Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Cancerogenesis is closely associated with deregulated cell proliferation and, consequently, aberrant cell cycle control. The first phase of the cell cycle (G1) comprises important steps for initiation of DNA replication and subsequent cell division. The activation and coordination of G1 phase is accomplished by enzymes of serine/threonine kinase family. As members of this protein family and important regulators of early cell cycle machinery, cyclin-dependent kinases 4 and 6 (Cdk4/6) associate with regulatory protein cyclin D, and phosphorylate retinoblastoma protein pRb. Hyperphosphorylated pRb dissociates from E2F transcription factors and triggers transcription of genes required for further G1 phase progression. Hence, Cdk4/6 were identified as essential and critical activators of G1 phase in human embryogenesis, homeostasis, and cancer development; G1 phase progression in cell cycle by phosphorylation of retinoblastoma protein pRb and thua, activation of gene transcription.
In 80% of human tumors the Cdk4/6-cyclin D/ pRb/ E2F pathway is altered provoked by multiple mechanisms. In tumor formation, hyperactivation of Cdk4/6 is often a result of overexpression, silencing, and epigenetic alteration of their regulators or substrates. On the other hand, disruption of Cdk4/6-associated cell cycle control in cancer is also caused directly by mutations and amplification of Cdk4/6 themself. Cdk4/6 protein amplification was found in a wide spectrum of solid tumors and blood cell cancer, e.g., gliomas, lymphomas, melanomas, carcinomas, and leukemias. In consequence, Cdk4/6 were considered to be attractive targets for pharmacological anti-cancer drug development. In the recent years, Cdk4/6 inhibitors of high potency and selectivity against other kinases, especially other cyclin-dependent kinases, were developed and evaluated. One of these compounds, a pyrido[2,3-d]pyrimidine-7-one derivative currently is undergoing clinical trials for cancer therapy.
Though, potent and selective pyrido[2,3-d]pyrimidine-7-one Cdk4/6 inhibitors are not only promising new compounds for cancer therapy, but also for visualization and functional characterization of human tumors. Radiolabeled Cdk4/6 inhibitors could be of particular interest for the assessment of Cdk4/6 protein status and Cdk4/6 activity of human tumors by non-invasive imaging technique positron-emission-tomography (PET). PET affords the opportunity of three-dimensional imaging of physiological processes in vivo. Additionally, PET would provide pharmacological data of radiolabeled Cdk4/6 inhibitors, which may help to estimate the applicability of the compounds for tumor therapy. In this regard, positron-emitting Cdk4/6 inhibitors were designed, synthesized and characterized in our institute for the first time. The radiolabeled compounds and their nonradioactive analogs are based on the lead structure of pyrido[2,3-d]pyrimidine-7-one CKIA.
First, iodine-containing pyrido[2,3-d]pyrimidine-7-one derivatives CKIA and CKIB were evaluated concerning their efficacy and suitability as Cdk4/6 inhibitors in human tumor cell lines. The compounds showed both significant and specific inhibition of tumor cell proliferation and G1 phase arrest by targeting the Cdk4/6-cyclin D/ pRb/ E2F signaling pathway [2]. The iodine substituent of CKIA and CKIB represents an attractive site for an isotopic substitution with the positron emitter iodine-124 (124I). 124I-labeled Cdk4/6 inhibitors [124I]CKIA and [124I]CKIB were evaluated concerning their radiopharmacological properties in cellular radiotracer uptake studies, biodistribution studies, and small animal PET studies in NMRI nu/nu mice bearing the human squamous cell carcinoma tumor FaDu [3]. With 4.18 d half-life, 124I affords extended radiopharmacological evaluation and imaging studies using PET. Nevertheless, high positron energy and minor positron emission (26%) are disadvantages, especially for the resolution of PET images. ....

We utilize the contactless inductive flow tomography (CIFT) for visualizing the flow of GaInSn in a model of continuous steel casting. Since for thin slab casting the velocity can be assumed to be mainly two-dimensional it is sufficient to apply only one external magnetic field and to measure the induced fields at the narrow faces of the mould. In a first step we show that a numerically determined flow field can be reconstructed by CIFT with an empirical correlation coefficient of about 75 per cent. Then we apply the method to various single-phase and two-phase flows in the real model and show that typical flow features can be reliably detected.

In the field of biomaterials, more specifically of materials which are used for medical implants, recent research is focused on the interface between implant material and biological environment. Among crystalline and glassy bone substitutes calcium- and phospho­rus-based oxides are of special interest, because their chemical composition can be adjusted to natural bone. Materials containing an appropriate ratio of oxides of calcium, phos­phorus and other physiologically compat­ible constitutents such as silicate and alkalis are bioactive and degradable in vivo. Therefore, the strategy in using such bone substitute implants is that these materials are slowly degraded inside the body and successively substituted by natural bone tissue.
Especially granular media with particles from appropriate calcium alkali orthophosphates, such as [Ca2KNa(PO4)2], exhibit a strongly en­han­ced biodegradability, but the sponge-like structure of the bone can not be remodelled with granulates. Yet, gene­ra­tive manufacturing techniques (rapid proto­typing) nowadays allow to build up even large, three-dimensional structures that are adapted to macro-/microscopic structural bone charac­te­ristics.
However, the natural bioactivity of calcium phosphates and related inorganic compounds is limited. bone remodelling is impeded, in particular when larger bone defects are to be restored by this class of material. Yet, the growth of bone tissue can significantly be stimulated by so-called Bone Morphogenetic Proteins (BMPs), proteins that are synthesized during build-up of bone tissue by the human body. Since a couple of years it has become possible to produce BMPs synthetically and couple them to surfaces of bone replacement materials. After the successful bioactivation of metallic Titanium-based prosthetic surfaces with BMP, the present study is devoted to elucidating the mechanism of protein coupling and especially the desorption kinetics of BMP on mineral surfaces.
Those experimental studies are accompanied by a scale-bridging simulation of the BMP sorption process from physiologic solution as a function of the local pH-value and the structure formation at the solid-liquid interface. With this knowledge the project BioMin yields a significant contribution to develop and manufacture tailored bone substitute implants, so that degradation of the substitute material and build-up of new bone tissue can go hand-in-hand in vivo.

In the field of biomaterials, more specifically of materials which are used for medical implants, recent research is focused on the interface between implant material and biological environment. Among crystalline and glassy bone substitutes calcium- and phospho­rus-based oxides are of special interest, because their chemical composition can be adjusted to natural bone. Materials containing an appropriate ratio of oxides of calcium, phos­phorus and other physiologically compat­ible constitutents such as silicate and alkalis are bioactive and degradable in vivo. Therefore, the strategy in using such bone substitute implants is that these materials are slowly degraded inside the body and successively substituted by natural bone tissue.
Especially granular media with particles from appropriate calcium alkali orthophosphates, such as [Ca2KNa(PO4)2], exhibit a strongly en­han­ced biodegradability, but the sponge-like structure of the bone can not be remodelled with granulates. Yet, gene­ra­tive manufacturing techniques (rapid proto­typing) nowadays allow to build up even large, three-dimensional structures that are adapted to macro-/microscopic structural bone charac­te­ristics.
However, the natural bioactivity of calcium phosphates and related inorganic compounds is limited. bone remodelling is impeded, in particular when larger bone defects are to be restored by this class of material. Yet, the growth of bone tissue can significantly be stimulated by so-called Bone Morphogenetic Proteins (BMPs), proteins that are synthesized during build-up of bone tissue by the human body. Since a couple of years it has become possible to produce BMPs synthetically and couple them to surfaces of bone replacement materials. After the successful bioactivation of metallic Titanium-based prosthetic surfaces with BMP, the present study is devoted to elucidating the mechanism of protein coupling and especially the desorption kinetics of BMP on mineral surfaces.
Those experimental studies are accompanied by a scale-bridging simulation of the BMP sorption process from physiologic solution as a function of the local pH-value and the structure formation at the solid-liquid interface. With this knowledge the project BioMin yields a significant contribution to develop and manufacture tailored bone substitute implants, so that degradation of the substitute material and build-up of new bone tissue can go hand-in-hand in vivo.

Simulations of materials behaviour are an important component of materials development when measurements are indirect and gain from theoretical interpretation, when the 'ideal' experiment is impeded by technological limitations, or when novel concepts and possible routes to their practical implementation are explored. Empirical physical models can be specifically tailored and have been employed successfully for the first two tasks, but the transfer to new tasks beyond the original application requires careful parameter reassessment. Quantum mechanical models, on the other hand, afford an a priori parameter-free access to materials properties on the nanoscale. In particular the density-functional theory provides computationally efficient access to the electronic structure of materials in the electronic ground state. Derived quantities such as forces, stresses, and responses to external electric or magnetic fields allow for the calculation of atom arrangements, lattice constants, elastic tensors, polarisabilities, dielectric and piezoelectric constants, or conductivity of nanosized systems or of systems with nanoscale building blocks. After a short introduction to the fundamentals of density-functional theory the applicability and the limitations of the approach for condensed matter systems will be discussed.

The magnetostatic interactions of colloidal particles, “capped” with radially magnetized Co/Pt multilayers, are modeled. Motivated by experiment the particles are arranged in microscopic two-dimensional clusters on a hexagonal lattice and are free to rotate. The thermodynamically stable states of clusters containing up to 108 particles are calculated theoretically by means of Monte Carlo simulations in the framework of multipole expansion. It is shown analytically that radially magnetized hemispheres have higher-order multipole moments beyond the dipole. Depending on geometrical details also even order moments appear. The even order moments break the inversion symmetry of the magnetic potential of a single particle. For a specific mixing ratio of dipole and quadrupole moments, the experimentally observed antiferromagnetic 120° Néel state in the clusters is found.

The success of most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources is contingent upon the development of an appropriate source to generate the electrons with an unprecedented combination of high-brightness, low emittance and high average current.
An elegant way is to combine the high brightness of RF guns with the superconducting technology. This concept was first proposed at the University of Wuppertal*. In 2002, the successful operation of a SRF photo-injector could be demonstrated at FZD for the 1st time**. However, this type of injectors is still in the R&D phase.
Challenges are the design of the cavity with its specific geometry, the choice of the photocathode type, its life time, a possible cavity contamination, the problems on coupling of high-average power into the cavity and the risk of beam excitation of higher order cavity modes.
During the last years several R&D projects have been launched. Most of them pursue different approaches to deal with these issues. This contribution gives an overview on the progress of the SRF photo-injector development based on the most prominent projects in the world.

The state-of-art DC guns with GaAs type photocathodes have been successfully operated as polarized electron sources for accelerators, but the beam emittance is regretfully very high because of the bunch
compressing after the gun. Though not all of the high energy physics experiments using polarized beams are sensitive to the source emittance, but a new source with lower emittance can simplify the injector
system and lower radiation load during the beam transport. Normal conducting rf gun can produce beams with low emittance, but the limit on vacuum is still an open question for the currently designed RF guns. In
this paper a new type of polarized source is reported: FZD polarized SRF gun, i.e. FZD superconducting rf gun with GaAs-type photocathode. The SRF gun is able to produce 1mA CW beam with 9.5MeV energy
and 1 mm mrad emittance. It has higher accelerating field and thus lower emittance than DC guns, at the same time much better vacuum condition than RF guns. Based on the successful running experience
in last two years, SRF gun applied with GaAs type cathode is considered as a promising alternative for current polarized guns. Some interesting questions will be discussed here, including the back bombardment
on cathode, cathode dielectric loss in strong RF field and the cathode time response.

Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
To investigate the involved phenomena and their complex interplay, new experiments on steam bubble condensation in vertical co-current steam/water flows have been have been carried out in the TOPFLOW test facility in Dresden, which consists of an 8m long vertical DN200 pipe (inner diameter: 195mm). Steam is injected into the pipe and the development of the bubbly flow is measured at different height levels with a wire mesh sensor. By varying the steam nozzle diameter (1mm or 4 mm) the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore they condensate slower (see figure). In addition to previous experiments (Lucas & Prasser, 2007) also the steam velocity is measured by correlating the signals of two wire mesh sensors installed in a small distance to each other. In the new experiment also the pressure drop along the pipe is measured as well as the temperature at selected points (Lucas et al., 2009). The additional sensors allow for choosing a defined gas inflow pressure as well as a distinct sub-cooling temperature at the injection location. Here steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 4 Kelvin were applied. Due to the pressure drop along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section.
In second part of the present contribution, the new TOPFLOW condensation experiments are compared with simulations using an extended MUSIG approach. This approach has been developed in cooperation with ANSYS-CFX for the computation of condensation in polydispersed bubbly flows with CFD. This extended MUSIG approach includes the transition of bubbles to smaller size groups due to condensation as well as the shift of the bubble size distribution due to pressure changes. In the second part of the present contribution, simulations with the extended MUSIG approach are compared with the new TOPFLOW condensation experiments. The new CFD approach is able to catch all relevant phenomena qualitatively, such as bubble condensation and evaporation (if the saturation temperature falls below the water temperature) and radial bubble size segregation. Crucial for the condensation simulations is the modeling of coalescence and breakup, which still needs to be improved. The presented condensation experiments and the extended MUSIG approach are a useful basis for validating models for polydispersed bubbly flows.

The superconducting rf photoinjector (SRF photoinjector) is one of the latest application of SC technology in the accelerator field. Since superconducting cathodes with high QE are not available up to now, normal conducting cathode material is the main choice for the SRF photoinjectors. However, the compatibility between the cathode and the cavity is one of the challenges for this concept. The SRF gun with Cs2Te cathode has been successfully operated under the collaboration of BESSY, DESY, FZD, and MBI. In this paper, some experience gained in the gun commissioning will be concluded. The results of the properties of Cs2Te photo cathodes in the cavity will be presented, such as the Q.E., life time, regeneracy, dark current and thermal emittance. At the same time, the cavity quality is showed to be steady before and after the cathode working.

The amount of hydrogen in semiconductors can highly influence electrical, physical and chemical properties on a microscopic as well as on a macroscopic scale. Many applications in the micro electronics industry, in solar cell research and in surface science require the precise knowledge of the actual hydrogen concentration and its concentration distribution near the surface. Nuclear Reactions Analysis (NRA) has been successfully established as a standard technique in chemical analysis within recent decades. In the particular case of hydrogen depth profiling the so-called ¹⁵N-method became one of the most successful, non-destructive and standard-free analysing technique. This method is based on the nuclear reaction ¹⁵N(¹H,αγ)¹²C, which is characterized by a pronounced resonance at 6.385 MeV. By variation of the initial ¹⁵N-ion energy the depth in the sample where the ¹⁵N resonance energy is reached can be easily adjusted according to the particular ion stopping in the material. Thus, a depth sensitive measurement of the absolute H-concentration becomes feasible. Using grazing incident angles the depth resolution near the surface can reach 1 nm. Detection limits under optimum conditions are as low as 0.05 at%. Fundamentals of the ¹⁵N-method and experimental set-up at the 6 MV accelerator at the FZD as well as particular examples of hydrogen depth profiling in ongoing state-of-the-art experiments are presented.

Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N₂:O₂ during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 °C the crystalline polymorph anatase and rutile phases have been
developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.

More and more electron accelerator projects for FELs, ERLs or 4th generation light sources require “super” electron beams with high brightness, low emittance, and high average current. Under this background, much attention is paid on the research and development of new electron sources. A Superconducting RF photoinjector within a collaboration of HZB, DESY, FZD, and MBI is designed to improve the beam quality for ELBE IR-FEL users, and at the same time to test this kind of promising injector concept. The main design parameters of this gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. In this paper the results of the RF and beam parameter measurements with Cs2Te photo cathodes will be presented, and the experience for the gun running gained at the first beam experiment will be concluded, including the life time and the compatibility of the normal conducting photocathode in SC cavity, the cavity properties after the cathode’s inserting.

We report experiments on the impact of 2.5 MeV proton irradiation on self-diffusion and dopant diffusion in germanium (Ge). Self-diffusion under irradiation reveals an unusual depth independent broadening of the Ge isotope multilayer structure. This behavior and the observed enhanced diffusion of B and retarded diffusion of P demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This fundamental finding opens up unique ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that hinders the fabrication of Ge-based nanoelectronic devices.

Background
Cyclin-dependent kinases 4 and 6 (Cdk4/6) are important components of cell cycle activation in G1 phase and play critical roles in dysfunction of growth control during cancerogenesis. The aim of our study was the evaluation of new fluorine containing pyrido[2,3 d]pyrimidin-7-one derivatives (CKIC, CKID and CKIE) concerning their efficacy and suitability as Cdk4/6 inhibitors and, after fluorine-18 radiolabeling, as radiotracers for imaging of tumors by positron emission tomography (PET).

Materials and methods
Small molecule inhibitors CKIC, CKID and CKIE were analyzed concerning their biological and radiopharmacological properties in human tumor cell lines HT-29, FaDu and THP-1. Cell cycle distribution of cells was determined by flow cytometry DNA analysis and effects on cell growth were measured. Phosphorylation of retinoblastoma protein (pRb) at Ser780 was analyzed by Western blotting. mRNA expression of the pRb affected genes E2F-1 and PCNA was measured with quantitative RT-PCR. Stability and radiotracer uptake studies with [18F]CKIE were performed.

Results
Cell cycle analyses showed a concentration-dependent (50 nM to 10 µM) increment of percentage of tumor cells in G1 phase after 24 h of incubation with CKIC, CKID and CKIE, with CKIE to be more potent than CKIC and CKID. Cell growth studies indicated reduced tumor cell numbers after 48 h of treatment with 1 µM (< 75%) and 10 µM (< 30%) CKIE and 10 µM (< 70%) CKIC or respectively CKID. Cdk4 specific phosphorylation at pRb Ser780 is decreased in a concentration dependent manner after 24 h of incubation with CKIE. Downregulation of E2F-1 and PCNA mRNA expression could be demonstrated after treatment with CKIE. [18F]CKIE indicated high stability in physiological buffer and cell culture medium. Cellular radiotracer uptake using [18F]CKIE increased with time amounting to 46.3±11.2 %ID/mg protein in HT-29 and 46.2±13.8 %ID/mg protein in FaDu cells, respectively, after 60 min at 37°C. Uptake of [18F]CKIE could be blocked with nonradioactive CKIE dependent on concentration (e.g., 23.5±3.7 %ID/mg protein with 5 µM CKIE after 60 min at 37°C).

Conclusion
CKIE was identified as the most potent fluorine containing pyrido[2,3 d]pyrimidin-7-one derivative analyzed in our study causing arrest of tumor cells in G1 phase due to inhibition of the Cdk4/6/ pRb/ E2F pathway. In vitro radiotracer uptake studies using [18F]CKIE demonstrated tumor cell uptake, which is an important prerequisite for further PET studies in tumor-bearing mice.

Das Ziel dieser Forschungsarbeiten ist die Entwicklung eines neuen bifunktionellen Chelatorsystemes für eine stabile Komplexierung thiophiler Radiometallnuklide wie Re 188 oder Tc 99m. Neben der Radionuklidfixierung soll dieses Ligandsystem reaktive Zentren (z. B. Aktivester, Maleinimid, Isothiocyanat) zur kovalenten Bindung an verschiedene zielsuchende Einheiten (Antikörper, -fragmente, Peptide, usw.) besitzen. Je nach verwendetem Radionuklid und gebundenem biologisch aktiven Adressmolekül können verschiedene Krankheitsbilder diagnostiziert (Tc-99m) und therapiert (Re 188) werden.
Ausgehend von Verbindung 1 können über die Bildung des Anhydrids 3 und anschließen-der Reaktion mit sekundären Aminen (u. a. Morpholin, 1 Aza-kronenether) unter-schiedliche thiolgeschützte Derivate 4 synthetisiert werden. Hierbei besteht die Möglichkeit, mittels ent-sprechender Amine die pharmakologischen Eigenschaften des späteren Konjugates zu beeinflussen. Die Ausbeuten bis Verbindung 4 sind nahezu quantitativ. Durch Überführung von 4 in das Carbonsäurechlorid, Verbrückung mit boc-geschütztem Norspermidin (Ausbeute 72 %) und Entschützung der einzelnen Schutzgruppen (quant.) erhält man die tetradendaten Liganden 6.
Es gelang zudem, dieses Ligandsystem durch die Reaktion von Bernstein-säureanhydrid mit dem sekundären Amin und Überführung der terminalen Carboxylgruppe in einen Aktivester an eine 5‘-hexylamin-modifizierte DNA zu binden. Beginnende radioaktive Markierungsstudien mit Tc-99m und Re-188 werden zeigen, ob diese 188Re-DMMS-DNA-Konjugate für etwaige Pretargeting-Ansätze zur Therapie von Tumorerkrankungen verwendet werden können.

The study is focused on improvement of the free electron mobility in Al-doped ZnO films grown by reactive pulsed magnetron sputtering. At optimum growth conditions low-absorbing films are obtained with a Hall mobility of 46 cm² V ⁻¹s⁻¹, a free electron density of 6.0x10²⁰ cm⁻³, and an electrical resistivity of 2.26x10⁻⁴ cm. The relation between the mobility and free electron density for different growth conditions is discussed in terms of ionized impurity scattering, impurity clustering, and grain boundary limited transport.

Despite the fact, that thin films of transparent conductive oxides (TCOs) are already in use as transparent electrodes for thin film solar cells, there are still questions whether it is possible to further improve their electrical and optical properties. Moreover the fundamental mechanisms that govern the incorporation and activation of dopants in the host lattice are only partially understood. Therefore this study is focused on Al doped ZnO (AZO) as one of the most used TCOs. By relating parameters of film growth to structure and properties the abovementioned questions were addressed. In particular it is of big interest to increase the Hall mobility while maintaining a high free carrier concentration to obtain highly conductive films which show low absorption in the near IR and visible spectral range.

The AZO films were grown using reactive pulsed magnetron sputtering (RPMS) on fused silica and sapphire substrates. The oxygen partial pressure during deposition was precisely controlled by exploiting the gettering of the reactive gas by the sputtered metal at constant oxygen gas flow. This was combined with different substrate temperatures (T_S=RT-550 °C) and Al concentrations (c_Al=0.5-8.7 at %). The film structure was studied by X-ray diffraction (XRD), cross-sectional TEM and atomic force microscopy, while the elemental composition was determined by elastic recoil detection analysis. Further characterization was done by spectroscopic ellipsometry and Hall-effect measurements in van-der Pauw geometry.

It was shown for every Al concentration there is a maximum Hall mobility which can be reached at a certain optimum substrate temperature and oxygen partial pressure which are interrelated. The recent achievement of a high Hall mobility of 46 cm²/Vs at a free electron density of 6.0x10²⁰ cm^-3 in reactive pulsed magnetron sputtered (RPMS) ZnO:Al demonstrates that the RPMS technique is suitable for the production of high quality TCO films [1].

A comparison of the results with data from other publications reveals an underlying physical limit of mobility in polycrystalline TCO films in general. For different growth conditions and target Al concentrations the relation between the mobility and free electron density can be explained in terms of ionized impurity scattering, impurity clustering and grain boundary limited transport.
Moreover epitaxial undoped and Al doped ZnO films were grown on sapphire substrates and studied by extensive XRD analysis. It was found that these films possess a high degree of in-plane orientation with a rotation of their hexagonal lattice by 30° with respect to the substrate.

[1] S. Cornelius et al, Appl. Phys. Letters 94, 042103 (2009)

The particle-in-cell algorithm (PIC) is one of the most widely used algorithms in computational plasma physics. With the advent of graphical processing units (GPUs) large-scale plasma simulations on inexpensive GPU clusters are in reach. We present an implementation of a fully relativistic plasma PIC algorithm for GPUs based on the NVIDIA CUDA library. It supports a hybrid architecture consisting of single computation nodes interconnected in a standard cluster topology, each node carrying one or more GPUs. The inter-node communication is realized using the Message Passing Interface (MPI). The simulation code PIConGPU presented in this work is to our knowledge the first scalable GPU cluster implementation of the PIC algorithm in plasma physics.

The study describes for the first time the application of Cu(I)-mediated 1,3-dipolar [3+2]cycloaddition for the labelling of proteins with the short-lived positron emitter fluorine-18 as exemplified with azide-functionalized human serum albumin (HSA).

Flow fields in the safety research of nuclear reactors are usually complex and often involve two-phase (gas-liquid) flows, where one of the phases is continuous and the other phase consists of disperse bubbles. It is well-known that bubble coalescence and breakup can lead to significant variations in the bubble size distribution, which influences the relative motion of bubbles, i.e. the redistribution of gas-liquid interface. To model the dynamic evolution of the disperse gaseous phase, the population balance equation (PBE) has to be solved together with the classical hydrodynamic Euler/Euler simulation. The Inhomogeneous MUSIG (MUltiple-Size-Group) model implemented in the CFX 12.0 commercial CFD code is one kind of efficient method for the solution of the PBE [1, 2]. However, the closure models for bubble coalescence and breakup were diagnosed as one weak point in the application of this approach [3, 4].
In the previous work, a generalized model was proposed for the modeling of bubble coalescence and breakup, which considers all important mechanisms, e.g. turbulent fluctuation, laminar shear, wake entrainment and eddy capture and interfacial slip velocity. The first test in a 1D Test Solver has shown that the new model is capable of tracing the evolution of bubble size distribution and radial gas volume fraction in vertical pipe flow [5, 6].
In the present study, the new model was implemented into CFX 12.0 through user FORTRAN subroutines and serves as new constitutive relations of the MUSIG approach. Two-dimensional axisymmetric multi-fluid simulations were performed for air-water flows in a large vertical pipe (DN 200). Simulation results for the evolution of bubble size distribution, radial gas volume fraction, Sauter mean bubble diameter as well as gas velocity were compared to the TOPFLOW experiment. The extents of the calculation grid are, x: 0~0.1m, z: 0.221~1.021m. The flow is in the z-direction.

Spatial self organization of metal nanoparticles and quasi-continuous multilayers in carbon-transition metal (TM=Co, Ni and Cu) composite thin films as a function of metal content, metal type and incoming flux energy is investigated. Films were grown by pulsed filtered cathodic vacuum arc (PFCVA) which produces a flux of film forming species in the form of ions with ‘natural’ hyperthermal energies in the range of ~20-50 eV. Since each arc pulse deposits less than one monolayer of ions, by rapidly alternating between cathodes it is possible to deposit compounds or nanocomposites. The metal content (nominal 10-50 at.%) was varied by changing the metal to carbon pulse ratio while the incoming beam energy was controlled by applying substrate bias of 0 V, -15 V and -30 V. The structure of the films was investigated by means of transmission electron microscopy and grazing incidence small angle x-ray scattering while the film composition was determined by elastic recoil detection analysis. The results demonstrate that the vertical self-organization occurs in all type of films. At low metal contents the formation of un-correlated encapsulated nanoparticles occurs. The increase in the metal content results in the formation of a vertically layered separated nanoparticle structure with well pronounced diagonal metal nanoparticle correlations, while the further increase in the metal content results in the formation of quasi-continuous metal/carbon multilayers. The periodicity of the vertical structure strongly depends on the film composition and the incoming ion energy. The observed vertical ordering is broken down by the thermal activation of the surface diffusivity by an additional thermal heating during the deposition. The results are discussed on the interplay of stochastic thermal effects and ion induced ballistic effects.

News Item: Kelvin probe force microscopy (KPFM) now has a good explanation, thanks to Christine Baumgart of the nanospintronics group at the Forschungszentrum Dresden-Rossendorf (FZD), Germany.

An SRF photoinjector has been successfully tested in FZD under the collaboration of BESSY, DESY, FZD, and MBI. In order to improve the gun cavity quality and thus reach a higher gradient, a new 3+1/2 superconducting cavity is being fabricated in cooperation with JLab. The modified cavity is made of large grain niobium, composed of one filter choke, one special designed half-cell (gun-cell) and three TESLA cavities. In this paper, the main updates of the new cavity design will be explained in detail. The deformation of the filter choke and the gun-cell, which is caused by pressure fluctuation in the He-line and also by the effect of the Lorentz force, will be minimized by stiffening between the filter choke and the gun-cell. Meanwhile, the cathode hole in the choke and gun-cell is enlarged for better rinsing. To simplify assembly, the NbTi pick-up will be welded directly on the wall of filter choke.

Working Group I of the 2009 Energy Recovery Linac Workshop focused on high-brightness, high-power electron beam sources for energy recovery linacs (ERLs), and relevant technology such as development of drive lasers. The WG1 summary paper was broken into two parts: DC guns and loadlocks; and RF guns and drive lasers. This was done both to retain more manageable paper sizes, and because SRF guns are in an earlier stage of development than DC guns. This paper describes the advances, concepts, and thoughts for the latter topics presented at the workshop.
There are many challenges to the successful operation of SRF guns as high-brightness, high-average-current beam sources. These combine the set of challenges for high-current SRF cavities (fabrication, cleaning and processing, HOM extraction, etc.), with challenges for high-average-current photocathode sources (photocathode fabrication, quantum efficiency and lifetime, drive laser technology, etc.). New challenges also arise from this combination, such as the requirement for having removable cathodes in an SRF cavity. Practical approaches have been, and are currently being, found to address the problems, and the base of knowledge and experience continues to grow.
Alternate ideas are also beginning to make inroads. Hybrid DC-SRF guns, pioneered by Peking University, offer promise for combining the best features of both technologies. Quarter-wave SRF cavities offer compact size for a given frequency, potentially easier fabrication than elliptical cells, and very high transit-time factors for quasi-DC operation. Also, the use of normal-conducting cavities, usually dismissed out of hand due to the required RF power consumption, may become practical with advanced cavity designs.
This paper summarizes the state-of-the-art of drive lasers, cathode development and RF gun-based injectors for ERL beam sources The focus in the field has been on DC and SRF guns to date, but interesting approaches for hybrid DC/SRF guns and normal-conducting RF guns are also presented. The paper concludes with discussions of operational issues and concerns, technical issues related to beam source realization, and future concepts.

kein Abstract verfügbar.

Quantum chemical calculations is capable of predicting various physicochemical properties of ions and molecules and may assist to further explore experimental chemistry. Among several different available theories, density functional theory (DFT) is a reasonable compromise between accuracy and computational time, and is nowadays widely used for the studies in physics, chemistry, and material science.
I will present several examples how DFT calculations can be used to better understand experimental actinide chemistry. The first example shows the calculations of luminescence properties of uranium(VI). The quenching of uranium(VI) luminescence in the presence of some types of organic and inorganic compounds are well reproduced by the DFT calculations and the quenching mechanism has been postulated. In another example, redox potentials of the actinide couple An(VI)/An(V) was studied for An = U, Np, Pu, Am. The unsolved question "What is the highest oxidation state of plutonium?" was discussed from theoretical viewpoint. The structures of various actinide complexes were also studied and they were disucussed together with EXAFS spectroscopy measurements at the Rossendorf Beamline in ESRF, France.

no abstract for this talk

Intrinsic ferromagnetism at room temperature has been observed in ZnO/sapphire films by implantation of 200 keV Ni2+ ions with fluences 6 × 1015, 8 × 1015, 1 × 1016 and 2 × 1016 ions/cm². Crystalline phases are identified by glancing angle X-ray diffraction (GAXRD), which shows no extra phase in the implanted films. Highest saturation magnetization (Ms) is observed in the film implanted with the fluence of 8 × 1015 ions/cm² as examined by SQUID magnetometry. This film has almost 80% transmittance across visible wavelength range and hence a potential candidate of transparent ferromagnetic semiconductor [TMS]. Defect like oxygen vacancies in the films are studied by X-ray photoelectron spectroscopy (XPS). Ferromagnetism of the films is explained on the basis of bound magnetic polaron (BMP) model.

kein Abstract verfügbar

We give a survey about the recent experiments on the helical magnetorotational instability (MRI) in the framework of the Potsdam ROssendorf Magnetic InStability Experiment (PROMISE). By comparing the experimental results with numerical simulations we show that the observed instability is indeed a global instability rather than a noise-triggered convective one. We also delineate the plans for further experiments on the azimuthal MRI and on the Tayler instability.

The magnetorotational instability (MRI) plays a crucial role for cosmic structure formation by enabling turbulence in Keplerian disks which would be otherwise hydrodynamically stable. With particular focus on MRI experiments with liquid metals, which have small magnetic Prandtl numbers, it has been shown that the helical version of this instability (HMRI) has a scaling behaviour that is quite different from that of the standard MRI (SMRI). We discuss the relation of HMRI to SMRI by exploring various parameter dependencies. We identify the mechanism of transfer of instability between modes through a spectral exceptional point that explains both the transition from a stationary instability (SMRI) to an unstable travelling wave (HMRI) and the excitation of HMRI in the inductionless limit. For certain parameter regions we find new islands of the HMRI.

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment.
We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches at a best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs.

In this paper a new method of determining the energy spread of a relativistic electron beam from a laser-driven plasma wakefield accelerator by measuring radiation from an undulator is presented. This could be used to determine the beam characteristics of multi-GeV accelerators where conventional spectrometers are very large and cumbersome. Simultaneous measurement of the energy spectra of electrons from the wakefield accelerator in the 55-70 MeV range and the radiation spectra in the wavelength range of 700-900 nm of synchrotron radiation emitted from a 50 period undulator confirm a narrow energy spread for electrons accelerated over the dephasing distance where beam loading leads to energy compression. Measured energy spreads of less than 1% indicates the potential of using a wakefield accelerator as a driver of future compact and brilliant ultrashort pulse synchrotron sources and free-electron lasers that require high peak brightness beams.

Electron bunches accelerated in the wakefield of a laser beam are expected to have pulse lengths below a hundred femtoseconds. Such pulse lengths cannot be measured by established accelerator diagnostics. However, with laser-driven electron beam generation it becomes possible to perform an all-optical measurement of the electron pulse length on a single-shot basis.
We present the analysis of data taken in 2005 at the ASTRA laser. A 400 mJ, 45 fs laser pulse is focused to a spot size of 8 mum FWHM using an f/16 parabolic mirror to accelerate electrons in a gas jet of 2 mm length. Terahertz transition radiation created in the passage of these electrons through a 50 mum Al foil is focused onto a 200 mum thick ZnTe crystal and brought into overlap with part of the ASTRA pulse negatively chirped to 5 ps.
The Terahertz pulse induces transient birefringence in the crystal via the electro-optical Pockels effect while the ASTRA pulse probes the resulting change in polarization and therefore the temporal structure of the Terahertz pulse.
We will focus on the details of the data analysis and show that the observed temporal signal can clearly distinguish between the quasi-monoenergetic electron bunch and the quasi-thermal tail of the electron distribution in a manner which is consistent with the measured electron spectra.

In dieser Arbeit sollte die Komplexierung von Europium(III) mit verschiedenen Aminosäuren untersucht, Komplexstabilitätskonstanten bestimmt und Aussagen über die Bindungsstärke dieser Liganden getroffen werden. Dazu wurden die proteinogenen Aminosäuren Tryptophan, Tyrosin, Phenylalanin, Threonin und Alanin ausgewählt und die Komplexierung mittels UV/VIS und zeitaufgelöster Laserfluoreszenzspektroskopie untersucht. Dabei wurde Europium als Analogelement für dreiwertige Actinide ausgewählt, da es nicht radioaktiv und dadurch einfach handhabbar ist. Da dreiwertige Lanthanide und Actinide sehr ähnliche Eigenschaften aufweisen, können Erkenntnisse mit dreiwertigen Lanthaniden in erster Nährung auf das Verhalten von dreiwertigen Actiniden übertragen werden. Die sehr guten Fluoreszenzeigenschaften des Europium(III) schaffen darüber hinaus die Voraussetzung zur Untersuchung der Bindung und Komplexierung mit unterschiedlichen Liganden in biologisch relevanten, niedrigen Konzentrationsbereichen. Anhand der ermittelten Komplexstabilitätskonstanten sollte abschließend die Speziation des Europiums in wässrigen Aminosäurelösungen ermittelt und der Beitrag dieser Stoffklasse zur Bindung von Schwermetallen in Biofluiden beurteilt werden.

Im Rahmen einer Literaturrecherche wurden Informationen über Modellumfang, Verifikations- und Validierungsstand sowie Einsatzgebiete verschiedener russischer Störfallcodes zusammengestellt. Dabei handelt es sich um die Programmgruppen KORSAR, TRAP, BIPR sowie das Programm TIGR und um die zur Erzeugung von reaktorphysikalischen Daten notwendigen Programme.

Environments with increased uranium concentrations such as uranium mining and processing sites are of a serious public concern due to the considerable chemical and radiological toxicity of this actinide. The mobility and toxicity of uranium in these environments are strongly influenced by a complex of geo-chemical and biotic factors. Microorganisms present in such habitats can influence the migration behaviour by both, direct enzymatic processes such as oxidation and reduction as well as by indirect processes such as biosorption at the cell surface or a passive uptake inside the cells. In addition, uranium can be immobilized in inorganic mineral phases via microbially generated ligands, like sulfide and phosphate, in a process termed biomineralization. Up to date nothing is known about the role of representatives of the third domain of life, the „Archaea” in the biomineralization process of uranium. The objective of the present work was to investigate the interactions of the archaeal strain S. acidocaldarius DSM 639 with U(VI) and to elucidate, in particular, the possible role of archaea in the biomineralization of this radionuclide. For this purpose we used a combination of wet chemistry, microscopic and spectroscopic analyses.

The chapter describes the general system of the SWR 1000 and the passive components that use natural circulation.

Scattering experiments with high-intensity lasers and multi-MeV electron beams are gathering great interest as new light sources. Such experiments, especially with ultrashort laser pulses are prepared at Forschungszentrum Dresden-Rossendorf using the superconducting linac ELBE as brilliant source of monoenergetic electrons with energies of 10-40 MeV. We present simulations of the scattering spectra focusing on the effects of temporal and spatial variations of intensity in short optical laser pulses (Laser strength parameter significantly above 1) and the resulting shift of the non-linear Compton edge as well as higher and very high harmonic radiation.

The relation of QED-Compton scattering of a high-intensity optical laser off relativistic electrons to Thomson scattering is quantified. This is important both for future technical applications as X-ray sources and background to other nonlinear QED effects (Unruh radiation etc.) The spectral density of scattered photons in the linear and nonlinear regimes is analysed and a scaling relation for the spectral density relating different scattering geometries with each other is derived. In such a way one can easily account for electron beam phase space effects and the line broadening of the spectral density.
In the nonlinear regime (a0~1) with ultrashort (fs) pulses, our analysis predicts a nontrivial sub-peak-structure for the spectral density. We propose experimental parameters to make the observation of the subpeaks feasible.

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In this presentation I will review our recent results obtained in low-dimensional and frustrated spin systems using high-field Electron Spin Resonance (ESR) at the National High Magnetic Laboratory, Tallahassee, USA, and the Dresden High Magnetic Field Laboratory, Germany. It includes the observation of the sine-Gordon behaviour of magnetic excitations in quantum spin-chain material Cu-PM, observation of the two-magnon bound states in the new candidate for the magnon Bose-Einstein condensation (BEC) NiCl2-4SC(NH2)2 (known as DTN), antiferromagnetic resonance in the frustrated hexagonal multiferroic material YMnO3, observation of the excitation spectrum in the spin-ladder material BPCB and others. The talk will give also a brief introduction into the recent development of the high-field ESR program at the High Magnetic Field Laboratory in Dresden.

Nanostructured silver films have demonstrated plasmonic functionality but suffer from the effects of environmental degradation. We aim to overcome this issue by encapsulating the silver in hard transparent ceramics. Silver nanoparticles were grown on Si and borosilicate glass substrates by magnetron sputtering in the temperature range of RT-300°C. Subsequently the Ag nanoparticles were capped in-situ by a boron nitride layer. The morphology and structure of the films was investigated by transmission electron microscopy, while the optical properties were determined by spectroscopic ellipsometry and optical absorption spectroscopy. The results demonstrate that a dense BN capping layer prevents the Ag segregation to the surface, thus exposure to the atmosphere. The films have a composite structure with nanosized silver particles separated by the amorphous boron nitride matrix. In addition, the BN matrix prevents the coalescence of the supported Ag islands, which is observed for non-capped Ag films. In films with a nominal silver thickness below 10 nm the optical properties can be tuned by adjusting the growth and post-growth annealing parameters (nominal thickness, temperature, annealing duration). The structure-optical property relationship is discussed on the basis of plasmon-polariton resonance and the film morphology.

During oblique metal vapor deposition perpendicular to ripples of pre-patterned surfaces, a chain-like formation of the metal nanostructures along the ripples have been observed. The structures are located on the slopes which point towards the evaporation source. The self-ordering of metal nanostructure has been observed neither for normal deposition nor for low-angle deposition parallel to the ripple direction.
The features of the metal nanostructure depend strongly on the evaporation angle. In this work, we studied the process of silver deposition on pre-patterned, oxidized Si surfaces by means of 3D lattice kinetic Monte Carlo simulations. The experimentally observed Ag nanostructures could be reproduced. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent deposition rate leads to a strongly selective Ag nanocluster nucleation on the surface because the nucleation rate depends on the square of the adatom concentration.

Relativistic Heavy-Ion Collisions and Jean Cleymans

...Das Ziel der Forschungen ist die Wechselwirkung und Mobilität von Actiniden (wie z. B. Uran, Plutonium, usw.) auf molekulare Ebene in Geo- und Biosystemen aufzuklären und auf makromolekulare Systeme zu übertragen. Anwendungen finden sie unter anderem in der Entwicklung und Einschätzung von Sanierungsmethoden im Uranerzbergbau oder der Aufklärung des Verhaltens störfallbedingter radioaktiver Kontaminationen in der Umwelt. Im Mittelpunkt der Forschung mit Uran stehen dessen Wechselwirkungen mit natürlichen Organika. Zu diesen Organika gehören auch die Bioliganden wie Saccharide, Peptide und Kohlenhydrate. Uran kommt in der Natur mit den Oxidationsstufen +4 und +6 vor. Unter den gegeben normalen oxidierenden Bedingungen ist aber nur die Oxidationsstufe +6 stabil. Daher ist zu untersuchen, ob unter nicht oxidierenden Bedingungen und durch Anwesenheit von Bioliganden die Bildung von vierwertigem Uran möglich ist, da bekannt ist, dass diese einen Einfluss auf den Oxidationszustand von Uran haben. Der wichtigste Unterschied dieser beiden Oxidationsstufen ist die Löslichkeit. Die geringe Löslichkeit von U(IV) führt zu einer Immobilisierung des Urans. Die Salze des sechswertigen Urans haben dagegen eine sehr große Löslichkeit. Durch die Anwesenheit von Bioliganden im Boden könnte es daher zu einer Anreicherung von Uran kommen, da diese die Fähigkeit besitzen, U(VI) zu U(IV) reduzieren. Eines dieser Bioliganden ist Vitamin C, welches reduzierende Eigenschaften aufweist. Ziel dieser Arbeit ist es, die Reduktion von sechswertigem Uran zu vierwertigem Uran durch Vitamin C zu untersuchen und mit UV/VIS-Spektroskopie nachzuweisen.

The photoluminescence of uranium(VI) is observed typically in the wavelength range 400 - 650 nm with the lifetime of several hundreds μs and is known to be quenched in the presence of various halide ions (case A) or alcohols (case B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state which exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photo-excited uranium(V)–radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand-to-metal charge transfer (LMCT) between uranium and halide ion. Consequently, larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in case A and B, and is driven by an electron transfer from the quencher to the UO22+ entity. The relative energetic stabilities of the triplet excited state define the "fate" of uranium so that in case A uranium(V) is oxidized back to uranium(VI), while in case B uranium remains as pentavalent.

In this thesis we investigate experimentally certain aspects of the interaction of terahertz (THz) radiation with intersubband transitions and excitonic transitions in semiconductor quantum wells.
The first part deals with a more fundamental view on an intersubband transition in a symmetric, undoped GaAs/AlGaAs multiple quantum well. After optical excitation of carriers, the considered electronic conduction intersubband transition is probed in the low-intensity linear regime using broadband THz pulses. These pulses are detected via field-resolved electro-optic sampling. While the sample’s terahertz absorption shows the expected single peak of the resonant intersubband transition, the differential transmission spectra, i.e. the photoexcitation-induced changes in transmission, display strong Fano signatures. On the basis of a microscopic theory, we show that they originate from a phase sensitive superposition of THz current and ponderomotive current. The latter one results from the wiggling motion of carriers induced by the accelerating THz field. Our findings demonstrate for the first time that the ponderomotive contribution has to be taken into account also at the lowest THz intensities. The following issues consider the interaction with THz pulses of higher intensity from the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf.
In one experiment we investigate efficient second order sideband generation in the GaAs/AlGaAs multiple quantum well mentioned above. To this end a near-infrared laser tuned to excitonic interband transitions is mixed inside the sample with the inplane polarized FEL beam to create the sum- and difference-frequencies between them. We compare the sideband efficiencies for the THz beam tuned to the interexcitonic heavy-hole light-hole transition and to the intraexcitonic heavy-hole 1s-2p transition. In the latter case we achieve a ten times higher n=+2 low-temperature efficiency around 0.1%. This value is comparable to previous studies in the literature, but our approach involves different transitions in a much simpler geometry. At room temperature the efficiency drops only by a factor of 7 for low THz powers.
The last part of this thesis addresses another fundamental quantum-mechanical phenomenon: the splitting of an absorption line in a strong THz field. In the same abovementioned quantum well sample the FEL wavelength is tuned near the intraexcitonic 1s-2p heavy-hole transition. The THz radiation induces a power-dependent splitting of the heavy-hole 1s exciton absorption line which manifests itself in the transmitted spectrum of a broadband near-infrared probe beam. The FEL-wavelength-dependent strength of this so-called Autler-Townes splitting is discussed on the basis of a simple two-level model.

We demonstrate that axial p-n junction silicon nanowire (Si NW) diodes can be fabricated over a large area (5` Si wafer) by applying two existing doping techniques in succession. We doped the lower segments of the NWs p-type, in situ during growth with boron by molecular beam epitaxy, and the upper segments n-type, ex situ with phosphorus by ion implantation and subsequent rapid thermal annealing. No structural defects were observed in the NWs by transmission electron microscopy after implantation and rapid thermal annealing. Electrical measurements of individual NWs showed excellent diode characteristics with ideality factors higher than 2. Such high ideality factor can be attributed to the surface-states assisted recombination-generation in the depletion region of the p-n junction. The combined doping technique reduces the unwanted lateral doping and the extended overlapping region between n and p-doped segments in the NWs which is common in pure in situ doping. Our fabrication technique can be easily applied to form arrays of Si NW diodes for solar cells and other applications.

Implantation of 18O into highly B-doped and undoped silicon provides the possibility to investigate the effect of B-doping and to distinguish the processes of in-diffusion and out-diffusion of oxygen by profiling of 16O and 18O, respectively. The simultaneous in- and out-diffusion of oxygen was observed at 1000°C under oxidizing conditions. For silicon, heavily B-doped to concentrations of ≥ 1019 B cm-3, oxygen tends to diffuse out toward the surface. Moreover, a fraction of the oxygen from both sources, implanted 18O and in-diffused 16O, also migrates deep into the substrate and is trapped far beyond the mean ion range RP in the depth of x ≈ 3RP at the so-called trans-RP gettering peak.
In undoped silicon oxygen accumulation only takes place at vacancy-type defects introduced by ion implantation at a position shallower than RP.
The mobility of oxygen implanted into B-doped Si is higher than for implantation into undoped Si. Highly mobile defects are suggested to be formed in B-doped silicon beside the common mobile interstitial oxygen, Oi, and the immobile SiOX precipitates. These I OXBY defects may involve self-interstitials, I, and O and B atoms. The trans-RP peak appears due to the decay of these defects and the segregation of their constituents.

Bacteria in acidophilic biofilm communities, i.e. acid streamers and snotites, obtained from a subsurface mine in Königstein were visualized by fluorescence microscopy using four new fluorescent dyes (DY-601XL, V07-04118, V07-04146, DY-613). The pH of the bulk solution in which these bacteria thrive was pH 2.6 to 2.9. The new fluorescent dyes were all able to clearly stain and microscopically visualize in-situ the bacteria within the biofilm community without changing pH or background ion concentration. The commonly used fluorescent dyes DAPI and SYTO 59 were also applied for comparison. Both dyes, however, were not able to visualize any bacteria in-situ, since they were not stable under the very acid conditions.
In addition, dye V07-04118 and dye DY-613 also possess the ability to stain larger cells which were presumably eukaryotic origin and may be attributed to yeast cells or amoeba-like cells. PCR analyses have shown that the dominant bacterial species in these acidophilic biofilm communities was a gram negative bacterium of the species Ferrovum myxofaciens. The presented four new dyes are ideal for in-situ investigations of microorganisms occurring in very acid conditions, e.g. in acidophilic biofilm communities when in parallel information on pH sensitive incorporated fluorescent heavy metals should be acquired.

To characterize depressurization events the discharge over time needs to be determined as well as its composition. In depressurization research so far the use of gamma densitometers is well established [1]. An alternative technology is wire-mesh tomography. In the experiments carried out their usability to characterize the discharge while venting is investigated for the first time.
Application of wire-mesh tomography allows investigation of multiphase flows with high spatial and temporal resolution. The cross-sectional phase distribution in a vessel or pipe can be characterized based on local measurements of electrical conductivity of the fluid by means of crossing electrodes. This sensing technology was introduced about ten years ago as a conductivity measuring modality [2]. Since then it has been employed to the study of numerous single phase and two-phase flow phenomena, such as gas/water and steam/water two-phase flows in components in nuclear power plants, cavitation and pressure shock phenomena in fluid pipelines, water transport processes in soil and flow structures in bubble columns. The general design of a wire-mesh sensor can be seen in Figure 1. Additional information, such as flow rates, can be gained by combining signals of two wire-mesh sensors. By analysing the cross-sectional phase distributions of two distant sensors in a pipe with cross-correlation techniques one obtains velocity and consequently flow rate information.
First experiments using a setup equipped with wire-mesh sensors show that discharge over time and its composition can be measured. Analysis of experiments depressurizing a reactor filled 66.7% with water at a pressure of 5barg shows that in the horizontal pipe slug flow can be observed. Waves of the slug flow can be identified. A distinction between single-phase and two-phase discharge can be made using the sensors. Most importantly it can be seen, Figure 2, that comparing these experiments with experiments without sensors shows no differences in pressure decrease over time in the reactor and mass discharge.
Experiments depressurizing comparable foaming systems with the same experimental conditions show differing results. Foaming was achieved by adding Falterol, isobutanol and SDS. Results of the wire-mesh sensors are comparable to the results of non-foaming systems. Slug flow can be observed that can be characterized concerning mass discharge rates and composition. As shown in Figure 3 major differences crop up when looking at pressure decrease over time and mass discharge. The sensors either hinder the flow or foam the liquid which results in slower pressure decrease rates in the reactor. Thus longer periods of two-phase discharge can be observed. This increases the overall mass discharge from 23% to 39%.

x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the alphap process that describes a sequence of (alpha,p) reactions triggered by the 18Ne(alpha,p)21Na breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus 22Mg by measuring the 24Mg(p,t)22Mg reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of alpha-unbound states was identified and precise excitation energies were determined. Based on shell model and alpha-cluster model calculations we predict the level parameters for determining the stellar reaction rate of 18Ne(alpha,p)21Na for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

Due to their narrow domain walls, nanowires with high uniaxial out-of plane anisotropy are interesting candidates for spin-momentum transfer studies. Since high current densities can change or destroy the wires investigated, weak pinning potentials allowing the controlled and reliable depinning of domain walls at low current densities are desirable. A prerequisite for the preparation of a domain wall at such pinning sites are nucleation fields smaller than the fields required to depin the domain wall from the respective pinning site. We suggest two methods to tune the nucleation field of lithographically designed Co/Pt multilayer wires. The magnetization reversal of the wires is investigated by means of transmission X-ray microscopy. An up to fourfold reduction of the nucleation field could be achieved through altering the lateral shape of the wires or by depositing Fe stripes on top. The authors gratefully acknowledge financial support by the DFG and the DOE.

Bacterial envelope proteins, so called surface layers (S-layer) are widely spread pararcrystalline surface structures which coat the cells of lots of bacterial strains and all archaea. They are mostly composed of protein monomers which form via self-assembling high regular two dimensional arrays. The S-layer proteins we investigate are from bacterial strains recovered from uranium mining waste pile Haberland in Saxony, Germany.
Their S-layer proteins selectively bind uranium and protect the cells from its toxicity. These special S-layer characteristics make them interesting for many technological applications such as filter materials, biosensors, as functional surfaces, or for example as drug containers.
In order to produce S-layer proteins in a high efficient way a heterologous expression in Escherichia coli is essential. In our study, the S-layer-like protein SllB of Lysinibacillus sphaericus JG-A12 was expressed in E. coli Bl21. Noteworthy, recombinant protein production resulted in a high stability of the cells against mechanical and chemical treatment. These unusual cells were analyzed by light microscopy, AFM and TEM. All methods demonstrated a total changed cell morphology with long filaments in the beginning of the exponential growth stage and 5-200 µm long tube like transparent structures at the end of the exponential growth stage containing E. coli single cells. Analyses by SDS-PAGE, N-terminal sequencing and IR-spectroscopy showed that the tube-like structures consist of outer membrane associated with recombinant surface layer proteins. These findings point to a disordered cell division. However, the underlying mechanism of these morphological changes are not known and will be analyzed in future. The long filaments, in combination with high expression level, good growth and high stability make these unusual E. coli cells interesting for biotechnological applications. In addition, these results cast a new light on one of the best studied microorganisms.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Forschungszentrum Dresden-Rossendorf (FZD). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of FZD, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in some small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail and the flow behaviour observed with the high-speed camera is analysed.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, both parameters fail to properly correlate the data: a discrepancy is observed between the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes into account the effect of the fluid viscosities on the CCFL. Finally, the new parameter was validated successfully against the UPTF data. This shows that the proposed modification of the Wallis parameter allows a significant improvement for experimental series with variation of the viscosities.

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, two test models of were built: one at the Kobe University and the other at the TOPFLOW test facility of Forschungszentrum Dresden-Rossendorf (FZD). Both test facilities are devoted to optical measurement techniques, therefore, a flat hot leg test section design was chosen. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux condenser cooling mode appearing in some accident scenarios. The fluids used were air and water, both at room temperature. The pressure conditions were varied from atmospheric in Kobe to 3.0 bar absolute at TOPFLOW. According to the presented review of the literature, very few data is available on flooding in channels with rectangular cross-section, and no experiments were performed in the past in such rectangular models of a hot leg. Usually, the macroscopic effects of CCFL are represented in a flooding diagram, where the gas flow rate is plotted versus the discharge water flow rate. Commonly, the non-dimensional superficial velocity (also known as Wallis parameter) is used to plot the flooding diagram. However, the classical definition of the Wallis parameter contains the pipe diameter as characteristic length, which was originally defined by Wallis (1961) for counter-current flow limitation in vertical pipes and not in near horizontal channels with rectangular cross-section. In order to be able to perform comparisons with pipe experiments and to extrapolate to the power plant scale, the appropriated characteristic length should be determined.

Because the experimental projects on this subject at the Kobe University and at FZD were launched independently, a detailed comparison of both test facilities is presented. With respect to the CCFL behaviour, it is shown that the essential parts of the two hot leg test sections are very similar. This geometrical analogy allows to perform meaningful comparisons. However, clear differences concerning the dimensions of the cross-section (H x W = 150 x 10 mm² in Kobe, 250 x 50 mm² at FZD) allow to point out the right characteristic length for hot leg models with rectangular cross-sections. The hydraulic diameter, the channel height and the Laplace critical wavelength (leading to the Kutateladze number) were tested. The experimental results obtained on both test facilities show clearly that the channel height is the suited characteristic length. Finally, the experimental results are compared with similar experiments and empirical correlations for pipes available in the literature. In spite of the scatter of the data and of the different correlations, the overall agreement is good.

Microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins prevent the uptake and any sustainable damage of the cell by toxic and/or radioactive metals. The S-layers itself form highly ordered and mono-molecular envelopes around bacterial and archaeal cells. Noteworthy is their ability to self-assemble in suspension, on surfaces and at interfaces. Furthermore S-layers of different bacteria are able to fulfil different functions and thus may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defence of host organism, by other bacteria or by lytic enzymes. By combining these unique features of S-layer proteins, smart coatings on many different surface can be realized. Currently at the Institute of Radiochemistry, S-layer based functional coatings are under development for the production of (photo)catalytic active materials, metal selective filters or highly specific biosensors. Therefore possible applications are the elimination of pharmaceuticals and germs, the detoxification of metals, the removal of toxic metals, the recovery of noble metals or the detection of pharmaceuticals and other organic matter in water. Additionally, combinations of functionalities are possible using a layer-by-layer technique, offering a wide field for the development of new nanostructured biocomposites for environmental technology.

The core model DYN3D developed for 3-D analyses of steady states and transients in thermal reactors is being extended by a simplified P₃ (SP₃) version for hexagonal fuel assemblies with a view to new reactor types such as high-temperature reactors.

Reactor dynamics codes such as DYN3D use two-group cross sections (XS) which depend on local burnup, given in terms of the energy produced per fuel mass (MWd/kgHM). However, a certain burnup value can be reached under different spectral conditions depending on moderator density and other local parameters. Neglecting these spectral effects, i.e. applying the summary-burnup value only, can cause considerable errors in the calculated power density.
This paper describes a way to take into account spectral-history effects. It is shown that the respective XS correction linearly depends on the actual Pu-239 concentration. The applicability of the method was proved not only for usual uranium oxide fuel, but also for mixed uranium/plutonium oxide (MOX) and fuel assemblies with burnable absorber. The code DYN3D was extended by new subroutines which calculate the actual distribution of Pu-239 in the core and apply a spectral-history correction for the XS.

Protactinium is experiencing a renewal of interest in the frame of nuclear reactors based on thorium fuel. The isotopes 233Pa (intermediate in the production of the fissile 233U) and 231Pa (radiotoxic) are namely produced through nuclear reactions on 232Th: Aside from a possible use of thorium as nuclear fuel for energy production, studies on protactinium may provide additional information about the coordination chemistry of light actinides. The literature devoted to protactinium in aqueous solution is characterized by scarce and controversial thermodynamic data that originate from the strong tendency of Pa(V) towards hydrolysis and polymerization especially in non-complexing media. Modeling the behavior of this element in the reactor, in the reprocessing steps, in the geosphere and in physiological medium requires thermodynamic and structural data relevant to these various environments. The present work is the continuation of our previous studies devoted to hydrolysis and complexation of Pa(V) with sulfate ions. The aim is now to collect thermodynamic and structural data on Pa(V) in the presence of oxalic (H2C2O4) and diethylene-triamine-pentaacetic (H5DTPA) acids.
The apparent formation constants of Pa(V) complexes with oxalate and DTPA5- were deduced from tracer level experiments using the isotope 233Pa at ~10 12 M. At such low concentration of element, only partition or transport methods based on radiation detection can be used5. In this work, the technique of solvent extraction involving the chelating agent thenoyl-trifluoro-acetone (TTA) was chosen. The aqueous phase was a mixture of NaClO4, HClO4 and H2C2O4 or H5DTPA. The dissociation constants H2C2O4 or H5DTPA were taken from references. Firstly, extraction data, collected at constant ionic strength and temperature allowed to determine the maximum order of Pa(V) complexes, the mean charge of the predominant complex in aqueous phase and the number of TTA molecules per Pa atom in the extracted species. Secondly, a systematic study of the variations of the distribution coefficient D of Pa(V) as function of the free ligand concentrations performed at different temperature values, led to the determination of thermodynamic data relevant to complexation equilibria (formation constants, enthalpy and entropy variations). Figure 1 illustrates the variations of D as function of free DTPA5- concentration when temperature increases from 10 to 60°C. Whatever the temperature, these curves characterize the formation of a (1,1) complex that stability constant can be derived from the variations of (D0/D-1) as function of DTPA5-. At 25°C, the constant relative to the equilibrium PaO(OH)2+ + DTPA5- + H+ ↔ PaODTPA2- + H2O has been estimated to log1 = 29,0 ± 0,4 for an ionic strength equal to 3 M. In the oxalate system, the existence of the complexes (1,1) and (1,2) has been unambiguously demonstrated.
Since no structural information can be deduced from tracer level experiments, X-ray Absorption Spectroscopy measurements were performed on 231Pa samples in oxalic acid. As in concentrated sulfuric acid8, XANES spectra do not display the feature of the linear di-oxo bond that characterizes U, Np, Pu and Am at their higher oxidation states, whereas the analysis of EXAFS data has unambiguously demonstrated the presence of a short mono-oxo bond (1.73 Å).

The carbonate anion is one of the most important ligand in natural waters. The solubility of heavy metals like uranium is strongly affected by carbonate through the forming anionic complexes [1]. Uranium is well soluble in oxidation state VI. The oxidation state V is rather instable due to the fast disproportionation reaction. In contrast, the solubility of uranium IV is rather low. The situation changes completely in presence of carbonate. Because the disproportionation reaction of U(V) is strongly enforced by cation-cation interactions, strong ligands like carbonate are able to suppress this reaction. In consequence, U(V) can be stabilized over months in carbonate solution. Although U(IV) strongly tent to form polynuclear species and colloids, carbonate enhances its solubility by forming mononuclear U(IV) carbonato complexes. The coordination of U(VI) and U(V) has been described. The coordination of the limiting U(IV) carbonate complex is actual under debate. The aim of this study is to determine the coordination of the solution species and to preserve it, if possible, in a crystal structure. Because EXAFS provides only a radial distribution function of the next interatomic distances but no information on their spatial arrangement, the comparison with the crystal structure provide necessary information on the ligand arrangement. We used EXAFS again to follow the crystallization process and to proof that no rearrangement of carbonate occurs during the crystallization process.

Because uranium(IV) has a very low solubility over a wide pH range it is considered as immobile under anaerobic conditions. The solid uraninite may occur as nano-sized colloid which is very mobile in the environment. Conditions of the colloid formation and the reaction mechanisms will be discussed.

We present highly ordered Ag nanowire arrays with 35 nm periodicity grown on patterned templates. The optical properties measured using generalized ellipsometry exhibit strong anisotropy. Dielectric functions are calculated by fitting the Jones matrix elements with a biaxial layer model, accounting for both metallic behavior and localized surface plasmon resonances. The amplitude and wavelength maximum of the plasmon resonance perpendicular to the wires increase with increasing wire width and thickness. The dielectric coefficients of 10-mm-wide nanowires showa transition behavior from insulating inUVto metallic above 550 nm. Their potential application as polarizationdependent plasmonic-scattering transparent conductive electrodes is discussed.

The superconducting electron accelerator ELBE (Electron Linac with high Brilliance and low Emittance) at the Research Centre Dresden-Rossendorf (Germany) serves as a high-intensity bremsstrahlung photon-source delivering a pulsed beam (26 MHz) with very short bunches (<5 ps). The photons are being converted into positrons by means of pair production inside the target material thus forming an intense positron source.
The accelerator machine pulse is used as time reference allowing positron lifetime spectroscopy. We performed positron annihilation spectroscopy by pair production in different sample materials and used coincidence techniques to reduce the background due to scattered photons significantly in order resulting in spectra of extraordinary high quality.

The presentation gives an overview about the implementation of DYN3D into the NURESIM platform and the coupling with the thermal-hydraulic code FLICA-4.

Paramagnetic (PM) and superparamagnetic (SPM) Zn0.95Co0.05O epitaxial films display similar temperature and magnetic field dependent anisotropic magnetoresistance (MR) effects. The high structural quality of the PM films is confirmed by x-ray linear dichroism. A classical two-band model describes these MR effects well, and reveals the same intrinsic origin of the transport signatures in PM and SPM Zn0.95Co0.05O films. The temperature dependent resistivity of the respective films arises from a Mott variable-range hopping process. The absence of the anomalous Hall effect in the SPM film provides another evidence for lacking contributions from the SPM phase to the magnetotransport properties. Moreover, above the blocking temperature of SPM Zn0.95Co0.05O films, the M(H)-curve can be described by a Langevin function, indicating the presence of approximately 2 nm large magnetic nanoparticles. Therefore, only the contribution of PM Co2+ ions in Zn0.95Co0.05O films to the transport behavior can be found, thus demonstrating that 2 nm large magnetic Co nanoparticles does not interact with the carriers.

kein Abstract verfügbar

Ions and atoms are in their properties much alike. Except the electrical charge, which enables us to control the velocity and direction of ions in contrast to atoms in a fairly straight forward and precise way. Just the voltage of a ordinary car battery (12 V) can accelerate for instance an Ar+ ion to approximately 7.6 km/s – almost the velocity required to leave the earths orbit (1st cosmic velocity 11.2 km/s). If these fast projectiles impact on surfaces, their defined directionality and momentum provides for a game of billiard on smallest level possible. The extreme conditions of the collisions are widely utilized in materials science for unique analysis and non thermal synthesis methods, as for example just thermal excitation of Ar at room temperature (20°C) results in “only” 0.35 km/s.
The lecture will therefore introduce sources of ions and ways to control their energy and directionality (plasmas, accelerators, ion optics), with a short outlook on the underlying physics. Further, the basic principles of ion-surface interactions will be described and examples for their applications will be given, both for synthesis as well as analysis methods. For the first, thin film deposition and ion implantation methods, for the latter, ion-beam analysis methods, such as elastic recoil detection, Rutherford backscattering and nuclear reaction analysis, will be exemplarily elucidated.

In recent years, many NPPs have developed and implemented severe accident management guidelines (SAMG). It is the primary objective of developing SAMG to prevent or mitigate the consequences of severe accidents by keeping the reactor pressure vessel (RPV) integrity and reducing the load to the containment. In a hypothetical Station Blackout accident all active safety systems are unavailable. Without additional measures this would lead to heating-up of the reactor core with severe core degradation. To avoid or to limit the consequences of a possible core heat up, different accident management strategies can be applied.

This paper presents an assessment of early-phase accident management actions for VVER-1000 reactors. In particular Primary Side Depressurization (PSD) is investigated as a basic strategy for managing severe accidents under high pressure conditions.
In addition, Secondary Side Depressurization (SSD) is also being investigated. It aims at fast reduction of the secondary pressure and feeding the steam generators’ secondary side with water from the feed water tank or from a different source. In that way, the heat removal from the primary to the secondary side can be significantly enhanced and the core heat-up at high pressure can be delayed.

A number of simulations with different criteria for actuation of the PSD procedure and additional SSD were performed using the thermal-hydraulic system code ATHLET. This paper provides a detailed modelling of the reactor coolant system and the required safety systems, analysis of the thermal-hydraulic and safety parameters and description of the physical phenomena. Special attention is given to the possibilities of preventing or at least delaying an extended core heat-up depending on the availability of the operational and safety systems. The effectiveness of the applied accident management measures and the effect on the accident progression were studied in order to assess the maximum response time for operators’ intervention.

Ions accelerated from solid foils using ultra-intense laser pulses may have major impact on applications such as cancer therapy. While such ion beams typically have a low emittance and high charge density their maximum energy still falls short of therapy requirements. Analytic scaling laws for micrometer targets suggest an increase in maximum energy when reducing the pulse duration down to an optimum value. Further energy increase has recently been proposed when using ultra-thin foils or micro-structured targets.
We propose a new target design based on novel stacked foils which may lead to an acceleration of ions to even higher energies by a single high-intensity (~1020 -1021 W/cm² ) ultra-short laser pulse. In contrast to complex schemes relying on the use of synchronized laser pulses predicting a comparable ion energy gain, here the time interval between the irradiation of the individual foils is determined by their spacing.
We present an analysis of the fundamental acceleration mechanism and will focus on the electron dynamic during the laser interaction with the target. Based on thorough simulations and an analytic description of the laser interaction we will show how the enhanced electron dynamics in the early stages of the interaction leads to the gain in maximum ion energy observed in our simulations. Based on this analysis, for relevant target parameters we deduce optimum values and their scalings.

In dieser Diplomarbeit wurde die Zusammensetzung der EPS-Komponenten von natürlichen Biofilmen untersucht. Die Untersuchungen ergaben, dass die EPS der verschiedenen Biofilme sehr unterschiedliche Zusammensetzungen bezogen auf die Komponenten Proteine, Kohlenhydrate und Uronsäuren aufwiesen. Dabei war der Lipidgehalt in den Biofilmen am höchsten. Umweltfaktoren wie Standort oder fließendes Wasser wirken sich auf die Zusammensetzung der EPS aus.

In this work we report on a recent experiment where an energetic, well-collimated electron beam has been observed in the laser direction following the short pulse (600 fs) high-intensity laser interaction with ultra-thin solid foils. These results are in contrast to the typical low-energy divergent electrons accompanying ions in the target normal direction usually seen in solid targets.We observe the foils being preheated and expanded by ASE prior to the main pulse which makes them transparent for the laser. The experimental evidence as well as 2D particle-in-cell simulations suggest the excitation of a wakefield that can accelerate electrons to energies of tens of MeV.

Purpose:

To analyse short term and long term X-ray irradiation effects on proliferation, viability, glucose and amino acid uptake of murine melanoma cells in vitro and metastasis in vivo.

Materials and methods:

B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation (200 kV) in the range from 1-20 Gy. One, two and three days respectively 7, 14 and 21 days after treatment cells were analysed concerning cell growth, viability, proliferation, cell cycle distribution, glucose and amino acid transport. Moreover the capability of the cells for in vivo metastasis was examined.

Results:

As short term response on irradiation we detected decreased cell growth, viability and arrest in the G2/M phase of the cell cycle. Long term response involves re-start of proliferation, increased cell growth and glucose uptake but still decreased viability and amino acid transport. In vivo metastasis is lost immediately after irradiation and regained to a low extent beyond two weeks time for recurrence of cells before injection.

Conclusions:

In vitro data suggest that surviving melanoma cells compensate the initial irradiation-dependent damage of proliferation within three weeks possibly by increase in glucose uptake. For metastasis in vivo the role of additional mechanisms is strongly suggested.

Purpose:

To assess the potential of using the residual phosphorylation of histone H2AX (γH2AX) after irradiation as a marker of radiosensitivity invitro.

Material and methods:

Confluent cell cultures of FaDu and SKX human squamous cell carcinoma lines were irradiated with graded single doses. Twenty-four hours after irradiation cells were seeded for standard colony forming assay (CFA). In parallel, staining for γH2AX was performed to visualise the residual foci.

Results:

In the CFA, FaDu showed a higher radioresistance than SKX. After analysis of the residual foci data, we constructed ‘predicted’ survival curves using two different methods. First, the proportion of nuclei with <3 foci was found to correlate closely with the observed surviving fraction (SF) in FaDu, with a slight overestimation of the true SF in SKX. Second, there was a strong linear correlation of the mean number of residual foci and observed −lnSF. Based on regression analysis, we calculated the SF for both cell lines based on the mean number of residual γH2AX foci. This second approach again led to a good correlation of predicted and observed SF values in FaDu and a (slight) overestimation in SKX.

Conclusion:In the two cell lines investigated the mean number of residual foci of γH2AX can be used to predict differences in the radiation dose response relationship invitro.

Two similar sets of odd-parity bands are observed in each of three even-even neighbors, Ru-108,Ru-110,Ru-112, from a study of prompt spontaneous-fission gamma rays at Gammasphere. A careful study of the odd-parity levels of these nuclei shows evidence for the features of chiral doubling. Comparisons are made with reported other candidates for chiral doubling.

Hydrogen absorbed in crystalline solids causes a lattice expansion and the formation of hydride phases. Contrary to free standing bulk samples, thin films are fixed at substrates, which prevent their in-plane expansion. This makes hydrogen-induced expansion of thin films highly anisotropic and leads to the formation of high stresses in hydrogen loaded thin films. As a consequence, lattice defects may be created in thin films loaded with hydrogen. This work reports about defects created by hydrogen loading in epitaxial Pd films deposited on Al₂O₃ substrates by cold cathode beam sputtering. Hydrogen-induced defects are characterized by positron annihilation spectroscopy performed with variable energy slo positron beams. Extended studies of defect depth profile and its development with increasing concentration of hydrogen are performed by measurement of Doppler broadening of annihilation profile using a continuous positron beam. Selected states are investigated also by positron lifetime spectroscopy on an intense pulsed positron beam. Firstly, the microstructure of virgin films is characterized. Subsequently, the hydrogen concentration in the films is increaxed step-by-step by electrochemical charging. The development of the film microstructure and the evolution of defects are investigated.

Defect studies of a ZrO2 + 9 mol. % Y2O3 single crystal were performed in this work using a high resolution positron lifetime spectroscopy combined with slow positron implantation spectroscopy. In order to elucidate the nature of positron trapping sites observed experimentally, the structural relaxations of several types of vacancy-like defects in zirconia were performed and positron characteristics for them were calculated. Relaxed atomic configurations of studied defects were obtained by means of ab initio pseudopotential method within the supercell approach. Theoretical calculations indicated that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and are most probably responsible for the saturated positron trapping observed in yttria stabilized zirconia single crystals. However, the calculated positron lifetime for zirconium vacancy is apparently longer than the experimental value corresponding to a single-component spectrum measured for the cubic ZrO2 + 9 mol. % Y2O3 single crystal. It was demonstrated that this effect can be explained by hydrogen trapped in zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy – hydrogen complexes represent deep positron traps with the calculated lifetime close to the experimental one. In zirconium vacancy – hydrogen complexes the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. The calculated bond length is close to 1 Å.

In this experimental and theoretical work we focus on the technique of pulsed laser annealing applied to the metastable ferromagnetic semiconductor GaMnAs. Analytical heatflow calculations are used to illustrate the position and time dependent temperature distribution during the laser annealing process. Such heatflow calculations will also play an indispensable role for the preparation of new diluted ferromagnetic semiconductors by ion implantation and subsequent annealing. The structural, magnetic, and magnetotransport properties of ferromagnetic GaMnAs have been probed in dependence on the annealing parameters, e.g. the number of laser pulses and the pulse length. Annealing with a single KrF laser pulse of 30 ns and 0.26 J/cm² with the photon energy above the GaAs bandgap energy leads to similar magnetic properties like annealing with a single 3 ns Nd:YAG laser pulse with the photon energy below the GaAs bandgap energy. We observed that possibly due to Mn diffusion and decreasing hole concentration, several laser pulses degrade the structural and magnetic properties of GaMnAs. Our results reveal the largest saturation magnetization for a single KrF laser pulse.

The as implanted sample at room temperature and post-annealed samples did not show Kerr effect, but the sample implanted with 1x1017 Fe ions/cm², heated at 300°C, showed a little Kerr effect although the magnetic sextets were not clearly observed in 57Fe CEM spectra. The Kerr effect disappeared after postannealing. This suggests that the number of magnetic defects decreases by absorption of oxygen [1]. We also showed that the bulk magnetization is enhanced by co-doping of Sb and Fe into SnO2 powder [2]. We have analyzed the nanostructure of SnO2 films doped with 57Fe by conversion electron Mossbauer spectroscopy (CEMS) and nuclear inelastic scattering (NIS) at SPring8. We implanted 57Fe with 5x1016 ions/cm2 into SnO2 films containing 0.1% Sb and 3% Sb at the substrate temperature of 500°C in vacuum. Kerr rotation angles for 0.1% Sb doped SnO2 film were larger than that for 3%Sb doped SnO2 films. The samples post-annealed at 400°C for 6 hours also showed the Kerr effect. DCEM spectra were measured by discriminating conversion electrons with a back scattered type of gas counter [3]. As the results, four subspectra were observed: two doublets are assigned to paramagnetic Fe3+ and Fe2+ species and two broad sextets to site A and site B of magnetite. For 0.1%Sb doped SnO2 films the relative area of the magnetite phase was larger than for 3%Sb doped SnO2 films. After post-annealing, two sextets changed into one broad sextet, which is due to fine maghemite. The ferromagnetic behaviors of Fe implanted tin oxide films were attributed mainly due to the formation of magnetite for the as implanted samples and of maghemite for the post-annealed samples, respectively, rather than magnetic defects.

SnO2 (3% Sb) films were implanted with 5x1016 57Fe ions/cm² at the substrate temperature of 500°C, and annealed at high temperatures between 400°C and 800°C . These films were characterized by depth selective conversion electron Mössbauer spectroscopy (DCEMS) using a back scattered type of gas proportional counter, and measured by Kerr effect magnetometer. Kerr effect measurements of the SnO2 films showed ferromagnetism at room temperature. The Mossbauer spectra of the as implanted films consisted of paramagnetic doublets of Fe3+ and Fe2+ species and two broad sextets, which showed site A and site B of fine magnetite. The Kerr rotation angles increase step by step with post-annealing up to 700°C. This phenomenon was attributed mainly to ferromagnetic maghemite produced by post-annealing.

Bacterial surface layers (S-layers) are the outermost protein-layer of many bacterial cells and archaea. The ability of the proteins to self-assemble on interfaces and surfaces to two-dimensional paracrystalline arrays, as well as the possibility to use these arrays as template for the deposition of nanoparticles makes them attractive for many technical applications such as filter materials, catalytic surfaces, electronic devices, or sensory surfaces.

Here we present a new concept of biosensors based on the application of S-layers. These biosensors are composed of three compounds:

1) Bacterial surface layer; these proteins are used for the nano-structuring of surfaces such as SiO2-wafers or glass; they provide a huge amount of orientated functional groups that can be used for coupling of molecules to the surface, thus introducing a high level of functionality in a small device
2) Aptamers, working as receptors; aptamers are oligonucleotides that specifically bind chemical compounds via their three-dimensional structure; the aptamers are coupled to S-layers
3) Fluorophores for detection, coupled to S-layers; two fluorophores are used as donor/acceptor pair; appropriate excitation/emission spectra and closest proximity permit FRET; FRET is interrupted when the analyte is binding to the aptamers

Our project that started in April 2009 aims the development of biosensors specific for pharmaceuticals such as antibiotics in waters. These chemicals are frequently found in surface waters and have been designated as a new class of pollutants. The novel sensor systems may facilitate the easy detection of these low-concentrated compounds.

The Lifshitz - Slezov theory is applied to study the metastable statesof the matrix damage clusters, MDs, and the copper enriched clusters, CECs, in neutron irradiated steels. It was found that under irradiation conditions the CECs are at the Ostwald stage for a neutron fluence of about 0.0002 dpa. The time dependence of number density, MDN, is determined by summarizing all differential equations of the master equation for MDs with neglecting of dimmers concentration in comparison with concentration of the single vacancies and subtraction of the number CECs that replace the MDs, namely vacancy clusters, due to the diffusivity of copper and other impurity atoms to them. For binary Fe-0.3wt%Cu under neutron irradiation with dose 0.026, 0.051, 0.10 and 0.19 dpa the volume content of the precipitates from the SANS experiment is found to be about 0.229, 0.280, 0.237 and 0.300 vol% respectively. The volume fraction of CECs in these samples is 0.195 vol% and the calculated volume fraction of MDs is 0.034, 0.085, 0.042 and 0.105 vol% for doses 0.026, 0.051, 0.10 and 0.19 dpa respectively.

A crucial point for the understanding of the von-Karman-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers.

Numerical simulations of a VKS-like dynamo with a large localized permeability distribution that resembles the shape of the flow driving impellers clearly demonstrate that the common simplified treatment of the impellers, by demanding vanishing tangential field components at the top and the bottom boundaries, is not justified. The high permeability domain within the dynamo active region provides an significant enhancement of the axisymmetric field mode, whereas the first non-axisymmetric mode remains nearly unaffected.

To circumvent the restrictions of Cowling's theorem, still some alpha-effect is required for a growing axisymmetric field. However, the scaling behavior with the value of the disk permeability indicates that the necessary magnitude of alpha can be very small. The applied (homogenous) alpha-effect should be regarded as the simplest example how the soft iron disks facilitate growing axisymmetric solutions at reasonable parameter values. A complementary and more detailed approach will have to consider a non-axisymmetric flow variation in terms of azimuthally drifting equatorial vortices that have been observed in water experiments reported by de La Torre & Burguette (2007).

The poster describes the method of time-resolved laser-induced fluorescence spectroscopy (TRLFS). It is a very sensitive experimental method, which enables studies at submicromolar concentrations relevant to environmental conditions. The poster presents various applications of the method in our scientific studies as well as in cooperations with other institutions.

We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga⁺ ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm x 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ~1.3 x 10^-15 m²/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.

Infra-red (IR) and Raman spectroscopy studies were used to characterize different polymer materials implanted with low energy Si⁺ ions (E = 30 keV, D = 1.10¹⁷ cm^-2). Two kinds of polymer were studied - poly-methyl-methacrylate (PMMA), and poly-propylene (PP). Silicon ion implantation resulted in the breaking down of bonds in the substrate structures, and the emergence of newly formed bonds. The IR and Raman studies thus show that the implantation of Si⁺ into PMMA and PP leads to the formation of amorphous and nano-crystalline graphite, predominantly in the PP samples. The presence of SiC particles and unreacted Si atoms is also observed in the implanted polymer material.

On the poster new findings on two different topics are presented --- related separately to geometric (Berry) phases in non-Hermitian quantum systems in higher-dimensional Hilbert spaces and to the specific realization properties of PT-symmetric quantum brachistochrones in two-qubit systems fulfilling the Aharonov-Anandan lower bound on quantum evolution times.
Specifically, in the first part of the poster we present new results on the holonomy properties of eigenvector bundles of non-Hermitian operators which can be mapped into simplest versally deformed n-th order Jordan blocks. (This generalizes earlier considerations on similar setups with 2-dimensional Jordan blocks [1].)
In the second part of the poster, we start from the embedding of the PT-symmetric brachistochrone into a Hermitian two-qubit system (as recently proposed in [2]) and show that the resulting evolution of the two-qubit system is itself a conventional quantum brachistochrone lying exactly on the non-local Lie-group orbit induced by one of the non-trivial entanglement generators.

[1] U. Günther, I. Rotter and B. Samsonov, "Projective Hilbert space structures at exceptional points", J. Phys. A 40, 8815 (2007), arXiv:0704.1291[math-ph].
[2] U. Günther and B. Samsonov, "Naimark-dilated PT-symmetric brachistochrone", Phys. Rev. Lett. 101, 230404 (2008),
arXiv:0807.3643[quant-ph].

Recently semiconductor nanocrystals (NC) attracted additional interest because they might have the potential for adapting solar cell devices to a broader irradiance spectra. It is believed that this could be realized by size-controlled bandgap engineering of multiple junction solar cells. The feasibility of bandgap shifts up to 2 eV has been proofed for NC's of Ge or Si in the size from 1 to 5nm [1].
However, the fabrication of dense (>10^-12cm²), small and equally sized NC’s in a suitable matrix remains still a remarkable challenge.

The main focus of this work is the manufacturing of Ge-NC superlattice structures in silica matrix for photovoltaic application. DC reactive sputtering was used to deposit sequentially GeOx and SiO2 layers on Si wafers with thermally oxidized silica surface layer (500 nm). The sputter rate from the elemental targets was quite small (< 0.2 Å/s) to achieve good layer quality. The GeOx and SiO2 layer thicknesses could be tuned independently with the deposition time. It was possible to vary the composition from elemental Ge to GeO2 by adjusting the partial pressure of oxygen (p = 0 to 0.02 Pa) in the sputter chamber (sputter gas: Ar, p = 0.5 Pa). With increasing substrate temperature (RT up to 400°C) the oxygen content had to be increased as well in order to get the same x-value. Subsequent annealing led to Ge crystallisation with intrinsic cut-off size due to the silica separation layers.

In-situ characterization revealed the temperature dependent growth of the Ge-NC by grazing incidence x-ray diffraction (GID) and the layer interface roughness by x-ray reflectometry (XRR). Ge-NC’s being 2 to 5 nm small could be detected above 500°C. Interface roughnesses of about 1 nm showed that the fabrication of very thin separation layers allowing direct tunnelling should be possible.

Ex-situ analysis via Rutherford backscattering (RBS) provided the matrix of dependencies between the temperature, the deposition rate, the partial pressure of oxygen and the stoichometry. With the help of transmission electron microscopy (TEM) it was possible to gain local information about shape, size and crystallinety of the Ge-NC’s. Raman spectroscopy allowed a more global view on the size and shape of the nanocrystals and on the ratio of amorphous and crystalline Ge parts.

[1] Martin A. Green, Third generation photovoltaics, Springer, 2006, ISBN 1437-0379

The CFD code ANSYS CFX has been coupled with the neutron-kinetic core model DYN3D. ANSYS CFX calculates the fluid dynamics and related transport phenomena in the reactor’s coolant and provides the corresponding data to DYN3D. In the fluid flow simulation of the coolant, the core itself is modeled within the porous body approach. DYN3D calculates the neutron kinetics and the fuel behavior including the heat transfer to the coolant. The physical data interface between the codes is the volumetric heat release rate into the coolant. In the prototype that is currently available, the coupling is restricted to single-phase flow problems. In the time domain an explicit coupling of the codes has been implemented so far.
Steady-state and transient verification calculations for a small-size test problem confirm the correctness of the implementation of the prototype coupling. This test problem was a mini-core consisting of nine real-size fuel assemblies. Comparison was performed with the DYN3D stand-alone code. In the steady state, the effective multiplication factor obtained by the ANSYS CFX/DYN3D codes shows a deviation of 9.8 pcm from the DYN3D stand-alone solution. This difference can be attributed to the use of different water property packages in the two codes. The transient test case simulated the withdrawal of the control rod from the central fuel assembly at hot zero power. Power increase during the introduction of positive reactivity and power reduction due to fuel temperature increase are calculated in the same manner by the coupled and the stand-alone codes. The maximum values reached during the power rise differ by about 1 MW at a power level of 50 MW. Beside the different water property packages, these differences are caused by the use of different flow solvers.

Within the FP7 NURISP project the 3D neutron-kinetic core model DYN3D has been implemented into the NURESIM platform. Further, the coupling of DYN3D with the thermal hydraulic code FLICA-4 has been accomplished for steady-state calculations using the NURESIM tools. Two different test cases were used to verify the coupling. Comparisons with DYN3D stand-alone calculations confirm the correctness of the code coupling.

Aqueous uranyl carbonate complexes play an important role in the hydrogeology of uranium mining areas and nuclear waste disposals. The uranyl carbonate complexes are strong and predominant at the range of pH 7-12. The chemical equilibrium is temperature dependent. From the temperature dependency of the equilibrium constant it is possible to determine the reaction enthalpy and entropy.
From absorption spectroscopy the concentration of the formed complex and then the equilibrium constant can be determined.
In our work thermodynamical data for the formation of the uranyl carbonate complex UO2(CO3)34- were determined by absorption spectroscopy. Therefore absorption spectra of solutions with uranyl ions and carbonate ions at pH 9 in the temperature range from 10°C to 70°C were recorded.