cr binary alloys with emphasis on the effect of irradiation temperature and fluence. Transmission electron microscopy results on the formation of irradiation-induced defects will be taken into account.

The influence of magnetohydrodynamic (MHD) convection on the thickness of an electrochemically deposited copper layer along a vertical plane cathode is examined. A magnetic gradient field, that induces a Lorentz force, establishes a vortical motion of the electrolyte which can be oriented either antiparallel or parallel to the natural convection. For the latter case, we show both experimentally and numerically that a sufficiently strong Lorentz force levels the inhomogeneities of the deposit thickness characteristic for deposition under pure natural convection.

High-power impulse magnetron sputtering (HiPIMS, also known as high-power pulsed magnetron sputtering, HPPMS) is a method for physical vapour deposition of thin lms which is based on magnetron sputter deposition. HiPIMS utilises extremely high power densities of the order of kW cm-2 in short pulses (impulses). A distinguishing feature of HiPIMS is its high degree of ionization of the sputtered metal and high rate of molecular gas dissociation. In this poster we present the study on the growth of C-W nanocomposite lms grown in DC (MS) and HiPIMS modes. For deposition, we have used 3 in C and C-W (90 to 10 at%) substrates. In order to prevent arcing, the depositions were carried out with three-pulse sequence followed by a long off-time. Film areal density was determined by Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA). Film microstructure was determined by Raman spectroscopy, X-Ray diraction, and transmission electron microscopy. Film mechanical properties were studied by nanoindentation and scratch test. We got extensive arcing with pure carbon. In contrast, for the compound target we got stable plasma condition with duty cycle as low as 1 %. Deposited films consist of WC nanoparticles embedded in a carbon matrix. From NRA and RBS, the film areal density of tungsten shows a small decrease concomitantly with the duty cycle (transition from pulsed DC to HiPIMS). In contrast, the film areal density of carbon remains constant. This implies that in different sputtering modes like Ar + dominated in the pulsed DC mode or a mixture of Ar/W ions in the HiPIMS mode the average sputtering rate of carbon is not affected. A collisional computer simulation using TRIDYN was carried out to show a considerable sputter yield amplication of carbon when irradiated with a mixture of Ar/W ions. This is in-line with the observed stable carbon film areal density, which can be attributed to the compensation of the change in sputtering ion composition by sputter yield amplication due to W-enrichment of the target surface. Film characterization shows that there is no signicant change between the films grown in DC and HiPIMS modes.

Carbon-based metal nanocomposites have been shown to be good material candidates for applications requiring optical selectivity. However their true potential usage largely depends on the optimization of their composition and microstructure. Diamond Like Carbon with different transition metals were grown on stainless steel and Inconel substrates using pulse filtered cathodic arc deposition from two repetitively pulsed cathodic arc sources with separate macroparticle filters. The influence of several transition metals (Ti, Zr, Cr, W, Mo, V and Nb) on their optical selectivity was investigated. Carbon metal-containing samples were prepared using two cathodic arc sources provided with a carbon cathode and a pure transition metal cathode. Different metal concentrations in the coatings were obtained by varying the average arc current of the metal pulsed cathodic arc source (Imetal). The volume fraction of metal was determined by combined Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) measurements. The structure of the deposited films was analyzed by Transmission Electron Microscopy (TEM), X-ray diraction (XRD) and Raman spectroscopy. In this study, the computer simulation program Coating Design (CODE) has been used to calculate optical properties of the different carbon-transition metal nanocomposites. The optical constants of various carbon-based nanocomposites were simulated using a physical model proposed by Bruggeman and Maxwell Garnett which averages the dielectric function of the components of the composite, which allows treating the composite system as an effective medium. The performed simulations allowed calculating the solar absorptance and thermal emittance of the nanocomposites. Varying the nanocomposite material configurations such as layer thickness, volume metal fraction, number of layers and multilayer stack resulted in new configurations that enhance the optical selectivity of these materials. Simulated reflectance was compared with spectrophotometry measurements of the deposited films with good agreement between them.

Ion irradiation of multielement surfaces can induce regular compositionally modulated surface roughness nanopattern formation such as ripples or nanodots. This kind of bottom-up nanopatterning can provide means to not only structure the solid surfaces but also to create ordered heterogeneous structures in three dimensions (3D) when performed in growth mode: the compositional surface nanopattern is continuously buried by incoming species while the surface is again restructured due to ion irradiation.
The present work is an experimental demonstration of this concept: 3D ordered nanocomposites are grown via ion induced two dimensional (2D, surface) nanopattern formation during bi-component film growth. The influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 30 at.% Ni) thin films will be reported. It will be shown that for certain growth conditions surface ripples form during oblique incidence low energy ion beam assisted deposition of C:Ni films. These surface ripples are compositionally modulated: Ni is located on the crests and carbon in the valleys. The film cross sections show periodic distribution of metal nanoparticles in a carbon matrix with the same periodicity as the surface ripples. As this 3D patterning effect has a physical origin, it can be expected to occur in many material systems. Such an approach holds high potential for the growth of functional nanocomposite films for a wide range of applications.

Die vorliegende Arbeit zeigt, wie innerbetriebliche Berichtserstellungsprozesse durch Unterstützung von IT-Systemen verbessert werden können. Im Speziellen geht es dabei um die prototypische Realisierung eines Berichtssystems am Helmholtz-Zentrum Dresden-Rossendorf e.V., wobei es den Mitarbeitern mithilfe des SharePoint-Add-In der Microsoft Reporting Services möglich ist, Berichte im SharePoint zu erstellen und diese dort zu hinterlegen.
Zur Umsetzung dieser Zielstellung wurde zunächst die Ausgangssituation anhand des Geschäftsprozesses sowie die Quelle der benötigten Informationen analysiert, um daraufhin ein entsprechendes Konzept zu erarbeiten. Dabei wurde eine, dem System zur Datenbeschaffung, nachgelagerte Datenbank erstellt, welche zur Sammlung aller berichtsrelevanten Informationen dienen soll und danach, nach vorheriger Beschreibung verschiedener Möglichkeiten, die oben genannte Realisierung ausgewählt wurde.
Im Anschluss daran wurde eine Kosten-Nutzen-Analyse durchgeführt, welche die Vorteile der durchgeführten Teilautomatisierung verdeutlicht.

This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.

Fragestellungen: Zur Qualitätssicherung der Partikelbestrahlungen von Tumorpatienten ist eine nicht-invasive, in-vivo Überwachung wünschenswert. Am OncoRay / TU Dresden / HZDR wird zur Zeit ein Prototyp einer Compton Kamera für die klinische Anwendung entwickelt, die eine solche Überwachung anhand der bildgebenden Messung prompter Gammastrahlung ermöglichen soll [1]. Aufgrund der Vielzahl der zu optimierenden Parameter wie Größe, Abstände und Material der Detektoren, zur Analyse der auftretenden Wechselwirkungen und zur Selektion von Ereignissen sind Monte Carlo Simulationen dabei unerlässlich.

Material und Methoden: Die betrachtete Compton Kamera ist aus einer Streuebene (CZT) und einer Absorberebene (CZT oder LSO) aufgebaut (Abb.1). Das Funktionsprinzip einer Compton Kamera basiert auf der Berechnung des Streuwinkels und damit der Eintreffrichtung des Photons mithilfe der gemessenen Energiedepositionen.
Zur Optimierung des Detektorsystems wurden Simulationen mit dem Monte Carlo Code GEANT4 Version 9.5 [2] durchgeführt. Neben der Untersuchung der Zählraten war die Charakterisierung der auftretenden Ereignisse das Ziel dieser Simulationen. Dabei wird eine koinzidente Energiedeposition in beiden Detektorebenen genau dann als nutzbares Ereignis angesehen, wenn in der Streuebene genau eine Compton Streuung und in der Absorptionsebene eine vollständige Absorption des Photons stattfand. Außer einer Punktquelle wurden Emissionen aus einer kugelförmigen Quelle mit 10 cm Durchmesser simuliert. Verschiedene Abstände des Detektors zur Quelle sowie unterschiedliche Anordnungen von Streuebene zur Absorptionsebene wurden angenommen. Des Weiteren wurden die Simulationen mit experimentellen Daten verglichen. Ferner wurde der Fehler, der durch die Abweichung zwischen simuliertem Schwerpunkt, der dem experimentellen Messpunkt nahe kommt, und dem Ort der Comptonstreuung im Streuer bzw. der Einfallsrichtung im Absorber untersucht.

Ergebnisse: Die Konfiguration aus CZT und LSO weist erwartungsgemäß eine höhere Ansprechwahrscheinlichkeit als der CZT-CZT Detektor auf (Abb.2), außerdem ist die Rate an nutzbaren Ereignissen deutlich höher (Abb.3). Die Abstände zwischen den Detektorebenen und der Abstand zur Quelle haben kaum Einfluss auf die Güte der Ereignisse. Eine Selektion von Ereignissen zur Minimierung des Rauschens anhand der Wechselwirkungstiefe in der Streuebene erscheint sinnvoll.

Zusammenfassung: Es wurden umfassende Simulationen mit GEANT4 zur Bewertung und Optimierung von möglichen Compton Kamera Systemen durchgeführt. Um die Güte der Simulationen zu bewerten wurden die Simulationsergebnisse mit experimentellen Daten verglichen.

Literatur

[1] Kormoll, T.: A Compton Camera for In-vivo Dosimetry in Ion-beam Radiotherapy. Diss.,
Technische Universität Dresden, Mathematik und Naturwissenschaften. Dresden, 2013

[2] Agostinelli, S. et al 2003 GEANT4 - a simulation toolkit Nucl. Instr. Meth. A 506(3) 250-303

This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with a parts per thousand yen10(15) He ions per cm(2). The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 x 10(-3) (-3) (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 A degrees C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of similar to 2.4 +/- A 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10(-6) (-3) (or 0.000006 dpa) and is suppressed at moderate defect densities of similar to 5 x 10(-4) (-3) (or similar to 0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 A degrees C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.

Nanostructures dramatically influence materials properties due to size, shape and interface effects. Thus the control over the structure at the nanoscale is a key issue in nanomaterials science. The growth of nanostructured thin films is governed by the atomistic processes at the very surface of the growing film. The interaction range of hyperthermal ions with solid surface is confined to some nanometers. Therefore energetic ion assistance during film deposition is of primary relevance in the context of the thin film nanostructuring.
Our recent activities in the field of ion-assisted physical vapor deposition (PVD) of nanocomposite films will be summarized with the focus on the growth-structure relationship of carbon-transition metal films. This class of materials is relevant in the context of tribology, sensing, fusion, electrochemistry, information storage, spintronics, solar-thermal energy conversion or as metamaterials. We have employed two paradigms involving the use of energetic ions:

• ion assisted PVD (ia-PVD), where the growing film is irradiate with assisting ion beam
• ionized PVD (i-PVD), where the depositing species are energetic ions themselves.

The design of an efficient and stable solar selective coating for photo-thermal conversion plants requires a complex study of the materials that composed the coating. The optimal optical properties for those absorber coatings are high solar absorptance in the wavelength range of 0.3 to 2.5 μm which corresponds to solar spectrum under atmospheric conditions and low thermal emittance in the infrared wavelength range.
Carbon-transition metal nanocomposites have been selected as absorber materials because they show appropriate optical properties as well as thermal and mechanical stability at high temperatures. The refractory metal carbide nanoparticles have been experimentally shown to stabilize the surrounding carbon matrix at least up to 700°C.
The computer simulation program CODE has been used to calculate solar absorptance and thermal emittance of various multilayers coatings material combinations of carbon - metal nanocomposites (NCTM). The optical properties of the inhomogeneous composite material were simulated with a physical model proposed by Bruggeman and Maxwell Garnett which average the dielectric function of the components of the composite. This allows treating the composite system as an effective medium.
This contribution compares simulated optical properties for different nanocomposite structural configurations (layer thickness, metal to carbon ratio). The calculated results are in the range of 0.91-0.97 for solar absorptance and 0.02 - 0.07 for thermal emittance at 300K.

Phase separation occurring on the surface of growing films provides unique means to influence the microstructure of composite materials. Here, the influence of ion assistance on the morphology of carbon-nickel nanocomposite thin films for different metal contents is investigated. Carbon-transition metal nanocomposites are relevant in the context of solar-thermal energy conversion, fusion, fuel cells, tribology or sensing. The films were grown by dual ion beam sputtering in a temperature range of RT-300°C. The growing films were irradiated by an assisting Ar ion beam with energies ranging from 50 to 130 eV. It is found that the nickel content drastically influences the morphology of the films: while films with low Ni contents show regular self-organized structures consisting of ordered Ni nanoparticles embedded in the carbon matrix, higher Ni contents predominantly exhibit a columnar morphology. The results are discussed on the basis of the interplay of ion-induced effects and phase separation modes.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379 is gratefully acknowledged.

A new class of linear accelerator (linac) based THz facilities, aiming to provide peak THz fields in the GV/m regime from highly charged, ultra-short relativistic electron bunches is currently studied and developed worldwide. These facilities are based on low emittance, electron beams delivered by a linear radio frequency (RF) driven accelerator followed by one or several magnetic chicanes that act as bunch compressor. THz radiation is then emitted coherently for wavelengths appropriately longer than the longitudinal electron bunch length upon one single pass through any of the typical sources of synchrotron radiation. This allows for an enormous flexibility in the generated spectral, spatial and temporal properties of the THz pulses. Together with the theoretically large scalability and simplicity of these sources, they are discussed as extension of the THz pulses from laser-based THz sources towards extreme transient THz fields and high repetition rates with more than 10 projects currently being pursued worldwide. In this respect it is timely to investigate if current idealized theoretical descriptions can be technically fully realized. As our contribution to this effort, in this paper it is shown by numerical and analytical calculations that the interference effects between different THz radiators, intrinsically emitting in the forward direction of a linac can crucially affect radiation properties.

CFD Workshop about the different projects and modelling strategies inside the Computational Fluid Dynamics Department of the Institute of Fluid Dynamics of HZDR, along with a brief introduction of other different institutes such as Resource Ecology, Material Research, Cancer Research, among others.

For quality assurance in particle therapy, a non-invasive, in-vivo range verification is highly desired. Particle Therapy Positron-Emission-Tomography (PT-PET) is the only clinically proven method up to now for this purpose. It makes use of the beta+-activity produced during the irradiation by the nuclear fragmentation processes between the therapeutic beam and the irradiated tissue. Since a direct comparison of beta+-activity and dose is not feasible, a simulation of the expected beta+-activity distribution is required. For this reason it is essential to have a quantitatively reliable code for the simulation of the yields of the beta+-emitting nuclei at every position of the beam path. In this paper results of the three-dimensional Monte-Carlo simulation codes PHITS, GEANT4, and the one-dimensional deterministic simulation code HIBRAC are compared to measurements of the yields of the most abundant beta+-emitting nuclei for carbon, lithium, helium, and proton beams. In general, PHITS underestimates the yields of positron-emitters. With GEANT4 the overall most accurate results are obtained. HIBRAC and GEANT4 provide comparable results for carbon and proton beams. HIBRAC is considered as a good candidate for the implementation to clinical routine PT-PET.

The accumulation of structural damage that is created in minerals upon corpuscular irradiation, has two apparently contrarious effects on their luminescence behaviour. First, irradiation may cause the generation of luminescent defect centres, which typically results in broad-band emissions. Such defect emissions are characteristic of low levels of radiation damage. Second, radiation damage depletes in general the luminescence of minerals, which is associated with broadenings and intensity losses of individual emission lines. Minerals that have suffered elevated levels of irradiation hence tend to be virtually non-luminescent. This review paper aims at giving an overview of the possible correlations of radiation damage and emission characteristics of minerals. After a brief, introductory summary of the damage-accumulation process and its causal corpuscular radiation, an array of examples is presented for how internal and/or external irradiation may change appreciably the emission of rock-forming and accessory minerals. As a detailed example for the complexity of changes of emissions upon damage accumulation, preliminary results of a case study of the photoluminescence (PL) of synthetic CePO4 irradiated with 8.8 MeV He ions are presented. Irradiation-induced spectral changes include (i) the initial creation, and subsequent depletion, of a broad-band, defect-related PL emission of orange colour, and (ii) gradual broadenings and intensity losses of PL lines related to electronic transitions of rare-earth elements, eventually leading to gradual loss of their splitting into multiple Stark levels (shown for the 4F3/2 → 4I9/2 transition of Nd3+).

This work gives a complete overview on the subject of nonconservative stability from the modern point of view. Relevant mathematical concepts are presented, as well as rigorous stability results and numerous classical and contemporary examples from mechanics and physics. It deals with both finite- and infinite-dimensional nonconservative systems and covers the fundamentals of the theory, including such topics as Lyapunov stability and linear stability analysis, Hamiltonian and gyroscopic systems, reversible and circulatory systems, influence of structure of forces on stability, and dissipation-induced instabilities. The book serves present and prospective specialists providing the current state of knowledge in the actively developing field of nonconservative stability theory. Its understanding is vital for many areas of technology, ranging from such traditional ones as rotor dynamics, aeroelasticity and structural mechanics to modern problems of hydro- and magnetohydrodynamics and celestial mechanics.

The genesis of the economic Zr-Nb-REE mineralisation at Khalzan Buregte, Western Mongolia was re-explored by field work, whole rock analysis (chemical composition, quantitative XRD mineral analysis) and by application of various transmitted light and electron microscopic techniques. Coarse-grained bodies, dikes, and volcanics of alkaline, silica-saturated rocks were contemporarily emplaced at subvolcanic to volcanic levels forming four alkaline massifs within the Khalzan Buregte area. The whole rock composition of the weakly altered magmatic rocks ranges from syenite to quartz monzonite and alkaline granite (alkali feldspar syenite to alkali feldspar granite according to mineral composition). Magmatic and hydrothermal processes contributed to the formation of economic concentrations of several high field strength elements (HFSE) as Zr, Hf, Nb, Ta, REE, and Y in the Khalzan Buregte deposit and in the nearby Tsakhir prospect. Magmatism with mixing of at least three melt types and, possibly, the formation of K-feldspar cumulates resulted in a local enrichment of Zr, Nb, and of the light rare earth elements (LREE) in the rocks up to a sub-economic level. There was, however, no significant increase in Y and the heavy rare earth elements (HREE). In contrast, hydrothermal alteration by silica- and carbonate-rich fluids yielded extreme concentrations of Zr, Nb, and LREE. Additionally, one of the late alteration events resulted in economic levels of Y and HREE. These fluids were rich in fluorine. There are new indications for two main alteration events causing ore formation: (1) an early, carbonatite-style and (2) a late by F-rich fluids. Multistage metasomatic alteration resulted in a pronounced chemical and mineralogical heterogeneity of the alteration assemblages. The main hosts of Zr (and Hf) in the ores are zircon and other zirconium silicates (gittinsite, catapleiite-(Ca), and elpidite). Nb (and Ta) is mainly contained in various types of pyrochlore (Khalzan Buregte) and – to a lesser extent – in fergusonite and some other minerals (Tsakhir). A large diversity of REE-bearing minerals includes oxides, fluoro-carbonates, and silicates that concentrate LREE, HREE, and Y.

Catalytic active open foam packings are promising to enhance the performance of tubular reactors for gas–liquid–solid reactions. In this paper the hydrodynamics of gas–liquid two-phase flow through foam packings in co-current downflow mode of operation are studied experimentally. In particular, the effects of gas and liquid superficial velocities and the pre-wetting mode of the packing (‘LEVEC’ and ‘KAN-LIQUID’) on pressure drop, liquid holdup, and axial liquid dispersion were researched. The experiments revealed multiplicity behavior of the hydrodynamic phenomena in the packed bed. The multiplicity has a significant impact on the forming of upper and lower parameter branches of hydrody- namics. Taking the aforementioned phenomena into account, new correlations are proposed to predict the pressure drop and the total liquid holdup. The occurrence of different flow regimes depending on the foam pore density, namely trickle flow regime and pulse flow regime, was observed. The results can be applied for a better understanding of the heat and mass transfer and overall chemical conversion of tubular reactors with catalytic active foam packings.

The photo-neutron cross-sections of 93Nb at the end point bremsstrahlung energies of 12, 14 and 16 MeV as well as 45, 50, 55, 60 and 70 MeV have been determined by the activation and the off-line γ-ray spectrometric techniques using the 20 MeV electron linac (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) Dresden, Germany and 100 MeV electron linac at Pohang Accelerator Laboratory (PAL), Pohang, Korea. The 93Nb(γ,xn,x=1-4) reaction cross-sections as a function of photon energies were also calculated using computer code TALYS1.4. The flux-weighted average values were obtained from the experimental and the theoretical (TALYS) values based on mono-energetic photons. The experimental values of present work are in good agreement with the flux-weighted theoretical values of TALYS 1.4 but are slightly higher than the flux-weighted experimental data of mono-energetic photons. It was also found that the theoretical and the experimental values of present work and literature data for the 93Nb(γ,xn) reaction cross-sections increase from the threshold values to a certain energy, where other reaction channels opens. However, the increase of 93Nb(γ,n) and 93Nb(γ,2n) reaction cross-sections are sharper compared to 93Nb(γ,3n) and 93Nb(γ,4n) reaction cross-sections. The sharp increase of 93Nb(γ,n) and 93Nb(γ,2n) reaction cross-sections from the threshold value up to 17-22 MeV is due to the Giant Dipole Resonance (GDR) effect besides the role of excitation energy. After a certain values, the individual 93Nb(γ,xn) reaction cross-sections decrease with increase of bremsstrahlung energy due to opening of other reaction channels.

A fully automatized radiosynthesis of (+)- and (−)-[¹⁸F]Flubatine ((+)- and (−)NCFHEB) by means of a commercially available synthesis module (TRACERlab FX FN) under GMP conditions is reported. Radiochemical yields of 30% within an overall synthesis time of 40 min were achieved in more than 70 individual syntheses. Specific activities were approximately 3000 GBq/μmol and radiochemical purity was determined to be at least 97%.

The influence of the metal content (Cu: 0–28 at.%) on the structural, mechanical and tribological properties
of amorphous carbon films grown by pulsed filtered cathodic vacuum arc deposition is investigated.
Silicon and AISI 301 stainless steel have been used as substrate materials. The microstructure, composition
and bonding structure have been determined by scanning electron microscopy, combined Rutherford backscattered spectroscopy-nuclear reaction analysis, and Raman spectroscopy, respectively. The mechanical and tribological properties have been assessed using nanoindentation and reciprocating sliding (fretting tests) and these have been correlated with the elemental composition of the films. A self-organized multilayered structure consisting of alternating carbon and copper metal nanolayers (thickness in the 25–50 nm range), whose formation is enhanced by the Cu content, is detected. The nanohardness and Young’s modulus decrease monotonically with increasing Cu content. A maximum value of the Young’s modulus of about 255 GPa is obtained for the metal-free film, whereas it drops to about 174 GPa for the film with a Cu content of 28 at.%. In parallel, a 50% drop in the nanohardness from about 28 GPa towards 14 GPa is observed for these coatings. An increase in the Cu content also produces an increment of the coefficient of friction in reciprocating sliding tests performed against a corundum ball counterbody. As compared to the metal free film, a nearly four times higher coefficient of friction value is detected in the case of a Cu content of 28 at.%. Nevertheless, the carbon–copper composite coatings produced a clear surface protection of the substrate despite an overall increase in wear loss with increasing Cu content in the range 3–28 at.%.

This paper presents an experimental study which in a first stage is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field configurations. Melt stirring has been realized by utilizing a rotating magnetic field. In a second step directional solidification of AlSi7 alloys from a water-cooled copper chill was carried out to verify the effect of a certain flow field on the solidification process and on the resulting mechanical properties. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were realized. Our results demonstrate the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields show their capability to homogenize both the grain size distribution and the corresponding mechanical properties.

This work is related to a novel approach of providing some new generation ultrastable (> 50 years), ultrahigh density (> 1 Tbit/sq.in.) data storage for archival applications. We used ion-implantation to write nanoscale data into hydrogenated amorphous silicon carbide (a-SiC:H) films. Wide bandgap a-SiC:H samples, Ga+ focused ion beam implanted, have been prepared. A range of samples has been focused ion beam patterned under dierent implantation conditions, with emphasis on dierent substrate temperatures (typically from 0C temperature to around room temperature). Some of the room temperature implanted samples were further annealed at +250C in vacuum. The focused ion beam patterned samples were then analysed using near-field techniques, like atomic force microscopy, to define optimum implantation conditions and the resulting consequences for archival data storage applications. The atomic force microscopy analysis of Ga+ focused ion beam implanted a-Si1-xCx:H samples at room temperature and at 0C revealed an increase of both the depth and the width of the individual lines within the focused ion beam written patterns at the lower temperature, as a result of an increased ion beam induced sputtering yield, in good agreement with the previous results for the case of Ga+ broad beam implantation in a-Si1-xCx:H and again suggesting that the best conditions for optical data storage for archival storage applications would be using Ga+ ion implantation in a-SiC:H films with an optimal dose at room temperatures. Similarly, the atomic force microscopy results confirm that no advantage is expected to result from post-implantation annealing treatments.

Integrated optics concerns mainly the generation, guiding, and detection of light. Especially bio sensing needs systems that incorporate electronic and photonic devices for the detection of harmful substances, like synthetic estrogens or plasticizers. We present recent developments in the integration of Si-based light emitters into a photonic circuit for a planar optical waveguide-based bio detection system. The growing demand for sensitive biochemical sensors in the environmental control, medicine or process technology results in the development of integrated sensors, which should show a high resolution over a wide concentration regime. In our first approach we deal with the integration of a Si-based light emitting device (LED) into a photonic circuit for the detection of harmful biological substances. Light injection into a waveguide is commonly obtained by using an external source coupled to the waveguide, e.g. an optical fiber via total internal reflection. For simplifying this injection process, we built Si-based LEDs consisting of a metal-oxide-semiconductor (MOS) structure, in which the oxide film contains group-IV and/or rare earth elements, incorporated by ion-beam synthesis [1, 2]. The Si-based LED exhibits strong electroluminescence, tunable from the visible up to the UV region depending on the rare-earth element (e.g. Gd, Tb, Eu, Nd, Er). Currently, the Si-based LEDs are already available and best efficiencies were achieved by Tb or Er implantation with an external quantum and power efficiency of 16% and 0.3%. LOCOS (local oxidation of silicon) processing and an additional layer of SiON were applied to the device to improve the electrical stability and operation time. Our concept bases upon a Si-based photonic circuit which consists of the integrated LED, working as the light source, a newly fabricated dielectric strip-waveguide below a bioactive layer and a receiver. The dielectric strip-waveguide has a Si3N4 or SiON core, in which the light should be guided, and a cladding of SiO2. The receiver should be a photodiode (e.g. Ge, Si). In this work, we focus on the development and characterization of the dielectric waveguides. For theoretical pre-analysis we are using the finite element method by the FlexPDE software for calculating the mode profiles and resonance frequencies according to the cross sections of the structures. The fabrication of the waveguides was done by plasma enhanced chemical vapor deposition (PECVD), photolithography and electron beam lithography. Obtained SEM results enabled an improvement of the fabrication recipe of the waveguides by using an additional Al-masking during the reactive ion etching (RIE). Furthermore, a new measurement setup is built up, which enables transmission measurements and the inspection of the beam profiles as well as the damping factors of the structures in dependence on their cross sections. In future, the theoretical calculations are going to be compared with the experimental results of transmission and beam profiling measurements. Moreover, the Si-based LED should be coupled with the waveguide e.g. by Bragg grating. Finally, this lab-on-a-chip system is showing a high potential to become an all-round applicable integrated sensor system, without using any external light sources or relay lenses, which is why it should be easily portable and customizale.

The Henties Bay-Outjo dyke swarm (HOD) in NW Namibia presents a well-exposed example of the magma feeder system for continental flood basalts. This study uses bulk-rock, mineral and melt inclusion compositions from dyke samples to define pressure-temperature crystallization conditions and thus contribute to understanding the magma plumbing and storage beneath the province. The thermobarometry calculations for near-equilibrium mineral-melt pairs (the latter proxied by whole-rock) indicate olivine crystallization at ~1170 to 1350°C and lower, overlapping, temperatures for clinopyroxene and plagioclase (~1070 to 1210°C) in keeping with the order of crystallization inferred from petrographic observation. The dykes yielding the highest temperatures (>1300 °C) are in a specific region of the HOD near the litho-tectonic boundary of the Neoproterozoic Kaoko and Damara Belts, where magma permeability of the crust may have been enhanced. Pressure estimates from clinopyroxene-melt pairs range from 0 to 10 kbar overall (13 dykes) indicating polybaric crystallization. The lowest pressures are recorded by clinopyroxene oikocrysts intergrown with plagioclase, which likely represent the dyke emplacement depths. Clinopyroxene phenocrysts and plagioclase free oikocryst cores yield a higher range of crystallization pressures at 4-6 kbar, corresponding to mid-crustal depths of 11-17 km. There is no spatial pattern in the pressure variations, suggesting a rather uniform level of magma stagnation and crystallization in all areas of the HOD. Partial crystallization at intermediate depths is consistent with the inference of entrained crystals and with geochemical evidence for crystal accumulation in some of the dykes. Comparison of model magma densities and the crustal density derived from seismic velocity profiles suggest the dyke magmas had positive buoyancy in the lower- and middle crust and near-neutral buoyancy in the upper crust. The depth of magma stagnation or pooling at 11-17 km depth may relate to this or to the brittle-ductile transition in the felsic Damara crust.

The level of expression of cannabinoid receptors type 2 (CB2) in healthy and diseased brain has not been fully elucidated. Furthermore, there is interest in the ultra-localisation of CB2 in brain. Positron emission tomography (PET) is a technique, which allows monitoring of very low amounts of radiolabelled compounds in living organisms. Here, we attached 18F as radiolabel at different sites of N-aryl-oxadiazolyl-propionamides as potential radioligands and investigated it’s influence on affinity and pharmacology of the compounds.

Methods: Compounds were synthesised according to our previously described route (Rühl et al. Org. Med. Chem. Lett. 2012; 2: 32). Affinities towards CB2 and CB1 were determined via competitive radioligand binding assays with XXX as blocking compound. For labelling of 1, a tosylat moiety as selected as optimal leaving group (LG). Labelling at the aromatic ring in 2 was achieved with trimethylammonium as LG. In vivo organ distribution was investigated on CD-1 mice by injection of ~ 300 kBq of radiotracer (in 200 ml isotonic solution) in the tail vein. At various times, the animals were anesthetized, organs of interest dissected and the percentage of injected dose per gram of wet tissue (% ID/g) calculated. Blocking studies were conducted by intraperitoneal pre-injection of 1 mg/kg SR144,528 dissolved in isotonic solution 10 min prior to the radiotracer. All animals were sacrificed at 60 min p.i., and radioactivity uptake was determined.

Results: 1) In both cases, good labelling yields (XX %) could be achieved.
2) The radiolabelled compounds show the same affinity and specificity towards CB2 as the reference compound. 3) The radiotracers undergo strong metabolism but 4) can cross the blood brain barrier (BBB). After five minutes, approximately 2 to 4% of intact radiotracer was found in the plasma. Nevertheless, 36% of ¹⁸F1 and 80% of ¹⁸F2 could be observed in the brain after 30 minutes. The main metabolite could be identified as the free acid derivative, which has no affinity towards the CB receptors.

Conclusions: The introduction of ¹⁸F into the lead structure does not affect the affinity and the selectivity towards the CB2 receptor. The radiotracers cross the BBB. However, the compounds undergo strong metabolism in plasma.

Ziel/Aim:

Das Enzym Phosphodiesterase 10A (PDE10A) besitzt eine Schlüsselrolle in der zellulären Signaltransduktion. Das einzigartige Expressionsmuster der PDE10A mit fast ausschließlicher Expression im Striatum macht dieses Enzym zu einem interessanten Target zur Behandlung neurodegenerativer Erkrankungen, die mit einer striatalen Dysfunktion einhergehen, beispielsweise Schizophrenie.¹ Molekulare Bildgebung mittels PET würde eine In-vivo-Untersuchung dieses Enzyms und seiner Expression in Zusammenhang mit neurologischen und pathologischen Prozessen erlauben.
Zu hochpotenten und selektiven PDE10A Inhibitoren zählt die Substanzklasse der 1-Arylimidazo[1,5-a]chinoxaline.² Deren Wirkstoffstruktur wurde als Leitstruktur zur Entwicklung eines F-18 markierten PETTracers für die PDE10A gewählt.

Methodik/Methods:

Verschiedene Referenzverbindungen auf Basis des Imidazo[1,5-a]chinoxalingerüsts wurden durch Derivatisierung mit 2-Fluorpyridinresten hergestellt. Die ortho-Position zum Stickstoff des Pyridinrings wurde gewählt, um die nukleophile Einführung eines F-18 in einer späteren Radiosynthese zu erleichtern und hohe spezifische Aktivitäten zu erzielen. Die Identität und Reinheit der Referenzverbindungen wurden mittels NMR, HRMS und HPLC bestimmt. Die inhibitorische Wirksamkeit auf humane, rekombinante PDE10A wurde in Enzymassays bestimmt.

Ergebnisse/Results:

Das benötigte Imidazo[1,5-a]chinoxalingerüst wurde erfolgreich über eine Mehrstufensynthese ausgehend von 2,6-Difluoranillin hergestellt. Zur Einführung unterschiedlicher 2-Fluorpyridinhaltiger Reste wurde die Palladium-katalysierte Suzuki-Kupplung verwendet. Durch eine Variation in der Reaktionssequenz konnte dieser Rest an unterschiedlichen Positionen des aromatischen Systems eingeführt werden (siehe Abbildung). Die erzielten Referenzverbindungen zeigten in Untersuchungen zur inhibitorischen Wirksamkeit eine hohe Affinität zu PDE10A (IC50 < 10 nM) und erwiesen sich als sehr selektiv für PDE10A im Vergleich zu anderen Phosphodiesterasen. Ein hochaffines Derivat wurde als Leitsubstanz ausgewählt, um ein F-18 markiertes Derivat herzustellen. Zurzeit wird an der organischen Synthese eines geeigneten Präkursors für die Radiosynthese gearbeitet.

Schlussfolgerungen/Conclusions:

Über einen divergenten Syntheseschritt, die Suzuki-Kupplung, wurden unterschiedliche 2-Fluorpyridinsubstituierte Inhibitoren hergestellt. Durch eine Variation der Reaktionssequenz war dies an unterschiedlichen Positionen möglich. Die pharmakologische Evaluierung zeigte, dass alle Referenzverbindungen sehr affin und selektiv sind.

Referenzen/References:

[1] Kehler et. al. Curr. Pharm. Design, 2011, 17, 137-150.
[2] Malamas et. al. J. Med. Chem. 2011,54, 7621-7638.

Excitons possess a hydrogen-like internal excitation spectrum with a characteristic energy scale in the THz range. We explore these internal degrees of freedom by using an intense THz free-electron laser to pump the 1s-2p intraexcitonic transition in GaAs and InGaAs multiquantum wells. The induced absorption changes are probed via interband absorption using a near-infrared femtosecond laser. We observe a splitting of the 1s exciton line, which can be explained by the Autler-Townes effect, also called AC Stark or Rabi splitting [1]. The behavior is, however, much more complex than for an ideal two-level system. Since for electric fields in the 10 kV/cm range the Rabi energy is already of the same order of magnitude as the 1s-2p transition energy, we are in fact clearly beyond the validity of the rotating wave approximation. At the highest fields, when also the ponderomotive energy (e2F2/4mw2) approaches the exciton binding energy, signatures of exciton field ionization are observed. Microscopic calculations based on the semiconductor Bloch equations including THz interaction show that the spectra can be reproduced, if the full set of higher exciton states is taken into account [2].
The experiments would not have been possible without the high-quality multiquantum well samples grown and provided to us by A. M. Andrews and G. Strasser (TU Vienna, Austria), and by G. Khitrova and H. M. Gibbs (Univ. Arizona, Tucson, USA), whose contributions are gratefully acknowledged.

A computer program is described which allows fully three-dimensional dynamic collisional simulations of ion irradiation effects in particular in nanosystems. The program is based on the well-known TRIDYN code which describes dynamic modifications along one dimension. In a computational volume composed of fixed and equisized voxels, local atomic density changes due to ion implantation or recoil relocation are relaxed to constant predefined atomic volumes. This is accomplished by interaction with neighboring voxels and by material transport from and to the surface. Arbitrary initial system shapes and elemental distribution can be defined as well as a wide range of irradiation conditions including non-uniform beam profiles. The paper addresses details of the involved algorithms, discusses potential artifacts with respect to surface sputtering, broadening of compositional profiles and surface contours. It demonstrates the capabilities of the program on the basis of examples for focused ion beam erosion, self-organized surface pattering, and ion implantation and sputter-shaping of nanostructures.

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Silicon Nanoparticles (Si NPs) have been studied for twenty years, and recently they have received a lot of attention because of their potential use in in vitro1and in vivo imaging2,3. Indeed Si NPs have shown no toxicity when uptaken by cells4, and display interesting luminescence properties as well as photo- and electro- stability which are suitable also for photoelectron application.5,6 Here we report on the synthesis of Si NPs via wet chemistry methods either by reducing Si(OMe)4 in reverse micelle1,7 or oxidizing Mg₂Si8. The size of Si NPs is 1.6 nm and 3.9 nm, respectively. The Si NPs have been characterized by high resolution transmission electron microscopy (HRTEM), infrared spectroscopy (IR), and their photophysical properties were investigated. The Si NPs exhibit very bright luminescence that is strongly dependent on their size, as already known, and can be functionalized with a variety of groups allowing different solubility and further derivatization. We indeed show that different labels can be covalently attached and even targeting groups can be attached for multimodal bio-imaging. The first experiments in in vivo conditions will be shown to demonstrate the potentiality of these ultrasmall particles.

References
[1] R. D. Tilley, et al. Angew. Chem. Int. Ed. 2005, 44, 4550 -4554.
[2] P. N. Prasad, et al. ACS Nano, 2010, 4, 5131-5138.
[3] P. N. Prasad, et al. ACS Nano, 2011, 5, 413-423.
[4] N. S. Wang, et al. J. Appl. Toxicol. 2009, 29, 52-60
[5] G. A. Ozin, et al. Nano Lett. 2011, 11, 1585-1590.
[6] M. P. M. Jank, et al. small 2011, 7, 2853-2857.
[7] L. De Cola, et al. small, 2008, 4, 1835-1841.
[8] S. M. Kauzlarich, et al. J. Am. Chem. Soc. 1999, 121, 5191-5195.
P

Rigid bispidine (3,7-diazabicyclo[3.3.1]nonane) derivatives form very stable complexes, particularly with first row transition metal ions. Furthermore, the bispidine skeleton opens suitable pathways to introduce biomolecules, which are important concerning the pharmaceutical targeting of such complexes. Therefore, bispidines are attractive bifunctional chelating agents for the development of target-specific copper-based radiopharmaceuticals.
In order to optimize the radiopharmaceutical behavior, further bispidine ligands have been developed with different denticity (tetra-, penta- and hexadentate), with pyridine and/or methoxypyridine donor groups and with the possibility to introduce functionalities, such as targeting units and fluorescence labels in view of pharmaceutical targeting and dual labeling (PET and optical imaging).
These ligands and the important properties of their CuII complexes, e. g. stabilities, ligand exchange kinetics, partition coefficients (64Cu: n-octanol/water) and biodistribution studies will be reported.

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile bioorthogonal conjugation techniques especially for the radiolabeling of biologically active high molecular weight compounds like peptides, proteins or antibodies. Taking into consideration that the introduction of fluorine-18 (t_1/2 = 109.8 min) proceeds under harsh conditions, radiolabeling of these biologically active molecules represents an outstanding challenge and is of enormous interest. Special attention has to be paid to the method of ¹⁸F-introduction. It should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. For these reasons and due to the high number of functional groups found in these compounds, a specific labeling procedure has to be developed for every bioactive macromolecule. Bioorthogonal strategies including the Cu-assisted Huisgen cycloaddition and its copper-free click variant, both Staudinger Ligations or the tetrazine-click reaction have been successfully applied and represent valuable alternatives for the selective introduction of fluorine-18 to overcome the afore mentioned obstacles. This comprehensive review deals with the progress and illustrates the latest developments in the field of bioorthogonal labeling with the focus on the preparation of radiofluorinated building blocks and tracers for molecular imaging.

Bei postulierten Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren können Korrosionsprozesse an feuerverzinkten Einbauten des Containments auftreten und in Folge dessen einen starken Anstieg der Zinkkonzentration im Kühlmittel bewirken. An Heißstellen wie z. B. an Brennstab-Hüllrohren können sich die Zink-Korrosionsprodukte unter Umständen schichtbildend abscheiden. Neben der Abscheidung von Zinkborat, die bei Kühlmitteltemperaturen von 90 °C beobachtet wurde, kann durch Thermohydrolyse eine Umwandlung in schwerer lösliche Verbindungen bis hin zum Zinkoxid erfolgen und durch anwachsende Ablagerungen die thermofluiddynamischen Prozesse im Kern beeinflussen. Eine Freisetzung von Partikelsystemen mit breitem Größenspektrum, welche sich an Kernkomponenten oder Rückhaltevorrichtungen anlagern können, ist hierbei durch das Abplatzen von Partikelagglomeraten aus den Abscheidungen und im Kern ablaufende Kristallisations- und Umwandlungsprozesse möglich. Nach dem Einsetzen des Korrosionsprozesses erfolgt nachweislich auch nach Entfernung der Korrosionsquellen eine weitere Abscheidung von Zink-Korrosionsprodukten an Heißstellen. Es existiert somit eine Quelle für die Bildung unlöslicher Feststoffe im Primärkreis in der Spätphase eines KMV.
Im Rahmen eines BMWi-Verbundprojektes (FKZ 1501430 und 1501431) werden die physikochemischen Grundlagen und die thermohydraulischen Auswirkungen der Zink-Korrosionsproduktbildung und –ablagerung mit Hilfe von Experimenten an unikalen Versuchseinrichtungen des HZDR bzw. der HS Zittau/Görlitz untersucht.

In this paper Rayleigh-Benard convection has been investigated under the influence of a DC magnetic field. Similar configurations can be found in geophysical or steel production. Our group reported recently that spontaneous flow reversals of quasi two-dimensional rolls randomly occur in Rayleigh-Benard convection of liquid metal exposed to a horizontal magnetic field (Yanagisawa, et al., PRE, 2011). In fluid layers with relatively large aspect ratios (see Fig.1 (a)) the convection roll pattern becomes isotropic. However, the rolls are aligned with the magnetic field direction if the Lorentz force becomes comparable to the buoyancy or larger. In our experiment, where the fluid layer has a dimension of 200 * 200 * 40 mm (corresponding to an aspect ratio of 5), the convection pattern can show 3, 4 or 5 rolls regimes depending on the Rayleigh number Ra and the Chandrasekhar number Q. Flow reversals occur spontaneously between these steady states in the Ra-Q parameter space. A new regime has been found in experiments conducted at Chandrasekhar numbers in a magnetic system at HZDR. In this regime the flow reversals occur regularly. The non-dimensional characteristic time of the reversal normalized by circulation time of the roll is around 100, being similar to the characteristic time of the ‘random’ flow reversals reported by Yanagisawa, et al. Detailed observations reveal that movements of each cell toward the reversal start just after the last reversal occurs unlike the random flow reversals.

Neutron total cross sections of ¹⁹⁷Au and ^natTa have been measured at the nELBE photoneutron source in the energy range from 0.1 – 10 MeV with a statistical uncertainty of up to 2% and a total systematic uncertainty of 1%. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5 ps) with a short flight path of 7 m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources.

Non-linear Compton scattering in ultra-short intense laser pulses is discussed with the focus on angular distributions of the emitted photon energy. This is an observable which is accessible easily experimentally. Asymmetries of the azimuthal distributions are predicted for both linear and circular polarization. We present a systematic survey of the influence of the laser intensity, the carrier envelope phase and the laser polarization on the emission spectra for single-cycle and few-cycle laser pulses. For linear polarization, the dominant direction of the emission changes from a perpendicular pattern with respect to the laser polarization at low-intensity to a dominantly parallel emission for high-intensity laser pulses.

.Employing new precision data of the equation of state of the SU(3) Yang-Mills theory (gluon plasma) the dilaton potential of the gravity dual is adjusted in the temperature range (1 - 10) T_c in a bottom-up approach. The ratio of bulk viscosity to shear viscosity follows then as zeta/eta approx\pi Delta v_s^2 for Delta v_s^2 < 0.2 and achieves a maximum value of 0.95 at Delta v_s^2 approx 0.32, where Delta v_s^2 is the non-conformality measure, while the ratio of shear viscosity to entropy density is known as (4 \pi)^{-1} for the considered special set-up with Hilbert action on the gravity side.

We present principle setup and design parameters of the PENELOPE system. It is scheduled as a direct diode-pumped PW system for laser-plasma experiments. The five-stage chirped pulse amplifier chain with a target pulse energy of 200J is based on Yb:CaF2.

We present an all diode-pumped picosecond solid-state Master-oscillator power-amplifier (MOPA) for extending laser ion-cooling to broad momentum spread applications. The challenge of the system lies in the generation of bandwidth-limited pulses with a pulse duration of 70ps and energies at the 100µJ level. The pulses with a duration of 170fs were generated in a commercial Yb:KGW mode-locked oscillator with a repetition-rate of 50MHz. Inside a subsequent regenerative amplifier with an intra-cavity dielectric grating the pulse bandwidth is reduced by 5 orders of magnitude which corresponds to 20pm at a center-wavelength of 1028nm. The system allows a tuning range between 1028 and 1032nm. Finally, the output is frequency quadrupled (forth harmonic generation) to 257nm, which is in the range of the cw laser lines used for laser-cooling. Due to thermal and damage issues the average power was limited to 50mW in the infra-red at a maximum repetition rate of 500Hz.

We report the first short-pulse amplification results to several hundred millijoule energies in ceramic Yb:LuAG. We have demonstrated ns-pulse output from a diode-pumped Yb:LuAG disk amplifier at a maximum energy of 580 mJ and a peak optical-to-optical efficiency of 28% at 550 mJ. We also compare our results with Yb:YAG within the same amplifier system based on active mirror design. Previous works reporting on diode-pumped Yb:YAG amplifiers with similar pulse energies or even more than 1 J either demonstrated a maximum optical-to-optical efficiency around 10% or relied on cryogenic cooling, and/or based on bulk material. While cryogenically cooled lasers allow for even higher efficiencies the gain spectrum is narrowed dramatically for both Yb:YAG and Yb:LuAG. Pulses as short as 2 ps, corresponding to a gain bandwidth of about 1 nm, can be amplified at room temperature, whereas at liquid nitrogen temperature the gain bandwidth reduces by about one order of magnitude. Hence, we also studied the spectral response of both materials at room temperature. Although the peak absorbtion cross section of Yb:LuAG around 940 nm is lower compared to Yb:YAG the broader absorption spectrum is more suitable for using pump diodes without wavelength stabilization. Furthermore, we report on CPA-free picosecond amplification to the 100mJ level in Yb:YAG demonstrating the potential of the active mirror approach for efficient energy extraction at low fluences without optical damage or nonlinear effects such as self phase modulation (SPM) or self-focusing.

With the first demonstration of direct diode-pumped TW lasers with pulse energies of 1 J and more a scaling of this approach for use in PW-class laser systems became feasible. The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. In order to minimize the required pump peak power and therefore the initial costs a broad-band Ytterbium doped laser material with a long fluorescence lifetime (i.e. Yb:glass or Yb:CaF2) is chosen. A total pump peak-power of 1.2 MW is scheduled assuming a pump pulse duration of 2 ms and an envisioned optical-to-optical conversion efficiency of 10% before compression. Pulses as short as 60 fs having an energy of 25 nJ are generated in a commercial Yb:KGW oscillator at a center wavelength of 1035 nm. In order to employ CPA technique the pulses are stretched to 2 ns in a grating stretcher having grating constant of 1760 lines per mm. The amplifier-chain consists of a regenerative amplifier and 4 subsequent multipass amplifiers. While the regenerative amplifier produces a gain 40.000 gain narrowing is required to be suppressed by intra-cavity spectral shaping. At the sub-mJ energy level a bandwidth of 25 nm was achieved out of the regenerative amplifier. Two booster amplifiers with an energy of 100mJ and 1J output were also demonstrated. The full amplifier system will consist of two more multipass amplifiers each having a gain of 10-16 in order to achieve the desired pulse energy.

Basics of ultra-short pulse generation and amplication towards high energies are presented. We focussed on scaling issues and applications of high-intensity laser systems. Furthermore, diode-pumping of high energy lasers was discussed.

We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms can be generated and amplified, containing between 50 and 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps in a chirped pulse amplification scheme. The first amplifier stage, which is described in detail in this work, is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled to 915 mJ at longer pump duration. This corresponds to an efficiency as high as 25% from absorbed pump energy to extracted energy. This is – to our knowledge – the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) have been put into contact with Eu or Ni enriched solutions. The concentrations ranged from 10−3 to 10−5 mol.L−1 for Eu and 10−3 mol.L−1 for Ni and the sorption durations ranged from one week to one month. In order to elucidate the retention mechanisms of these elements into calcite, Rutherford Backscattering Spectrometry (RBS) has been carried out. This technique is well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance). Moreover, using the fluorescence properties of Europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage have also been carried out. Results show that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

We investigate bulk ion heating in solid CD2-Al-CD2 buried layer targets and ionization dynamics in solid copper target irradiated by ultra-short relativistic laser pulses. The potential techniques such as small angle X-ray scattering, Faraday rotation, and resonant coherent X-ray diffraction imaging to probe relative physical processes in high power laser plasma interactions using X-ray free-electron lasers are also presented.

Based on the potent phosphodiesterase 10A (PDE10A) inhibitor PQ-10, we have synthesised thirty-two derivatives to determine relationships between their molecular structure and binding properties. Their roles as potential positron emission tomography (PET) ligands as well as the inhibitory potency to PDE10A and other PDEs have been evaluated and the metabolic stability has been determined in vitro. According to our findings, halogenalkyl substituents at position 2 of the quinazoline moiety and/or halogenalkyloxy substituents at position 6 or 7 affect not only the compounds' affinity, but also their selectivity. As a result of substituting the methoxy group for a monofluoroethoxy or difluoroethoxy group (19d and 19c) at position 6 of the quinazoline ring, the selectivity to PDE10A primarily increased compared to PDE3A. The same result was obtained by 6,7-difluoride substitution on the quinoxaline moiety (35). Finally, the fluorinated compounds 16a, 19a-d, 29 and 35 (IC50 PDE10A 11-65 nM) showed the highest inhibitory potential. Further, fluoroethoxy substitution at position 7 of the quinazoline ring improved metabolic stability in comparison to the lead structure, PQ-10.

Surface patterning by ion beams is a well-established technique to create self-organized regular surface patterns. The type of these patterns depends on the ion species, their energy, fluence, target temperature and angle of incidence. Emerging applications of these patterns are under discussion in particular for electronic, photonic and magnetic nano devices. The irradiation of different matter with focused monatomic ions like Ga or Bi is a well-known application. Here, a novel approach is presented, the use of heavy polyatomic Bi2+ and Bi3+ ions, promising high intensity sputtering and new kinds of surface morphology. The ultra-heavy Bi ions emitted from a liquid metal ion source (LMIS) in a mass separated FIB instrument are directed to the GaAs surface. Whereas the irradiation with monatomic Bi-ions at normal incidence creates a deep sputtering crater without any strong pattering or Ga precipitates on the crater bottom which is still known from Ga FIB irradiation. But the much heavier projectiles Bi2+ and Bi3+ lead also to a Ga droplet formation on the GaAs crater base. With increasing projectile mass, i.e. higher deposited energy in the stopping cascade of polyatomic ions more and also smaller Ga droplets are found. The phenomenon of surface evolution investigated for monatomic as well as heavy Au and Bi dimer and trimer ions is presented in dependence of the ion species, the energy, the angle of incidence as well as the target temperature in the range from RT up to 400°C.

The very high erosion rates of heavy projectiles, in particular Bi dimer and trimer ions on different substrates were investigated in relation to the ion incidence angle. In the case of high angle irradiation attended by a ripple structure formation the erosion rate is decreased due to the wide variety of surface angles faced to the beam. On the eroded surfaces very regular, high-amplitude dot and ripple patterns on Ge and Si are formed under the heavy polyatomic ion impacts, which differs significantly from surface mor-phologies formed by monatomic ion irradiation [1]. Dot and ripple heights equal to their wavelengths can be achieved. The Bi2+ and Bi3+ ions are extracted from a liquid metal ion source [2], are mass separated, focused and scanned using a focused ion beam sys-tem. Studies are performed for fluences of 1e14 to 1e17 ions/cm2 in the ion impact angle range from normal to 85°. In Ge hexagonally ordered dot patterns with ~30 nm diameter and nearly the same height are found in the incidence angle range from 0° to 30° for Bi3++ ions [3] followed by a smoothening region up to 60°. Incidence angles from 60° to 80° cause a pronounced ripple structure on the Ge surface. For nearly grazing incidence, shingles perpendicular to the beam direction are found. FIB cross section imaging shows that the slope of the shingles is parallel to the ion incidence direction. The angle-dependent behaviour of pattern formation is summarized in a phase diagram.
[1] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[2] L. Bischoff, W. Pilz, P. Mazarov and A.D. Wieck, Applied Physics A99 (2010) 145.
[3] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Nucl. Instr. and Meth. B 272 (2012) 198.

Der σ1-Rezeptor kommt hauptsächlich in den Mitochondrien-assoziierten Membranen des endoplasmatischen Reticulums vor¹und wird zunehmend als biologisches Target für die Behandlung von Tumoren und neurologischen Erkrankungen, wie Depression, Angstzuständen oder Neurodegeneration, erkannt.^2a,2b
Durch die hohe Affinität zum σ1-Rezeptor, die Spezifität gegenüber anderen Rezeptoren sowie weitere pharmakologische Eigenschaften stellt (R)-(+)-Fluspidin einen potenziellen ¹⁸F-Tracer für den Einsatz in der Positronen-Emissions-Tomographie (PET) zur bildgebenden Diagnostik o. g. Erkrankungen dar.³ Die Evaluierung eines PET-Tracers erfordert u. a. detaillierte Untersuchungen zu dessen Metabolismus sowie eine Charakterisierung der Metabolite.
Neben der aufwendigen Gewinnung von Metaboliten aus Gewebematerialien oder der chemischen Synthese von potenziellen Metaboliten, hat deren Darstellung mittels elektrochemischer Oxidation eine zunehmende Bedeutung für die Strukturaufklärung von Radiometaboliten erlangt. So können Proben ohne biologische Matrix in vergleichbar kurzer Zeit mit geringem Aufwand hergestellt werden.

Für die Generierung von Metaboliten wurde die in das ROXY-System (Fa. Antec) implementierte elektrochemische Zelle (μPrepCell) mit der Arbeitselektrode Glassy Carbon eingesetzt. Die Umsetzung von (R)-(+)-Fluspidin (50 μM) in Ammoniumformiat-Puffer (20 mM) und 50 % Acetonitril bei pH 7,4 erfolgte bei jeweils konstanter Spannung von 1,0 - 1,4 V und einer Durchflussrate von 50 μl/min. Die Reaktionslösungen wurden off-line mittels HPLC und MS untersucht.

Als Hauptprodukt der elektrochemischen Umsetzung von (R)-(+)-Fluspidin entstand das Desbenzyl-Derivat , welches bereits bei Versuchen mit Leber-Mikrosomen als Metabolit zugeordnet werden konnte.³ Weiterhin konnten vor allem Mono- und in geringerem Ausmaß auch Dioxidationsprodukte des (R)-(+)-Fluspidins nachgewiesen werden. Auch die Substitution des Fluoratoms durch eine Hydroxylgruppe wurde beobachtet.

Es konnte gezeigt werden, dass mit Hilfe der elektrochemischen Oxidation mögliche Metaboliten des (R)-(+)-Fluspidins zugänglich sind. Durch Korrelation mit Daten der Radio-HPLC bietet sich im Rahmen von In-vivo-Studien an Tieren und am Patienten die Möglichkeit, Radiometabolite zu identifizieren, welche mit strukturaufklärenden analytischen Verfahren nicht direkt charakterisiert werden können.
Die elektrochemische Oxidation ist eine effiziente Methode zur Vorhersage der metabolischen Stabilität, die auch in der Entwicklung metabolisch stabiler Radiotracer für PET zunehmenden Einsatz finden kann.

1 Duncan G., Wang L. 2005; Experimental Eye Research 81: 121–122.
2a Cobos E.J. et al. 2008; Curr. Neuropharmacol 6: 344–366.
2b Hayashi T., Su T.P. 2008; Expert Opin. Ther. Targets. 12: 45–58.
3 Fischer S. et al. 2011; Eur. J Nuclear Medicine and Molecular Imaging 38: 540-51.

Ytterbium-doped garnets are attractive for use in high-energy diode-pumped solid-state lasers due to their spectral and thermal properties. Recently, Yb:LuAG was investigated as a promising candidate for kW thin-disk lasers because of its superior thermal conductivity especially at high doping concentrations compared to Yb:YAG. In this paper we demonstrate high-energy ns-pulse multipass amplification in Yb:YAG and Yb:LuAG towards 500mJ. The study presented here has confirmed that further scaling of both efficiency and pulse energy is possible by a further reduction of Yb-doping level reducing the gain per disk.

Tetravalent actinides, An(IV), are usually assumed to be little mobile in near-neutral environmental waters because of their low solubility. However, there are certain geochemical scenarios during which mobilization of An(IV) in a colloid-borne (waterborne) form can not be ruled out. A compilation of colloid-borne forms of tetravalent actinides described so far for laboratory experiments, field experiments and real-world scenarios is given. It is intended to be a knowledge base and a tool for those who have to interpret actinide behavior under environmental conditions. Colloids containing structural An(IV) and colloids carrying adsorbed An(IV) are considered. Their behavior is compared with the behavior of An(IV) colloids observed after the intentional or unintentional release of actinides into the environment. A list of knowledge gaps as to the behavior of An(IV) colloids is provided and items which need further research are highlighted.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) beschäftigt sich unter anderem mit der Untersuchung von verfahrens-technischen Prozessen und fluiddynamischen Phänomenen in Mehrphasenkontaktapparaten.
Die dazugehörige Untersuchung von Mehrphasenströmungen, die Modellentwicklung sowie die Validierung numerischer Berechnungsverfahren erfordern belastbare experimentelle Daten.
Für ein neuartiges Reaktorkonzept mit geneigt rotierendem Festbett soll die Reaktionsführung hinsichtlich der Raum-Zeit-Ausbeute einer Modellreaktion (Hydrierung von α-Methylstyrol zu Cumol) untersucht werden.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) beschäftigt sich unter anderem mit der Untersuchung verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate.
Ein solches neuartiges Reaktorkonzept mit dem Ziel der Prozessintensivierung durch periodische Betriebsweise stellt der geneigt rotierende Festbettreaktor dar. Im Gegensatz zum zeitlich-periodischen Reaktorbetrieb erfolgt die Prozessintensivierung hier durch Aufprägung einer örtlichen Periodizität unter ansonsten stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich in Form von Neigung und Drehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der interdisziplinären Projektarbeit ist ein Verfahren zur experimentellen Untersuchung der flüssig-fest Stoffübertragung im geneigt rotierenden Festbettreaktor umzusetzen. Die Stoffübertragung stellt einen Schlüsselparameter der Makrokinetik heterogener Reaktionssysteme dar und kann somit zur Leistungsbewertung des neuen Reaktorkonzepts herangezogen werden.