Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

32337 Publications
Correlation between self-diffusion in Si and the migration mechanisms of vacancies and self-interstitials: An atomistic study
Posselt, M.; Gao, F.; Bracht, H.;
The migration of point defects in silicon and the corresponding atomic mobility are investigated by comprehensive classical molecular dynamics simulations using the Stillinger-Weber potential and the Tersoff potential. In contrast to most of the previous studies both the point defect diffusivity and the self-diffusion coefficient per defect are calculated separately so that the diffusion-correlation factor can be determined. Simulations with both the Stillinger-Weber and the Tersoff potential show that vacancy migration is characterized by the transformation of the tetrahedral vacancy to the split vacancy and vice versa and the diffusion-correlation factor is about 0.5. This value was also derived by the statistical diffusion theory under the assumption of the same migration mechanism. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. Molecular dynamics simulations using the Stillinger-Weber potential show, that the self-interstitial migration is dominated by a dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor are different, namely 0.59 and 0.69 for the dumbbell and the interstitialcy mechanism, respectively. The latter value is nearly equal to that obtained by the statistical theory which assumes the interstitialcy mechanism. Recent analysis of experimental results demonstrated, that in the framework of state-of-the-art diffusion and reaction models the best interpretation of point defect data can be given by assuming. The comparison with the present atomistic study leads to the conclusion that the self-interstitial migration in Si should be governed by a dumbbell mechanism.
Keywords: point defects, silicon, migration, diffusion

Publ.-Id: 11141 - Permalink


High-resolution oil-gas two-phase flow measurement with a new capacitance wire-mesh tomograph
Thiele, S.; Da Silva, M. J.; Hampel, U.; Abdulkareem, L.; Azzopardi, B. J.;
The experimental investigation of flow phenomena plays an important role in many fields of research as well as in industrial applications. Wire-mesh tomography allows the study of flows with high spatial and temporal resolution. This tomography modality was introduced about ten years ago and since then it has been employed to investigate a number of single phase and two-phase flow phenomena. In this paper, a new developed wire-mesh tomograph based on capacitance (permittivity) measurements has been employed on a vertical 67 mm diameter pipe up which air and silicone oil mixtures flow under controlled conditions. The wire-mesh sensor consists of two planes of wires forming an angle of 90° and having a small separation between them. An associated electronics measures the local capacitance between the gaps of all crossing points. Thus, the wire-mesh system yields cross-sectional images of the phase distribution. The present system reaches temporal resolution of up to 5 000 frames per second and has a spatial resolution of 2.8 mm. Two visualization techniques were used to display the measured wire-mesh data: (i) virtual sectional side views and (ii) virtual side projections. In the former one the values of phase fraction of the central electrode are displayed along the time. Such an image obtains the character of a side view to the flow on a vertical plane cut through the pipe along the diameter. The second visualization technique applied is the calculation of virtual side projections using a simplified ray-tracing algorithm. Here the three-dimensional phase fraction distribution is assumed to be illuminated by parallel white light and the light intensity departing in the direction of a virtual observer is calculated. Both visualization techniques complement each other in the visualization of flow structures. Different gas and oil flow rates where investigated thus obtaining a variety of flow patterns. All four major accepted flow patterns bubbly, slug, churn and annular flow are reported here. The high-speed capability and the good spatial resolution of the system enable an examination of the flow to be carried out with a high degree of detail. Thus, the spatial resolution is sufficient to detect individual bubbles. Furthermore, quantitative insights of the flow can be obtained by the calculation of axial and radial gas content profiles which are determined by integration of the measured data over appropriate partial volumes.
Keywords: high-speed measurement, capacitance measurement, flow visualization
  • Contribution to proceedings
    5th International Symposium on Process Tomography, 25.-26.08.2008, Zakopane, Poland
    5th International Symposium on Process Tomography, Lodz, Poland: Technical University of Lodz, 978-83-7283-271-9, PT08_cr7
  • Poster
    5th International Symposium on Process Tomography, 25.-27.08.2008, Zakopane, Poland

Publ.-Id: 11140 - Permalink


Defect Mediated Desorption of the KBr(001) Surface Induced by Single Highly Charged Ion Impact
Heller, R.; Facsko, S.; Wilhelm, R.; Möller, W.;
The formation of nanometer sized monoatomic deep pits on the KBr (001) surface induced by individual impacts of slow (1keV/amu) highly charged Xe ions has been investigated. The volume of the pits have been determined by atomic force microscopy and show a strong dependence on the ions potential energy. The imaging of single ion impact sites allowed us to determine total potential sputter yields from atomically flat (001) terraces. From the dependence of the pit formation ability on the ions initial charge state and the comparison of low and high fluence irradiations we found evidence that defect agglomeration into complex defect centers plays a major role in the desorption process induced by the potential energy.
Keywords: Highly Charged Ion, Defect Mediated Desorption, DIET, Alkali Halides, Frenkel Defects, Potential Sputtering
  • Physical Review Letters 101(2008)9, 096102

Publ.-Id: 11139 - Permalink


Aqueous Uranium(VI) Hydrolysis Species Characterized by Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy
Müller, K.; Brendler, V.; Foerstendorf, H.;
The speciation of uranium(VI) in micromolar aqueous solutions at ambient atmosphere was studied by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and by speciation modeling applying the updated NEA thermodynamic data base. It can be shown that reliable infrared spectra of micromolar U(VI) solutions are obtained abolishing the restrictions of previous spectroscopic investigations to millimolar concentrations and, consequently, to the acidic pH range. A significant change of the U(VI) speciation can be derived from the spectral alterations of the absorption band representing the antisymmetric stretching mode (ν3) of the UO22+ ion observed upon lowering the U(VI) concentration from the milli- to the micromolar range at a constant pH value 4. The acquisition of spectra of diluted U(VI) solutions allows the increase of the pH up to 8.5 without the risk of formation of colloidal or solid phases. The infrared spectra are compared to the results of the computed speciation patterns. Although a complete interpretation of the spectra can not be given at this state of knowledge, the spectral data strongly suggest the presence of monomeric U(VI) hydroxo species already showing up at a pH value ≥ 2.5 and dominating the speciation at pH 3. This is in contradiction to the predicted speciation where the fully hydrated UO22+ is expected to represent the main species at pH values below 4. At ambient pH, a more complex speciation is suggested compared to the results of the computational modeling technique. The predicted dominance of the UO2(CO3)34− complex at pH ≥ 8 by was not confirmed by the infrared data. However, the infrared spectra indicate the formation of hydroxo complexes obviously containing carbonate ligands.
Keywords: uranium(VI), speciation, infrared spectroscopy, ATR, modeling

Downloads:

Publ.-Id: 11138 - Permalink


Entwicklung einer Elektret-Ionisationskammer für die Dosimetrie in gemischten Neutronen-Gamma-Feldern.
Pawelke, J.;
no abstract available
  • Other report
    Dresden: Diplomarbeit, TU Dresden, Institut für Strahlenschutzphysik, 1990
    85 Seiten

Publ.-Id: 11135 - Permalink


Neutron dosimetry using electret detectors.
Seifert, H.; Dörschel, B.; Pawelke, J.;
no abstract available
  • Kernenergie 34(1991)7-8, 344-348

Publ.-Id: 11134 - Permalink


Comparison of calculated and measured neutron sensitivities of an electret albedo dosemeter.
Seifert, H.; Dörschel, B.; Pawelke, J.; Hahn, T.;
no abstract available
  • Radiation Protection Dosimetry 37(1991)1, 13-18

Publ.-Id: 11133 - Permalink


The influence of environmental conditions on charge stability and dosimetric properties of electret ionization chambers.
Stoldt, C.; Prokert, K.; Dörschel, B.; Hanisch, S.; Pawelke, J.;
no abstract available
  • Kernenergie 33(1990)1, 37-41

Publ.-Id: 11132 - Permalink


Two-color pump-probe studies of intraminiband relaxation in doped GaAs/AlGaAs superlattices
Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.;
The miniband relaxation dynamics of electrons in doped GaAs/AlGaAs superlattices are investigated by two-color infrared pump-probe experiments. By this technique, we are able to separate the different contributions from inter- and intraminiband relaxations to the transient behavior after an ultrafast excitation. In particular, the intraminiband relaxation is studied for different miniband widths below and above the optical phonon energy of GaAs. For minibands wider than this critical value, we find fast relaxation, nearly constant for different excitation intensities, whereas for narrow minibands, a strong temperature and intensity dependence of the relaxation is found. The results are in good agreement with previously published Monte Carlo simulations.
Keywords: superlattice, intraminiband dynamics, miniband relaxation

Publ.-Id: 11131 - Permalink


Synthesis and evaluation in vitro and in vivo of a 11C-labeled cyclooxygenase-2 (COX-2) inhibitor
Wüst, F.; Knieß, T.; Bergmann, R.; Pietzsch, J.;
The radiosynthesis and radiopharmacological evaluation of 1-[11C]methoxy-4-(2-(4-(methanesulfonyl) phenyl)cyclopent-1-enyl)-benzene [11C]5 as novel PET radiotracer for imaging of COX-2 expression is described\. The radiotracer was prepared via O-methylation reaction with [11C]methyl iodide in 19% decay-corrected radiochemical yield at a specific activity of 20–25 GBq/lmol at the end-of-synthesis within 35 min. The radiotracer [11C]5 was evaluated in vitro using various pro-inflammatory and tumor cell lines showing high functional expression of COX-2 at baseline or after induction. In vivo biodistribution of compound [11C]5 was characterized in male Wistar rats. Compound [11C]5 was rapidly metabolized in rat plasma, and more pronounced, in mouse plasma. In vivo kinetics and tumor uptake were demonstrated by dynamic small animal PET studies in a mouse tumor xenograft model. Tumor uptake of radioactivity was clearly visible overtime. However, radioactivity uptake in the tumor could not be blocked by the pre-injection of nonradioactive compound 5. Therefore, it can be concluded that radioactivity uptake in the tumor was not COX-2 mediated.
Keywords: Positron emission tomography; Cyclooxygenase; COX-2 inhibitor; Carbon-11; Inflammation; Cancerogenesis

Publ.-Id: 11130 - Permalink


Förderprogramm Immissions- und Klimaschutz, Bilanz 1999
Maletti, R.; Enkelmann, W.;
Der Bericht enthält die Ergebnisse des Jahres 1999 zu folgenden Fördermaßnahmen des Sächsischen Staatsministeriums für Umwelt und Landwirtschaft:
- Förderprogramm "Vorhaben des Immissions- und Klimaschutzes einschließlich der Nutzung erneuerbarer Energien"
- Sonderprogramm "Hausbrand im grenznahen Raum"
- Sächsische Solarinitiative 1999/2000
Gesondert werden die geförderten Energie-Projekte dargestellt, mit denen Sachsen zur Weltausstellung EXPO 2000 in Hannover vertreten ist.
Die Bearbeitung der Förderprogramme und -projekte erfolgte durch den im Forschungszentrum Rossendorf ansässigen Projektträger Umwelt und Energie.
Keywords: Förderprogramme, Immissions- und Klimaschutz, erneuerbare Energien, Luftreinhaltung, EXPO 2000
  • Other report
    Dresden: Sächsisches Druck- und Verlagshaus, 2000
    36 Seiten

Publ.-Id: 11129 - Permalink


Pattern competition in homogeneously heated fluid layers
Cartland-Glover, G. M.; Generalis, S. C.;
Simulations examining pattern competition have been performed on a horizontal homogeneously heated layer that is bounded by an isothermal plane above an adiabatic plane. Several different circulation patterns arose as the heating regime applied to the horizontal layer was modified. The sequence of the patterns formed as the Grashof number was increased had the following order: laminar, z-axis rolls, squares, hexagons and pentagons, pentagons and then two different square modes of differing orientations. Fourier analysis was used to determine how the key modes interact in the presence of different patterns.
  • Contribution to proceedings
    Proceedings of the 5th European Thermal-Sciences Conference, 18.-22.05.2008, Eindhoven, the Netherlands

Publ.-Id: 11128 - Permalink


Solarinitiative 1999/2000 für sächsische Städte und Gemeinden
Maletti, R.; Voigt, P.;
Die Solarinitiative 1999/2000 ist eine Aktion des Sächsischen Staatsministeriums für Umwelt und Landwirtschaft. Die Initiative verbindet sich mit der bundesweiten Motivationskampagne "Solar - na klar!" des Bundesdeutschen Arbeitskreises für Umweltbewußtes Management e.V. (B.A.U.M.). Das Ziel der beiden Aktionen ist die verstärkte Nutzung der Solarwärme. In Sachsen wurde der Projektträger Umwelt und Energie des Sächsischen Staatsministeriums für Umwelt und Landwirtschaft im Forschungszentrum Rossendorf e.V. mit der Umsetzung der beiden Kampagnen beauftragt.
Keywords: Solarwärme, Solarinitiative, "Solar - na klar!"
  • Lecture (Conference)
    6. Europäische Konferenz "Solarenergie in Architektur und Stadtplanung", 12.-15.09.2000, Bonn, Deutschland

Publ.-Id: 11127 - Permalink


Ergebnisse der staatlichen Förderung von Vorhaben der Errichtung und des Betriebes von kleinen Sonnenkollektoranlagen in Sachsen
Maletti, R.;
Im Beitrag wird ein Überblick über die in den Jahren 1991 bis 1998 in Sachsen errichteten und geförderten kleinen Sonnenkollektoranlagen gegeben. Es wird dargelegt, dass bei Errichtung und Förderung seit 1997 erhöhtes Augenmerk auf Qualität und Effizienz der Anlagen gelegt wird. Des Weiteren wird festgestellt, dass zum Zeitpunkt der Berichterstattung die Solarerträge im Allgemeinen zu niedrig und die daraus resultierenden Wärmepreise zu hoch sind.
Keywords: Solarenergie, Sonnenkollektoranlagen, Anlagenkosten, Förderung, Solarinitiative
  • Contribution to proceedings
    Neuntes Symposium "Thermische Solarenergie", 05.-07.05.1999, Kloster Banz, Staffelstein, Deutschland
    Ergebnisse der staatlichen Förderung von Vorhaben der Errichtung und des Betriebes von kleinen Sonnenkollektoranlagen in Sachsen, 334-340

Publ.-Id: 11126 - Permalink


Fabrication of self-assembled L10 ordered FePt nanoislands by conventional DC magnetron sputtering
von Borany, J.; Cantelli, V.; Christalle, E.; Mücklich, A.; Talut, G.; Grenzer, J.;
L10 ordered, c-axis oriented FePt thin films belong to the most promising ferromagnetic materials for future magnetic storage media. The coercivity of such films can be significantly improved if changing from homogeneous to granular films or even to arrays of FePt nanoislands.
This contribution describes the formation of self-assembled FePt nanoislands at single-crystalline Si(001) or amorphous SiO2/Si substrates after conventional DC magnetron sputtering. FePt is sputtered (0.5 Å/s) from an alloy target at a substrate temperature of approx. 300°C to an equivalent film thickness of 10 nm. The island formation and the low-temperatureL10 ordering are stimulated by an ultrathin Ag buffer layer. The well-separated FePt islands exhibit a quite regular size of typical 20 - 30 nm. X-ray diffraction investigations reveal the existence of L10 ordered FePt grains; a preferred orientation of the grains has been found for the islands deposited at the crystalline substrate. However, it is noteworthy that the island formation is obtained both for crystalline and amorphous substrate surfaces which is of significant practical relevance. The enhanced coercivity of patterned FePt films with respect to homogeneous FePt layers has been confirmed by SQUID measurements. The formation of the nanoisland structure is discussed in terms of the adatom surface mobility, the influence of energetic ions and the ratio of surface to stress-energy during thin film deposition.
Keywords: Magnetic thin films, Sputter deposition, Nanoparticle
  • Poster
    E-MRS 2007 Spring Meeting, 28.05.-01.06.2007, Strasbourg, France

Publ.-Id: 11125 - Permalink


X-ray Absorption Studies of the Interaction between Uranium(VI) and Silica-Gel-Bound Tetraazamacrocycles
Giachini, L.; Faure, S.; Meyer, M.; Nguyen, L. V.; Batifol, B.; Chollet, H.; Guilard, R.; Scheinost, A. C.; Hennig, C.;
The development of separation processes aimed at the selective uptake of toxic metal ions from dilute wastewaters and industrial process streams is of paramount importance for preventing environmental contamination but still remains a challenging scientific task. In that viewpoint, solid-liquid extraction using chelating agents grafted on hydrophilic supports is appealing, mainly because the affinity and selectivity of the scavenging material towards the targeted species can be fine-tuned by molecular design.1,2 We have synthesized a series of N-functionalized tetraazamacrocyclic ligands covalently bound on the surface of amorphous silica-gel beads for the selective extraction of actinides.2,3 In collaboration with the CEA Centre of Valduc, one of these materials has been prepared on a semi-industrial scale (Scheme 1) and used in the final decontamination step of real effluents for removing the residual α-emitters (U, Pu, Am) contained at the sub-ng/L level.
Keywords: macrocycles uranium EXAFS nuclear waste reprocessing
  • Lecture (Conference)
    Actinide XAS 2008, 15.-17.07.2008, Saint-Aubin, France

Publ.-Id: 11124 - Permalink


Spectroscopic Verification of the Mineralogy of an Ultrathin Mineral Film on Depleted Uranium
Baumann, N.; Arnold, T.; Foerstendorf, H.; Read, D.;
The alteration of a depleted uranium (DU) disc in contact with a synthetic pore water, as simulant for fertilized agricultural soil, was studied by exposing the DU to a Ca-phosphate solution (2.5 • 10−3 M Ca, 1 • 10−3 M P). Within 12 months this contact resulted in the formation of a thin film of a secondary uranium mineral on the metallic DU. The reaction product was analysed both with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and infrared spectroscopy (IR). The TRLFS spectra obtained were compared with spectra of natural occurring uranium reference minerals which could have formed under the specified experimental conditions. IR was used as a complementary analytical technique for spectroscopic characterization of the natural minerals and of the unknown mineral film on DU. Both techniques identified the reac-tion product on DU as a U(VI) phosphate phase, but only TRLFS provided its unequivo-cal identification as meta-autunite based on the positions of the fluorescence emission maxima at 487.8, 502.0, 523.6, 547.0, 572.1, and 600.6 nm and two fluorescence lifetimes of 410 ± 15 ns and 3300 ± 310 ns. These findings demonstrate the enhanced performance and sensitivity of the TRLFS technique for mineralogical characterization of thin sur-face films.
  • Environmental Science & Technology 42(2008)22, 8266-8269

Publ.-Id: 11123 - Permalink


Irradiation-induced promigratory phenotype of melanoma cells: role of S100A4-RAGE interaction
Haase, C.; Wolf, S.; Pietzsch, J.;
Metastases are a devastating and debilitating complication of melanoma with a poor prognosis for the patient. The treatment of metastases would be either radiation only or surgery combined with adjunctive postoperative radiation therapy. S100A4 (metastasin) is known to play a direct role in these metastatic processes. We hypothesize that RAGE (receptor for advanced glycation endproducts) is a putative receptor for S100A4. However, the role of S100A4-RAGE interaction in melanoma metastasis is still unclear. The purpose of this study was to find out how mouse B16-F10 melanoma cells restrained to irradiation. Furthermore, we examined changes in the S100A4-RAGE interaction and the ability for migration of irradiated melanoma cells in the presence of tumor associated macrophages. B16-F10 cells were exposed to single dose irradiation (5 Gy, 20 Gy) and mouse RAW 264.7 cells were used as a model for tumor-associated macrophages. S100A4 and RAGE expression in these cells was quantified via real-time RT-PCR and Western-blot analysis three and six days after irradiation. Cell migration was investigated with B16-F10 cells six days after irradiation in a 24-transwell chamber for 16 h and 24 h. Furthermore, migration was influenced by seeding RAW cells as a chemoattracant into the lower compartments and recombinant S100A4 as a stimulus to the upper compartments. After labeling the cells with Calcein-AM the migratory cells were quantified in a standard fluorescence microplate reader. The total number of vital irradiated B16-F10 cells is significantly decreased with increasing dose up to 20 Gy and up to six days, thereby altering morphological appearance. Surprisingly, in surviving B16-F10 cells expression of S100A4 and RAGE significantly increased three and six days after 20 Gy (p<0.05). Furthermore, irradiated B16-F10 cells showed higher migratory activity supposed due to enhanced expression of S100A4 and RAGE. In the presence of RAW cells and/or recombinant S100A4 a further increasing migration activity of irradiated cells (20 Gy) was found. Our findings suggest an association of melanoma and macrophages with alterations of their migratory and invasive activity after irradiation due to a perpetual para-/autocrine expression mechanism of extracellular S100A4 and RAGE, and thereby changing functional properties of melanoma cells towards a promigratory phenotype. This study was supported in part by the Deutsche Forschungsgemeinschaft (grant Pi 304/1-1).
  • Poster
    20th Meeting of the European Association for Cancer Research, 05.-08.07.2008, Lyon, France
  • Abstract in refereed journal
    EJC Supplements 6(2008)9, 21

Publ.-Id: 11122 - Permalink


Characterization of dose-dependent metabolic changes in melanoma cells after irradiation in vitro and in vivo
Mosch, B.; Müller, K.; Pietzsch, J.;
Background:
Although irradiation is a powerful tool for the therapy of solid tumors, single cells often elude this treatment and constitute a basis for recurrence of the primary tumor and formation of metastases. This rises the question if irradiation-dependent metabolic changes could be responsible for a predisposition of certain cells to show enhanced survival and migratory activity. The aim of our study was to investigate metabolic properties of irradiated melanoma cells and thus to develop and validate appropriate in vitro and in vivo models to characterize new radiopharmaceuticals for diagnosis and therapy of metastases and solid tumors.

Materials and methods:
We applied different single-dose X-ray irradiation (1, 2, 5, 7, 10, and 20 Gy) to murine B16-F10 melanoma cells. At particular times we analyzed cell viability, growth properties, clonogenic regrowth capability, cellular proliferation, and expression of cell cycle markers. Furthermore, we analyzed the cellular uptake of the radiotracers 2-[18F]Fluor-2-desoxy-D-glucose and 3-O-Methyl-[18F]fluor-L-DOPA, providing information about the glucose and amino acid metabolism before and after irradiation. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of untreated and irradiated cells to form lung metastases.

Results:
In a dose-dependent manner we detected a decrease in the viability, growth properties and tracer uptake of the melanoma cells. These findings appeared particularly in the period 3 to 6 days after irradiation. In contrast, already one day after irradiation cell cycle analyses showed an increase in the number of G2/M phase cells and the expression of G2-phase markers in irradiated compared to untreated cells. Further we demonstrated an influence of irradiation according to the ability to form lung metastases in the mouse.

Conclusions:
Our results indicate that the combination of different in vitro and in vivo approaches is useful for a detailed characterization of metabolic changes in melanoma cells after irradiation. Additionally, the presented approach gives information about dose-dependent effects. These models enable us to characterize new radiotracers and furthermore, to investigate metabolic effects of applied radiopharmaceuticals in combination with experimental radiation therapy.
  • Poster
    20th Meeting of the European Association for Cancer Research, 05.-08.07.2008, Lyon, France
  • Abstract in refereed journal
    EJC Supplements 6(2008)9, 129

Publ.-Id: 11121 - Permalink


Laser Teilchenbeschleunigung a) Relativistische Optik b) Hochleistingslaser c) Anwendungen d) Status am FZD
Sauerbrey, R.; Schramm, U.;
Tutorial lecture series on laser particle acceleration
  • Invited lecture (Conferences)
    XXXIX Arbeitstreffen Kernphysik, 21.-29.02.2008, Schleching, Germany

Publ.-Id: 11120 - Permalink


Modification of charge compensation in semi-insulating semiconductors by high energy light ion irradiation
Kabiraj, D.; Grötzschel, R.; Ghosh, S.;
High energy light ions have been used to engineer the electrical properties of semi-insulating InP and GaAs by creation and annihilation of native defects. Due to light mass, high energy ions lose most of their energy during flight inside the material by electronic excitation, which also modifies the charge states of the defect. Imbalance in charge compensation caused by irradiation induced defect engineering results in the modification of resistivity of the semi-insulating samples. The activation energies of the defect levels responsible for the modified resistivity have been estimated from the measurement of thermally activated currents. It is shown that the modified charge compensation is due to annihilation and/or creation of native defects depending on the material (GaAs or InP) and the fluence of irradiated ions. It has also been observed that annealing does not have any effect on modified compensation in InP, but in the case of GaAs, compensation recovers after thermal annealing.
Keywords: Semi-insulating semiconductors; High energy ion irradiation

Publ.-Id: 11119 - Permalink


Zur Bestimmung von Reaktivitätswerten bei Störungsmessungen mit Incore-Detektoren an einem WWER-1000 des KKW Saporoshje
Maletti, R.;
Zur systematischen Untersuchung der Ortseffekte bei Reaktivitätsmessungen können die in der Spaltzone von Leistungsreaktoren vorhandenen Elektronen-Emissions-Detektoren mit Rhodium-Emitter genutzt werden. Im vorliegenden Beitrag werden Versuchsdurchführung, Messanordnung und Verfahren der Signalbehandlung vorgestellt, die die gleichzeitige Messung des Neutronenflussdichteverhaltens an nahezu 100 Detektorpositionen gestatten. Im Artikel werden Ergebnisse von erstmalig an einem Reaktor des Typs WWER-1000 vorgenommenen Reaktivitätsstörungsmessungen genannt: Die Ortseffekte äußern sich derart, dass bei ausgeführten Änderungen der Reaktorleistung von etwa 2% die Incore-Detektoren Neutronenflussdichteänderungen bis maximal 20% registrieren, wobei die größten Änderungen in Nähe der Störzentren auftreten. Durch sogenannte Kanalreaktivitätsmessungen kann der Einfluss der Ortseffekte auf eine mit systematischen Fehlern behaftete Ermittlung von Reaktivitätswerten bzw. wichtigen reaktorphysikalischen Kenngrößen weitestgehend eliminiert werden. Die anhand der Messergebnisse getroffenen Aussagen werden durch vergleichende Berechnungen zur dreidimensionalen Reaktordynamik bekräftigt.
Keywords: Reactivity parameters, perturbation measurements, in-core detectors, neutron flux behaviour, space dependence, channel reactivity measurements, VVER-1000, NPP Saporoshje
  • Other report
    ZfK Rossendorf bei Dresden: ZfK-Report 716, 1990
    22 Seiten

Publ.-Id: 11117 - Permalink


Hydrogen, oxygen and carbon losses during 15N bombardment of PMMA layers
Rudolph, W.; Grambole, D.; Groetzschel, R.; Heiser, C.; Herrmann, F.; Neelmeijer, C.; Knothe, P.;
We have studied the behaviour of thin PMMA layers during high energy 15N irradiation. Employing the 1H(15N, αγ)12C and 12C(d, p)13C reactions after 15N preirradiation we determined the total energy loss of 15N ions as well as the hydrogen, carbon, and oxygen contributions in dependence upon the 15N fluence φ. Due to release effects the energy losses of the 15N ions within the PMMA films are reduced to about 0.3 of the initial values at φ = 5 × 1014 cm-2. At fluences φ > 2 × 1014 cm-2 the (oxygen plus carbon) contribution becomes constant and the change of the energy loss can be explained by hydrogen release alone.
  • Nuclear Instruments and Methods in Physics Research B 33(1988), 803-807

Publ.-Id: 11116 - Permalink


Experimentelle Untersuchungen zur Ortsabhängigkeit bei Reaktivitäts-Störungsmessungen
Maletti, R.; Ziegenbein, D.; Kröger, J.;
Mit der vorliegenden Arbeit werden erste systematische experimentelle Untersuchungen zur Ortsabhängigkeit von dynamischen Reaktivitätsmessungen an Leistungsreaktoren des Typs WWER vorgelegt und mit den Ergebnissen theoretischer Untersuchungen verglichen. Es wird gezeigt, dass die durch Simulation mit dem eindimensionalen Programm DYNAMIC erhaltenen theoretischen Ergebnisse das charakteristische Verhalten in Bezug auf die axiale Ortsabhängigkeit der gemessenen Parameter richtig widergeben. Insbesondere wird die These gestützt, dass im Flussmaximum in guter Näherung das dem Einpunktmodel der Neutronenkinetik entsprechende Verhalten gemessen wird.
Keywords: Rheinsberg akw1 reactor, reactor kinetics, disturbances, space dependence, control rod worths, power coefficient, one-dimensional calculations
  • Kernenergie 23(1980)11, 380-383

Publ.-Id: 11115 - Permalink


Compositional Changes of PMMA Layers during 15N Bombardment
Rudolph, W.; Grambole, D.; Heiser, C.; Herrmann, F.; Neelmeijer, C.;
The behaviour is investigated of thin PMMA films during 15N2+ ion bombardment at EN = = 6.50 MeV. Using the 1H(15N, alpha gamma)12C and 12C, 16O(d, p) reactions the hydrogen, carbon, and oxygen contents of the layers are measured in dependence on the 15N2+ ion fluence. Strong losses of all three elements are observed and a dependence of the film composition on the nitrogen ion fluence.
  • Physica Status Solidi (A) 112(1989), 765-768

Publ.-Id: 11114 - Permalink


Space Dependence of Reactivity Parameters on Reactor Dynamic Perturbation Measurements
Maletti, R.; Ziegenbein, D.;
Practical application of reactor-dynamic perturbation measurements for on-power determination of differential reactivity weight of control rods and power coefficient of reactivity has shown a significant dependence of parameters on the position of outcore detectors. The space dependence of neutron flux signal in the core of a VVER-440-type reactor was measured by means of 60 self-powered neutron detectors. The greatest neutron flux alterations are located close to moved control rods and in height of the perturbation position. By means of computations detector positions can be found in the core in which the one-point model is almost valid.
Keywords: Reactor-dynamic measurements, reactivity parameters, neutron flux behaviour, space dependence
  • Contribution to proceedings
    IAEA/NPPCI Specialists' Meeting on "New Instrumentation of Water Cooled Reactors", 23.-25.04.1985, Dresden, DDR
    Space Dependence of Reactivity Parameters on Reactor Dynamic Perturbation Measurements

Publ.-Id: 11113 - Permalink


The influence of iron, fluorine and boron implantation on the magnetic properties of graphite
Höhne, R.; Esquinazi, P.; Heera, V.; Weishart, H.; Setzer, A.; Spemann, D.;
Iron, fluorine and boron ions were implanted into highly oriented pyrolytic graphite (HOPG). The samples were characterized before and after ion implantation as well as after heat treatments in vacuum by measurements of the magnetic moment and element analysis.
Whereas the main magnetic contribution remains diamagnetic the paramagnetic one clearly increases with implantations and correlates with the amount of implanted ions. It is shown that a large part of the paramagnetic contribution is caused by the structural disorder created by particle bombardment using iron, fluorine or boron. All implanted HOPG samples show practically no change of the small ferromagnetic signal observed in their virgin state. No particular influence of iron on the ferromagnetic properties of HOPG is observed, up to 4000 mg/g Fe-concentration in the implanted region. For comparison, ferrous sulphates were added to ultra-clean graphite powder. This iron addition increases the number of paramagnetic spins proportional to the iron content in the untreated samples. In heat-treated samples however, a clear ferromagnetic behaviour is observed due to the formation of a ferromagnetic iron compound.
Keywords: graphite, ion implantation, magnetism

Publ.-Id: 11112 - Permalink


Entwicklung und Validierung des Druckstoßprogramms DYVRO Mod. 3
Neuhaus, T.; Schaffrath, A.; Ronneberger, R.; Altstadt, E.;
Druckstöße in Rohrleitungssystemen entstehen, wenn eine Flüssigkeit oder ein Gas durch das plötzliche Öffnen oder Schließen einer Armatur, die Änderung der Drehzahl einer Pumpe, in Folge von Rohrleitungsbrüchen usw. beschleunigt oder abgebremst wird. Hierbei entstehen Druckwellen, die erhöhte Innendrücke verbunden mit mechanischen Spannungen in den Rohrleitungswänden sowie zeitabhängige axiale Kräfte auf Rohrleitungen und deren Halterungen hervorrufen können. Durch Reflexionen der Druckwellen können Unterdrücke entstehen, die bei Unterschreiten des lokalen Sättigungsdrucks zur Bildung von Dampfblasen (Kavitation) führen können. Bei dem Zusammenfall der Dampfblasen können weitere, sekundäre Druckstöße auftreten, die die primären Druckwellen überlagern. Die Ausbreitungsgeschwindigkeit von Druckwellen hängt zum einen von den Eigenschaften des Fluids (speziell dessen Kompressibilität und Dichte) und zum anderen von den mechanischen Eigenschaften des Rohrleitungssystems (Elastizitätsmodul und Querkontraktionszahl) sowie dessen Geometrie (Durchmesser des Rohrs und Wanddicke) ab. Druckstöße sind oftmals die Ursache für Beschädigungen an Rohrleitungen und Rohrleitungshalterungen und stellen daher für viele verfahrenstechnische Anlagen ein Problem dar.

Die TÜV NORD SysTec GmbH & Co. KG beschäftigt das Druckstoßprogramm DYVRO entwickelt und qualifiziert. Der vorliegende Beitrag beschreibt die nun hinsichtlich des verwendeten partiellen Differentialgleichungssystems und der eingesetzten Numerik überarbeitete Programmversion DYVRO Mod. 3 und deren Validierung anhand repräsentativer Experimente (u.a. anhand des Simpson-Experiments sowie anhand eines Versuches an der Cold Water Hammer Test Facility). Die Ergebnisse der Validierungsrechnungen werden anschließend mit eigenen oder fremden Rechnungen mit Systemcodes (hier ATHLET und RELAP ) sowie dem Druckstoßprogramm WAHA verglichen. Bei diesen Vergleichen werden u.a. die Ergebnisse des im 5. EU-Rahmenprogramm geförderten Forschungsvorhabens WAHALOADS mit einbezogen. Die Vergleiche zeigen eine sehr gute Übereinstimmung der Rechenergebnisse von DYVRO mit den Experimenten sowie den Ergebnissen des WAHA-Codes. Die Ergebnisse der Druckstoßcodes WAHA und DYVRO sind – sowohl im einphasigen als auch im zweiphasigen Bereich - deutlich besser als die der Systemcodes.
Keywords: Water hammer, pressure wave, pipe systems
  • atw - International Journal for Nuclear Power (2008)2

Publ.-Id: 11111 - Permalink


Atomistic simulation of amorphous germanium
Gabriel, A.; Posselt, M.;
Electrical doping of Ge is usually performed by ion implantation and subsequent annealing. In many cases ion bombardment leads to formation of an amorphous layer. During annealing the layer recrystallizes by solid-phase epitaxial regrowth. In order to investigate this process by classical molecular dynamics simulations, first of all amorphous Ge with realistic properties must be prepared. This is the subject of the present work. The atomistic simulations use the Stillinger-Weber interatomic potential with a parameter set that yields correct or reasonable structural, thermodynamic and defect properties of diamond-structure Ge. In the first simulation step liquid Ge is prepared. Then, the system is cooled down slowly to 300 K using the method of Luedtke and Landman which was applied to simulate amorphous silicon. Finally, an equilibration at 300 K and zero pressure is performed. The characterization of amorphous Ge obtained in this manner includes density and cohesive energy, radial distribution function and static structure factor, coordination number, bond-angle distribution, distribution of interatomic distances as well as melting temperature and heat of fusion. The simulation results show very good agreement with experimental data and are consistent with previous theoretical investigations.
Keywords: Computer simulation, amorphous Germanium
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11110 - Permalink


Discontinuity of capacitance at the onset of surface superconductivity
Morawetz, K.; Lipavsky, P.; Mares, J. J.;
The effect of the magnetic field on a capacitor with a superconducting electrode is studied within the Ginzburg-Landau (GL) approach. It is shown that the capacitance has a discontinuity at the onset of the surface superconductivity B_{\rm c3} which is expressed as a discontinuity in the penetration depth of the electric field into metals. Estimates show that this discontinuity is observable with recent bridges for both conventional and high-T_{\rm c} superconductors of the type-II.
  • Open Access LogoNew Journal of Physics 11(2009)023032, 1-8

Publ.-Id: 11109 - Permalink


THz detection with scalable photoconductive antennas
Peter, F.; Winnerl, S.; Nitsche, S.; Dreyhaupt, A.; Schneider, H.; Helm, M.; Köhler, K.;
We present studies on nonresonant photoconductive THz detectors and emitters. Our system consists of a large-area terahertz detector based on an interdigitated electrode structure and an emitter with similar electrode geometry [1]. Emitters based on this concept stand out due to their high efficiency for conversion of near-infrared radiation into far-infrared radiation. The main advantage of the scalable antennas as compared to conventional photoconductive antennas is that they do not require tight focusing of the THz and gating beams. While the emitter is fabricated on semi-insulating GaAs, we compare different detection antennas based on ion-implanted and low temperature grown (LT) GaAs, respectively. We discuss which material properties affect the performance and noise level of our system and discuss the role of the carrier lifetime upon the measured THz signal. The best signal-tonoise ratios are found for N+ dual energy implantations (0.4 MeV and 0.9 MeV) with doses in the 1013 cm−2 range and for (LT) GaAs.
[1] F.Peter, S.Winnerl, S. Nitsche, A. Dreyhaupt, H. Schneider, M.Helm, Appl. Phys. Lett. 91, 081109 (2007)
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 11108 - Permalink


Fe-implantation for rear-facet coatings of InP-based quantum cascade lasers
Wienold, M.; Semtsiv, M. P.; Dressler, S.; Masselink, W. T.; Potzger, K.; Winnerl, S.; Helm, M.;
Fe-implantation is used to create a high-resistivity layer at the rear facet of an InP-based quantum cascade laser (lambda = 3.9 mu m), subsequently coated with a metallisation of Cr (5 nm) and Au (200 nm). The coatings lead to a 3.7-fold increase of front-facet power and a 20–30% reduction in threshold current density compared to uncoated lasers.
Keywords: quantum cascade laser, ion implantation
  • Electronics Letters 44(2008), 293-284

Publ.-Id: 11107 - Permalink


Two-color pump-probe spectroscopy of electron dynamics in superlattices
Wagner, M.; Stehr, D.; Schneider, H.; Winnerl, S.; Helm, M.; Andrews, M.; Roch, T.; Strasser, G.;
We report on two-color pump-probe measurements to investigate the intraminiband dynamics of doped GaAs/AlGaAs SLs with different miniband widths smaller or larger than the optical phonon energy. We have analyzed the cooling behaviour at low temperature. We employed infrared pulses from a free-electron laser to excite electrons to the upper miniband at the center of the SL mini-Brillouin zone and the interminiband transition was probed at the zone edge with broadband THz pulses. After relaxation to the ground miniband the electronic distribution is heated up which results in more absorption at the zone edge. When the distribution cools down this induced absorption signal decays, leading to decay times of 40-50 ps for a miniband width smaller and 3.5 ps for a width larger than the optical phonon energy. This difference in time constants can be explained by the new relaxation channel through polar optical phonons. Additionally we performed measurements at room temperature where the lower miniband is already occupied at the zone edge. Thus no induced absorption and fast decay times are observed.
Keywords: pump-probe, intraminiband dynamics, superlattice, cooling
  • Lecture (Conference)
    72. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.08, Berlin, Germany

Publ.-Id: 11106 - Permalink


Effect of isothermal annealing on electrical and optical properties of Al-doped ZnO films
Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Möller, W.;
The aim of present work is to investigate mechanisms of Al incorporation and its effects on electrical and optical properties of ZnO
films. Highly c-axis textured polycrystalline thin films of insulating ZnO were implanted by 110 keV Al+ ions and then annealed at 520 °C. The films were characterized by Hall effect, four-point probe, spectroscopic ellipsometry and x-ray diffraction techniques. The films are
nanocrystalline in as-implanted state. Their dielectric function shows broadened features near the band gap energy and increased, compared
to unimplanted films, absorption in the near IR and visible spectral range. If the implantation dose is below 2x10^16 cm−2, the free electron
density, Ne, increases after annealing and the film resistivity decreases monotonously during annealing. If the dose is above 2x10^16 cm−2, Ne
decreases after annealing while film resistivity reaches minimum and then increases during the treatment. The annealing decreases optical
absorption in the near IR and visible and improves film crystallinity. The behavior of the film electrical properties may be explained by the
interplay between oxygen vacancies formation and Al donor activation.
Keywords: Al-doped ZnO, ion implantation, reactive pulsed magnetron sputtering, spectroscopic ellipsometry
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11105 - Permalink


Gültigkeitsprüfung von Prozeßinformationen mittels analytischer Redundanz und Paritätsraumdarstellung
Maletti, R.; Stein, H.;
Ständig steigende Anforderungen bezüglich optimaler Prozeßführung und Gewährleistung hoher Anlagensicherheit erfordern in zunehmendem Maße den erweiterten Einsatz rechnergestützter Beratungs- und Diagnosesysteme. Mit dem Beitrag wird der internationale Stand auf dem Gebiet der Gültigkeitsprüfung von Sensorsignalen mittels analytischer Redundanz und Parity-space-Darstellung aufgearbeitet, insbesondere wird das Parity-space-Verfahren in geschlossener mathematischer Form dargeboten.
Keywords: Signaldiagnose, Gültigkeitsprüfung von Sensorsignalen, Sensorvalidierung, Parity-space-Verfahren; sensor validation, parity space technique
  • Messen, Steuern, Regeln 32(1989)9, msr 8855

Publ.-Id: 11104 - Permalink


Die Benutzung eines modifizierten Simplex-Algorithmus zur Verfahrensoptimierung in der Mikroelektronik
Maletti, R.;
Im Artikel werden Anwendungsmöglichkeiten eines Simplex-Verfahrens zur Prozessoptimierung bei der Herstellung mikroelektronischer Bauelemente gezeigt. Anhand ausgewählter Beispiele der Plasmaätztechnologie wird die Einsatzbreite für die optimale Versuchsplanung, die Bestimmung von Modellgrößen für Simulationsrechnungen und die Ermittlung von Parametern der in situ Prozesskontrolle angedeutet.
Keywords: Simplexmethode, Versuchsplanung, Optimierung, Simulation, Modellierung, Mikroelektronik, Dünnschichttechnik, Plasmaätzen, Substratgrabenätzen, Laserinterferometer; simplex-method, experimental planning, optimization, simulation, modelling, microelectronics, thin-film technique, plasma etching, trench etching, laser interferometer
  • Wissenschaftliche Zeitschrift der Technischen Universität Dresden 37(1988)1, 279-282

Publ.-Id: 11103 - Permalink


Surface deformation caused by the Abrikosov vortex lattice
Lipavský, P.; Morawetz, K.; Kolavcek, J.; Brandt, E. H.;
In superconductors penetrated by Abrikosov vortices the magnetic pressure and the inhomogeneous condensate density induce a deformation of the ionic lattice. We calculate how this deformation corrugates the surface of a semi-infinite sample. The effect of the surface dipole is included.
  • Physical Review B 77(2008), 184509-1-184509-7

Downloads:

Publ.-Id: 11102 - Permalink


Thermal decomposition and new luminescence bands in wet, dry, and additional oxygen implanted silica layers
Fitting, H.-J.; Salh, R.; Schmidt, B.;
Wet and dry silica oxide layers have been treated thermally up to Ta = 1300 °C and were investigated by cathodoluminescence (CL) spectroscopy. Whereas the dry oxides after high temperature treatment show an increase of the yellow–red spectra region, contrary, in wet oxides the UV–blue region is enhanced. Even a new strong band in the near-UV region (NV) at 330 nm (3.76 eV) is found for wet oxides at liquid nitrogen temperature (LNT), but much broader and with lower intensity for room temperature (RT) in a triple band structure UV: 290 nm, NV: 330 nm, and V: 400 nm. These violet bands should be associated with a thermally decomposed and rapidly cooled-down silica network in presence of OH groups or even dissociated oxygen. Additional oxygen implantation into dry silica with high doses up to 1017 ions/cm2 and high thermal treatment T > 1100 °C leads as well to enhanced UV–NV–V luminescence emission bands supporting the fact that oxygen and structural decomposition play a decisive role in formation of near-UV luminescent defects in silica.
Keywords: Glass formation; Glass transition; Hydrogen in glass; Radiation effects; SEM S100; Optical properties; Luminescence; Silica; Defects; Short-range order; Thermal properties; Viscosity and relaxation; Structural relaxation

Publ.-Id: 11101 - Permalink


Room temperature photoluminescence from the amorphous Si structure generated under keV Ar-ion- induced surface rippling condition
Chini, T. K.; Datta, P. D.; Facsko, S.; Mücklich, A.;
We observe room temperature (RT) visible and infrared (IR) photoluminescence (PL) bands peaked around 680 and 1020 nm, respectively, from a silicon (Si) surface amorphized and patterned with ripples by 60 keV Ar+ bombardment at 60 degrees angle of ion incidence. However, the Si surface amorphized but not patterned under normal bombardment (0 degrees angle of ion incidence) condition shows a drastic reduction in the intensity of the visible PL along with the complete suppression of IR emission. The present work demonstrates that Ar ion irradiation at rippling condition may yield a porouslike light emitting amorphous silicon (a-Si) nanostructure.
Keywords: Si, Photoluminescence, Ion irradiation
  • Applied Physics Letters 92(2008)10, 101919

Publ.-Id: 11100 - Permalink


Aligned Silver Nanoparticles on Rippled Silicon Templates Exhibiting Anisotropic Plasmon Absorption
Oates, T. W. H.; Keller, A.; Facsko, S.; Mücklich, A.;
Aligned silver nanoparticles, grown by combining two simple bottom-up techniques, are reported. Physical vapor-deposited silver adatoms are shown to form nanoparticles preferentially in the valleys of rippled silicon templates prepared by low-energy ion bombardment. A 35-nm ripple periodicity produced highly aligned structures with a 0.21 eV polarization-dependent shift in the plasmon resonance peak. The speed and simplicity of the method is viable for cost-effective, large-scale production of mesoscale aligned nanostructures with adjustable periodicity.
Keywords: Self-organization, Self-alignment , Plasmon coupling, SERS, Island films

Publ.-Id: 11099 - Permalink


Investigation of planar channeling radiation on diamond and quartz crystals at electron energies between 14 and 34 MeV and probing the influence of ultrasonic waves on channeling radiation
Azadegan, B.;
Theoretical investigations and measurements of planar channeling radiation out off different crystallografic planes of diamond and quartz single crystalls at electron energies between 14 and 34 MeV have been performed. Based upon the obtained results a novel intense X-ray source has been designed and came into operation at ELBE. First experimental investigations of the influence of ultrasonic waves on the channeling radiation properties have been carried out on quartz crystalls.
Keywords: channeling radiation, diamond, quartz, ultrasound
  • Doctoral thesis
    Technische Universität Dresden, 2007
    110 Seiten

Publ.-Id: 11098 - Permalink


Comparative small-angle neutron scattering study of neutron-irradiated Fe, Fe-Cu, Fe-Ni-Mn and Fe-Ni-Mn-Cu
Bergner, F.; Lambrecht, M.; Ulbricht, A.; Almazouzi, A.;
Irradiation-induced damage in reactor pressure vessel steels covers a multitude of different features at the nanometer size scale. The nature, formation kinetics and relative importance of these features are not yet well understood in detail. It also turned out that there is no single experimental technique capable of closing all the remaining gaps. The present approach is based on the idea that significant progress can be achieved by investigating the same set of neutron irradiated model alloys of increasing complexity with several experimental techniques including transmission electron microscopy (TEM), atom probe tomography (APT), positron annihilation spectroscopy (PAS) and small-angle neutron scattering (SANS). The aim is to explore both complementarity and overlaps of the information gained from individual techniques and to close gaps by introducing proper models. In the present paper the results obtained by means of SANS are reported, self-consistent interpretation is given and the results are qualified for the discussion in combination with the other experimental techniques to be given in separate papers.

Publ.-Id: 11097 - Permalink


Factfile: S100A12
Pietzsch, J.;
S100A12 is a member of the S100 family of EF-hand calcium-binding proteins. Human S100A12 is predominantly expressed and secreted by neutrophil granulocytes and, therefore, has been assigned to the S100 protein subfamily of calgranulins. It is part of the innate immune response and linked to certain autoimmune reactions. Human S100A12 is markedly overexpressed in inflammatory compartments, and elevated serum levels of S100A12 are found in patients suffering from metabolic, neurodegenerative, inflammatory and neoplastic disorders. In this regard, interaction of calcium-activated S100A12 with the receptor for advanced glycation endproducts (RAGE) plays a central pathogenetic role.
  • Open Access LogoCalcium Binding Proteins 3(2008), 18-21

Publ.-Id: 11096 - Permalink


Correlates of local cerebral blood flow (CBF) in normal pressure hydrocephalus patients before and after shunting—A retrospective analysis of [15O]H2O PET-CBF studies in 65 patients
Klinge, P. M.; Brooks, D. J.; Samii, A.; Weckesser, E.; van den Hoff, J.; Fricke, H.; Brinker, T.; Knapp, W. H.; Berding, G.;
Objectives:
Findings in local cerebral blood flow (rCBF) in Normal pressure hydrocephalus (NPH) have always been challenged by the variable and inconsistent relation to clinical symptoms before and after shunt treatment. [15O]H2O PET data from a consecutive cohort of 65 idiopathic NPH patients were retrospectively analyzed questioning whether the functional status before and after shunt treatment might correlate with local blood flow.

Patients and methods
Using statistical parametric mapping (SPM99, Wellcome Department of Cognitive Neurology, London), the [15O]H2O uptake was correlated with the preoperative clinical scores, graded according to a modified Stein and Langfitt score. Furthermore, differences in the uptake in the pre-and post-shunt treatment study after seven to 10 days in patients with and without clinical improvement were studied.

Results
A higher clinical score significantly correlated with a reduced tracer uptake in mesial frontal (k = 1239 voxel, Z = 4.41) and anterior temporal (k = 469, Z = 4.07) areas. In the mesial frontal areas, tracer uptake showed significant reciprocal changes in the clinically improved vs. the unimproved patients.

Conclusion
Matched with the existing literature, the regional blood flow alterations are suggested relevant to the NPH syndrome and to post-treatment functional changes. The present rCBF findings warrant prospective studies on the accuracy of neuroimaging studies as they may provide a more specific insight into disease mechanisms.
Keywords: Hydrocephalus; NPH; PET; Blood flow; Metabolism; Imaging

Publ.-Id: 11095 - Permalink


PET und Bestrahlungsplanung - technische Aspekten / PET and Radiation Treatment Planning - Technical Aspects
Wolf, U.; Hofheinz, F.; Oehme, L.; van den Hoff, J.;
Zusammenfassung

Die Integration der PET in die Bestrahlungsplanung wirft verschiedene technische Probleme auf, welche zurzeit überwiegend noch nicht zufriedenstellend gelöst sind, gegenwärtig aber intensiv untersucht werden. Erste Lösungen für Teilaspekte wie etwa die geometrisch korrekte ROI-Abgrenzung und die Übersetzung dieser Information in DICOM-RT-Structure-Sets für den Import in die Bestrahlungsplanungssysteme existieren mittlerweile, sind aber noch nicht allgemein verfügbar. Es ist jedoch zu erwarten, dass sich die dynamische technische Entwicklung in den nächsten Jahren fortsetzen und zu einer Lösung der noch bestehenden Probleme führen wird.


Abstract

Integration of PET into radiation treatment planning causes several technical problems, which have not yet been solved satisfactory up to now, but which are currently investigated intensively. First solutions of some aspects such as geometrically correct ROI delineation and the translation of this information into DICOM-RT Structure Sets for import into the radiation treatment planning systems have already been developed, but are not yet generally available. It is to be expected, however, that the dynamic technical development will continue in the next years and lead to solution of the currently persisting problems.
Keywords: PET, CT - radiation treatment planning - DICOM-RT - 3D-ROIs - volumetry

Publ.-Id: 11094 - Permalink


PET in der Strahlentherapie: Perspektiven / PET in Radiation Oncology - Perspectives
Baumann, M.; Beuthien-Baumann, B.; Zips, D.;
Zusammenfassung
Die Positronen-Emissions-Tomografie (PET) hat einen wichtigen Stellenwert in der modernen Strahlentherapie erlangt. Die Integration der funktionellen PET-Daten in die Bestrahlungsplanung wurde durch die Fusion von CT und PET in einem Gerät wesentlich erleichtert. Entwicklungs- und Optimierungsbedarf besteht jedoch in der Definition der Tumorgrenzen im PET und im Umgang mit Atembewegungen. Neben dem am häufigsten zur Anwendung kommenden Radiopharmakon 18F-Fluordesoxyglukose (FDG) sind die Anwendung von Hypoxiemarkern und Radiotracerentwicklungen für die Visualisierung anderer definierter radiobiologischer Resistenzmechanismen wünschenswert.

Abstract
Positron emission tomography (PET) has evolved as an important tool in modern radiotherapy. Integration of functional PET data into radiation treatment planning is facilitated due to PET-CT scanner, optimizing data fusion. Optimization of definition of tumour borders and reduction of movement artifacts is warranted. Besides the application of 18F-fluorodeoxyglucose (FDG) utilization of tracers visualizing hypoxia and the development of novel tracers depicting other defined biological mechanisms of radioresistance is a promising avenue for future research.
Keywords: PET, CT - FDG - radiation treatment planning - radiation biology - hypoxia - theragnostics

Publ.-Id: 11093 - Permalink


Hydrolysis and dimerization of Th4+ ion
Tsushima, S.;
Hydrolysis of Th4+ in aqueous solution was studied by density functional theory (DFT) calculations. First, stable coordination numbers (CNs) of Th4+ hydrolysis products were studied systematically, and it was found that the CN significantly decreases as a stepwise hydrolysis reaction proceeds. The fourth hydrolysis product Th(OH)40 has CN 6 with an octahedron coordination. Th(OH)40 can readily form a dimer complex Th2(OH)80 via a Th-OH-Th bridging through an exergonic reaction with a Gibbs energy change of -24.0 kJ/mol. Consequently, dimerization inhibits Th(OH)40 to stay as stable aqueous species. The calculated result is in agreement with the fact that there is no direct evidence to confirm the presence of Th(OH)40 while oligomeric species such as Th4(OH)160 are presumably present. Similar calculations on the Th4+ disulfato complex reveal that the CN and the average Th-O distance of Th(SO4)20 remain almost the same as those in the Th4+ aquo ion, which is also in agreement with experimental data.
Keywords: Hydrolysis, tetravalent, actinide, thorium, quantum chemistry

Publ.-Id: 11092 - Permalink


Ion-induced nanopatterns on silicon: experiment, theory, and application
Keller, A.; Facsko, S.; Möller, W.;
It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
In this talk, recent experimental results on the evolution of ripple morphologies on Si(100) surfaces during high-fluence ion sputtering will be presented and compared to numerical integrations of the damped Kuramoto-Sivashinsky equation. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.
  • Lecture (others)
    Seminar, 15.02.2008, Madrid, Spain
  • Lecture (others)
    Seminar, 27.02.2008, Madrid, Spain

Publ.-Id: 11091 - Permalink


Medical Physics Activities in the Integrated EU Project BioCare
Möckel, D.;
Presentation of the Medical Physics Activities in the Integrated EU Project BioCare
  • Invited lecture (Conferences)
    3rd Meeting of the Scientific Advisory Board of OncoRay, 28.02.2008, Dresden, Deutschland

Publ.-Id: 11090 - Permalink


The interplay of PVD growth parameter and nanostructuring of C:Co and C:V nanocomposites
Berndt, M.; Abrasonis, G.; Krause, M.; Mücklich, A.; Kolitsch, A.; Möller, W.;
The growth regimes of C:V and C:Co nanocomposite thin films (metal content of ~15 and 30 at.%) grown by ion beam co-sputtering in the temperature range of RT-500°C are investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy at two excitation wavelengths (532 nm and 785 nm) have been used to characterize the microstructure of carbon and metal coexisting constituents of the nanocomposites. In order to reveal the influence of the transition metal on the encapsulating matrix, pure carbon films were deposited at the same temperatures.
C:Co and C:V nanocomposites exhibit a fine-grained structure at deposition temperatures below 300°C. At higher temperatures C:Co films tend to form nanocolumns, whereas the globular structure is preserved for C:V. X-ray patterns show low degree of crystallinity of the nanoparticles in C:Co and C:V composites.
Raman spectroscopy results show that the presence of metal significantly enhances the formation of aromatic clusters. This enhancement occurs independently on metal nanoparticle size, shape and phase.
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.2.2008, Berlin, Germany

Publ.-Id: 11089 - Permalink


Room temperature ferromagnetism in ZnO films due to defects
Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Setzer, A.; Esquinazi, P.; Meinecke, C.; Grundmann, M.;
ZnO films were prepared by pulsed laser deposition on a-plane sapphire substrates under N2 atmosphere. Ferromagnetic loops were obtained with the SQUID at room temperature, which indicate a Curie temperature much above room temperature. No clear ferromagnetism was observed in intentionally Cu-doped ZnO films. This excludes that Cu doping into ZnO plays a key role in tuning the ferromagnetism in ZnO. 8.8 % negative magnetoresistance probed at 5 K at 60 kOe on ferromagnetic ZnO proves the lack of s-d exchange interaction. Anomalous Hall effect (AHE) was observed in ferromagnetic ZnO as well as in non-ferromagnetic Cu-doped ZnO films, indicating that AHE does not uniquely prove ferromagnetism. The observed ferromagnetism in ZnO is attributed to intrinsic defects.
Keywords: diluted magnetic semiconductor, ZnO, ferromagnetism, anomalous Hall effect, magnetoresistance

Publ.-Id: 11088 - Permalink


Enzymatic properties of an ecto-nucleoside triphosphate diphosphohydrolase from Legionella pneumophila; substrate specificity and requirement for virulence
Sansom, F. M.; Riedmaier, P.; Newton, H. J.; Dunstone, M. A.; Müller, C. E.; Stephan, H.; Byres, E.; Beddoe, T.; Rossjohn, J.; Cowan, P. J.; D'Apice, A. J. F.; Robson, S. C.; Hartland, E. L.;
Legionella pneumophila is the predominant cause of Legionnaires’ disease, a severe and potentially fatal form of pneumonia. Recently, we identified an ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) from L. pneumophila, termed Lpg1905, which enhances intracellular replication of L. pneumophila in eukaryotic cells. Lpg1905 is the first prokaryotic member of the CD39/NTPDase1 family of enzymes that are characterized by the presence of five apyrase-conserved regions (ACR) and the ability to hydrolyse nucleoside tri- and diphosphates. Here we examined the substrate specificity of Lpg1905 and showed that apart from ATP and ADP, the enzyme catalysed the hydrolysis of GTP and GDP but had limited activity against CTP, CDP, UTP and UDP. Based on amino acid residues conserved in the ACR regions of eukaryotic NTPDases, we generated five site directed mutants, Lpg1905E159A, R122A, N168A, Q193A and W384A. While the mutations, E159A, R122A, Q193A and W384A abrogated activity completely, N168A resulted in decreased activity because of less affinity for nucleotides. When introduced into the lpg1905 mutant strain of L. pneumophila, only N168A (and not the isoforms E159A, R122A, Q193A and W384A) partially restored the ability of L. pneumophila to replicate in THP-1 macrophages. Following intratracheal inoculation of A/J mice, none of the Lpg1905E159A, R122A, Q193A, W384A or N168A isoforms were able to restore virulence to an lpg1905 mutant during lung infection, thereby demonstrating the importance of NTPDase activity to L. pneumophila infection. In addition, the kinetic studies undertaken here demonstrated important differences to mammalian NTPDases, which may be exploited in the design of novel inhibitory compounds to microbial NTPDases for use as anti-infective agents.
  • Journal of Biological Chemistry 283(2008)19, 12909-12918

Publ.-Id: 11087 - Permalink


Magnetic properties of amorphous, p-type conducting CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2
Xu, Q.; Schmidt, H.; Zhou, S.; Potzger, K.; Helm, M.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Grundmann, M.;
CuCr0.95Mg0.05O2 has been reported to be p-type oxide semiconductor with the highest conductivity determined by the Seebeck effect [1]. We prepared conductive, polycrystalline and amorphous CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films on a-plane sapphire substrates by pulsed laser deposition under different O2 partial pressure and substrate temperature. Hall measurements were performed to study the majority carrier type in these films. The polycrystalline CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films are n-type conducting up to 290 K, while in amorphous CuCr0.95Mg0.05O2 and CuCr0.93Mg0.05Mn0.02O2 films the type of majority charge carriers changes from n-type to p-type around 270 K. Interestingly, the structure has little influence on the magnetic properties of the films. The well-known antiferromagnetic to paramagnetic transition was observed in both polycrystalline and amorphous CuCr0.95Mg0.05O2 films at 25 K, while the CuCr0.93Mg0.05Mn0.02O2 films revealed no antiferromagnetic ordering below 25 K.
[1] R. Nagarajan et al. J. Appl. Phys. 89, 8022 (2001)
Keywords: diluted magnetic semiconductor, p-type oxide, Hall effect
  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 11086 - Permalink


High energy Xe+ ion beam induced ripple structures on silicon
Hanisch, A.; Grenzer, J.; Facsko, S.; Winkler, I.; Biermanns, A.; Grigorian, S.; Pietsch, U.;
Ion beam bombardment on semiconductor surfaces leads to welldefined morphological structures in the nanoscale range. Due to the impact of ions a self-organized wave-like surface structure develops. Ion bombardment causes an amorphization of a surface-adjacent layer of several nanometers and creates a periodical structure on the surface as well as at the amorphous-crystalline interface. We investigate the dependence of the periodicity on the crystallography of (100) silicon bombarded with Xe+ ions, the ion beam incidence and the azimutal angle of the sample surface. So far we found that the ripple wavelength scales with the ion energy in a range of 5 to 70 keV. In order to understand the initiation of the ripple formation we also ask the question which role the initial surface structure plays. Therefore we investigate the formation of ripples on pre-structured and rough surfaces such as wafers with an intentional miscut. Therefore, we not only introduce a certain initial roughness but also vary the orientation of the (100) lattice plane in respect to the surface. We try to distinguish between ion beam induced surface defects (sputter erosion) and the influence of the crystalline Si lattice (strain) on the ripple formation.
Keywords: nanostructures ion-beam patterning
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.08, Berlin, Germany

Publ.-Id: 11085 - Permalink


X-ray scattering and diffraction from Xe-induced ripples in crystalline silicon
Biermanns, A.; Pietsch, U.; Grigorian, S.; Grenzer, J.; Facsko, S.; Hanisch, A.; Carbone, D.; Metzger, H.;
The formation of surface-nanostructures with a characteristic size ranging from several nanometer up to microns has attracted significant interest in the last decades in the context of fabrication of novel opto-electronic and storage devices. One kind of those nanostructures are wave-like patterns (ripples) produced by an interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by surface diffusion. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe+ -ions using ion-energies up to 40keV. During the sputtering, an amorphous surface-layer is formed followed by a rather sharp interface towards crystalline material, showing the same morphology as the surface. The structures of the amorphous layer and the amorphous-crystalline interface were studied by means of grazingincidence - small angle scattering (GISAXS) and diffraction (GID) using synchrotron-radiation. We found that the crystal structure at the interface is expanded along the ripples, caused by the creation of defects inside the surface region, whereas this expansion is strongly reduced across the ripples. This different relaxation may play a driving role in pattern formation at the interface.
Keywords: ion-beam erosion X-ray scattering nanostructures
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.08, Berlin, Germany

Publ.-Id: 11084 - Permalink


Magnetoresistance in n-type conducting Co-doped ZnO
Xu, Q.; Hartmann, L.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Spemann, D.; Grundmann, M.;
Series of Co-doped Al-codoped ZnO films with electron concentration at 5 K ranging from 8.31017 cm-3 to 9.91019 cm-3 were prepared by pulsed laser deposition under different O2 pressure and substrate temperature. The magnetoresistance (MR) effect was studied between 5 K and 290 K with fields up to 6 T, showing large electron concentration and temperature dependence. A large positive MR of 124 % has been observed in the film with the lowest electron concentration of 8.31017 cm-3, while only negative MR of –1.9 % was observed in the film with an electron concentration of 9.91019 cm-3 at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin-splitting of the conduction band [1]. The negative MR is attributed to the magnetic field suppressed weak localization [1]. The modelled superimposed positive and negative MR agrees well with the experimentally observed MR and hints towards the physical origin of MR in Co-doped ZnO [2].
[1] P. A. Lee and T. V. Ramakrishnan, Rev. Mod. Phys. 57, 287 (1985)
[2] Q. Xu, L. Hartmann, H. Schmidt, H. Hochmuth, M. Lorenz, D. Spemann, and M. Grundmann, Phys. Rev. B 76, 134417 (2007)
Keywords: diluted magnetic semiconductors, ZnO, magnetoresistance, exchange interaction, weak localization
  • Lecture (Conference)
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 11083 - Permalink


Polycrystalline Mn-alloyed indium tin oxide films
Scarlat, C.; Schmidt, H.; Xu, Q.; Vinnichenko, M.; Kolitsch, A.; Helm, M.; Iacomi, F.;
Magnetic ITO films are interesting for integrating ITO into magnetooptoelectronic devices. We investigated n-conducting indium tin oxide (ITO) films with different Mn doping concentration which have been grown by chemical vapour deposition using targets with the atomic ratio In:Sn:Mn=122:12:0, 114:12:7, and 109:12:13 [1]. The average film roughness ranges between 30 and 50 nm and XRD patterns revealed a polycrystalline structure. Magnetotransport measurements revealed negative magnetoresistance for all the samples, but high field positive MR can be clearly observed at 5 K with increasing Mn doping concentration. Spectroscopic ellipsometry (SE) has been used to prove the existence of midgap states in the Mn-alloyed ITO films revealing a transmittance less than 80%. A reasonable model for the ca. 250 nm thick Mn-alloyed ITO films has been developed to extract optical constants from SE data below 3 eV. Depending on the Mn content, a Lorentz oscillator placed between 1 and 2 eV was used to model optical absorption below the band gap.[1]C. Baban et al. E-MRS 2007, Straßbourg.
  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11081 - Permalink


Empirical pseudopotential calculation of strain induced birefringence in ZnO
Fritsch, D.; Schmidt, H.;
One big challenge in the fabrication of ZnO-based heterostructure devices is the lattice mismatch between ZnO films and substrates and the different thermal expansion coefficients inducing biaxial strain. There is currently also much interest in ZnO doped with 3d transition metal ions for spintroncis applications and the detection of ferromagnetic signatures by magneto-optical measurements of ordering induced birefringence being most intense around the critical point structure of the dielectric function. A quantitative understanding of Zeeman splitting far away from the center of Brillouin zone is still an open question and requires a separation of strain and magnetic field induced modifications of electronic band strcucture. We report on the effect of strain on the birefringence in ZnO films grown on Al2O3 or on SiC substrates. The imaginary part of the dielectric function has been calculated b means of the empirical pseudopotential method. Thereby we also accounted for relativistic effects in form of te spin-orbit interaction, for the energy-dependence of the crystal potential through the use of nonlocal model potentials, and for excitonic conrtibutions to the dielectric functiuon fue to discrete excitonic states and Coulomb enhanced band-to-band transitions.
Keywords: ZnO, birefringence
  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11080 - Permalink


Magnetism of the high spin molecules [Mn4L6](BF4)2·2CH3-CN·H2O and [CrIIIMnII3 (PyA)6Cl3]
Prinz, M.; Raekers, M.; Kuepper, K.; Chaudhuri, P.; George, S. J.; Neumann, M.;
We have studied the electronic and magnetic structure of high spin molecules by spectroscopic investigations in combination with theoretical calculations. We present results on [MnII4 L6](BF4)2·2CH3CN·H2O (Mn4)and the hetero nuclear, spin frustrated molecule [CrIIIMnII3 (PyA)6Cl3] (CrMn3), which have been studied using X-ray photoelectron spectroscopy (XPS), X-ray absorption and emission spectroscopy (XAS, XES), and X-ray magnetic circular dichroism (XMCD). Magnetic measurements of Mn4 show a magnetization saturation of about 20 μB/f.u. at a magnetic field of B = 7 T and a temperature of T = 2 K. From XMCD measurements of Mn4 at T = 5 K and B = 5 T we obtained a high magnetic moment of 18.5 μB/f.u, whereas a quenching of the Mn orbital moments was observed (morb = 0.4 μB/f.u.). The element selective MnII and CrIII dichroic signals of the CrMn3 complex at B = 5 T and T = 5 K where recorded. For the three MnII ions a magnetic moment of 15 μB was determined. For both complexes we will present a comparison to XAS/XMCD charge transfer multiplet calculations.
Keywords: magnetic high spin molecules, electronic structure, x-ray magnetic circular dichroism
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11079 - Permalink


Manganese implanted GaAs films
Bürger, D.; Schmidt, H.; Xu, Q.; Kolitsch, A.; Winnerl, S.; Schneider, H.; Zhou, S.; Potzger, K.; Helm, M.; Biehne, G.; Gottschalch, V.;
Electron spin preservation has been proven in unmagnetic GaAs over several μm by time-resolved luminescence measurements. The synthesis of Mn-alloyed GaAs has introduced a controllable spin degree of freedom in the GaAs device technology. Approx. 1 μm thick n-type (Si) and p-type (Zn) GaAs films have been grown on highly conducting n- and p-GaAs substrates by metalorganic chemical vapour deposition. For magnetotransport measurements reference samples have been grown on insulating substrates. Mn+ ion beam implantation with 300/150 keV at 200°C yielded a boxlike Mn-implantation profile of the 250 nm thick GaAs surface layer with a nominal implantation dose dependent Mn content of 1 and 5 at%. Rapid thermal annealing has been performed at 650°C for 10 s. Magnetic properties have been investigated by means of SQUID-magnetometry. The relation between concentration of free charge carriers, defect formation and magnetoresistance effects in manganese implanted GaAs will be discussed.
Keywords: GaAs, ion implantation, magnetic semiconductor, magnetoresistance, DLTS
  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11078 - Permalink


Charge accumulation in a type-II Ge/Si heterostructure
Henkel, C.; Biehne, G.; Grundmann, M.; Wagner, G.; Stoffel, M.; Schmidt, O. G.; Schmidt, H.;
The main motivation for mixing a small amount of Ge into Si for example by the self-organized growth of a stack of Ge dots into Si [1], is the controlled modification of the electronic band structure in strained Si namely charge carrier mobility and optical transition probabilities [2]. We report on charge accumulation in fivefold stacks of Ge quantum dots embedded in the n-region of a p+n-Si diode. By means of thermal admittance spectroscopy, capacitance voltage and deep level transient spectroscopy measurements [3] electron confinement in the type II Ge/Si-heterostructures, barrier effects of the quantum wells and wetting layers and defect states in the n-region of the sample associated with the surrounding Si-matrix have been probed. By relating these results to the self consistently modeled electronic band-structure and capacitance voltage characteristic charge accumulation in quantum confined electron states in the investigated type II Ge/Si-heterostructures is clearly revealed.
[1] A. Malachias, T. H. Metzger, M. Stoffel, O.G. Schmidt and V. Holy, Thin Solid Films 515, 5587 (2007)
[2] O.G. Schmidt and K. Eberl, Phys. Rev. B 61, 20 (2000)
[3] M. Gonschorek, H. Schmidt, J. Bauer, G. Benndorf, G. Wagner, G.E. Cirlin and M. Grundmann, Phys. Rev. B 74, 115312 (2006)
Keywords: Ge/Si, space charge spectroscopy
  • Poster
    72. Annual Meeting of the DPG and DPG Spring Meeting of the Condensed Matter Division, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11077 - Permalink


High Resolution Measurement of the Thermal Expansion Coefficient of Semiconductor Multilayer Lateral Nanostructures
Brueser, B.; Pietsch, U.; Grigorian, S.; Panzner, T.; Grenzer, J.; Zeimer, U.;
We measured the thermal expansion coefficient of a vertically stacked multi-quantum-well structure buried under a thick GaAs top layer before and after lateral patterning of the GaAs top layer. After patterning the thermal expansion coefficient of the whole multi-quantum-well structure differs from that of the planar structure by about 20%. Based on calculations in terms of methods of finite elements the effect is explained by the influence of the strain field originating from the bottom edges of the etched nanostructure. Due to the long range nature of this strain field the strain release within the individual quantum wells changes as a function from the distance from the valley.
Keywords: nanostructrues, X-ray scattering
  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany
  • Physica Status Solidi (A) 205(2008)2, 316-320

Publ.-Id: 11076 - Permalink


X−ray investigations on CoSi2 nano wires manufactured by focused ion beam synthesis
Grenzer, J.; Bischoff, L.; Biermanns, A.;
Nanowires and chains of nanoparticles are of emerging interest in nano-electronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices; CoSi2 is a promising material due to its CMOS-compatibility in micro-electronics technology. It shows metallic behaviour with low resistivity and high thermal stability. It is well known that cobalt disilicide films can be formed in silicon by implanting Co in stoichiometric concentration and a subsequent annealing procedure. Ion beam synthesis allows the fabrication of epitaxial buried or surface CoSi2 layers on silicon. Sub-micron patterns with feature dimensions much smaller than 100nm can be directly produced by writing focused ion beam (FIB) cobalt implantation.
We have studied the strain of the Si host lattice in the surrounding area of a single nanostructures depending on their crystallographic orientation using high resolution x-ray diffraction in combination with a highly focused (≈ 3µm) x-ray beam at the beam line ID1 at the ESRF. The pattern measured directly on the wire shows a small peak indicating tensile strain (approx. −1.4%). This feature can be only found if the beam focused on a nano wire whereas its intensity changes
with the layer width.
Keywords: nao wire; x-ray scattering
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany
  • Poster
    9th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, XTOP 2008, 15.-19.09.2008, Linz, Austria

Publ.-Id: 11075 - Permalink


Interaction between molten corium UO2+X - ZrO2- FeOy and VVER vessel steel
Bechta, S. V.; Granovsky, V. S.; Khabensky, V. B.; Krushinov, E. V.; Vitol, S. A.; Sulatsky, A. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Tromm, W.; Altstadt, E.; Fichot, F.; Kymalainen, O.;
In case of an in-vessel corium retention (IVR) the deterioration of vessel steel properties can be caused both by the steel melting and by its physicochemical interaction with corium. The interaction behavior has been studied in the medium-scale experiments with a prototypic corium within the METCOR project. The resulting experimental data give an insight into the steel corrosion during its interaction with UO2+x-ZrO2-FeOy melt in air and steam. It has been observed that the corrosion rate is almost the same in air and steam atmosphere; if the temperature on the interaction interface increases beyond a certain level, corrosion intensifies, which is explained by the formation of liquid phases in the interaction zone. The available experimental data have been used for developing a correlation of corrosion rate versus heat flux density and temperature.
Keywords: Physiochemical Corium-steel interaction, vessel ablation
  • Contribution to proceedings
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP), 08.-12.06.2008, Anaheim, California, United States
  • Lecture (Conference)
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP '08), 08.06.-12.08.2008, Anaheim, California, United States

Publ.-Id: 11074 - Permalink


European Research on the Corium issues within the SARNET Network of Excellence
Journeau, C.; Bonnet, J. M.; Godin-Jacqmin, L.; Piluso, P.; Tarabelli, D.; Altstadt, E.; et al.;
Within SARNET, the corium topic covers all the behaviors of corium from early phase of core degradation to in or ex-vessel corium recovery with the exception of corium interaction with water, direct containment heating and fission product release. The corium topic regroups in three work packages the critical mass of competence required to improve significantly the corium behavior knowledge.
The spirit of the SARNET networking is to share the knowledge, the facilities and the simulation tools for severe accidents, so to reach a better efficiency and to rationalize the R&D effort at European level. Extensive benchmarking has been launched in most of the areas of research. These benchmarks were mainly dedicated to the recalculation of experiments, while, in the next periods, a larger focus will be given to integral experiments or reactor applications. Eventually, all the knowledge will be accumulated in the ASTEC severe accident simulation code through physical model improvements and extension of validation database. This paper summarizes the progress that has been achieved in the frame of the networking activities. A special focus is placed on the melt pool and debris coolability and corium-concrete interaction, in which, the effects due to multidimensional geometries and heterogeneities has been shown, during SARNET, to play a crucial role and for which further research is still needed.
Keywords: Nuclear reactors, severe accident, in-vessel cooling ex-vessel corium cooling
  • Contribution to proceedings
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP'08), 08.-12.06.2008, Anaheim, United States
    Proceedings of ICAPP ‘08
  • Lecture (Conference)
    2008 International Congress on Advances in Nuclear Power Plants (ICAPP'08), 08.-12.06.2008, Anaheim, California, United States

Publ.-Id: 11073 - Permalink


Progress on PWR lower head failure predictive models
Koundy, V.; Fichot, F.; Willschuetz, H.-G.; Altstadt, E.; Nicolas, L.; Lamy, J.-S.; Flandi, L.;
A good understanding of the mechanical behaviour of the reactor pressure vessel (RPV) lower head is necessary both for severe accident assessment and for the definition of appropriate accident mitigation strategies. Indeed, a well-characterized failure of the lower head leads to a better evaluation of the quantity and kinetics with which core material can escape into the containment. These are the initial conditions for several ex-vessel events such as direct heating of the containment or molten core-concrete interaction.
In this context, the objectives of the joint on-going work of the WP10-2 group of SARNET are: 1) improvement of predictability of the time, mode and location of RPV failure; 2) development of adequate models with the ultimate aim of being included into integral codes; 3) interpretation / analysis of experiments with models / codes combined with sensitivity studies; and 4) better understanding of the breach opening process in order to better characterize the corium release into the containment.
Different approaches are considered: a simplified but well predicting model recently implemented in the severe accident Astec and Icare-Cathare codes, and viscoplasticity models implemented in the Cast3m, Ansys and Code_Aster finite element codes. Several failure criteria are considered: stress criterion, strain criterion and damage evaluation (coupled way or post-evaluation).
In this paper, the OLHF-1 experiment has been used to assess the models, to perform sensitivity studies and to evaluate failure criteria that could be applied in the case of reactors. All the partners performed 2D axisymmetric analyses, allowing the evaluation of time, mode and location of vessel failure. Nevertheless, CEA conducted further 3D calculations in order to study crack propagation and the corresponding results will be presented separately at the end of the paper. The numerical formulation of the different models used is given and a comparison of experimental and numerical results is presented. The paper also shows the progress made with the objective of defining failure criteria that can be used for reactor vessel applications.
Keywords: lower head failure, severe accident, pressurized water reactor, in-vessel melt retention
  • Nuclear Engineering and Design 238(2008), 2420-2429

Publ.-Id: 11072 - Permalink


U(VI) sorption onto environmental relevant minerals: vibrational spectroscopy and complementary tools
Müller, K.; Foerstendorf, H.; Krepelova, A.; Baumann, N.; Brendler, V.;
The sorption onto minerals along groundwater flow paths is an important mechanism determining the migration behaviour of uranium(VI) in the natural environment. The U(VI) surface complexation on several mineral phases was studied applying different spectroscopic methods. Using ATR-FTIR spectroscopy an in-situ investigation of U(VI) sorption onto kaolinite and titanium dioxide was performed at a micromolar concentration range. Thin mineral films are deposited on the surface of the crystal of an ATR flow cell. When U(VI) passes through the cell, characteristic absorption changes are observed representing sorption processes of U(VI) on the mineral surfaces. From the spectra the formed sorption complexes can be deduced.
The characteristic asymmetric stretching vibration of the uranyl ion is red-shifted by 40 cm–1 upon surface complexation of the UO22+ ion on kaolinite probably indicating strong sorption due to inner-sphere surface complexation. In homology, red shifts were also observed in the IR spectra of the titanium dioxide system, but the extent of the frequency shifts differs among different TiO2 samples.
In order to gain more information of the U(VI) complexes formed on the kaolinite surface, time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied [1]. Two U(VI) surface species, differing in the amount of water molecules in their coordination environment, could be identified. For the U(VI)-TiO2 system significant different spectroscopic response was observed for anatase and rutile. TRLFS investigations of anatase suspensions were hampered by strong quenching effects of the mineral phase. In contrast, the measurements of U(VI) in the rutile suspensions yield reasonable results.
A third spectroscopic method used for the characterization of the formed U(VI) complexes on surfaces of kaolinite and ferrihydrite is extended X-ray absorption fine structure (EXAFS) [2].
The obtained spectroscopic results serve as a data base for the development and the parameterization of models describing surface complexation phenomena.

1. Krepelova, A.; Brendler, V.; Sachs, S.; Baumann, N.; Bernhard, G. Environmental Science & Technol-ogy 2007, 41, (17), 6142-6147.
2. Reich, T.; Moll, H.; Arnold, T.; Denecke, M. A.; Hennig, C.; Geipel, G.; Bernhard, G.; Nitsche, H.; Allen, P. G.; Bucher, J. J.; Edelstein, N. M.; Shuh, D. K., Journal of Electron Spectroscopy and Related Phe-nomena 1998, 96, (1-3), 237-243.
  • Lecture (others)
    Seminar at National Commission of Atomic Energy (CNEA) of Argentina, 21.04.2008, San Martin, Argentina

Publ.-Id: 11070 - Permalink


Alpha-radiation damage in diamond
Nasdala, L.; Gigler, A. M.; Wildner, M.; Grambole, D.; Zaitsev, A. M.; Harris, J. W.; Hofmeister, W.; Milledge, H. J.; Satitkune, S.;
We studied both the extent and distrubution of structural damage in diamond crystals that was generated through either natural or artificial irradiation with alpha particles (i.e., He2+ ions with energies in the MeV range), and the related formation of colour-centres. A range of non-destructive micro-techniques was applied. The generation of damage in the (crystalline) diamond is accompanied by lattice expansion, which is detected by a down-shift of the diamond LO=TO Raman band (compare [1]). This expansion is why radiation-damaged spots at the surface of natural diamond crystals often have an up-domed shape. At high irradiation doses ≥1016 ions per cm2, diamond may be transformed locally into an amorphous state (maximum damage generated at the far ends of helium trajectories).
Visible radiation-induced green colouration of diamond (mainly caused by a broad absorption band at ∼16000 cm-1 assigned to the GR1 centre) is generated at moderate doses of 1014−1015 He ions per cm2 [2,3]. This irradiation resulted in a lowly damaged state (maximum damage ≤0.005 dpa).
[1] Nasdala et al. (1995) Eur. J. Mineral. 7, 471−478. [2] Vance et al. (1973) Miner. Mag. 39, 349−360. [3] Zaitsev, A.M. (2001) Optical porperties of diamond. Springer, 502 p.
  • Lecture (Conference)
    Goldschmidt 2008, 13.-18.07.2008, Vancouver, Canada
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 72(2008)12, A672

Publ.-Id: 11069 - Permalink


Numerical and experimental modeling of the melt flow in a traveling magnetic field for Vertical Gradient Freeze crystal growth
Galindo, V.; Grants, I.; Lantzsch, R.; Paetzold, O.; Gerbeth, G.;
A Traveling Magnetic Field (TMF) is attractive for Vertical Gradient Freeze crystal growth as it offers a direct flow driving mechanism. A combination of the driving TMF with a superimposed DC magnetic field leads to a damping effect on the fluctuations of the flow velocity, which have to be reduced in order to get a crystal with enhanced material properties. We present numerical and experimental results on the TMF driven flow in an isothermal model fluid in a cylindrical geometry. The TMF is generated by a system of six equidistant coils, which are fed by a three phase current power supply to create an up- or downward directed traveling field. Special attention is focused on the skin effect of the electromagnetic fields for varying field frequency, and its influence on the resulting melt velocity. The stability of the flow was analyzed with help of a spectral code. Critical values for the driving force and the period of the oscillating flow near those critical points were found in a good concordance with experiments.
Keywords: Traveling Magnetic Field Vertical Gradient Freeze crystal growth Numerical and experimental modeling
  • Lecture (Conference)
    79th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 31.03.-04.04.2008, Bremen, Germany

Publ.-Id: 11068 - Permalink


Revised and extended level scheme of the doubly-odd nucleus 188Ir
Jungclaus, A.; Modamio, V.; Egido, J. L.; Schwengner, R.; Algora, A.; Bazzacco, D.; Escrig, D.; Fernandez, M. A.; Fraile, L. M.; Lenzi, S.; Marginean, N.; Martinez, T.; Napoli, D. R.; Ur, C. A.;
High-spin states in the doubly odd Z = 77 nucleus 188Ir were studied using the reaction 186W(7Li, 5n) at 59 MeV and the GASP spectrometer for gamma-ray detection. The level structures recently suggested to be built on the known 4.1(3) ms isomeric state of this nucleus have been considerably revised and extended and an isomer with a lifetime of 17.7(2) ns has been identified within the main decay sequence. In addition two rotational bands built on low spin states below the ms isomer have been observed for the first time. The basic features of the excitation scheme of 188Ir are discussed within the Hartree-Fock-Bogoliubov theory within the Lipkin-Nogami approach with the finite-range density-dependent Gogny force.
Keywords: Nuclear structure, gamma-ray spectroscopy, Hartree-Fock-Bogoliubov theory.

Publ.-Id: 11066 - Permalink


Computational study of anisotropic epitaxial recrystallization in 4H-SiC
Gao, F.; Zhang, Y.; Posselt, M.; Weber, W. J.;
Two nano-sized amorphous layers were created within a crystalline cell to study anisotropic expitaxial recrystallization using molecular dynamics (MD) methods in 4H-SiC. Both amorphous layers were created with the normal of the amorphous-crystalline (a-c) interfaces along the [0001] direction, but one had a microscopic extension along the [(1) over bar2 (1) over bar0] direction, i.e. the dimension along the [(1) over bar2 (1) over bar0] direction is much larger than that along the [(1) over bar 010] direction (I-x model), and the other had a microscopic extension along the [(1) over bar 010] direction (I-y model). The amorphous layer within the I-x model can be completely recrystallized at 2000 K within an achievable simulation time, and the recrystallization is driven by a step-regrowth mechanism. On the other hand, the nucleation and growth of secondary ordered phases are observed at high temperatures in the I-y model. The temperature for recrystallization of the amorphous!
layer into high-quality 4H-SiC is estimated to be below 1500 K. Compared with other models, it is found that the regrowth rates and recrystallization mechanisms depend strongly on the orientation of 4H-SiC, whereas the activation energy spectra for recrystallization processes are independent of any specific polytypic structure, with activation energies ranging from 0.8 to 1.7 eV.
Keywords: computer simulation, SiC, recrystallization, defects

Publ.-Id: 11065 - Permalink


The liquid lead taget at nELBE
Galindo, V.; Erlebach, S.; Gerbeth, G.; Weiss, F.-P.;
The radiation source ELBE (Electron Linear accelerator with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf (FZD) has a superconducting linear accelerator with electron energies up to 40 MeV as a central instrument, and it will be used to produce sub-ns neutron pulses by stopping the electrons in a heavy radiator and producing neutrons by bremsstrahlung photons through (gamma,n) reactions. The neutron radiator consists of a liquid lead circuit. The volume of the radiator for the neutron production is chosen as small as possible in order to avoid multiple n scattering, which would broaden the neutron pulse. Power deposition of the electron beam in the small radiator volume of 1cm3 reaches up to 25 kW and any solid high Z number material would melt. A liquid lead target circulated by an electromagnetic pump is presented as a suitable solution. The heating power introduced by the electrons is removed through an additional heat exchanger. Typical flow velocities of the lead are between 1 m/s and 5 m/s in the radiator section. From the thermal and mechanical point of view, molybdenum turned out to be the most suited target wall material in the region where the electrons impinge on the neutron radiator. Model experiments in a pilot facility and numerical simulations of the flow, temperature and thermal stress distributions in the loop and
simulation of the efficiency of a lead-GaInSn-water heat exchanger are presented.
Keywords: liquid lead neutron target
  • Lecture (Conference)
    Workshop on modern methods using fast neutrons for research related to the transmutation of nuclear waste, 13.-15.02.2008, Dresden, Germany

Publ.-Id: 11064 - Permalink


Experimental nuclear astrophysics deep underground at Gran Sasso
Bemmerer, D.;
The Laboratory Underground for Nuclear Astrophysics (LUNA) in the Gran Sasso underground facility, Italy, has been designed to measure low cross sections for astrophysical purposes. The 3He(alpha,gamma)7Be study at LUNA has recently been completed [1,2], and the impact of the data on big-bang nucleosynthesis and solar 7Be and 8B neutrinos will be discussed. During the year 2007, two measurement campaigns have been performed at LUNA: First, a precision study of ground state capture in the 14N(p,gamma)15O reaction. This study will help in the interpretation of the 15O neutrino data expected from the Borexino detector at Gran Sasso. Second, a study of the 25Mg(p,gamma)26Al reaction producing radioactive 26Al, a tracer of live nucleosynthesis in our galaxy. Gamma-rays from 26Al have been observed in the satellite-based Integral gamma-ray observatory.

The scientific program for the next years at the current LUNA 400 kV accelerator includes the study of the 2H(alpha,gamma)6Li reaction for big-bang nucleosynthesis and the study of 15N(p,gamma)16O and several other reactions of the CNO cycles. In closing, selected experiments that would benefit from the background suppression that is evident deep underground will be reviewed.

[1] D. Bemmerer et al. (LUNA collab.), Phys. Rev. Lett. 97, 122502 (2006)
[2] F. Confortola et al. (LUNA collab.), Phys. Rev. C 75, 065803 (2007)
  • Invited lecture (Conferences)
    Seminar Nukleare Astrophysik, 10.01.2008, München, Deutschland

Publ.-Id: 11063 - Permalink


Experimentelle Nukleare Astrophysik im Felsenkeller
Bemmerer, D.;
Recent photoactivation experiments involving irradiations at the ELBE bremsstrahlung facility and underground gamma-counting in the Felsenkeller underground laboratory (VKTA Dresden) are presented. In addition, data from a feasibility study on in-beam gamma-spectrometry studies in shallow underground laboratories are shown here.
  • Invited lecture (Conferences)
    Kolloquium 25 Jahre Niederniveaumesslabor Felsenkeller, 31.01.2008, Dresden, Germany

Publ.-Id: 11062 - Permalink


The strong correlation between structural properties of the buffer layer and the exchange bias phenomena
Liedke, M. O.; Cantelli, V.; Grenzer, J.; Markó, D.; Mücklich, A.; Fassbender, J.ORC
The exchange coupling strength as a function of the buffer layer thickness is investigated for several carefully chosen seed materials. The crystal microstructure of the ferromagnetic(FM)-antiferromagnetic(AF) interface is directly related to the roughness and dimensionality of the buffer layer surface, which scales not only with such parameters as a texture and grain sizes but can be discussed as well in the frame of the wetting behavior of subsequent films. Particularly, it is shown that strong wetting between the substrate and the next layer can decrease the surface dimensionality and improve the growth conditions for the subsequent films. Thus, the smoothness of the FM-AF interface improves significantly which leads to a much stronger exchange coupling across the interface. In addition, it is demonstrated that the magnitude of the exchange bias is proportional to the grain sizes distribution, which is in good agreement with theoretical predictions.
Keywords: exchange bias, buffer layer, wetting, grain sizes, thermal fluctuations, roughness, unidirectional anisotropy
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 11061 - Permalink


In-beam PET measurements of biological half-lives of 12C irradiation induced β+-activity
Fiedler, F.; Sellesk, M.; Crespo, P.; Jülich, R.; Parodi, K.; Pawelke, J.; Pönisch, F.; Enghardt, W.;
no abstract available
Keywords: in-beam PET, washout, ion therapy
  • Contribution to external collection
    in: GSI Scientific Report 2006 GSI Report 2007-1, Darmstadt: GSI, 2007, 364

Publ.-Id: 11060 - Permalink


Auf dem Weg zu einer Strahlentherapie mit laserbeschleunigten Teilchen - erste Dosis-Effekt-Kurven für laserbeschleunigte Elektronen
Beyreuther, E.; Enghardt, W.; Hümmerich, J.; Karsch, L.; Lessmann, E.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
Fragestellung: Die klassischen Teilchenbeschleuniger bieten einige 10 Pikosekunden (Elektronen) bzw. Nanosekunden (Protonen und Ionen) lange Pulse der Partikelstrahlung an. Mit der neuartigen Technologie der Laserbeschleunigung ist es möglich kürzere Teilchenpakete (einige 10 Femtosekunden) mit wesentlich geringerer Pulsfrequenz (einige Hertz gegenüber Megahertz) bei höherer Pulsintensität zu erhalten. Für eine Verwendung dieser Technologie in der Strahlentherapie muss eine möglicherweise andere biologische Wirksamkeit, sei es durch eine die andere Zeitstruktur oder durch die höhere Pulsdosisleistung, gegenüber den klassischen Teilchenstrahlen untersucht werden. Im Vortrag werden die weltweit ersten Zellbestrahlungen mit laserbeschleunigten Elektronen vorgestellt und diskutiert.
Methodik: Die Experimente wurden an dem 10-Terrawatt-Lasersystem JETI in Jena durchgeführt. Die Elektronenpakete haben eine Länge von ca. 150 fs und eine Wiederholrate von 2,5 Hz. Wichtige Vorraussetzungen für strahlenbiologische Experimente waren die Anpassung des Lasersystems, der Aufbau einer geeigneten Strahlführung und eines Dosimetriesystems. Bei einer ersten Serie von in-vitro Zellbestrahlungen mit Strahlendosen im Bereich von 0,3 bis 5 Gy wurde die Anzahl der Doppelstrangbrüche zu verschiedenen Zeitpunkten nach Bestrahlung in zwei Zelllinien bestimmt.
Ergebnisse: Das Lasersystem wurde erfolgreich für Zellbestrahlungen angepasst, d.h. die Zellproben werden homogen ausgeleuchtet und die Strahleigenschaften sind gut reproduzierbar. Die applizierte Dosis kann in Echtzeit monitoriert werden. Dadurch wird die Kontrolle und Steuerung der Zellbestrahlungen erleichtert. Eine genaue Dosisbestimmung ist nach der Bestrahlung mit Filmen, die am Zellkulturhalter befestigt waren, für jede Probe einzeln möglich. Das Gesamtsystem kann für systematische Untersuchungen eingesetzt werden, wie in einer ersten Zellbestrahlung demonstriert wurde. In diesem Experiment wurden Dosis-Effekt-Kurven bestimmt. Um eindeutige Aussagen zu erhalten, müssen die in Auswertung befindlichen Daten mit weiteren Experimenten ergänzt werden.
Schlussfolgerungen: In Zukunft werden systematische Messungen für verschiedene Tumor- und Normalgewebszellen sowie verschiedene biologische Endpunkte durchgeführt.
  • Lecture (Conference)
    14. Jahrestagung der Deutschen Gesellschaft für Radioonkologie / 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik, 01.-04.05.2008, Wien, Austria
  • Contribution to proceedings
    14. Jahrestagung der Deutschen Gesellschaft für Radioonkologie / 25. Jahrestagung der Österreichischen Gesellschaft für Radioonkologie, Radiobiologie und Medizinische Strahlenphysik, 01.-04.05.2008, Wien, Austria
    Auf dem Weg zu einer Strahlentherapie mit laserbeschleunigten Teilchen - Erste Dosis-Effekt-Kurven für laserbeschleunigte Elektronen.: Strahlenther. Onkol. 184 (2008) 51

Publ.-Id: 11059 - Permalink


Spectral singularities and self-orthogonality of eigenvectors
Günther, U.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.; Rotter, I.; Samsonov, B.;
A brief overview of some mathematical aspects connected with the occurrence of spectral singularities will be presented. Based on simple matrix models we discuss stratified manifolds in parameter spaces on which the matrix eigenvalues degenerate. We comment on discriminant sets and similarity relations to canonical Jordan structures, demonstrate the mechanism underlying the formation of self-orthogonal (isotropic) eigenvectors, relate it to corresponding projectors. Special emphasis will be laid on the break-down of similarity transformations, the formation of corresponding transformation singularities and their resolution via projective extensions. Structural links to ultrarelativistic spinor models will be sketched. Finally, we comment on versal deformations and an unfolding rule for higher-order spectral singularities connected with the Hessenberg type of the perturbation.
Keywords: spectral, singularity, Jordan structure, exceptional point, self-orthogonality, isotropy, versal deformation, projective extension, ultra-relativistic limit, Hessenberg matrix
  • Invited lecture (Conferences)
    Experimental Realizations of Self-Orthogonality, 23.-28.03.2008, Haifa, Israel

Publ.-Id: 11058 - Permalink


Bacterial interactions with uranium: an environmental perspective
Merroun, M.; Selenska-Pobell, S.;
The presence of actinides in radioactive wastes is of major concern because of their potential for migration from the waste repositories and long-term contamination of the environment. Studies have been and are being made on inorganic processes affecting the migration of radionuclides from these repositories to the environment but it is becoming increasingly evident that microbial processes are of importance as well. The relevance of microorganisms to actinide behavior arises from the overlap of the biosphere with the geosphere and the transformations that occur because of their interactions. The present study is intended to give a brief overview of the key processes implicated in the interaction of actinides e.g. uranium with bacterial strains isolated from different extreme environments relevant to radioactive repositories. A complex methodological approach involving a combination of wet chemistry, transmission electron microscopy, and advanced solid state speciation techniques is used. Fundamental understanding of the interaction of these bacteria with U will be useful for developing appropriate radioactive waste treatments, remediation and long-term management strategies as well as for predicting the microbial impacts on the performance of the radioactive waste repositories.
Keywords: Uranium, Bacteria, Interaction mechanisms, Multidisciplinary approach, Radioactive wastes

Publ.-Id: 11057 - Permalink


Anwendung des in-beam PET Therapiemonitorings auf Präzisionsbestrahlungen mit Helium-Ionen
Fiedler, F.;
no abstract available
Keywords: in-beam PET, ion therapy, 3He
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-494 2008

Downloads:

Publ.-Id: 11056 - Permalink


XAS study of Am2Zr2O7 pyrochlore - Evolution under alpha self irradiation.
Martin, P.; Belin, R.; Valenza, P.; Pieragnoli, A.; Scheinost, A.;
Management of long-lived nuclear wastes is, after safety, the main issue of nuclear industry, both in terms of scientific challenge as well as public acceptance. Among the different options that have been envisioned and explored for minor actinides over the past thirty years, two alternatives currently remain: long term disposal in a safe repository or nuclear wastes “burning” in a so-called transmutation process. Materials selected for such applications have to meet the following criteria: high incorporation amount of actinides, good structural and chemical stability, low thermal dilatation and resistance to radiation.
Among the various ceramics envisaged, zirconia based pyrochlore oxides of composition An2Zr2O7 (An=actinide) appear to be a very good candidate. Results obtained with lanthanide pyrochlores submitted to ion-beam irradiation show that Zr based pyrochlores, unlike Ti based, remain crystalline with a transition from pyrochlore structure to a defect fluorite structure [1]. However, this strong radiation tolerance still has to be confirmed on alpha emitter materials (e.g. americium). In that prospect, 241Am2Zr2O7 sample was synthesized [2] and its evolution under the effect of alpha self-irradiation as a function of time was followed by XRD. Figure 1 shows the transition from the pyrochlore phase to a defect-fluorite phase after ~200 days as the superstructure peaks (marked ) slowly vanish and completely disappear after about 200 days [3].
Keywords: Americium, zirconium, pyrochlore, XAS
  • Contribution to proceedings
    Plutonium Futures "The Science" 2008, 07.-11.07.2008, Dijon, France

Publ.-Id: 11055 - Permalink


A non-Hermitian PT-symmetric Bose-Hubbard model: eigenvalue rings from unfolding higher-order exceptional points
Graefe, E.-M.; Günther, U.; Korsch, H.-J.; Niederle, A.;
We study a non-Hermitian PT-symmetric generalization of an N-particle, two-mode Bose-Hubbard system, modeling for example a Bose-Einstein condensate in a double well potential coupled to a continuum via a sink in one of the wells and a source in the other. The effect of the interplay between the particle interaction and the non-Hermiticity on characteristic features of the spectrum is analyzed drawing special attention to the occurrence and unfolding of exceptional points (EPs). We find that for vanishing particle interaction there are only two EPs of order N+1 which under perturbation unfold either into [(N+1)/2] eigenvalue pairs (and in case of N+1 odd, into an additional zero-eigenvalue) or into eigenvalue triplets (third-order eigenvalue rings) and (N+1)mod 3 single eigenvalues, depending on the direction of the perturbation in parameter space. This behavior is described analytically using perturbational techniques. More general EP unfoldings into eigenvalue rings up to (N+1)th order are indicated.
Keywords: Hubbard model, Bose-Einstein condensate, non-Hermitian operators, PT-symmetry, Krein space, exceptional points, Jordan block, Jordan chain, singularities, LeVerrier-Faddeev technique, Newton diagram technique

Publ.-Id: 11054 - Permalink


Effekt der Bestrahlungsdosis auf die lokale Tumorkontrolle korreliert mit prätherapeutischer [18F]FDGAufnahme von FaDu-Tumoren in Nacktmäusen
Schütze, C.; Beuthien-Baumann, B.; Bergmann, R.; Hessel, F.; Kotzerke, J.; Baumann, M.;
Hintergrund:
In vielen Tumoren unterschiedlicher Patienten wie auch innerhalb eines individuellen Tumors kann eine heterogene [18F]FDGAufnahme nachgewiesen werden. Derzeit ist nicht bekannt ob diese intratumorale Heterogenität mit dem Ansprechen von Tumorsubvolumina korreliert und als biologischer Marker für eine heterogene Dosis-Verschreibung z.B. Dosis-Eskalation partieller Volumina verwendet werden kann. Für diese Fragestellung haben wir in einer präklinischen Modellsituation die Heterogenität der [18F]FDG-Aufnahme und den Dosis-Effekt in einer einzelnen, in Nacktmäusen transplantierten humanen Tumorzelllinie untersucht.

Methoden:
Die hSCC Zelllinie FaDu wurde subkutan auf das Hinterbein von NMRI Nacktmäusen transplantiert. Ab einem Tumordurchmesser von 7 mm erfolgte die Aufnahme in das Experiment. Jedes Tier erhielt eine [18F]FDG-PET-Untersuchung (microPET® P4, CTI) direkt vor Bestrahlung zur Bestimmung des Maximum Standardized Uptake Value (SUVmax). Die Einzeldosisbestrahlungen mit 25 Gy oder 35 Gy erfolgten
unter ambientem Blutfluss mit 200 kV Röntgenstrahlen (0.5 mm Cu, ∼ 1 Gy min-1). 62 Tiere wurden in dieser Studie untersucht, davon befinden sich noch fünf Tiere im Follow-up. Experimenteller Endpunkt war die lokale Tumorkontrolle am Tag 120 nach Bestrahlung.

Ergebnisse:
Die Spanne der SUVmax-Werte reichte von 0.72 bis 3.47, der Median war 1.59. Die lokalen Tumorkontrollraten für alle 62 Tiere betrugen 28% nach Bestrahlung mit 25 Gy und 57% nach 35 Gy (Kaplan-Meier-Analyse, Logrank-Test p = 0.007). Im nächsten Schritt wurde eine univariate
Analyse der Dosis-Effekt-Beziehung für die entsprechend des Median SUVmax stratifizierten Tiere durchgeführt. Für Tumoren < Median SUVmax
betrug die lokale Kontrolle 37% nach 25 Gy vs. 47% nach 35 Gy (p = 0.37). Im Gegensatz dazu fand sich ein signifikanter Unterschied der lokalen
Tumorkontrollraten für Tumoren > Median SUVmax (15% nach 25 Gy vs. 68% nach 35 Gy, p = 0.002). In der multivariaten Cox-Analyse mit
Strahlendosis und SUVmax als kontinuierliche Variablen, konnte eine signifikante Verringerung des Rezidivrisikos mit ansteigender Strahlendosis
(p = 0.007) und ein grenzwertig, signifikanter Effekt des SUVmax-Wertes nachgewiesen werden (p = 0.06).

Zusammenfassung:
Diese Daten zeigen einen größeren Effekt der Bestrahlungsdosis auf die lokale Kontrolle in Tumoren mit initial hoher [18F]FDG-Aufnahme im Vergleich zu Tumoren derselben Tumorlinie mit niedriger [18F]FDG-Aufnahme. Diese Ergebnisse unterstützen die Hypothese, dass ein prätherapeutisches [18F]FDG-PET wichtige Informationen für die Verschreibung einer heterogenen Bestrahlungsdosis liefern kann. In dieser Studie wurde nur ein Tumormodell und Einzeldosisbestrahlung untersucht. Weitere Experimente mit anderen Tumormodellen und fraktionierter Bestrahlung sind notwendig.

Gefördert im Rahmen des EU-Projektes „BioCare“ Molecular Imaging for Biologically Optimized Cancer Therapy #505785.
  • Poster
    DEGRO 2007,13. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 07.-10.06.2007, Hannover, Deutschland
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 183(2007)1, 63
    DOI: 10.1007/s00066-007-1001-1

Publ.-Id: 11053 - Permalink


Erste Dosis - Effekt - Kurven für laserbeschleunigte Elektronen
Beyreuther, E.; Enghardt, W.; Hümmerich, J.; Karsch, L.; Lessmann, E.; Nicolai, M.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
Das Verbundprojekt "onCOOPtics - Hochintensitätslaser für die Radioonkologie" hat sich zum Ziel gesetzt eine neuartige und auf Laser basierende Technologie zur Erzeugung von Teilchenstrahlung für die Krebstherapie zu implementieren. Im Unterschied zu den klassischen, in der Strahlentherapie eingesetzen, Partikelstrahlungen, bestehen diese neuartigen Teilchenstrahlen aus wesentlich kürzeren Teilchenpaketen (einige 10 Femtosekunden gegenüber Piko- bzw. Nanosekunden Länge), die mit geringerer Pulsfrequenz (einige Hz statt MHz) aber höherer Pulsdosisleistung erzeugt werden. Diese Unterschiede in den Strahleigenschaften und ihr Einfluss auf die biologische Wirksamkeit müssen hinsichtlich eines möglichen Therapieeinsatzes untersucht werden; erste in - vitro Zellbestrahlungsexperimente mit laserbeschleunigten Elektronen hierzu werden im Vortrag vorgestellt.
Die ersten Experimente wurden mit dem 10 TW - Lasersystem JETI der Universität Jena durchgeführt. Mit diesem Lasersystem werden Elektronen aus einem Gasjet - Target heraus beschleunigt, wobei Elektronenpakete mit einer Länge von ca. 150 fs und einer Wiederholfrequenz von 2,5 Hz erzeugt werden. Das Lasersystem wurde an strahlenbiologische Erfordernisse, d.h. ausreichend großer Strahlfleck und hohe Dosisleistung, sowie von Bestrahlung zu Bestrahlung gut reproduzierbare Strahleigenschaften, angepasst und Zellbestrahlungen mit zwei verschiedenen Zelllinien im Dosisbereich von 0,3 bis 5 Gy durchgeführt. Zur Kontrolle der Experimente wurden verschiedene Systeme zur Strahl- bzw. Dosismonitorierung und retrospektiven Dosisbestimmung eingesetzt. Während der Bestrahlungen wurde die Elektronenstrahlintensität mit einem Faraday - Cup überwacht und die Dosisleistung im Strahl mittels Ionisationskammern gemessen. Die am Zellort applizierte Dosis wurde nach der Bestrahlung mittels Filmdosimeter, welche direkt vor den Zellproben positioniert waren, bestimmt.
Eine erste strahlenbiologische Charakterisierung der laserbeschleunigten Elektronen erfolgte mit dem Nachweis von DNS Doppelstrangbrüchen über die Antikörper - Doppelmarkierung von g - H2AX und 53BP1, zwei Molekülen, die direkt nach Bestrahlung an den Doppelstrangbrüchen der DNS aktiviert werden. Für beide untersuchten Zelllinien konnten erste Dosis - Effekt - Kurven dieses biologischen Endpunkts für verschiedene Zeitpunkte nach Bestrahlung bestimmt werden. Eindeutige Aussagen, auch im Vergleich zu verschiedenen Referenzstrahlungen, werden aber erst nach Abschluss der Experimentreihe möglich sein.
Ein Ausblick auf zukünftige Arbeiten mit verschiedenen Zelllinien und weiteren biologischen Endpunkten wird ebenfalls im Vortrag gegeben.
  • Poster
    17. Symposium Experimentelle Strahlentherapie und klinische Strahlenbiologie, 28.02.-01.03.2008, Dresden, Germany
  • Contribution to proceedings
    17. Symposium Experimentelle Strahlentherapie und klinische Strahlenbiologie, 28.02.-01.03.2008, Dresden, Germany
    Band 17: Selbstverlag, 1432-864X

Publ.-Id: 11052 - Permalink


BACOPP-D as treatment in patients with advanced Hodgkin lymphoma
Naumann, R.; Wetzko, K.; Haenel, A.; Friedrichsen, K.; Zschuppe, E.; Schmidt, H.; Moelle, M.; Dawel, M.; Beuthien-Baumann, B.; Schwanebeck, U.; Ehninger, G.; Haenel, M.;
Introduction.
The development of the escalated BEACOPP regimen let to an improved outcome in patients with advanced Hodgkin Lymphoma (HD9 study of the GHSG). However, the application of high dose etoposide (cumulative 4,8 g/m2 per 8 cycles) seems to be associated with an
increased incidence of secondary MDS and AML, respectively. Therefore, the aim of our ongoing multicenter pilot study is to evaluate the efficacy
and toxicity of the etoposide free as well as dose intensified BACOPP-D protocol.

Methods.
Since May 2000 a total of 115 patients with Hodgkin Lymphoma (HL) stage IIB, III, and IV were treated with BACOPP-D which included cyclophosphamide 1250 mg/m2 (d1), adriamycin 25 mg/m2(d1+2), dacarbazine 250 mg/m2 (d1-3), procarbazine 100 mg/m2 (d1-7), prednisolone 40 mg/m2 (d1-14), bleomycin 10 mg/m2(d8) and vincristine 1,4 mg/m2 (maximum 2 mg, d8) at three-weekly intervals with granulocyte colony-stimulating factor (G-CSF). A consolidating involved field radiation (30 Gy) was performed only in patients who achieved less than CR following chemotherapy. Initial staging and post-treatment control included PET monitoring.

Results.
Until now 97 patients (median age 35 years, range 17-65; 61 male, 36 female) are assessable for toxicity and treatment outcome. We analyzed the acute toxicity for 728 cycles of BACOPP-D. CTC/WHO grade III/IV haematological toxicities per patient were observed as follows:
leukopenia 93%, anemia 39%, and thrombocytopenia 33%. CTC grade III/IV non-haematological side effects included documented infection (4%) and lung toxicity (one patient with reversible bleomycininduced pneumonitis). A total of 85 patients (88%) achieved complete remission, 9 patients (9%) achieved partial remission, three patients (3%) had progressive disease. At a median observation time of 39 months (0,9-77 months), six patients have relapsed, and nine deaths were documented (4 HL-specific and 3 treatment related deaths, 1 death due to ruptured Meckel diverticulum with peritonitis, one 65 year-old woman died in CR following myocardial infarction caused by coronary heart disease). One patient developed a second neoplasia (hypopharyngeal carcinoma in an alcoholic). The overall survival and freedom from treatment failure rates at 39 months were 91% and 85%, respectively.

Discussion.
BACOPP-D regimen appears as a feasible and safe treatment protocol with moderate acute toxicity in patients with advanced HL. No secondary AML or MDS occured until now.
  • Open Access LogoAbstract in refereed journal
    Haematologica -The Hematology Journal 92(2007)5, 69
  • Poster
    7th International Symposium on Hodgkin Lymphoma, 03.-07.11.2007, Köln, Deutschland

Publ.-Id: 11051 - Permalink


Comparison of three quantum chemical ab initio methods for band structure calculations: the hydrogen fluoride chain
Bezugly, V.; Albrecht, M.; Birkenheuer, U.;
Three different many-body wave-function-based ab initio methods for the calculation of correlated (or quasi-particle) band structures of periodic systems are presented: the local Hamiltonian approach, the incremental self-energy method, and the crystal orbital variant of the algebraic diagrammatic construction. All three methods explicitly exploit the local nature of electron correlation, and by consequently switching to representations in localized Wannier orbitals O(N) scaling could be achieved in all three cases. These methods were applied to single (HF)2 zigzag chains as found in solid hydrogen fluoride using the same geometries and basis sets. Essentially identical quasi-particle band structures were obtained, corroborating the appropriateness of the different concepts pursued in each of the presented quantum chemical correlation methods for band structures of infinite systems.
Keywords: quantum chemistry, electronic structure, band structure, electron correlation, local correlation methods, excited-states, hydrogen fluoride chains
  • Open Access LogoJournal of Physics: Conference Series 117(2008), 012006

Publ.-Id: 11050 - Permalink


Experimental CFD grade data for stratified two-phase flows
Vallee, C.; Lucas, D.; Beyer, M.; Pietruske, H.; Schütz, P.; Carl, H.;
Stratified two-phase flows were investigated at two test facilities with horizontal test-sections. For both, rectangular channel cross-sections were chosen to provide optimal observation possibilities for the application of optical measurement techniques. In order to show the local flow structure, high-speed video observation was applied, which delivers the high resolution in space and time needed for CFD code validation.

The Horizontal Air/Water Channel (HAWAC) is made of acrylic glass and allows the investigation of air/water co-current flows at atmospheric pressure and room temperature. At the channel inlet, a special device was designed for well-defined and adjustable inlet boundary conditions. For the quantitative analysis of the optical measurements performed at the HAWAC, an algorithm was developed to recognise the stratified interface in the camera frames. This allows to make statistical treatments for comparison with CFD calculation results. As an example, the instable wave growth leading to slug flow is shown from the test-section inlet. Moreover, the hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was investigated in this closed channel. The structure of the hydraulic jump over time is revealed by the calculation of the probability density of the water level. A series of experiments show that the hydraulic jump profile and its position from the inlet vary sensibly with the inlet boundary conditions due to the momentum exchange between the phases.

The second channel is built in the pressure vessel of the TOPFLOW facility, which is used to perform air/water and steam/water experiments at pressures of up to 5.0 MPa and temperatures of up to 264°C, but under pressure equilibrium with the vessel inside. In the present experiment, the test-section represents a flat model of the hot leg of the German Konvoi pressurised water reactor scaled at 1:3. The investigations focus on the flow regimes observed in the region of the elbow and of the steam generator inlet chamber, which are equipped with glass side walls. An overview of the experimental methodology and of the acquired data is given. These cover experiments without water circulation, which can be seen as test cases for CFD development, as well as counter-current flow limitation experiments, representing transient validation cases of a typical nuclear reactor safety issue.
Keywords: two-phase flow, stratified flow, horizontal flow, high-speed video observation, image processing, hot leg
  • Contribution to proceedings
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
    Paper HOR-05
  • Poster
    XCFD4NRS - Experiments and CFD Code Applications to Nuclear Reactor Safety, 10.-12.09.2008, Grenoble, France
  • Nuclear Engineering and Design 240(2010), 2347-2356
    DOI: 10.1016/j.nucengdes.2009.11.011

Publ.-Id: 11049 - Permalink


Nuclear physics in astrophysics III
Bemmerer, D.; Grosse, E.; Junghans, A.; Schwengner, R.; Wagner, A.;
Introduction to the proceedings volume of the Europhysics Conference "Nuclear Physics in Astrophysics III", March 2007, Dresden

Publ.-Id: 11048 - Permalink


Untersuchung von Spektraleigenschaften kugelsymmetrischer alpha2-dynamos mit Techniken der Funktionalanalysis und Operatortheorie, Singularitätentheorie und Bifurkationstheorie
Gerbeth, G.; Stefani, F.; Günther, U.;
Kosmische Magnetfelder werden durch Selbsterregung in strömenden elektrisch leitfähigen Flüssigkeiten erzeugt. Lang andauernde Phasen relativer Feldstabilität können dabei von kurzen Phasen mit hoher Dynamik und damit einhergehenden Feldumpolungsprozessen unterbrochen werden. Jüngste numerische Untersuchungen an einem einfachen Dynamo-Modell im Sättigungsregime, dem kugelsymmetrischen alpha2-Dynamo mit algebraischem alpha-Quenching, deuten darauf hin, dass dynamische Feldumpolungen für eine Vielzahl von Dynamo-Konfigurationen auftreten und sich unter geeigneten Bedingungen eventuell sogar experimentell erzeugen lassen. Als wesentliches Kriterium für das Auftreten einer Feldumpolung konnte bisher das Vorhandensein eines spektralen Entartungspunktes mit Phasenübergang von nichtoszillierendem zu oszillierendem Dynamo-Regime in der Nähe des spektralen Nullpunktes identifiziert werden. Im Rahmen des einjährigen DFG-Projektes wurden anhand einfacher Dynamo-Modelle theoretische Grundlagenuntersuchungen zur Dynamik von Feldumpolungen durchgeführt.
  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    FZD\FWS\2008\03

Publ.-Id: 11047 - Permalink


Nonlinear multidimensional cosmological models with form fields: stabilization of extra dimensions and the cosmological constant problem
Günther, U.; Moniz, P.; Zhuk, A.;
We consider multidimensional gravitational models with a nonlinear scalar curvature term and form fields in the action functional. In our scenario it is assumed that the higher dimensional spacetime undergoes a spontaneous compactification to a warped product manifold. Particular attention is paid to models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for solitonic form fields. It is shown that for certain parameter ranges the extra dimensions are stabilized. In particular, stabilization is possible for any sign of the internal space curvature, the bulk cosmological constant and of the effective four-dimensional cosmological constant. Moreover, the effective cosmological constant can satisfy the observable limit on the dark energy density. Finally, we discuss the restrictions on the parameters of the considered nonlinear models and how they follow from the connection between the D-dimensional and the four-dimensional fundamental mass scales.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction, higher order curvature corrections

Publ.-Id: 11046 - Permalink


Multidimensional cosmology and asymptotical AdS
Günther, U.; Moniz, P.; Zhuk, A.;
A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative curvature. As a consequence, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on the parameters of the considered non-linear models.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction

Publ.-Id: 11045 - Permalink


Asymptotical AdS from nonlinear gravitational models with stabilized extra dimensions
Günther, U.; Moniz, P.; Zhuk, A.;
We consider non-linear gravitational models with a multidimensional warped product geometry. Particular attention is payed to models with quadratic scalar curvature terms. It is shown that for certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative constant curvature. In this case, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. As a consequence, the homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets a restriction on the parameters of the considered non-linear models.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction

Publ.-Id: 11044 - Permalink


Gravitational excitons - fluctuating particles from extra dimensions
Günther, U.; Zhuk, A.;
We show that for warped product space-times the conformal (geometric moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external space-time. These scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. On the other hand, they provide possible values for the effective cosmological constant.
Keywords: String theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction, dark matter
  • Contribution to external collection
    W. Janke, A. Pelster, H.-J.Schmidt, M. Bachmann: Fluctuating paths and fields. Dedicated to Hagen Kleinert on the occasion of his 60th birthday., Singapore: World Scientific, 2001, 981-02-4648-X, 721-728

Publ.-Id: 11043 - Permalink


Gravitational excitons as dark matter
Günther, U.; Zhuk, A.;
In earlier work it was pointed out that for warped product spacetimes the conformal (geometrical moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external spacetime. Here we show that these scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. Masses of the gravexcitons are defined by the form of the effective potential of the theory and the stabilization scales of the internal space. This implies that different stabilization scales result in different types of DM. An essential role is played by the effective potential. On the one hand, its minima fix possible stabilization scales of the internal spaces; on the other hand, they provide possible values for the effective cosmological constant.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction, dark matter
  • Contribution to proceedings
    Cosmology and Particle Physics (CAPP 2000), 17.-28.07.2000, Verbier, Switzerland
    Proceedings of the Conference on Cosmology and Particle Physics (CAPP 2000), New York: Springer, 1-56396-986-6, 371-374

Publ.-Id: 11042 - Permalink


Remarks on dynamical stabilization of internal spaces in multidimensional cosmology
Günther, U.; Zhuk, A.;
The possibility of dynamical stabilization of an internal space is investigated for a multidimensional cosmological model with minimal coupled scalar field as inflaton. It is shown that a successful dynamical compactification crucially depends on the type of interaction between the geometrical modulus field and the inflaton and its decay products. In the considered model a stable compactification can be ensured via trapping of the modulus field by a minimum of the effective potential.
Keywords: moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction

Publ.-Id: 11041 - Permalink


Stabilization of internal spaces in multidimensional cosmology
Günther, U.; Zhuk, A.;
Effective 4-dimensional theories are investigated which were obtained under dimensional reduction of multidimensional cosmological models with a minimal coupled scalar field as matter source. Conditions for the internal space stabilization are considered and the possibility for inflation in the external space is discussed. The electroweak as well as the Planck fundamental scale approaches are investigated and compared with each other. It is shown that there exists a rescaling for the effective cosmological constant as well as for gravitational exciton masses in the different approaches.
Keywords: moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction

Publ.-Id: 11040 - Permalink


Multidimensional perfect fluid cosmology with stable compactified internal dimensions
Günther, U.; Zhuk, A.;
Multidimensional cosmological models in the presence of a bare cosmological constant and a perfect fluid are investigated under dimensional reduction to 4-dimensional effective models. Stable compactification of the internal spaces is achieved for a special class of perfect fluids. The external space behaves in accordance with the standard Friedmann model. Necessary restrictions on the parameters of the models are found to ensure dynamical behavior of the external (our) universe in agreement with observations.
Keywords: moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction

Publ.-Id: 11039 - Permalink


On stable compactification with Casimir-like potential
Günther, U.; Kriskiv, S.; Zhuk, A.;
Multidimensional cosmological models with a higher dimensional space-time manifold are investigated under dimensional reduction. In the Einstein conformal frame, the effective potential for the internal scale factors is obtained. The stable compactification of the internal spaces is achieved due to the Casimir effect. In the case of more than one internal space a Casimir-like ansatz for the energy density of the massless scalar field fluctuations is proposed. Stable configurations with respect to the internal scale factor excitations are found in the cases of one and two internal spaces.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction
  • Gravitation and Cosmology 4(1998), 1-16

Publ.-Id: 11038 - Permalink


Stable compactification and gravitational excitons from extra dimensions
Günther, U.; Zhuk, A.;
We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction. Stability due to different types of effective potentials is analyzed for specific configurations of internal spaces. Necessary restrictions on the parameters of the models are found and masses of gravitational excitons (small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials) are calculated.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction
  • Hadronic Journal 21(1998), 279-318

Publ.-Id: 11037 - Permalink


Gravitational excitons from extra dimensions
Günther, U.; Zhuk, A.;
We study inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold under dimensional reduction and show that small inhomogeneous excitations of the scale factors of the internal spaces near minima of effective potentials should be observable as massive scalar particles (gravitational excitons) in the external space-time.
Keywords: string theory, moduli stabilization, scalar-tensor theory, higher dimensional gravity, dimensional reduction
  • Contribution to proceedings
    8th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (MG 8), Jerusalem, Israel, 22-27 June 1997, 22.-27.06.1997, Jerusalem, Israel
    8th Marcel Grossmann Meeting on Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories (MG 8), Singapore: World Scientific, 981-02-3793-6, 517-519

Publ.-Id: 11036 - Permalink


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