Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Quantitative accuracy of MR-based attenuation correction in whole-body PET/MR

Schramm, G.; Langner, J.; Hofheinz, F.; Beuthien-Baumann, B.; Platzek, I.; Kotzerke, J.; Steinbach, J.; van den Hoff, J.

Objectives: In 2010, a hybrid whole body PET/MR system (Philips Ingenuity TF PET/MR) was installed at our institute. PET/MR is expected to offer many new possibilities in the field of quantitative bimodal functional imaging. Quantitative PET image reconstruction requires attenuation correction (AC) which is commonly based on a measurement of photon attenuation using either a transmission scan in stand-alone PET
(TRAC) or a CT scan in PET/CT systems. In PET/MR, however, AC is performed with a software-based approach (MRAC) using dedicated tissue segmentation and tissue type identification (air, lung, soft tissue) of an MR image. Here, we present a first evaluation of the accuracy of the vendor-provided MRAC in whole body investigations.
Methods: We performed sequential PET scans of 9 patients on a stand-alone Siemens ECAT HR+ and on the Ingenuity PET/MR with a time delay of approximately 2h. In addition to the standard reconstruction using MRAC, we performed a second reconstruction of the emission data from the PET/MR using the coregistered transmission-based attenuation maps from the HR+. For the two resulting PET image volumes, we performed a voxel-by-voxel correlation analysis and a comparison of the SUVs in different ROIs.
Results: The PET correlation analysis yielded a Pearson correlation coefficient of 0.93 and 0.96 and average deviations of 4% and 3% between the two reconstructed images for all voxels in the lung and in the torso, respectively. In one patient we observed failure of correct lung detection because of severe motion artifacts of the heart in the MR image. Accordingly we found a very large average deviation of 65% in the lung.
Conclusions: The MRAC algorithm generally yields satisfactory results with respect to soft tissue and air segmentation. The average deviation between PET images reconstructed with TRAC and MRAC is usually small and quantitative accuracy is adequate. Failure of segmentation occur rarely which necessitates manual intervention to achieve adequate segmentation.

  • Lecture (Conference)
    SNM 2012 annual meeting 2012, 09.-13.06.2012, Miami, Florida/USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 53(2012), 373

Publ.-Id: 17443

Charakterisierung von Rezeptor-Tyrosinkinasen der Eph/Ephrin-Familie bei humanen Melanomzelllinien

Komadina Garcia Meza, D.

kein Abstract verfügbar

  • Bachelor thesis
    Hochschule für Technik und Wirtschaft, Fakultät Maschinenbau/Verfahrenstechnik, Studiengang Chemie, 2012
    56 Seiten

Publ.-Id: 17442

Neutron induced by an α-beam incident on a deuterium gas target, and the background for a study of the 2H(α,γ)6Li reaction at LUNA

Anders, M.; Trezzi, D.; Bellini, A.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Costantini, H.; Corvisiero, P.; Elekes, Z.; Erhard, M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Junker, M.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Szücs, T.

The production of the stable isotope 6Li in standard Big Bang nucleosynthesis has recently attracted much interest. This is so because some recent observations in metal-poor stars suggest that a cosmological 6Li plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of 7Li abundances and would point to a primordial origin of 6Li, contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang 6Li production must be revisited. The present work reports on the neutron-induced background encountered in a new study of the 2H(α,γ)6Li reaction. In the experiment, an α-beam from the ultra-low background underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3 MeV neutrons on well-shielded high purity germanium detectors has been studied in detail. Data have been taken at 280 and 400 keV α-beam energy and for comparison also using an americium-beryllium neutron source. The ramifications for the planned 2H(α,γ)6Li measurement are discussed.

Keywords: Big Bang nucleosynthesis; Inelastic neutron scattering; Gas target; Geant4 simulation; AmBe neutron source; LUNA

Publ.-Id: 17440

Neutronics analysis around the spallation target for the MYRRHA ADS design

Ferrari, A.

The present study has been done in the framework of the Central Design Team european project (CDT), which has the goal to design the FAst Spectrum Transmutation Experimental Facility (FASTEF), able to demonstrate efficient transmutation of high level waste and associated ADS technology. On the FASTEF design will be based the MYRRHA facility at SCK•CEN in Mol (Belgium), which should start the construction phase in 2015. The heart of the system is a 100 MW lead-bismuth eutectic (LBE) cooled reactor, working both in critical and sub-critical modes. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV, 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core.
Starting from the initial need to assess the shielding of the reactor building and to characterize the irradiation of the materials in the last part of the proton beam-line, an extensive simulation study has been done to define the radiation fields around the spallation target, with special attention to the neutron component. Using a description that includes the last part of the proton beamline and the LBE spallation target, neutron yields and spectra have been computed with both Monte Carlo codes FLUKA (version 2011.2) and MCNPX (version 2.6.0), where in the second case different fragmentation/ evaporation models have been compared. As second step the neutron fluence behavior has been estimated in the whole structure around the reactor core, including fission neutrons. In this case a full MCNPX model has been used, including the vertical part of the proton beamline, the spallation target, the reactor core and the structure around, from the coolant until the external vessel, the reactor cover and the shielding walls. With the aim to compare the results, an additional simulation has been performed with the FLUKA code, using neutron source terms evaluated in the previous MCNPX calculations on suitable surfaces close to the reactor core. The results of the neutronics analysis are presented, together with the main implications on the design solutions.

Keywords: ADS; spallation sources; FLUKA; MCNPX

  • Lecture (Conference)
    13th International Conference on Nuclear Reaction Mechanisms, 11.-15.06.2012, Varenna, Italy

Publ.-Id: 17439

Development of [18F]Flubatine, a promising radiotracer for the imaging of α4β2 nicotinic acetylcholine receptors (nAChRs)

Hoepping, A.; Smits, R.; Fischer, S.; Hiller, A.; Funke, U.; Deuther-Conrad, W.; Sattler, B.; Sabri, O.; Steinbach, J.; Brust, P.

The density of nicotinic acetylcholine receptor (nAChR) subtypes is reduced in brain of Alzheimer’s disease (AD) patients. Imaging of α4β2 receptors, the predominant subtype, could thus contribute to early diagnosis of AD. Existing radiotracers for α4β2 nAChRs have suffered from inadequate affinity, or very slow binding kinetics, but the novel compound [18F]Flubatine presents several advantages. Both enantiomers display high affinity in vitro and fast cerebral binding kinetics in living mice and pigs. Initial human PET imaging studies have confirmed high uptake in the thalamus, low non-specific binding, and attainment of equilibrium binding in less than two hours. Dosimetry studies in healthy human volunteers indicate that effective doses for (-)-[18F]Flubatine (< 10 mSv/300 MBq) are compatible with application in routine clinical studies.
We have described the organic synthesis of enantiomerically pure (–)-Flubatine and (+)-Flubatine. Moreover, several precursors with different protecting groups and leaving groups have been synthesized for optimised radiosynthesis. The best radiochemical results were obtained with a trimethylammonium precursor carrying a Boc-protecting group, employing a two-step radiosynthesis. Radiolabelling under phase transfer conditions afforded the protected 18F-intermediate in yields of 90%. Subsequent deprotection under mild conditions gave the final products with a radiochemical yield of 70±5%, and specific activity >350 GBq/µmol. [18F]Flubatine was stable in dilute HCl, NaOH and K2CO3 solutions, as well as under physiological conditions.

  • Lecture (Conference)
    Seventh International Symposium on Radiohologens (7th ISR 2012), 15.-19.09.2012, Whistler, B.C., Canada

Publ.-Id: 17438

Design, synthesis, and preliminary in vitro and in vivo pharmacological evaluation of 4-{4-[2-(4-(2-substitutedquinoxalin-3-yl)piperazin-1-yl)ethyl]phenyl}thiazoles as atypical antipsychotic agents

Chandra Sekhar, K. V. G.; Rao, V. S.; Deuther-Conrad, W.; Sridhar, D.; Nagesh, H. N.; Kumar, V. S.; Brust, P.; Kumar, M. M. K.

A series of 4-{4-[2-(4-(2-substitutedquinoxalin-3-yl)piperazin-1-yl)ethyl] phenyl} thiazoles were synthesized in an effort to prepare novel atypical antipsychotic agents. The compounds were designed, synthesized, and characterized by spectral data (IR, 1H NMR, and MS) and the purity was ascertained by microanalysis. The D2 and 5-HT2A affinity of the synthesized compounds was screened in vitro by radioligand displacement assays on membrane homogenates isolated from rat striatum and rat cortex, respectively. Furthermore, all the synthesized final compounds (10a–g; 11a–g; 12a–g) were screened for their in vivo pharmacological activity in Swiss albino mice. D2 antagonism studies were performed using climbing mouse assay model and 5-HT2A antagonism studies were performed using quipazine-induced head twitches in mice. It was observed that none of the new chemical entities exhibited catalepsy and 12d, 11f, and 10a were found to be the most active compounds with 5-HT2A/D2 ratio of 1.23077, 1.14286, and 1.12857, respectively, while the standard drug risperidone exhibited 5-HT2A/D2 ratio of 1.0989. Among the twenty one new chemical entities, three compounds (12d, 11f, and 10a) were found to exhibit better atypical antipsychotic activity as they were found to have higher Meltzer index than the standard drug risperidone.

Keywords: Schizophrenia; Atypical antipsychotics; Quinoxalines; Phenyl thiazoles

Publ.-Id: 17437

Simulation and prototyping of 2 m long resistive plate chambers for detection of fast neutrons and multi–neutron event identification

Elekes, Z.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Caesar, C.; Cowan, T. C.; Hehner, J.; Heil, M.; Kempe, M.; Rossi, D.; Röder, M.; Simon, H.; Sobiella, M.; Stach, D.; Reinhardt, T.; Wagner, A.; Yakorev, D.; Zilges, A.; Zuber, K.; for the R3B Collaboration

Resistive plate chamber (RPC) prototypes of 2 m length were simulated and built. The experimental tests using a 31 MeV electron beam, discussed in details, showed an efficiency higher than 90% and an excellent time resolution of around σ=100 ps. Furthermore, comprehensive simulations were performed by Geant4 toolkit in order to study the possible use of these RPCs for fast neutron (200 MeV–1 GeV) detection and multi–neutron event identification. The validation of simulation parameters was carried out via a comparison to experimental data. A possible setup for invariant mass spectroscopy of multiple neutron emission is presented and the characteristics are discussed. The results show that the setup has a high detection efficiency and is capable of determining the momentum of the outgoing neutrons and reconstructing the relative energy between the fragments from nuclear reactions.

Keywords: prototyping; simulation; Geant4; resistive plate chamber; nuclear reaction; multi–neutron; event reconstruction

Publ.-Id: 17436

Natural Circulation Phenomena and Modelling for Advanced Water Cooled Reactors

Krepper, E.

The role of natural circulation in advanced water cooled reactor design has been extended with the adoption of passive safety systems. Some designs utilize natural circulation to remove core heat during normal operation. Most passive safety systems used in evolutionary and innovative water cooled reactor designs are driven by natural circulation. The use of passive systems based on natural circulation can eliminate the costs associated with the installation, maintenance and operation of active systems that require multiple pumps with independent and redundant electric power supplies. However, considering the weak driving forces of passive systems based on natural circulation, careful design and analysis methods must be employed to ensure that the systems perform their intended functions.

Keywords: natural circulation; nuclear reactor safety; passive systems

  • Open Access Logo Contribution to external collection
    N. Aksan, J.-H. Choi: Natural Circulation Phenomena and Modelling for Advanced Water Cooled Reactors, IAEA-TECDOC-1677, Vienna: IAEA, 2012, 978-92-0-127410-6

Publ.-Id: 17435

r3-Innovative Technologien für Ressourceneffizienz -Strategische Metalle und Mineralien

Dürkoop, A.

  • Poster
    Strategische Rohstoffe - Risikovorsorge. 4. Symposium Freiberg Innovationen, 19.-20.04.2012, Freiberg, Deutschland

Publ.-Id: 17434

"Das Helmholtz-Institut Freiberg für Ressourcentechnologie"

Dürkoop, A.; Gutzmer, J.

Vorstellung des Helmholtz-Instituts Freiberg für Ressourcentechnologie

  • Invited lecture (Conferences)
    18. Firmenkolloquium Beak Consultants GmbH, 04.05.2012, Freiberg, Deutschland

Publ.-Id: 17433

Current quests in low-energy experimental nuclear astrophysics

Bemmerer, D.

The state of the art of low-energy experiments for nuclear astrophysics is reviewed, with an emphasis on the nuclear physics of the Sun, and on the production of the supernova marker titanium-44. An outlook will be given on the topics to be addressed at future underground low-energy ion accelerators, an important complement to the studies at FAIR.

Keywords: Nuclear Astrophysics LUNA Felsenkeller Solar abundance problem supernova nucleosynthesis

  • Lecture (Conference)
    Workshop on Open questions in Galactic chemical evolution, 08.-09.05.2012, Heidelberg, Germany

Publ.-Id: 17432

Precise nuclear physics for the Big Bang and our Sun

Bemmerer, D.

There are a wealth of precise observations on our nearest star, the Sun, including spectroscopical, helioseismological, and neutrino data. The Sun may therefore be an ideal testing ground for stellar models, which have to be applied to scenarios where much less is known. After the long-standing solar neutrino problem had been spectacularly resolved one decade ago, hopes were high to develop the standard solar model to a precision of a few percent. However, a new discrepancy has since cropped up, called the solar abundance problem. In the talk, it will be discussed how nuclear physics experiments may help improve our understanding of the Sun. The impact of new nuclear data on the creation of the three lightest chemical elements in the first minutes of our universe will also be shown.

Keywords: Nuclear Astrophysics Felsenkeller LUNA Solar abundance problem

  • Invited lecture (Conferences)
    HIC for FAIR Kolloquium Gießen, 03.05.2012, Gießen, Deutschland
  • Invited lecture (Conferences)
    Seminar Institut für Angewandte Physik, 04.05.2012, Frankfurt am Main, Deutschland

Publ.-Id: 17431

2‐D Positronen‐Lebensdauerspektroskopie

Wagner, A.

First experiments ausing a multi-detector setup for 2-D tomographic Positron Annihilation Lifetime Spectroscopy are presented.

Keywords: multi-detector tomographic Positron Annihilation Lifetime Spectroscopy

  • Lecture (Conference)
    Treffen deutscher Positronengruppen, 28.02.-01.03.2012, Dresden, Deutschland

Publ.-Id: 17430

Taming of Ga droplets on DLC layers – Size tuning and local arrangement with nanometer accuracy

Philipp, P.; Bischoff, L.; Schmidt, B.

A new method for the fabrication of spherical gallium nanoparticles (Ga-NPs) on diamond-like carbon (DLC) layers with high precision in their desired diameter and positioning is presented. The basic principle is the pre-patterning of a DLC film by focused Ga+ ion beam irradiation and subsequent annealing. During thermal treatment the evolution of single Ga NPs with spherical shape on irradiated areas is driven by phase separation and surface segregation of Ga from the supersaturated DLC layer. Shape and size of the implanted areas as well as the ion fluence serve as a Ga reservoir for the NP evolution which is strongly correlated with the NP diameter. For the formation of segregation seeds to avoid random segregation of the NPs small spots are additionally implanted with Ga within the irradiated areas. The NP evolution is than assessed to the seed position and the material for the Ga NP growth is gathered from the surrounding reservoir. Using this technique Ga NPs were fabricated with a diameter ranging from 40 nm up to several hundred nm. Prospective applications i.e. in the field of plasmonics arise from the arrangement in chains as well as in periodical two-dimensional arrays with defined NP size and interparticle distance.

Keywords: gallium droplets; nanoparticles; diamond-like carbon; focused ion beam; segregation; plasmonics

  • Lecture (Conference)
    56th international conference on electron, ion, and photon beam technology and nanofabrication (EIPBN), 29.05.-01.06.2012, Waikoloa Village, Hawaii, USA
  • Nanotechnology 23(2012)47, 475304
    Online First (2012) DOI: 10.1088/0957-4484/23/47/475304

Publ.-Id: 17429

Activation studies around the proton beamline for the MYRRHA ADS design

Ferrari, A.; Biarrotte, J.-L.; Perrot, L.; Saugnac, H.; VandePlassche, D.

The design of sub-critical accelerator-driven systems requires high energy and high power proton accelerators, of the order of hundreds MeV and some MW for the proposed demonstration experiments. The use of high energy Mega-Watt beams presents many serious challenges for various aspects of accelerator design, radiation shielding and reliable operations, being the induced activation a central problem.
A key issue is the introduction of low-activation materials to improve the accessibility and the long-term treatment of the irradiated elements, maintaining - and sometimes improving - the shielding efficiency with a suitable material configuration. In this work a simulation study based on the FLUKA Monte Carlo transport code is presented: different solutions for the main beam dump of the 600 MeV, 4 mA MYRRHA proton beamline are investigated and discussed. For each proposed solution a complete analysis of the secondary radiation fields and of the residual activation is shown: the inventory of the produced radionuclides and the residual ambient dose equivalent at different distances from the dump are estimated, both for short-term and long-term irradiation conditions and for all the significant cooling times.

Keywords: Accelerator-driven systems; activation; shielding; Monte Carlo

  • Lecture (Conference)
    Accelerator Radiation Induced Activation (ARIA 2011), 15.-19.05.2011, Ma'ale Hachamisha, Israel

Publ.-Id: 17428

Shielding and activation studies around the proton beamline for the MYRRHA design

Ferrari, A.; Merk, B.; Konheiser, J.

Accelerator-driven systems (ADS) are one of the options studied for the transmutation of nuclear waste in the European Community. The design of sub-critical ADS requires high energy and high power proton accelerators, of the order of hundreds MeV and some MW for the proposed demonstration experiments. The use of high energy Mega-Watt proton beams, in combination with a nuclear reactor core operating in sub-critical or critical mode, presents many challenges for various aspects of the design. Radiation shielding and minimization of the induced activation are key points.
The present study has been done in the framework of the Central Design Team european project (CDT), which has the goal to design the FAst Spectrum Transmutation Experimental Facility (FASTEF), able to demonstrate efficient transmutation of high level waste and associated ADS technology. The heart of the system is a 100 MW LBE cooled reactor, working both in critical and sub-critical modes. A beamline aims to transport a 600 MeV, 4 mA proton beam produced by a linear accelerator up to the spallation target for the neutron production, which is located inside the reactor core. Based on the FASTEF design, the MYRRHA facility, which should enter the construction phase in 2015, will be built at SCK•CEN in Mol (Belgium). MYRRHA is conceived as a multi purpose facility: as technology demonstrator for lead-bismuth cooled fast reactor, as demonstrator for efficient transmutation, and as high flux irradiation facility for material testing and medical isotope production.
An extensive simulation study has been done to assess the shielding of the reactor building and the proton accelerator, as well as to fix the activation problems that have a heavy influence on the beamline and building design. Here the shielding assessment around the proton accelerator is presented, together with the optimization of the elements of the beamline that are devoted to the partial or total beam absorption (beam dump, collimators). This study has been fully carried out by using the FLUKA code, which has the unique feature to perform the transport of the residual radiation via a full Monte Carlo method, allowing in addition modifications in the geometry and material characterization from the prompt to the residual radiation transport. It will be shown how a suitable material configuration, with the introduction of low-activation materials, is a key issue: it will improve the accessibility and the long-term treatment of the irradiated elements allowing to maintain - and sometimes to improve – the shielding efficiency.

Keywords: Accelerator-driven systems; radiation transport; Monte Carlo; shielding

  • Lecture (Conference)
    International Conference of Transport Theory (ICTT-22), 12.-16.09.2011, Portland, Oregon, USA

Publ.-Id: 17426

Tin sorption to magnetite nanoparticles under anoxic conditions

Dulnee, S.; Banerjee, D.; Rossberg, A.; Scheinost, A. C.

The long-lived fission product 126Sn is of substantial interest in the context of nuclear waste disposal in deep underground repositories. However, the redox state (di- or tetravalent) under the expected anoxic conditions is still a matter of debate. We therefore investigated sorption and oxidation of Sn(II) in the presence of a typical corrosion product, magnetite (FeIIFeIII2O4), with a mean particle size of 9.4 nm. In order to simulate waste disposal conditions, the experiments were performed under strictly anoxic conditions in a glovebox at <2 ppm O2. Macroscopic parameters (pH, Eh, [Sn], [Fe]) were monitored along with redox state and local structure of Sn (X-ray absorption spectroscopy) and Fe (XPS) as a function of time, pH, and surface loading.
Magnetite rapidly sorbed Sn(II), reducing Sn concentration within 0.5 h from 10 to 0.0084 μμM. Tin was strongly sorbed by magnetite across a wide pH range from 3 to 9. Reduced sorption at pH <3 is in line with electrostatic repulsion between the positively charged surface of the magnetite nanoparticles (IEP ~6.7) and cationic Sn2+ or Sn4+ complexes. The reduced sorption at pH > 9 is in line with the transition from Sn(OH)20 to the anionic Sn(OH)3- which occurs at pH 9. Across the pH range 3-9 and reaction periods ≥1 h, EXAFS-derived sixfold oxygen coordination and XANES edge energy positions of ~29207 eV both indicate the presence of Sn(IV) at the magnetite surface. EXAFS shell fitting as well as Monte Carlo simulations showed formation of edge-sharing complexes of Sn(IV) with FeO6 octahedra (Sn-Fe distance of 3.15 Å), and formation of corner-sharing complexes with FeO4 tetrahedra (Sn-Fe distances of 3.60 Å). Even after the longest reaction periods of 1 month, we did not observe incorporation of Sn(IV) into the (compatible) magnetite structure. Also, precipitation of SnO2 was not observed in spite of an (initial) supersaturation.
In order to elucidate the reaction pathway, we also studied Fe in solution and at the surface (XPS). Starting with the PZC and increasing with [H+], the magnetite surface released Fe(II) into solution (0.11 g/L at pH 2). After addition of Sn(II), however, [Fe] in solution decreased as a function of Sn loading, in spite of the expected increase of structural Fe(II) due to the coupling to Sn(II) oxidation. This suggests a re-adsorption and possible re-precipitation of Fe(II) at the magnetite surface. Nevertheless, due to a protonation at low pH, Fe(II) again re-dissolved as a function of time. With XPS we were not able to detect an adequate increase of the Fe(II)/Fe(III) ratio at the surface, supporting an electron redistribution between bulk and surface Fe centers.
In conclusion, our study demonstrates that Sn is strongly retained by magnetite across a wide pH range, forming stable surfaces complexes and stabilising the magnetite surface against dissolution.

Keywords: tin; xafs; radionuclide; redox; magnetite

  • Lecture (Conference)
    The 22nd V.M. Goldschmidt Conference, 24.-29.06.2012, Montreal, Canada

Publ.-Id: 17425

Abiotic U(VI) Reduction by Biogenic Mackinawite

Veeramani, H.; Qafoku, N.; Pruden, A.; Monsegue, N.; Kukkadapu, R.; Murayama, M.; Newville, M.; Lanzirotti, A.; Scheinost, A. C.; Hochella, M. F.

Biogenic mackinawite (FeS) produced by Shewanella putrefaciens CN32 is submicron in size but nanosized in one dimension (film-like morphology)
Biogenic FeS is very reactive evident by its propensity to reduced U(VI) and rapid oxidation to form lepidocrocite upon exposure to air.
U(VI) reduction is observed in the pasteurized control indicative of a non-enzymatic redox process.
XAS and nanodiffraction techniques (bulk and nanoscale analyses) confirm the formation of UO2.
UO2 particles are nanoparticulate measuring c.a. 2.5 nm in size.
The present work suggests that a remediation strategy could potentially incorporate subsurface abiotic redox interactions between biogenic Fe(II)-bearing minerals such as mackinawite & contaminant U(VI) to immobilize U as UO2 – an in-situ waste form.

Keywords: Mackinawite; uranyl; reduction; XAFS

  • Poster
    The 22nd V.M. Goldschmidt Conference 2012, 24.-29.06.2012, Montreal, Canada

Publ.-Id: 17424

Phase-Based Profiling in GPGPU Kernels

Dietrich, R.; Schmitt, F.; Widera, R.; Bussmann, M.

More and more computationally intensive scientific applications make use of hardware accelerators like general purpose graphics processing units (GPGPUs). Compared to software development for typical multi-core processors their programming is fairly complex and needs hardware specific optimizations to utilize the full computing power. To achieve high performance, critical parts of a program have to be identified and optimized. This paper proposes an approach for performance analysis of CUDA kernel source code regions, which for the first time allows measuring the execution times within GPGPU kernels. We developed a tool, which implements the presented method and supports the application developer to easily identify hot spots within the kernel. The presented tool uses compile time code analysis to automatically instrument suitable instrumentation points for minimal program perturbation and further provides support for manual instrumentation. To the best of our knowledge this is the first approach, which allows for scalable runtime analysis within GPGPU kernels. Combined with existing performance analysis techniques this facilitates obtaining the full potential of modern parallel systems.

Keywords: performance analysis; tracing; profiling; GPGPU; CUDA; accelerators; many-core

  • Lecture (Conference)
    41st International Conference on Parallel Processing Workshops, 10.-13.09.2012, Pittsburgh, USA
  • Contribution to proceedings
    41st International Conference on Parallel Processing Workshops, 10.-13.09.2012, Pittsburgh, USA
    Proceedings of the 41st International Conference on Parallel Processing Workshops, 978-1-4673-2509-7, 414-423
    DOI: 10.1109/ICPPW.2012.59

Publ.-Id: 17423

Neue proteinbasierte biosorptive Materialien zur (Rück-)gewinnung von Metallen

Pollmann, K.; Kutschke, S.; Lehmann, F.; Matys, S.; Raff, J.

Viele Mikroorganismen haben spezielle Oberflächenstrukturen entwickelt, die eine hohe Affinität zu Metallen besitzen. Diese Strukturen können zur Entwicklung von Filtermaterialien genutzt werden, um Metalle aus stark verdünnten wässerigen Lösungen zu binden und zurückzugewinnen.
Derartige biosorptive Materialien gewinnen zunehmend an Bedeutung für industrielle Anwendungen. Vorteile sind die nahezu vollständige Entfernung der Metalle, die geringen Kosten und die häufig gute Verfügbarkeit, ihre Regenerationsfähigkeit sowie die Möglichkeit der Gewinnung abgetrennter Metalle [1-3]. Ihre Leistungsfähigkeit ist vergleichbar mit der von Ionenaustauscher¬materialien, und sie liefern häufig bessere Ergebnisse als Aktivkohle oder natürliche Zeolithmaterialien [3]. Die Anwendung der Biomaterialien in Säulen erfordert meist ihre Immobilisierung auf geeigneten Trägermaterialien. Herausforderungen bei der Herstellung derartiger Biokompositen sind eine hohe Materialstabilität bei gleichzeitigem Erhalt der Funktion.
In unserer Gruppe werden Hüllproteine (S-Layer) von Bakterien zur Entwicklung von derartigen Materialien verwendet. Diese Proteine bilden auf den Zelloberflächen und nach ihrer Isolation auf Trägermaterialien durch Selbstorganisation zweidimensionale Gitterstrukturen aus. Sie eignen sich zur Beschichtung von unterschiedlichsten Trägermaterialien, aber auch zur Einbettung in Keramiken. Derartig immobilisierte Proteine wurden bereits zur Uranentfernung aus Wässern eingesetzt [4]. Neben Uran werden aber auch Edelmetalle wie Palladium oder Platin oder toxische Elemente wie Arsen gut gebunden. In der Präsentation werden Ergebnisse dieser Arbeiten vorgestellt und Perspektiven zur weiteren Entwicklung von Filtermaterialien zur selektiven Aufkonzentrierung von strategisch relevanten Metallen aufgezeigt.
[1] Volesky, B., Biosorption of heavy metals. 1990, Boca Raton, Florida: CRC Press. 396.
[2] Volesky, B., Advances in biosorption of metals: Selection of biomass types. FEMS Microbiology Reviews, 1994. 14: p. 291-302.
[3] Matheickal, J.T. and Q. Yu, Biosorption of Lead(II) from aqueous solutions by Phellinus badius. Minerals Engineering, 1997. 10(9): p. 947-957.
[4] Raff, J., et al., Biosorption of uranium and copper by biocers. Chem. Mater., 2003. 15: p. 240-244.

  • Lecture (Conference)
    ProcessNET Jahrestagung 2012, 10.-13.09.2012, Karlsruhe, Deutschland

Publ.-Id: 17422

Design of Bio-based Multifunctional Composite Materials Using Self-assembling Bacterial S-layer Proteins

Pollmann, K.; Weinert, U.; Günther, T.; Suhr, M.; Vogel, M.; Bobeth, C.; Lehmann, F.; Matys, S.; Kutschke, S.; Raff, J.

Nanoscalic bio-inorganic hybrid materials are very attractive for various technical applications. Especially the use of self-assembling highly ordered proteins as part of such hybrid materials is an attractive approach and offer new possibilities to add novel properties to surfaces. In our group we use the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells as nanostructures for the assembly of novel materials. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. These features are used for the nano-patterning of various technical surfaces. The regular distributed pores of these paracrystalline arrays are binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1, 2]. In addition, the proteins can be modified with organic groups, thus adding additional functions to the nanocoatings.
We will present new results on the fabrication of S-layer based functional composite materials. The S-layer coatings are used as template for the bio-inspired mineralization and formation or deposition of various inorganic nanoparticles such as Pd, Pt, Au, ZnO and TiO2. The thus fabricated hybrid materials exhibit interesting chemical, physical and mechanical properties that can be used for different applications. Current projects concentrate on the development of photocatalytic materials based on S-layer supported metal oxide coatings. In another project we used TiO2 deposited on S-lLayer proteins for the high efficient removal of arsenic from waters.
Multifunctionality can be introduced to the materials either by genetic or by chemical engineering. In such an approach, we used S-layers for the assembly of sensory layers. These S-layers are functionalized by aptamers (oligonucleotides) that work as receptor and two different fluorophores working as donor/acceptor for detection via FRET. The binding of the analyte to the aptamer should influence the fluorescence, ideally causing the interruption of the FRET.
[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68

  • Lecture (Conference)
    MSE 2012 - Materials Science Engineering, 25.-27.09.2012, Darmstadt, Deutschland

Publ.-Id: 17421

Kleine Kumpel – Metallgewinnung mit Bakterien

Pollmann, K.

Metallgewinnung mit Bakterien

  • Lecture (others)
    Lange Nacht der Wissenschaft Dresden, 05.07.2012, Dresden, Deutschland

Publ.-Id: 17420

Bergbau mit Bakterien

Pollmann, K.

Bergbau mit Bakterien

  • Poster
    4. Symposium Freiberger Innovationen, 19.-20.04.2012, Freiberg, Deutschland

Publ.-Id: 17419

Kleine Kumpel – Bergbau mit Bakterien

Pollmann, K.

Überblick über Biomining

  • Lecture (others)
    Tag des offenen Labors, 12.05.2012, Dresden, Deutschland

Publ.-Id: 17418

A CMFD-Model for multi-scale interfacial structures

Hänsch, S.; Lucas, D.; Krepper, E.; Höhne, T.

In many two-phase flows a mixture of both stratified and dispersed flow regimes is encountered. Depending on the interfacial scale resolving and averaging methods are established for the numerical simulation of these special flow regimes. However, multiphase flows that cover a wide range of scales should be investigated considering coexistent segregated and dispersed flow. The simulation of such flows is a challenging task which led to the recent field of research known as multi-scale CMFD-simulations. Especially the transitions between different flow regimes play an essential role for a better understanding of many flow applications. No general technique for the simulation of such a flow situation has evolved yet. This contribution introduces a new CMFD-strategy of a generalized two-phase flow (GENTOP) dealing with such complex flow situations.
Currently, the GENTOP-concept is presented using a three-field two-fluid simulation based on the Eulerian methodology. The flow is described by a continuous liquid phase, a polydispersed gas phase, consisting of different bubble size groups, and a continuous gas phase. By using the framework of the recently developed inhomogeneous Multiple Size Group (MUSIG)-model, transfers between different bubble sizes due to coalescence and breakup processes are described. The GENTOP-concept extends this framework by adding a continuous gas phase summarizing all gas structures characterized by an interfacial scale large enough to be resolved. Thus, two gaseous fields are assumed, each field having its own set of mass-, momentum- and energy balance. An additional interface stabilizing force is introduced enabling the resolution of the gas-liquid interface. By modelling an additional mass transfer between the continuous and the polydispersed gas phase, transitions between different gas morphologies can be considered. The modelling of interfacial transfer requires a detection of interfacial structure in order to accurately involve the resolved gas-liquid interface. Based on the Algebraic Interfacial Area Density (AIAD)-model a generalized formulation for interfacial area density and drag has been found considering free surfaces within a multi-field simulation. This new concept can provide a more general insight into non-homogeneous multiphase flows by capturing continuous as well as polydispersed gas structures simultaneously.
Many multiphase flows relevant for industrial and scientific issues can be described by the GENTOP-concept. One of them is the impingement of a liquid jet on a water pool with an associated bubble entrainment playing a key role for nuclear safety issues during a loss-of-coolant accident. This flow phenomenon shows the mass transfer from a continuous into a polydispersed gas phase forming a bubble plume of different bubble sizes. Various multiphase flows with high gas fractions show inverse transfers from a dispersed into a continuous gaseous morphology such as the transition from bubbly to slug flow in a vertical pipe. This paper presents the principles of the new concept and illustrates them within such representative flow situations using the CFD-code CFX 13.0. First computational results are compared to experiments carried out at HZDR and theoretical data reported in literature. Both characteristic polydispersed and continuous gas structures are captured and show qualitative agreement. Further developments will concentrate on new generalized closure models for coalescence and breakup processes between continuous and dispersed gas phases.

Keywords: multi-fluid model; MUSIG; AIAD; gas-liquid interface; flow regime transition; air entrainment

  • Contribution to proceedings
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Südkorea
  • Lecture (Conference)
    CFD4NRS-4, The Experimental Validation and Application of CFD and CMFD Codes in Nuclear Reactor Technology, 10.-12.09.2012, Daejeon, Südkorea

Publ.-Id: 17417

Transport Coefficients in Gluodynamics: From Weak Coupling towards the Deconfinement Transition

Bluhm, M.; Kämpfer, B.; Redlich, K.

We study the ratio of bulk to shear viscosity in gluodynamics within a phenomenological quasiparticle model. We show that at large temperatures this ratio exhibits a quadratic dependence on the conformality measure as known from weak coupling perturbative QCD. In the region of the deconfinement transition, however, this dependence becomes linear as known from specific strongly coupled theories. The onset of the strong coupling behavior is located near the maximum of the scaled interaction measure. This qualitative behavior of the viscosity ratio is rather insensitive to details of the equation of state.

Publ.-Id: 17416

Experimentelle Untersuchung der Stoffübertragung in einem geneigten rotierenden Festbettreaktor

Wiezorek, M.

Das Institut für Fluiddynamik beschäftigt sich unter anderem mit der Untersuchung mehrphasiger verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate und -reaktoren.
Ein solches neuartiges Konzept stellt der geneigte und rotierende Festbettreaktor dar. Im Gegensatz zur herkömmlichen zeitlich-periodischen Betriebsweise vertikaler Rieselbettreaktoren erfolgt die Prozessintensivierung hier durch die Aufprägung einer örtlichen Periodizität unter stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich durch die Wahl von Reaktorneigung und Reaktordrehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der Diplomarbeit wurde der Einfluss von Reaktorneigung und -drehzahl auf die Stoffübertragung bei ausgewählten Gas- und Flüssigkeitsdurchsätzen am Beispiel des flüssigkeitsseitigen Stoffdurchgangskoeffizienten untersucht und im Vergleich zum etablierten Rieselbettreaktor bewertet.

Keywords: Fixed bed reactor; Mass transfer; Inclination; Rotation

  • Diploma thesis
    TU Dresden, 2012
    0125 Seiten

Publ.-Id: 17415

Calibration of a single-shot M-IR spectrometer from (2-12µm)

Debus, A.; Zarini, O.; Couperus, J. P.; Irman, A.; Seidel, W.; Schramm, U.

Conclusion of the calibration campaign at the IR-FEL (FELBE) with detailed results on the calibration of a prism-based spectrometer using an MCT array detector in the wavelength range from 2-12 µm. An outlook onto the next stage of development, i.e. extension into the NIR, VIS and UV, is given.

Keywords: mercury cadmium telluride detector; MCT detector; mid-IR; spectrometer calibration; black body; FELBE; IR-FEL

  • Lecture (others)
    Group seminar, 20.2.2012, Dresden, Germany

Publ.-Id: 17414

Ptychographic X-ray computed tomography at the nanoscale

Debus, A.

Presentation in the Oncoray Journal Club. Explained to a mainly medicine- and biology-oriented audience the benefits of a recent Nature paper: "Ptychographic X-ray computed tomography at the
nanoscale." (September 2010)

Topics addressed in presentation:

  • What is this all about and what can one do with it? (+ link to biology and medicine as modern x-ray imaging)
  • How does it work?
  • What are the technical requirements and limitations?
  • Briefly addressed towards the end: Current directions in research (challenges) and who works on it (people)

Keywords: x-ray imaging; ptychography; synchrotron source; x-ray tomography; nanoscale resolution

  • Lecture (others)
    Oncoray Journal Club, 3.5.2012, Oncoray, House 31, University Hospital, Dresden, Germany

Publ.-Id: 17413

Brilliant radiation sources by laser-plasma accelerators and optical undulators

Debus, A.

This thesis investigates the use of high-power lasers for synchrotron radiation sources with high brilliance, from the EUV to the hard X-ray spectral range. Hereby lasers accelerate electrons by laser-wakefield acceleration (LWFA), act as optical undulators, or both. Experimental evidence shows for the first time that LWFA electron bunches are shorter than the driving laser and have a length scale comparable to the plasma wavelength. Furthermore, a first proof of principle experiment demonstrates that LWFA electrons can be exploited to generate undulator radiation.

Building upon these experimental findings, as well as extensive numerical simulations of Thomson scattering, the theoretical foundations of a novel interaction geometry for laser-matter interaction are developed. This new method is very general and when tailored towards relativistically moving targets not being limited by the focusability (Rayleigh length) of the laser, while it does not require a waveguide.

In a theoretical investigation of Thomson scattering, the optical analogue of undulator radiation, the limits of Thomson sources in scaling towards higher peak brilliances are highlighted. This leads to a novel method for generating brilliant, highly tunable X-ray sources, which is highly energy efficient by circumventing the laser Rayleigh limit through a novel traveling-wave Thomson scattering (TWTS) geometry. This new method suggests increases in X-ray photon yields of 2-3 orders of magnitudes using existing lasers and a way towards efficient, optical undulators to drive a free-electron laser.

The results presented here extend far beyond the scope of this work. The possibility to use lasers as particle accelerators, as well as optical undulators, leads to very compact and energy efficient synchrotron sources. The resulting monoenergetic radiation of high brilliance in a range from extreme ultraviolet (EUV) to hard X-ray radiation is of fundamental importance for basic research, medical applications, material and life sciences and is going to significantly contribute to a new generation of radiation sources and free-electron lasers (FELs).

Keywords: brilliant radiation sources; x-ray; traveling-wave Thomson scattering; TWTS; laser-wakefield acceleration; LWFA; electron bunch duration measurement; THz interferometry; undulator; synchrotron source; free-electron laser; VLS grating; EUV; Thomson scattering

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-022 2012
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 17412

Elektromagnetische Felder und Elektronendynamik in der Travelling-Wave Thomsonstreuung

Steiniger, K.

Travelling-Wave Thomsonstreuung (TWTS) ist eine neuartige Thomsonstreuungsgeometrie mit großer Strahlungsausbeute pro Puls, bei der ultrakurze Laserpulse mit verkippten Pulsfronten als optische Undulatoren oder lichtgetriebene Freie-Elektronen-Laser für relativistische Elektronenpulse genutzt werden. Auf diese Weise können Röntgenstrahlungspulse mit hohem Kontrast und schmaler Bandbreite erzeugt werden.
Zur Untersuchung der Propagation von TWTS-Pulsen wird in dieser Arbeit ein wellenoptischer, analytischer Formalismus entwickelt, welcher die zeitliche Entwicklung des elektrischen Feldes eines hochintensiven und ultrakurzen Laserpulses mit Dispersionseigenschaften nach Beugung an VLS-Gittern beschreibt. Damit können die durch Dispersion verursachten Veränderungen am Laserpuls bei der Beugung in beliebiger Ordnung numerisch analysiert werden. Das habe ich genutzt, um für zwei Beispiele die TWTS-Pulse zu charakterisieren. Für eines der Beispiele wird anhand der Ergebnisse eine vereinfachte Darstellung des Pulses abgeleitet und die Dynamik eines relativistischen Elektrons bei der Wechselwirkung mit dem Puls und gestreuter Strahlung beschrieben. Daraus werden Schlüsse für die Anwendbarkeit des Schemas als Freie-Elektronen-Laser gezogen.

Keywords: Travelling-Wave Thomson Scattering; X-ray; VLS gratings

  • Diploma thesis
    TU Dresden, 2012
    89 Seiten

Publ.-Id: 17411

The Effect of the Growth Rate on the Microstructure of multi-crystalline Silicon

Schmid, E.; Würzner, S.; Funke, C.; Galindo, V.; Pätzold, O.; Stelter, M.

This paper presents an experimental study of the influence of the growth rate on the microstructure of multi-crystalline silicon (mc-Si). Crystals with a diameter of 105 mm were grown from an inductively heated, well-mixed melt by the conventional vertical Bridgman technique. Axial and vertical samples were prepared from the crystals to analyze the grain structure as well as the distribution of dislocations and precipitates. The results show that the growth rate influences the microstructure of the crystals mainly at the beginning of the solidification process. Growth with a low growth rate, for instance, favors the formation of radially elongated grains near the bottom of the crystal and suppresses the heterogeneous nucleation of SiC precipitates at the inner crucible wall. The effect of the grain shape is restricted to the bottom region of the crystals, whereas the precipitates are identified to be the origin of dislocations or dislocation clusters propagating throughout the crystal during growth. As a consequence, the dislocation density in a slowly grown crystal is found to be significantly lower than in a fast grown crystal.

Keywords: A1. Directional solidification; A2. Bridgman technique; B2. Semiconducting silicon; A1. Crystal structure; A1. Defects

Publ.-Id: 17410

Functional properties of nickel cobalt oxide thin films

Iacomi, F.; Calin, G.; Scarlat, C.; Irimia, M.; Doroftei, C.; Dobromir, M.; Rusu, G. G.; Iftimie, N.; Sandu, A. V.

Cobalt–nickel oxide films of known stoichiometry (x = Ni / (Co + Ni) = 0.30–0.63) were deposited on glass slides by using a spin-coating method and were UV irradiated for 2 h. The structure and morphology of thin films evidenced nanocrystalline spinel structures. Thin films with x = 0.63–0.5 have a mixed phase structure and good sensing properties for ethanol. Thin films with x = 0.30–0.40 have a single spinel phase, are ferrimagnetic and highly conductive at 300 K and have magnetoresistance ratios of 5–8%. Four-probe measurements indicate an insulator–metal transition at temperatures slightly below ferromagnetic Curie temperature. Metallic Ni and Co particles improve thin film functional properties.

Keywords: Spinel structure; Electrical properties; Magnetic properties; Gas sensor

Publ.-Id: 17409

Dipole Strength on the Tail of the Giant Dipole Resonance

Schwengner, R.

– Photon-scattering experiments at ELBE
– Data analysis
– Results
– Comparison of experimental results with model predictions
– Implications for reaction rates

Keywords: Photon scattering; bremsstrahlung; photoabsorption; dipole strength distribution; photonuclear and radiative-capture reaction rates; QRPA; RQTBA; QPM; shell model

  • Invited lecture (Conferences)
    The nuclear dipole polarizability and its impact on nuclear structure and astrophysics, 18.-22.06.2012, Trento, Italien

Publ.-Id: 17408

Electron-positron pair creation in short intense laser pulses

Nousch, T.; Seipt, D.; Kämpfer, B.

We study finite-size effects in the process of e+ e− pair production via the non-linear Breit-Wheeler process in ultra short laser pulses. Based on the Nikishov-Ritus method we use laser dressed electron and positron wave functions to derive the differential and total pair production cross section, focusing on the effects of a finite pulse duration. Hence, we go beyond the infinite laser pulse approximation and provide a more exact description of experiments with modern femtosecond laser systems.

Keywords: pair creation; short laser pulses; electron; positron

  • Poster
    ENLITE12 Laser-Plasma Interaction at Ultra-High Intensity, 16.-20.04.2012, Dresden, Deutschland

Publ.-Id: 17407

Aqueous Uranium(VI) Complexes with Acetic and Succinic Acid: Speciation and Structure Revisited

Lucks, C.; Rossberg, A.; Tsushima, S.; Foerstendorf, H.; Scheinost, A. C.; Bernhard, G.

We employed density functional theory (DFT) calculations, and ultraviolet–visible (UV-Vis), extended X-ray absorption fine-structure (EXAFS) and attenuated total reflection Fourier-transform infrared (IR) spectroscopy analyzed with iterative transformation factor analysis (ITFA) to determine the structures and the pH-speciation of aqueous acetate (ac) and succinate (suc) U(VI) complexes. In the acetate system, all spectroscopies confirm the thermodynamically predicted pH-speciation by Ahrland (1951), with the hydrated uranyl ion and a 1:1, a 1:2 and a 1:3 U(VI)-ac complex. In the succinate system, we identified a new 1:3 U(VI)-suc complex, in addition to the previously known 1:1 and 1:2 U(VI)-suc complexes and determined the pH-speciation for all complexes. The IR spectra show absorption bands of the antisymmetric stretching mode of the uranyl mojety (υ3(UO2)) at 949, 939, 924 cm−1 and at 950, 938, 925 cm−1 for the 1:1, 1:2 and 1:3 U(VI)-ac and U(VI)-suc complexes, respectively. IR absorption bands at 1535 and 1534 cm−1 and at 1465 and 1462 cm−1 are assigned to the antisymmetric υ3,as(COO) and symmetric υ3,s(COO) stretching mode of bidentately coordinated carboxylic groups in the U(VI)-ac and U(VI)-suc complexes. The assignment of the three IR bands (υ3(UO2), υ3,as(COO) υ3,s(COO)) and the stoichiometry of the complexes is supported by DFT calculations. The UV-Vis spectra of the equivalent U(VI)-ac and U(VI)-suc complexes are similar suggesting common structural features. Consistent with IR spectroscopy and DFT calculations, EXAFS showed a bidentate coordination of the carboxylic groups to the equatorial plane of the uranyl moiety for all uranyl ligand complexes except for the newly detected 1:3 U(VI)-suc complex, where two carboxylic groups coordinate bidentately and one carboxylic group coordinates monodentately. All 1:1 and 1:2 complexes have a U-Owater distance of ~2.36 Å, which is shorter than the U-Owater distance of ~2.40 Å of the hydrated uranyl ion. For all complexes the U-Ocarboxyl distance of the bidentately coordinated carboxylic group is ~2.47 Å, while the monodentately coordinated carboxylic group of the 1:3 U(VI)-suc complex has a U-Ocarboxyl distance of ~2.36 Å, i.e. similar to the short U-Owater distance in the 1:1 and 1:2 complexes.


Publ.-Id: 17406

Pair production in short laser pulses near threshold

Nousch, T.; Seipt, D.; Kämpfer, B.; Titov, A. I.

The e+ e− pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit-Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold √s = 2m a similar enhancement of the pair production rate as for circular polarization. The strong subthreshold enhancement is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

Keywords: pair production; Volkov states; short laser pulses; subthreshold

Publ.-Id: 17405

Boltzmann Transport Theory applied to Bi2Te3

Hölzer, M.; Hinsche, N. F.; Ernst, A.; Mertig, I.; Zahn, P.

Boltzmann transport theory for electrical and thermal transport in Bi2Te3 will be discussed

  • Lecture (Conference)
    Thermoelectric properties related to nanostructure and dimensionality in Bi2Te3 nanomaterials, 05.-06.07.2012, Darmstadt, Deutschland

Publ.-Id: 17404

Anomalous Hall effect as a Fermi surface property

Mook, A.; Pientka, F.; Mertig, I.; Zahn, P.

the calculation of the intrinsic anomalous Hall conductivity as a pure Fermi surface property is demonstrated

  • Poster
    DPG Frühjahrstagung, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17403

Thermoelectric Transport in Bi2Te3/Sb2Te3 heterostructures

Hinsche, N. F.; Yavorsky, B. Y.; Mertig, I.; Zahn, P.

thermoelectric properties of Bi2Te3/Sb2Te3 superlattices are discussed

  • Lecture (Conference)
    DPG Frühjahrstagung, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17402

Thermoelectric Transport in strained Si and Si/Ge heterostructures

Zahn, P.; Hinsche, N. F.; Mertig, I.

thermoelectric properties of Si strained along (111) and Si/Ge(111) superlattices are discussed

  • Lecture (Conference)
    DPG Frühjahrstagung, 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17401

Virtual Institute MEMRIOX

Zahn, P.; Gemming, S.

presentation of the planned activities, pre-requisites and know-how of the newly established Helmholtz Virtual Institute Memeriox

  • Invited lecture (Conferences)
    Topical Problems in Theoretical Physics, 11.01.2012, Chemnitz, Deutschland

Publ.-Id: 17400

Near order structure of transparent conducting oxides: X-ray absorption study of Al-doped ZnO and ZnMgO in low doping regime

Zajac, D. A.; Ellmer, K.; Bikowski, A.; Vinnichenko, M.

ZnO belongs to the class of wide band gap semiconductors (Eg>3eV), with Eg=3.37eV, and exhibits very interesting optical and electrical properties. Used as a transparent conductive oxide (TCO) electrode in optoelectronic devices [1], ZnO has been developed as a low costs material, an alternative to commonly used and indium tin oxide (ITO). Due to the required transparency, at least in the solar spectral range and a low resistivity, ZnO has to be doped degenerately. While doping with Al leads to the required high carrier concentration [1], alloying with Mg increases the band gap up to 4.5 eV [2]. However, the increase of the conductivity by the increase of the carrier concentration (i.e. reaching the level of N=10^21cm^-3) can lead to a significant increase of the absorption of the light. Therefore, many researches focus on the increase of the electron mobility μ, in accordance with formula ρ=(eNμ)^-1.
The electron mobility is determined by the typical scattering processes in semiconductors, among other the extrinsic scattering on dopants and defects in the film. Since Al doped ZnO and ZnMgO layers, used for transparent electrodes are polycrystalline films, this process can be connected directly with dopants but also with local structure defects as Zn or/and O vacancies, stacking faults and grain boundaries are. These together with the small crystallographic domain size, in the range of 100nm, preferred growing orientation in c axis (perpendicular to the substrate), together with the Al and Mg dopants ionic radius smaller than for Zn [3] (respective crystal radii in tetrahedral coordination are: Al3+ 0.53Å, Mg2+ 0.71Å and Zn2+ 0.74Å), can cause the decrease of the local ordering of the samples.
In this paper we present XAS measurements on the Al doped ZnO and ZnMgO. The XANES spectra were fitted with the simulation program FEFF9 [4]. First results on the Al K edge, see Figure 1, show that the Al substitutes preferably the Zn lattice site in the material. For both dopants, Al and Mg, the spectra show a similar behaviour. The only clearly visible difference, the decrease of the intensity of the first peak for Al and Mg doped ZnO, in comparison to Al doped ZnO, can be attributed to the higher doping level (a similar effect is observed for double Al substitution of ZnO). The comparison of the experimental data with the simulation shows that the measured samples (3 at. % Al doped ZnO and 3 at. % Al doped ZnMgO (6 at.% Mg)) are in the low doping regime, where only single ion doping can be considered. The effect of the expansion of the c axis and the compression of a axis for the growth on glass substrate is also observed.

Acknowledgments: This work was supported by the German Ministry for Economy (AiF Köln).

[1] K. Ellmer, A. Klein, B. Rechs (Eds.), "Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells", Springer, Berlin (2008)
[2] S. Choopun, R. D. Vispute, W. Yang, R. P. Sharma, T. Venkatesan, H. Shen, “Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1-xO alloy films” Appl. Phys. Lett. 80 (2002) 1529
[3] R.D. Shannon, “Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides”, Acta Cryst. A32 (1976) 751
[4] J.J. Rehr, J.J. Kas, M.P. Prange, A.P. Sorini, Y. Takimoto, F. Vila, “Ab initio theory and calculations of X-ray spectra”, Comptes Rendus Physique 10 (2009) 548-559

  • Poster
    11th International School and Symposium on Synchrotron Radiation in Natural Science, 20.-25.05.2012, Krakow, Poland

Publ.-Id: 17399

Advanced thermal processing for advanced electronics and photovoltaics

Skorupa, W.

This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits.
Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Regarding photovoltaic applications, we dealt with two aspects: (i) the ion beam doping and thermal processing of so-called dirty silicon demonstrating a distinct improvement of the minority carrier diffusion length compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation
Whereas all these examples base on solid phase processing the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (NanoLett. 11, 2814 (2011)). Moreover a new approach of measuring temperatures in the subsecond time range will be mentioned as well as the interesting field of large area-low cost electronics.

  • Invited lecture (Conferences)
    IX-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 25.-28.06.2012, Kazimierz Dolny, Poland

Publ.-Id: 17398

Recent developments of TiO2:Nb sputtered with high deposition rates from a rotatable magnetron system

Junghähnel, M.; Fietzke, F.; Vinnichenko, M.; Cornelius, S.

The persistent competition for the cost-effective production of solar cells and displays requires low cost and high throughput production of transparent conductive oxides (TCOs). Nb-doped titania (TiO2:Nb) is a promising novel TCO material for these applications. The results of investigations of TiO2:Nb thin film deposited on large area substrates by sputtering with high deposition rates are reported. As a deposition method we used the direct current sputtering of a 780 mm length substoichiometric oxide tubular target arranged in a rotatable magnetron system in a pilot scale inline sputtering plant. The films were grown on unheated substrates and then thermally annealed at temperatures of 450°C. The influence of the magnetron magnetic field strength and oxygen partial pressure in the sputtering gas on the properties and structure of TiO2:Nb was investigated. A 100 nm thin film deposited on Borofloat® substrate shows after annealing a resistivity of 9.4 x 10-4Ωcm, 82% transmittance in the visible range and a refractive index of ~2.5 (λ=550 nm). The film properties were compared with those of the films grown using a planar oxidic target.

Keywords: magnetron sputtering; transparent conductive oxide; TiO2:Nb; electrical and optical properties

  • Lecture (Conference)
    55th Annual Society of Vacuum Coaters Technical Conference, 28.04.-03.05.2012, Santa Clara, USA

Publ.-Id: 17397

Lorenz function of Bi2Te3/Sb2Te3 superlattices

Hinsche, N. F.; Mertig, I.; Zahn, P.

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi2Te3/Sb2Te3 superlattices and their bulk constituents. It was found that already for the bulk materials Bi2Te3 and Sb2Te3, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi2Te3/Sb2Te3 superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.

Keywords: density functional theory; thermoelectric transport; Bi2Te3; Sb2Te3; heterostructures; Lorenz function

Publ.-Id: 17396

Experimental hypoxia does not influence Eph receptor and ephrin ligand expression in human melanoma cell lines

Pietzsch, J.; Reißenweber, B.; Komadina Garcia Meza, D.; Mosch, B.

Experimental evidence links the receptor tyrosine kinases EphA2 and EphB4 to melanoma progression and metastasis. Another factor contributing to melanoma invasion-metastasis cascade is hypoxia. However, data on the influence of tumor hypoxia on regulation of Eph receptors and their ephrin ligands are scarce. This study aimed at clarifying whether hypoxia influences expression and synthesis of EphA2 and EphB4 and, furthermore, ephrinA1 and ephrinB2, respectively, in four human melanoma cell lines (A375, A2058, MeWo, and MelJuso). In order to investigate Eph/ephrin expression under hypoxic conditions we used cell monolayer cultures as extrinsic hypoxia models and A2058 spheroids as intrinsic hypoxia model. Hypoxic conditions were approved by measurement of VEGF expression and cellular uptake of [18F]fluoromisonidazol ([18F]FMISO). In all models, both VEGF expression and ([18F]FMISO) uptake increased under hypoxic conditions. In normoxia, EphA2, EphB4, ephrinA1, and ephrinB2 expression was detectable in all cell lines showing a substantially varying extent. Protein synthesis of EphA2 was detected in all cell lines and, moreover, of EphB4 in A375 and A2058 cells. However, no effect of experimental hypoxia on Eph/ephrin expression and protein synthesis could be observed. The findings contribute to debating the hypothesis that hypoxia is an important regulator of Eph/ephrin expression in tumors.

  • Poster
    Melanocytes and Melanoma, 18.-20.06.2012, Malmö, Sweden
  • Contribution to proceedings
    Melanocytes and Melanoma, 18.-20.06.2012, Malmö, Sweden
    Melanocytes and melanoma: from basic science to clinical applications. Rönnstrand L, Steingrímsson E (Eds.), 72

Publ.-Id: 17395

Thermoelectric transport in Bi2Te3/Sb2Te3 superlattices

Hinsche, N. F.; Yavorsky, B. Y.; Gradhand, M.; Czerner, M.; Winkler, M.; König, J.; Böttner, H.; Mertig, I.; Zahn, P.

The thermoelectric transport properties of Bi2Te3/Sb2Te3 superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given.

Keywords: density functional theory; thermoelectric transport; Bi2Te3; Sb2Te3; heterostructures; Lorenz function

Publ.-Id: 17394

Non-Perturbative Two-Photon Compton Effect in Strong Short Laser Pulses

Seipt, D.; Kämpfer, B.

In relativistically strong laser fields with intensities well above 10^19 W/cm^2, multi-photon emission processes are important in collisions of relativistic electron beams with the laser pulse. We present results on the coherent two-photon process (double Compton scattering) in the presence of strong and short laser pulses, taking into account the finite temporal pulse length exactly for the first time.

Keywords: two-photon Compton; double Compton; short laser pulses; Volkov; Dirac-Volkov propagator

  • Invited lecture (Conferences)
    Laser-Plasma Interaction at Ultra-High Intensity, 2nd Dresden Exchange on Laser-Plasma Interaction Theory, ENLITE, 16.-20.04.2012, Dresden, Deutschland

Publ.-Id: 17393

Non-perturbative two-photon Compton scattering in pulsed laser fields

Seipt, D.; Kämpfer, B.

In relativistically strong laser fields with intensities well above 10^19 W/cm^2, multi-photon emission processes are important in collisions of relativistic electron beams with the laser pulse. We present results on the coherent two-photon process (double Compton scattering) in the presence of strong and short laser pulses, taking into account the finite temporal pulse length exactly for the first time.

Keywords: two-photon Compton; double Compton; short laser pulses; Volkov; Dirac-Volkov propagator

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP), 12.03.2012, Stuttgart, Deutschland

Publ.-Id: 17392

Thermoelectric transport in strained Si and Si/Ge heterostructures

Hinsche, N. F.; Mertig, I.; Zahn, P.

The anisotropic thermoelectric transport properties of bulk silicon strained in the [111]-direction were studied by detailed first-principles calculations focusing on a possible enhancement of the power factor. Electron and hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high-temperature and high-doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of a [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole doping was drastically suppressed due to quantum-well effects, while under electron doping an enhanced power factor was found. For this, we state figures of merit of ZT = 0.2 and 1.4 at T = 300 and 900 K for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features.

Keywords: Thermoelectric and thermomagnetic effects; Density functional theory; Deformation and plasticity; Condensed matter; Semiconductors; Si; Ge; Si/Ge(111); heterostructures

Publ.-Id: 17391

Pygmy dipole strength in 86Kr and systematics of N=50 isotones

Schwengner, R.; Massarczyk, R.; Rusev, G.; Tsoneva, N.; Bemmerer, D.; Beyer, R.; Hannaske, R.; Junghans, A. R.; Kelley, J. H.; Kwan, E.; Marta, M.; Raut, R.; Schilling, K. D.; Tonchev, A.; Tornow, W.; Wagner, A.

The dipole strength of the N=50 nucleus 86Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE and using quasi-monoenergetic gamma rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HIgS facility. A high-pressure gas target was used. We identified 42 levels up to an excitation energy of 10.1 MeV. Simulations of gamma-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a recent (gamma,n) experiment at HIgS. The enhanced E1 strength found in the range from 6 to 10 MeV is compared with that in the N = 50 isotones 88Sr, 90Zr, and 92Mo and with predictions of calculations within the quasiparticle-phonon model.

Keywords: Photon scattering; bremsstrahlung; polarized gamma rays; photoabsorption cross section; gamma-ray strength function; random-phase-approximation; quasiparticle-phonon model

Publ.-Id: 17390

Carrier and phonon dynamics in graphene

Malic, E.; Winnerl, S.

We present mciroscopic theory on the relaxation dynamics in graphene as well as experimental results. The excitation energies ccover the complete infrared spectral range.

  • Lecture (others)
    1st Workshop of the Priority Programme Graphene, 04.-08.12.2011, Rothenfels, Deutschland

Publ.-Id: 17389

Taking the fast lane on laser acceleration

Bussmann, M.; Kluge, T.; Zeil, K.; Metzkes, J.; Kraft, S.; Debus, A.; Couperus, J. P.; Jochmann, A.; Irman, A.; Bock, S.; Loeser, M.; Siebold, M.; Burau, H.; Hübl, A.; Widera, R.; Pausch, R.; Zarini, O.; Steiniger, K.; Schramm, U.; Cowan, T. E.

At Helmholtz-Zentrum Dresden-Rossendorf ultra-short high-power laser pulses drive sources of electron, ion and X-ray pulses. Close collaboration of experimental and theoretical studies drive the understanding and optimization of these sources for applications such as laser-driven ion beam tumour therapy.
When working close to the experiment fast simulation results and surveys of large parameter spaces are mandatory. We have developed a new code that works on accelerator hardware to return simulation results in hours instead of weeks. These fast response times allow us to add physical effects not yet available in simulation due to time constraints. We present simulations using our code PIConGPU, a particle-in-cell code working on graphic processing units, which show what is in reach of simulations based on modern hardware.
Besides developing new simulation software we work on making numerical and analytical models of laser-driven particle acceleration more realistic in order to better predict the outcome of experiments. This is necessary since our focus lies on optimum control of laser-driven radiation sources for applications. We present results on laser-driven ion acceleration and its applications that show how realistic models influence our experimental strategy.
We end with an outlook on why we see data analysis of large-scale simulations as an integrated part of our joint experimental and theoretical program and how we plan to integrate this into our daily work.

Keywords: particle in cell; electron; ion; acceleration; simulation; x-ray

  • Invited lecture (Conferences)

Publ.-Id: 17388

Switching magnetization by 180° with an electric field

Fechner, M.; Zahn, P.; Ostanin, S.; Bibes, M.; Mertig, I.

Magnetoelectric coupling allows for manipulating the magnetization by an external electric field or the electrical polarization by an external magnetic field. Here, we propose a mechanism to electrically induce 180 degree magnetization switching combining two effects: the magnetoelectric coupling at a multiferroic interface and magnetic interlayer exchange coupling. By means of first-principles methods, we investigate a ferroelectric layer in contact with a Fe/Au/Fe trilayer. The calculations show that the interface magnetism is strongly coupled to the ferroelectric layer. Furthermore, under certain conditions a reversal of polarization causes a sign reversal of the interlayer exchange coupling which is results in a 180 degree switching of the free layer magnetization. We argue that this magnetoelectric coupling mechanism is very robust and can find applications in magnetic data storage.

Keywords: 85.80.Jm; 31.15.A-; 75.30.Et; 85.75.-d; first principles electronic structure; magnetic multilayer; magneto-electric coupling; magnetic interlayer exchange coupling

Publ.-Id: 17387

Frames per Second Laser Plasma Simulations - Making large scale simulations really fast ... or slow

Bussmann, M.; Berninger, F.; Burau, H.; Cowan, T. E.; Debus, A.; Hübl, A.; Kluge, T.; Pausch, R.; Schramm, U.; Widera, R.; Hönig, W.; Juckeland, G.; Nagel, W.; Schmitt, F.

Many-core compute architectures such as graphic cards will be the building blocks of next-generation Exaflop computers. With these architectures, complex laser plasma simulations can run on a frames-per-second rate, decreasing the waiting time to get results to hours instead of weeks. Thus, large surveys for optimum acceleration parameters come in reach. This will enable theoreticians and experimentalists to discuss and understand the physics behind particle acceleration scenarios instead of simply adding a few pretty simulation pictures to a publication. When considering future applications of ultra-intense lasers, new physics will have to be taken into account. It is thus not only mandatory to make simulations fast, but to then add new physical effects into the code. This will require new strategies to leverage the power of next-generation supercomputers. We propose potentially successful techniques to get the most out of upcoming HPC systems based on our experience with PIConGPU and show what is already possible today.

Keywords: particle in cell; gpu; laser; plasma; acceleration; radiation; lwfa; simulation

  • Invited lecture (Conferences)
    15th Advanced Accelerator Concepts Workshop, 10.-15.6.2012, Austin, TX, United States of America

Publ.-Id: 17386

Taming Laser Plasma Interactions: PIConGPU

Bussmann, M.; Burau, H.; Widera, R.; Hübl, A.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Dietrich, R.; Juckeland, G.; Nagel, W.; D’Humières, E.

We present PIConGPU, an implementation of a three-dimensional fully relativistic particle-in-cell (PIC) code for GPU clusters. PIConGPU can simulate laser matter interaction at relativistic laser intensities, for example to investigate laser particle acceleration schemes.

Keywords: gpu; particle in cell; laser; plasma; simulation; parallel computing

  • Invited lecture (Conferences)
    Accelerated HPC Symposium, 16.-17.5.2012, San Jose, CA, USA

Publ.-Id: 17385

First-principles calculations of the Berry curvature of Bloch states for charge and spin transport of electrons

Gradhand, M.; Fedorov, D. V.; Pientka, F.; Zahn, P.; Mertig, I.; Györfy, B. L.

Recent progress in wave packet dynamics based on the insight of Berry pertaining to adiabatic evolution of quantum systems has led to the need for a new property of a Bloch state, the Berry curvature, to be calculated from first principles. We report here on the response to this challenge by the ab initio community during the past decade. First we give a tutorial introduction of the conceptual developments we mentioned above. Then we describe four methodologies which have been developed for first-principle calculations of the Berry curvature. Finally, to illustrate the significance of the new developments, we report some results of calculations of interesting physical properties such as the anomalous and spin Hall conductivity as well as the anomalous Nernst conductivity and discuss the influence of the Berry curvature on the de Haas–van Alphen oscillation.

Publ.-Id: 17384

PIConGPU - Bringing Large-Scale Laser Plasma Simulations to GPU Supercomputing

Bussmann, M.; Juckeland, G.

With powerful lasers breaking the Petawatt barrier, applications for laser-accelerated particle beams are gaining more interest than ever. Ion beams accelerated by intense laser pulses foster new ways of treating cancer and make them available to more people than ever before. Laser-generated electron beams can drive new compact x-ray sources to create snapshots of ultrafast processes in materials. With PIConGPU laser-driven particle acceleration can be computed in hours compared to weeks on standard CPU clusters. We present the techniques behind PIConGPU, detailed performance analysis and the benefits of PIConGPU for real-world physics cases.

Keywords: particle in cell; gpu; plasma; laser; parallel computing

  • Lecture (Conference)
    GPU Technology Conference, 14.-17.5.2012, San Jose, CA, USA

Publ.-Id: 17383

Frames per Second is the new CPU hours - Particle-in-Cell Simulations on large GPU clusters

Bussmann, M.; Widera, R.; Burau, H.; Hübl, A.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Juckeland, G.; Nagel, W.

GPUs are one implementation of the many-core architecture that could be an important building block of future Exascale HPC-systems.
I present PIConGPU, an electromagnetic particle-in-cell code for laser-plasma interaction, discussing the important building blocks and techniques implemented in PIConGPU to leverage the power of large-scale GPU clusters.
PIConGPU hints at what to expect in the near-term future of massively-parallel particle-in-cell simulations in terms of parameter surveys, new physics modules and large-scale simulations.

Keywords: gpu; particle in cell; simulation; relativistic; parallel computing; laser; plasma

  • Invited lecture (Conferences)
    IAG Seminar, 04.05.2012, Stuttgart, Deutschland

Publ.-Id: 17382

A high peak brightness Thomson scattering x-ray source using high-power lasers

Bussmann, M.; Debus, A.; Steiniger, K.; Pausch, R.; Couperus, J. P.; Jochmann, A.; Irman, A.; Kraft, S.; Siebold, M.; Schramm, U.; Cowan, T. E.

Thomson scattering of high-power laser pulses from relativistic bunches of electrons is a promising technique to deliver ultra-short x-ray pulses of high peak brightness. X-ray pulses in the multi-keV regime are obtainable using few MeV electrons delivered by conventional accelerators.

With laser-accelerated electrons photon energies of several MeV can be reached. We introduce concepts to improve the peak brightness of these beams using high power lasers and compare simulation results to experiment. Analytic models show that long interaction lengths could be obtained by spatio-temporal tayloring of the laser pulse. This Travelling-Wave Thomson Scattering technique would allow to produce narrow-bandwidth X-ray pulses of high peak brightness.

Keywords: thomson scattering; laser pulse; relativistic; radiation; travelling wave; x-ray; electron beam

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.3.2012, Stuttgart, Deutschland

Publ.-Id: 17381

PIConGPU - Bringing a GPU-driven PIC code to large machines

Bussmann, M.; Burau, H.; Widera, R.; Hübl, A.; Debus, A.; Kluge, T.; Schramm, U.; Cowan, T. E.; Schmitt, F.; Juckeland, G.; Nagel, W.; D'Humières, E.; Kilian, P.; Ganse, U.; Siegel, S.; Spanier, F.

We present recent results on PIConGPU, a charge-conserving 3D relativistic particle-in-cell code running on graphic processors. We discuss best practices on how to implement the particle-in-cell algorithm on this new hardware and run it on large GPU clusters. We show that these codes have become mature enough to be considered for real life applications, delivering fast response time even for large physical problems.

Keywords: particle in cell; simulation; gpu; relativistic; parallel computing; laser; plasma

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.3.2012, Stuttgart, Deutschland

Publ.-Id: 17380

Laser Cooling and Optical Diagnostics for Relativistic Ion Beams

Bussmann, M.; Stuhr, U.; Siebold, M.; Schramm, U.; Winters, D.; Kühl, T.; Kozhuharov, C.; Dimopoulou, C.; Nolden, F.; Steck, M.; Geppert, C.; Sanchez Alarcon, R. M.; Nörstershäuser, W.; Stöhlker, T.; Beck, T.; Walther, T.; Tichelmann, S.; Birkl, G.; Wen, W.; Ma, X.

Cooling of ion beams is essential for precision experiments at future storage rings. Laser cooling is one of the most promising techniques to reach high phase space densities at relativistic ion energies for all ion species which provide suitable atomic cooling transitions.

Establishing laser cooling as a standard technique at future storage rings requires laser sources that can address ion beams with large initial velocity spreads.

Without optical diagnostics however, the dynamics of ions at very low temperatures cannot be resolved, as conventional beam diagnostics reach their resolution limits.

We discuss concepts and techniques that pave the way for making laser cooling a reliable tool at future storage rings, some of which can already be tested at the ESR at GSI.

Keywords: laser cooling; ion beam; storage ring; relativistic

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.3.2012, Stuttgart, Deutschland

Publ.-Id: 17379

Laserspektroskopie an relativistischen 209-Bi82+ und 209-Bi80+ Ionen am Speicherring ESR der GSI

Geppert, C.; Lochmann, M.; Sanchez, R. M.; Hammen, M.; Frömmgen, N.; Will, E.; Botermann, B.; Andjelkovic, Z.; Jöhren, R.; Mader, J.; Hannen, V.; Weinheimer, C.; Winters, D.; Kühl, T.; Litvinov, Y.; Stöhlker, T.; Dax, A.; Bussmann, M.; Wen, W.; Thompson, R.; Nörtershäuser, W.

Die genaue Bestimmung der Hyperfeinstrukturaufspaltung (HFS) von hochgeladenen Ionen erlaubt im Abgleich mit theoretischen Berechnungen einen Test der QED. Die Messung an schweren und hochgeladenen Ionen erlaubt einen Test der QED in starken Feldern.

Im Rahmen der LIBELLE (E083)-Kollaboration am Helmholtzzentrum für Schwerionenforschung (GSI) wurden hierzu wasserstoff- und lithium-ähnliches Bismut bei Geschwindigkeiten von β=0.7 im Speicherring ESR gespeichert und mittels Laserspektroskopie untersucht. Nach 12-jähriger Suche wurde nun erstmals der verbotene HFS-Übergang im lithium-ähnlichen Bismut gefunden.

Keywords: Spektroskpie; Speicherring; QED; relativistsich; Ionenstrahl; hochgeladene Ionen; starke Felder

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.3.2012, Stuttgart, Deutschland

Publ.-Id: 17378

Electron temperature in laser-solid interaction

Kluge, T.; Huang, L.; Debus, A.; Zeil, K.; Bussmann, M.; Schramm, U.; Cowan, T. E.

Recent theoretical results have led to a new understanding of how to derive the temperature of hot electrons generated in laser-solid interactions from the laser intensity.

We present new scaling laws for electron temperature with laser intensity. We then focus on the implications of our findings for applications such as laser-driven ion acceleration and laser-driven fusion using buried-layer targets.

Keywords: electron temperature; laser; solid; interaction; relativistic

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.3.2012, Stuttgart, Deutschland

Publ.-Id: 17377

Laboratory Astrophysics Research at HZDR

Schlenvoigt, H.-P.; Ramakrishna, B.; Kraft, S.; Herrmannsdörfer, T.; Schramm, U.; Cowan, T.

The „Helmholtz-Zentrum Dresden-Rossendorf“ (HZDR) research center covers a wide area of fundamental research in the fields of matter, health and energy. In particular for the first domain, a key topic is the behavior of matter in strong fields. The center operates several large-scale facilities of excellent research: The „Dresden High Magnetic Field Laboratory“ (HLD), the accelerator and radiation source ELBE and the high-intensity laser system DRACO.
In view of preparatory research and training for the upcoming x-ray free electron laser XFEL at Hamburg, an initiative was taken in order to combine the expertises of generating ultra-strong magnetic fields, high-power laser-matter interaction, plasma physics, radiation physics and material science. The junction of all of these fields settles exactly at laboratory astrophysics.
We will present our experiences in the individual fields, outline the project and discuss possible experiments.

  • Poster
    9th International Conference on High Energy Density Laboratory Astrophysics (HEDLA2012), 30.04.-04.05.2012, Tallahassee, USA

Publ.-Id: 17376

Direct Imaging Of Effective Spin Meron Pairs In Magnetic Multilayers

Wintz, S.; Körner, M.; Gemming, S.; Erbe, A.; Raabe, J.; Quitmann, C.; Fassbender, J.

Spin textures have been an interesting topic of magnetism research for many years. Within this field, magnetic vortices have attracted much attention, due to their non-trivial topology and the various dynamic modes they exhibit. Such a magnetic vortex consists of a planar, flux-closing magnetization curl that turns out of the plane in the central nanoscopic core region. In a single vortex, typically no significant radial magnetization components are present. Recent investigations show that this also holds true for multilayer vortex systems with bilinear interlayer exchange coupling (IEC).
Here we report on pairs of diverging-converging spin vortices occurring in patterned magnetic multilayers (Co/Rh/NiFe). These effective meron states can be understood as a superposition of the topological meron state (defined by a perfectly radial magnetization distribution) and a regular tangential vortex. Using magnetic scanning transmission x-ray microscopy (STXM) we directly image the individual effective merons in both ferromagnetic layers with high lateral resolution. Supporting SQUID measurements and micromagnetic simulations reveal that a significant biqudratic IEC is necessary to stabilize the states observed.

  • Poster
    The 21th International Colloqium on Magnetic Films and Surfaces (ICMFS), 24.-28.09.2012, Shanghai, China

Publ.-Id: 17375

Attempt to detect primordial 244Pu on Earth

Lachner, J.; Dillmann, I.; Faestermann, T.; Korschinek, G.; Poutivtsev, M.; Rugel, G.; Lierse Von Gostomski, C.; Türler, A.; Gerstmann, U.

With a half-life of 81.1 Myr, 244Pu could be both the heaviest and the shortest-lived nuclide present on Earth as a relic of the last supernova(e) that occurred before the formation of the Solar System. Hoffman et al. [Nature (London) 234, 132 (1971)] reported on the detection of this nuclide (1.0 × 10−18 g 244Pu/g) in the rare-earth mineral bastnäsite with the use of a mass spectrometer. Up to now these findings were never reassessed. We describe the search for primordial 244Pu in a sample of bastnäsite with the method of accelerator mass spectrometry (AMS). It was performed with a highly sensitive setup, identifying the ions by the determination of their time-of-flight and energy. Using AMS, the stripping to high charge states allows the suppression of any molecular interference. During our measurements we observed no event of 244Pu. Therefore, we can give an upper limit for the abundance of 244Pu in our sample of the mineral bastnäsite of 370 atoms per gram (1.5 × 10−19 g244Pu/g). The concentration of 244Pu in our sample of bastnäsite is significantly lower than the previously determined value.

Keywords: Elemental abundances in Universe; r-process (nuclear astrophysics); properties of superheavy elements

Publ.-Id: 17374

Environment Controlled Dewetting of Rh−Pd Bilayers: A Route for Core−Shell Nanostructure Synthesis

Abrasonis, G.; Wintz, S.; Liedke, M. O.; Aksoy, A. F.; Krause, M.; Kuepper, K.; Banerjee, D.; Liu, Z.; Gemming, S.

Chemical environment plays a significant role on the size, shape, or surface composition of nanostructures. Here, the chemical environment effects are studied in the context of core−shell nanoparticle synthesis. The environment driven dynamics and kinetics of Rh/Pd bilayers is investigated by in situ ambient pressure X-ray photoelectron spectroscopy. Thin Rh (∼1.5 nm)/Pd (∼ 1.5 nm) bilayers were grown on thermally oxidized Si substrates. The films were heated in CO or NO environments or heated in vacuum with a subsequent NO/CO cycling. This study demonstrates that not the initial stacking sequence but the chemical environment plays a crucial role in controlling the surface composition. Heating in CO results in a surface enrichment of Pd at ∼200°C and is followed by film dewetting at ∼300 °C. Heating in NO results in progressive oxidation of Rh starting at ∼150 °C, which stabilizes the film continuity up to >∼375 °C. The film rupture correlates with the thermal destabilization of the surface oxide. Heating in vacuum results in a significant increase in surface Pd concentration, and the following NO/CO cycling induces periodic surface composition changes. The quasi-equilibrium states are ∼50% and ∼20% of Rh/(Rh + Pd) for NO and CO environments, respectively. Possible surface composition change and dewetting mechanisms are discussed on the basis of the interplay of thermodynamic (surface/oxide energy and surface wetting) and kinetic (surface oxidation and thermally induced and chemically enhanced diffusion) factors. The results open alternative ways to synthesize supported (core−shell) nanostructures with controlled morphology and surface composition.

  • Journal of Physical Chemistry C 116(2012), 14401-14407
    Online First (2012) DOI: 10.1021/jp302908x

Publ.-Id: 17373

Search for superheavy elements with 292 ≤ A ≤ 310 in nature with accelerator mass spectrometry

Ludwig, P.; Faestermann, T.; Korschinek, G.; Rugel, G.; Dillmann, I.; Fimiani, L.; Bishop, S.; Kumar, P.

There is a possibility that small traces of long-lived superheavy elements (Z ≥ 104) still exist in nature. An ultrasensitive search for such superheavy elements has been conducted at the Maier-Leibnitz Laboratory in Garching (Germany) by means of accelerator mass spectrometry. A sample of raw platinum has been scanned for 13 different masses in the range 292 ≤ A ≤ 310. The masses A = 292 and 298 were scanned in pure osmium and pure lead fluoride, respectively. For each mass, several hours of background-free data were recorded. Since no events could be attributed to superheavy elements, upper limits on their abundances in the sample materials on the order of 10−14–10−16 were established.

Keywords: Properties of superheavy elements; time-of-flight mass spectrometry in chemical analysis; charged-particle beams sources and detectors; beams; charged-particle in accelerators

Publ.-Id: 17372

Lanthanide induced linkage of phosphorylated organic acids

Kretzschmar, J.; Barkleit, A.; Paasch, S.; Brunner, E.

Lanthanides have become a useful tool in NMR spectroscopy within the last 40 years. Due to their paramagnetic properties they can be utilized as probes to determine the binding sites of biologically or environmentally relevant organic molecules as they cause significant line broadenings and / or paramagnetic induced shifts.
In our former and actual research we investigate the interactions between actinides and biomolecules, revealing the structure as well as thermodynamic and kinetic behaviour. Lanthanides can easily be used as inactive analogues for trivalent actinides in consequence of their similar chemistry.
We found out that lanthanide ions are able to act as linkers to build up polymeric structures of bifunctional organic acids such as phosphorylated amino acids. For instance, in the case of O-phospho-L-serine the lanthanide ions can serve as a bridge between the carboxylate and the phosphate group of two amino acid molecules to form macromolecules with repetitive units. Solid state NMR spectroscopy was the most feasible tool for structure elucidation, proving that both the phosphate and the carboxylic group are involved in the complexation. By means of 1D and 2D methods it was confirmed that both functional groups lose their protons and, thus, must be the binding sites for the lanthanides, whereas the protons of the amino group are unaffected.
The interactions between the lanthanides (Eu3+, La3+) and the phosphorylated acids can be monitored by solution 31P-NMR spectroscopy and confirmed by dynamic light scattering. After mixing the reactants, colloids are formed immediately. After some minutes up to hours the formed aggregates precipitate. Different temperature, pH and ionic strength conditions may be object of further investigations.

Keywords: lanthanides; lanthanum(III); europium(III); phosphorylated amino acid; NMR spectroscopy

  • Lecture (Conference)
    Festkörper-NMR-Methoden und Anwendungen in der Materialforschung, 29.07.-02.08.2012, Oberjoch, Deutschland

Publ.-Id: 17371

Effect of low energy He+-ion irradiation on structural and magnetic properties of thin Pt/Cr/Co multilayers

Tripathi, J. K.; Liedke, M. O.; Strache, T.; Sarangi, S. N.; Grotzschel, R.; Gupta, A.; Som, T.

In this work, we report on the changes in structural and magnetic properties of [Pt (0.7 nm)/Cr (x nm)/Co (0.5 nm)](x) (15)/Si, x = 0.1 and 0.2 nm, due to 10 keV He+-ion irradiation at room temperature in the fluence range of 2 x 10(15)-5 x 10(16) ions-cm(-2). Enhancement in the coercivity values with a fairly square magnetization reversal loop (for both the multilayers), upon irradiation to the fluence of 5 x 10(16) ions-cm(-2) was observed. Above finding is discussed in the realm of ion beam mixing, leading to the CoCrPt ternary alloy phase formation, after low-energy He+-ion irradiation.

Keywords: He+; ion irradiation; Pt; Co; multilayers; mixing; magnetic anisotropy

  • Nuclear Instruments and Methods in Physics Research B 272(2012), 96-99

Publ.-Id: 17370

Reduced order modelling and optimization of an electromagnetically controlled shear layer

Metzkes, H.; Stiller, J.; Weier, T.; Albrecht, T.; Gerbeth, G.

In previous work it has been found that active flow control on a separated shear layer of an airfoil is able to increase lift by 50 percent. It was shown, the effect of control depends on various parameter like amplitude, frequency waveform of the signal. The electromagnetic actuator we use, induces a mainly wall normal body force. As the force amplitude is proportional to the external applied voltage a wide range of time signals can be generated.
Due to the variety of actuating variables present work was focused to study the variation of unique parameters. Our aim is to set up an optimization method including a wide range of variables to find the most effective constellation. In order to reduce the numeric costs for the optimization we use a reduced order model. The model is derived by projecting the Navier-Stokes equation to a basis derived from proper orthogonal decomposition (POD). The POD modes are computed from autocorrelated snapshots of a high fidelity solution (Direct Numerical Simulation or Large Eddy Simulation). To cope with pressure effects due to open boundaries we adopted the approach of Noack et al. (2005). The choice of the snapshots restricts the area of application of the model. For this reason the optimization has to be combined with a trust region method . As there are several references dealing with cylinder wake flow, we validate the approach with the flow past a circular cylinder with Re = 100. In order to work out a suitable strategy for controling separated shear flows we consider the backward-facing step as a simple, but yet characteristic example. As a particular challenge we plan to address the reduced order representation of short forcing peaks and a robust selection of snapshots within the trust region iteration of the optimizer.

Keywords: backward facing step; Lorentz force; flow control

  • Lecture (Conference)
    European Fluid Mechanics Conference 9 (EFMC9), 09.-13.09.2012, Rom, Italien

Publ.-Id: 17369

Separated flow response to single pulse actuation

Albrecht, T.; Weier, T.; Gerbeth, G.; Williams, D. R.

The response of a separated flow over a two-dimensional wing to a short duration disturbance from a Lorentz force leading-edge actuator is presented. The transient flow structures and lift force measurements were obtained from PIV measurements. The dependence of the lift response on actuator pulse duration, pulse amplitude, and direction of actuation was documented. The flow structures in the separated shear layer were identified using Finite Time Lyapunov Exponent (FTLE) method. The direction of the actuator pulse had a significant effect on the initial development of the shear layer, but the larger scale envelope of the separated flow had essentially the same response, irrespective of the direction of actuation.

Keywords: flow separation; Lorentz force; FTLE

  • Lecture (Conference)
    51st AIAA Aerospace Sciences Meeting, 07.-13.01.2013, Grapevine, USA
  • Contribution to proceedings
    51st AIAA Aerospace Sciences Meeting, 07.-13.01.2013, Grapevine, USA
    Proceedings of the 51st AIAA Aerospace Sciences Meeting
    DOI: 10.2514/6.2013-849
  • AIAA Journal 53(2015)1, 190-199
    Online First (2014) DOI: 10.2514/1.J053026

Publ.-Id: 17368

Autonome Sensorpartikel zur Prozessdiagnose in Großbehältern

Reinecke, S.; Hampel, U.

Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde das Konzept autonomer Sensorpartikel entwickelt und getestet. Die Sensorpartikel sind auftriebsneutral und bewegen sich frei mit der vorherrschenden Strömung im Prozess. Die integrierte Messelektronik erfasst die Signale der internen Messfühler für die Temperatur, die Eintauchtiefe und die Beschleunigung in einem autonomen und energieeffizienten Messregime. Die Validierung des Messsystems erfolgte unter realen Strömungsbedingungen in einem Versuchsfermenter. Die aufgenommenen Messda-ten und die daraus extrahierten Prozesskenndaten charakterisieren den Zustand des Prozesses und die Strömungsbedingungen.

Keywords: Strömungsfolger; Sensorpartikel; Autonomer Sensor; Parametererfassung; Fernüberwachung; Bioreaktor

Publ.-Id: 17367

A unifying picture of helical and azimuthal magnetorotational instability, and the universal significance of the Liu limit

Kirillov, O.; Stefani, F.; Fukumoto, Y.

The magnetorotational instability (MRI) plays a key role for cosmic structure formation by triggering turbulence in the rotating flows of accretion disks that would be otherwise hydrodynamically stable. In the limit of small magnetic Prandtl number, the helical and the azimuthal version of MRI are known to be governed by a quite different scaling behaviour than the standard MRI with a vertical applied magnetic field. Using the short-wavelength approximation for an incompressible, resistive, and viscous rotating fluid we present a unified description of helical and azimuthal MRI, and we identify the universal character of the Liu limit for the critical Rossby number.
From this universal behaviour we are also led to the prediction that the instability will be governed by a mode with an azimuthal wavenumber that is proportional to the ratio of axial to azimuthal applied magnetic field, when this ratio becomes large and the Rossby number is close to the Liu limit.

Keywords: helical and azimuthal magnetorotational instability; inductionless limit; Keplerian rotation; accretion disk

Publ.-Id: 17366

Coulomb Blockade effects in FePt nanoparticles

Erbe, A.; Wiesenhütter, U.; Pohl, D.; Rellinghaus, B.; Fassbender, J.

In order to correlate the size and crystallinity of FePt nanoparticles with their respective electrical and mangeto-electrical properties individual nanoparticles are contacted using electron beam lithography. The particles are prepared from gas phase on electron transparent SiN membranes which allows the transmission electron microscopy of the same nanoparticle which is characterized electrically. This procedure results in junctions, in which single FePt nanoparticles are connected to external leads. These junctions are tested electronically by measuring the current-voltage characteristics at various gate voltages, temperatures and magnetic fields. We observe Coulomb Blockade effects which are in agreement with the dimensions obtained from the TEM studies. The results of the magnetic nanoparticles are compared to measurements taken on Au nanoparticles of similar sizes.

Keywords: nanoelectronics; magnetic data storage; Coulomb Blockade effects

  • Invited lecture (Conferences)
    DPG Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Germany

Publ.-Id: 17365

A single-channel microparticle sieve based on Brownian ratchets

Verleger, S.; Grimm, A.; Kreuter, C.; Tan, H. M.; van Kan, J. A.; Erbe, A.; Scheer, E.; van der Maarel, J. R. C.

We present a novel device for the separation of microparticles in a single channel, which is made of inversely asymmetric Brownian ratchets. It enables separation into two different fractions with an adjustable threshold and can be modeled with good agreement. This device serves as proof of concept for an extremely compact class of microsieves.

Keywords: colloidal model systems; microfluidics

  • Lab on a chip 12(2012), 1238

Publ.-Id: 17364

Statistical Investigation of Current-Voltage Characterization in Single Molecule-Metal Junctions

Kirchner, T.; Briechle, B.; Scheer, E.; Wolf, J.; Huhn, T.; Erbe, A.

We show statistical measurements of single molecule-metal contacts using the mechanically controllable break junction technique. The measurements are carried out in a solvent, in order to allow in situ binding of the molecules to the metallic contacts during the measurements. Statistics is gathered by opening and closing the junctions repeatedly and recording current-voltage characteristics at various stages of the opening and closing curves. By modeling the data with a single level model we can extract parameters such as the position of the molecular energy level, which carries the current, and the coupling between the metal and the molecule. In first experiments we use this method to characterize di􏰹erent anchoring groups, which mediate the mechanical and electrical coupling between the metallic electrodes and the molecules. We use tolane molecules, which are structurally simple, as model systems for this purpose.

Keywords: molecular electronics; nanoelectronics; single molecule contacts

  • Open Access Logo Acta Physica Polonica A 121(2012), 410

Publ.-Id: 17363

Örtlich und zeitlich hoch aufgelöste Geschwindigkeits-, Beschleunigungs- und Kraftmessung an Plasma- und Lorentzkraft-Aktoren

Neumann, M.; Friedrich, C.; Büttner, L.; Grundmann, S.; Albrecht, T.; Weier, T.; Czarske, J.

Mittels erweitertem Laser-Doppler-Geschwindigkeitsprofilsensor wurde ein hoch aufgelöste, mehrkomponentige Vermessung von Strömungsfeldern durchgeführt, welche von Plasma- bzw. Lorentzkraft-Aktuatoren angetrieben wurden. Für den Einsatz der Aktuatoren zur aktiven Strömungskontrolle ist ein genaues Verständnis der jeweiligen Wirkungsweise erforderlich, was im Fall des Plasma-Aktuators noch nicht komplett vorliegt. Da Plasma-Aktuatoren im Allgemeinen mittels alternierender Hochspannung betrieben werden, ist eine hohe Zeitauflösung des Messsystems ebenso unabdingbar. Die gewonnen Messergebnisse, welche bis zu 100 mum nahe an der Aktuatoroberfläche gewonnen werden konnten, erlauben schließlich die Berechnung der induzierten Kraft und gewähren daher einen tieferen Einblick in das Funktionsprinzip. Es konnte somit ein wertvoller Beitrag zur Beschreibung des zeitlichen Verlaufs der erzeugten Kraft geleistet werden.

Keywords: plasma actuator; Lorentz force; flow control

  • Lecture (Conference)
    20. Fachtagung Lasermethoden in der Strömungsmesstechnik, 04.-06.09.2012, Rostock, Deutschland

Publ.-Id: 17362

Photonuclear and radiative-capture reaction rates for nuclear astrophysics and transmutation: 92-100Mo, 88Sr, 90Zr, and 139 La

Beard, M.; Frauendorf, S.; Kämpfer, B.; Schwengner, R.; Wiescher, M.

Experimental photoabsorption cross sections for the nuclei 92,94,96,98,100Mo, 88Sr, 90Zr, and 139La are used as an input for calculations of (γ,n), (γ,p), and (γ,α), as well as (n,γ), (p,γ), and (α,γ) cross sections and reaction rates at energies and temperatures relevant for nucleosynthesis network models and transmutation projects. The calculations are performed with the statistical-model code talys. The results are compared with those obtained by using different analytic standard parametrizations of γ-ray strength functions implemented in talys and with an energy-damped double-Lorentzian model. The radiative capture reaction cross sections are enhanced by the pygmy resonances in 88Sr, 90Zr, and 139La.

Publ.-Id: 17361

An experimental study of a bubble-driven liquid metal flow under the influence of a rotating magnetic field

Vogt, T.; Andruszkiewicz, A.; Eckert, S.; Eckert, K.; Odenbach, S.; Gerbeth, G.

In this study we investigate the flow structure in a liquid metal cylinder while a bubble driven recirculation flow is superposed with a rotating magnetic field (RMF). The measurements revealed the potential of the RMF to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume. Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.

Keywords: Bubble flow; rotating magnetic field; Mixing

  • Journal of Iron and Steel Research International 19(2012), 505-508
  • Lecture (Conference)
    7th International Conference on Electromagnetic Processing of Materials (EPM2012), 22.-26.10.2012, Beijing, China

Publ.-Id: 17360

The influence of natural convection and electromagnetically driven flows on segregation freckle formation

Shevchenko, N.; Boden, S.; Eckert, S.; Gerbeth, G.

Visualizations of the solidification process were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with a Ga-25wt%In alloy. Thermo-solutal convection in the solidifying melt gives rise to the development of vertical segregation channels (“chimneys”). The probability of chimney formation depends sensitively on variations of both the concentration and temperature distribution. A forced melt flow perpendicular to the growth direction accelerates the growth of the secondary dendrite arms on the upstream side and suppresses the development of secondary arms on the downstream side. The primary dendrite arm spacing is increased, whereas the secondary arm spacing remains unaffected. Flow-induced modifications of the local composition were observed within the mushy zone which may contribute to the formation of spacious segregation pattern.

Keywords: solidification; melt flow; forced convection; segregation; freckle formation; X-ray radiography

  • Lecture (Conference)
    7th International Conference on Electromagnetic Processing of Materials, 22.-26.10.2012, Bejing, China
  • Journal of Iron and Steel Research International 19(2012), 459-462

Publ.-Id: 17359

The impact of an oxidised surface on the melt flow driven by a rotating magnetic field in a cylindrical column

Eckert, S.; Shatrov, V.; Zhang, C.; Gerbeth, G.

This paper considers the situation where the liquid metal flow with a free surface covered by an oxide layer is driven by a rotating magnetic field. The cylindrical configuration was investigated in an experiment accompanied by numerical simulations. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if both forces are in the same order of magnitude. Our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Our numerical model was shown to be able to reproduce essential features of the phenomenon in a qualitative way.

Keywords: electromagnetic stirring; rotating magnetic field; free surface; oxide layer

  • Lecture (Conference)
    7th International Conference on Electromagnetic Processing of Materials, 22.-26.10.2012, Bejing, China
  • Journal of Iron and Steel Research International 19(2012), 536-539

Publ.-Id: 17358

Accelerated Atomistic Simulations of Nanostructure Evolution using Graphics Cards

Kelling, J.

  • Lecture (others)
    Seminar Topical Problems, 16.05.2012, Chemnitz, Deutschland

Publ.-Id: 17357

Influence of Eph receptors on melanoma cell properties after X-ray irradiation

Mosch, B.; Pietzsch, D.; Vogel, P.; Kunath, N.; Pietzsch, J.

X-ray irradiation has an influence on metastatic properties of tumor cells. Moreover, metastasis and cellular motility can be modified by EphA2 and EphA3, two members of the Eph receptor/ephrin family of receptor tyrosine kinases. However, a link between X-ray irradiation, Eph receptor expression, and modification of metastasis-relevant cellular properties has not yet been shown.
In this study, we irradiated one pre-metastatic and three metastatic human melanoma cells lines with X-rays and found impairment of cell growth and clonal growth. Regarding adhesion, an irradiation-induced increase paralleled by a decrease in migration was detected in Mel-Juso and Mel-Juso-L3 cells and, in part, also in A375 cells. These results indicate irradiation-induced anti-metastatic effects.
For EphA2 a decrease both in expression and activity at 7 days after irradiation was detected. In contrast, EphA3 was found to be up-regulated in 3 of 4 analyzed cell lines. Analyzing downstream signaling after irradiation decreased Src kinase phosphorylation, but unchanged focal adhesion kinase (FAK) phosphorylation was demonstrated. Our findings indicate that irradiation-induced downregulation of EphA2 and up-regulation of EphA3 in human melanoma cells is associated with anti-metastatic effects. The observed effects are assumed partly to be mediated by regulation of Src and FAK through EphA2.

  • Contribution to proceedings
    Melanocytes and melanoma, 18.-20.06.2012, Malmö, Schweden
    Melanocytes and melanoma: from basic science to clinical applications, Rönnstrand L, Steingrímsson E (Eds.), 32
  • Lecture (Conference)
    Melanocytes and Melanoma, 18.-20.06.2012, Malmö, Sweden

Publ.-Id: 17356

Lanthanide induced linkage of bifunctional organic acids

Kretzschmar, J.; Barkleit, A.; Paasch, S.; Brunner, E.

Lanthanides have become a useful tool in NMR spectroscopy within the last 40 years. Due to their paramagnetic properties they can be utilized as probes to determine the binding sites of biologically or environmentally relevant organic molecules as they cause significant line broadenings and / or paramagnetic induced shifts.
In our former and actual research we investigate the interactions, thermodynamic and kinetic behaviour of actinides and biomolecules. Lanthanides can easily be used as inactive analogues for trivalent actinides in consequence of their similar chemistry.
As one major result, determined by solution and solid state NMR spectroscopy, we have found out that lanthanide ions are able to act as linkers to build up polymeric structures of bifunctional organic acids such as pyromellitic acid [1] or phosphorylated amino acids. For instance, in the case of O-phospho-L-serine the lanthanide ions can serve as a bridge between the carboxylate and the phosphate group of two amino acid molecules to form repetitive macromolecules. The influence of pH and temperature has also been studied.
The results were confirmed by dynamic light scattering and FT-IR spectroscopy as well as by isothermal titration calorimetry and laser-induced fluorescence spectroscopy.
Future investigations will focus on actinides, in particular the trivalent americium ion, possibly showing similar chemical reactions.

[1] A. Barkleit, S. Tsushima, O. Savchuk, J. Philipp, K. Heim, M. Acker, S. Taut, K. Fahmy, Inorg. Chem. 50 (2011), 5451-5459.

Keywords: lanthanides; lanthanum(III); europium(III); phosphorylated amino acids; NMR spectroscopy

  • Poster
    GDCh FGMR 34th Annual Discussion Meeting - Advanced Magnetic Resonance for the Study of Dynamics in Biomolecules and Materials, 17.-20.09.2012, Halle/Saale, Deutschland

Publ.-Id: 17355

Synthesis and crystal structure of benzyl[(1S)-1-(5-amino-1,3,4-oxadiazol-2-yl)-2-phenylethyl]carbamate

Löser, R.; Nieger, M.; Gütschow, M.

The conversion of Z-phenylalanine hydrazide with cyanogen bromide resulted in the formation of the corresponding 2-amino-1,3,4-oxadiazole by spontaneous cyclization of the intermediary cyanohydrazide. The molecular structure of the product was confirmed by single crystal X-ray diffraction. Crystals of the title compound where obtained from a saturated solution in a mixture of petroleum ether and ethyl acetate and belong to the monoclinic space group P21 with unit cell parameters a =
9.8152(2) Å, b = 9.6305(2) Å, c = 9.8465(2) Å, beta = 116.785 (1)°. The asymmetric unit contains one molecule.

Keywords: 1,3,4-oxadiazoles; cyanohydrazides; hydrogen bonds; edge-to-face interactions

Publ.-Id: 17354

Crossover in the surface anisotropy contributions of ferromagnetic films on rippled Si surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Fritzsche, M.; Ranjan, M.; Keller, A.; Cizmár, E.; Zvyagin, S.; Facsko, S.; Potzger, K.; Lindner, J.; Fassbender, J.

We investigate the influence of a nanoscale periodic ripple morphology on the structure and magneto-crystalline anisotropy of thin ferromagnetic (FM) NiFe, Co, and Fe films. The ripples are created by ion beam erosion of the Si substrate. The periodic ripple structures induce a uniaxial magnetic anisotropy (UMA) in the FM films as confirmed by ferromagnetic resonance and magnetooptical Kerr effect measurements. The thickness dependence of the UMA reveals an abrupt transition. For a thin film regime there is a corrugated alignment of the magnetic moments and above a critical thickness one has dipolar interactions due to the sinusoidal surface modulations.

Keywords: ripples; magnetic anisotropy; uniaxial anisotropy; NiFe; Co; Fe; polycrystalline films; thin films; ion irradiation; MOKE; FMR; LLG

Publ.-Id: 17353

Electromagnetic excitation of a backward facing step flow

Weier, T.; Albrecht, T.; Wittwer, S.; Metzkes, H.; Stiller, J.; Gerbeth, G.

We consider the flow over a backward facing step under time periodic electromagnetic forcing. Velocity fields have been obtained by time resolved Particle Image Velocimetry in an electrolyte channel at a step height Reynolds number of 1875.
Growth rates of the shear layer instability fit reasonably well to the classical values of Michalke (1965). As expected, excitation with the most amplified frequency results in a minimal reattachment length xr. For moderate excitation amplitudes (characterized here by the interaction parameter N, i.e. the ratio of electromagnetic to inertial forces), forcing with frequencies outside the range of amplified disturbances has no influence on the reattachment length. This behavior is essential in explaining our findings for non sinusoidal excitation. In that case and for a fixed excitation frequency, neither the rms nor the peak value of N is able to collapse recirculation length reductions for different wave forms. However, using only the amplitude of the fundamental sine wave of the applied wave form in N rearranges the data in such a way that they follow a single line in fair approximation. The harmonics of all investigated wave forms have frequencies at least three times higher than the fundamental one and are beyond the range of amplification. In contrast, for separation control on an airfoil (Weier and Gerbeth, 2004) and larger interaction parameters, the peak value of N was found to determine control efficacy, regardless of the wave form.
Proper orthogonal decomposition of the flow fields shows dominant shear layer modes in case of the unforced flow. Under forcing, the time coefficients of the most energetic modes seem to be related to the flapping frequency of the reattachment region.

Keywords: backward facing step; Lorentz force; flow control

  • Lecture (Conference)
    9th European Fluid Mechanics Conference (EFMC9), 09.-13.09.2012, Rom, Italien

Publ.-Id: 17352

DFT investigation of the heterostructure GaP (001) on Si (001)

Steinbach, G.; Schreiber, M.; Gemming, S.

Semiconductor multilayers are a versatile tool in optoelectronics. The III-V/IV heterostructure GaP(001) on Si(001) provides a viable and almost lattice-matched stack making it suitable for device applications such as multi-junction solar cells. One of the main challenges still arises from the efficiency limitation due to symmetry breaking and imperfections at the buried GaP on Si interface. Here, we present a density-functional investigation of the interface using both the pseudopotential plane-wave code ABINIT and the all-electron augmented plane-wave code Wien2K. The study distinguishes between the Ga-rich and the P-rich interface termination of GaP in the (001) plane. Overall insight into the interface characteristics is gained from structural and electronic quantities. At the perfectly flat interface, the P-rich variant is found to exhibit higher stability. This is supported by the investigation of the atom distances and the local electronic system. Further, it could be shown that the impact of the interface is very local and does not reach far into the layers. Depending on the interface termination, the electronic system shows distinct behavior.

Keywords: gallium phosphide; silicon; heterostructure; photovoltaic; density-functional; DFT; interface

Publ.-Id: 17351

Electric Formation of Metal/SrTiO3 Junctions and its Correlation to Multi-Dimensional Defects

Meyer, D. C.; Stöcker, H.; Hanzig, J.; Hanzig, F.; Zschornak, M.; Abendroth, B.; Gemming, S.

Regarding the successful use of strontium titanate with different doping within resistive switching memory cells, the presence of crystallographic defects seems to be an important prerequisite. Standard explanations for resistive switching rely on the redistribution of oxygen vacancies, however, this motion can be enhanced or prevented by higher-dimensional defects. Intrinsic defects in crystalline SrTiO3 include point defects such as oxygen or strontium vacancies, line defects, stacking faults like Ruddlesden-Popper phases and precipitates (TiO2, SrO etc.). Electric formation of the metal/oxide/metal cells is widely used as an initial step to enable resistive switching, but the interaction of the multi-dimensional defects during this treatment remains questionable. This talk will present several measurements that were performed in situ, i.e. during the application of an electric field, to investigate the effects of the electric formation on the real structure.

Keywords: multiferroic; memristive; ferroelectric; oxide; perovskite; titanate; Ruddlesden-Popper; DFT; density-functional; X-Ray; XRD; defect

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17350

Gallium Phosphide - Silicon Interface: Structure and Anisotropy Investigations

Steinbach, G.; Gemming, S.; Döscher, H.; Hannappel, T.; Schreiber, M.

Gallium phosphide thin films on cheap silicon substrates are a promising III-V/IV heterostructure to be used in optoelectronic devices. As an almost lattice matched system with a band gap difference of 1.14 eV it includes applicability for multi-junction solar cells. The present study concerns discontinuities emerging at the boundaries of a GaP thin layer on a silicon substrate. The optical anisotropy of the (001) interface has been determined by an optical model applied to reflectance anisotropy spectroscopy measurements of the GaP/Si heterostructure. Density-functional calculations of the interface have been performed with both, the pseudopotential plane wave code ABINIT [1] and the all-electron augmented plane wave code Wien2K [2]. The study distinguishes between the Ga-rich and the P-rich interface termination. At the perfectly flat interface, the latter exhibits higher stability as indicated by the work of separation. More complex interface models also consider defects. The calculated density of states projected onto in-plane directions gives an indication for anisotropy. It aims at distinguishing interface termination and defects as origin of the experimentally observed reflectance anisotropy. [1] [2]

Keywords: gallium phosphide; silicon; photovoltaics; interface; density-functional

  • Poster
    DPG-Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17349

Conducting Molecules

Wieser, M.; Berger, S.; Kunze, S.; Gemming, S.; Grebing, J.; Erbe, A.; Morawetz, K.; Huhn, K.; Wolf, J.

no abstract available

Keywords: molecular electronics; nanoelectronics; Green's functions; conductance; single-molecule; organic FET; DFT; self-assembly

  • Lecture (others)
    Topical Problems in Theoretical Physics, 09.05.2012, Chemnitz, Deutschland

Publ.-Id: 17348

Virtual Institute MEMRIOX - Memory Effects in Resistive Ion-beam Modified Oxides

Gemming, S.; Dittmann, R.; Meyer, D. C.; Mikolajick, T.; Ronning, C.; Schmidt, H.; Waser, R.; Spaldin, N. A.; Basov, D.

The Virtual Institute (VI) „Memriox“ establishes a joint research initiative in the field of ion-tailored oxide-based memristive materials, to be pursued within a novel and unique combination of core competences from the Helmholtz centers Dresden-Rossendorf and Jülich and their university partners in Aachen, Dresden, Freiberg, and Jena. A nanoscale memristive switch may prove the ultimate future non-volatile memory and logic cell with a resistance set directly by electric currents. Thus, the nanoscale memristor has matured to a key player in strategies combining the virtues of the “More Moore” and “More than Moore“ concepts to drive the development of both miniature and functionalized electronic components for a resource-efficient “green“ computing.
Scientifically, the VI aims at stepping beyond the established layer-by-layer control of intrinsic defects during the synthesis of memristive homojunctions. For that purpose, the VI will employ the broad range of ion-beam techniques (HZDR and FSU Jena competence) to induce functionalized one- and two-dimensionally extended memristive nanoregions with high spatial precision. Nano-scale electronic and optical properties and functiona¬lities will be investigated at the partner institutions at the FZJ and the universities in Aachen, Freiberg, and Jena. Applica-bility will be assessed at the NaMlab facility of the TU Dresden. Associated partners at the U.C. San Diego (U.S.A.) and the ETH Zürich (Switzerland) extend the expertise on spectroscopy and simulation.
This combination of the VI partners’ profound, long-term expertise in complementary high-level synthesis, characterization and analysis techniques is unique in the German research area. It provides the ideal framework to explore the spatial limits of memristive elements and their environment hence the VI faces the challenges of the ‘More Moore’ concept, which is still less prominent in basic memristor research. The VI will thus make a significant, qualitatively and quantitatively distinct contribution to cutting-edge science, which aims at quantifying defect-related effects on memristive behavior according to the ‚More Than Moore‘ concept.

Keywords: memristor; memristive; oxide; titanate; ferrite; multiferroic

  • Lecture (others)
    HGF In-House Workshop PNI, 11.-12.06.2012, Freising, Deutschland

Publ.-Id: 17347

Thermodynamic treatment of morphogenesis of brine channels in sea ice

Thoms, S.; Kutschan, B.; Morawetz, K.; Gemming, S.

Sea ice is a very variable biotope with respect to extension,thickness, porosity or texture. Therefore the basic understanding of brine channel formation in sea ice is important for the interplay between the microbial colonization and their natural habitat. The early phase of brine channel formation in sea ice is considered. The first structures emerging during sea-ice formation are determined by the phase instability of the ice-water system in the presence of salt. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, salt). The free energy density involves two order parameters: one for the hexagonal ice phase with low salinity, and one for the liquid water with high salinity. A gradient dynamics minimizes the free energy with respect to the conservation of the salinity. The resulting model equations are solved numerically in one and two dimensions. The numerical solution shows a short-time behavior of structure formation where the freezing is assumed and a large-time broadening of the structure. A stability analysis provides the phase diagram where brine channels can be formed. In thermodynamics the parameters determine the supercooling or superheating region and the specific heat respectively. The size of the brine channels depends on the salinity and the temperature. With the help of realistic parameters the brine channel distribution is calculated and found in agreement with the measured samples.

Keywords: sea ice; brine; phase-field; modelling; binary system; nanostructure formation; reaction-diffusion equations

  • Contribution to proceedings
    EGU General Assembly 2012, 22.-27.04.2012, Wien, Österreich
    EGU General Assembly Conference Abstracts, Vol. 14, 6239

Publ.-Id: 17346

Band gap tuning of carbon nanotubes for sensor and interconnect applications — A quantum simulation study

Zienert, A.; Gemming, S.; Schuster, J.; Schulz, S. E.; Gessner, T.

Carbon nanotubes (CNTs) are a promising material for novel sensor and interconnect applications. In both cases, the device performance depends strongly on the electronic properties of the tubes. Methods for tuning the electronic structure and especially the band gap are highly desirable. A computational study of cobalt decorated CNTs, by means of density functional theory, reveals that very few cobalt atoms can have a significant impact on the electronic structure, turning semiconducting CNTs into the metallic state. This is further verified by quantum transport simulations. The influence of different amounts of cobalt is also investigated.

Keywords: CNT; nanotube; density-functional; transport; nanoelectronic

  • Contribution to proceedings
    9th International Multi-Conference on Systems, Signals and Devices (SSD), 20.-23.03.2012, Chemnitz, Deutschland
    Systems, Signals and Devices: IEEE, 978-1-4673-1590-6

Publ.-Id: 17345

Multifunctional oxides - influence of defects on the ferroic properties

Gemming, S.; Weissbach, T.; Zschornak, M.; Stöcker, H.; Meyer, D. C.; Leisegang, T.; Ronneberger, I.; Potzger, K.

Transition metal oxides exhibit many physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. The stoichiometry of transition metal oxides depends on the oxygen partial pressure and changes conductivity and ferroic properties. Ternary/quaternary oxides are discussed, which correlate local defect-induced structure changes with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional theory as basis for more large-scale simulations with effective Hamiltonians. Oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. For Sr/O excess SrO(SrTiO3)n phases with additional SrO planes occur, which change the X-Ray reflectivity. Ion-irradiation triggers additional point defects which can form stable aggregates. In YMn2O5 several antiferromagnetic phases coexist with ferroelectricity; YFeMnO5 exhibits only one commensurable ferrimagnetic phase. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the two compounds and relates them to crystal-field interactions.

Keywords: multiferroic; DFT; density-functional; oxide; titanate; ferrite; manganite

  • Poster
    DPG Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17344

Ion beam assisted deposition of nano-structured C:Ni films

Abrasonis, G.; Krause, M.; Mücklich, A.; Heller, R.; Heinig, K.-H.; Gemming, S.; Möller, W.

Nanostructures influence material properties dramatically due to size, shape and interface effects. Thus the control of the structure at the nanoscale is a key issue in nanomaterials science. The interaction of hyperthermal ions with solids is confined to the nanometer scale. Thus, it can be used to control the morphology evolution during multiphase film deposition. Ion-induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility for the phase separation. Here the growth-structure relationship of C:Ni (~15 at.%) nanocomposite films grown by oblique incidence (~45) ion beam assisted deposition is reported. The influences of the flux of an assisting Ar+ ion beam (0-140 eV) as well as of an elevated substrate temperature have been studied. The formation of elongated nickel nanoparticles is strongly promoted by the ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, but with the incoming ions. A window of conditions is established within which the ion assistance leads to the formation of regular composition modulations with a well defined periodicity and tilt. As the dominating driving force for the pattern formation is of physical origin, this approach might be applicable to other immiscible systems.

Keywords: ion-assisted growth; structure formation ECEMP; CNT; nickel; IBAD

  • Poster
    DPG Frühjahrstagung 2012, 26.-30.03.2012, Berlin, Deutschland

Publ.-Id: 17343

Multifunctional Oxides – Modifying the Ferroic Properties by Defects due to Irradiation, Doping and Annealing

Gemming, S.; Weissbach, T.; Zschornak, M.; Stöcker, H.; Meyer, D. C.; Leisegang, T.; Ronneberger, I.; Potzger, K.

Transition metal oxides exhibit a wealth of physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. In addition, transition metal oxides are sensitive to the chemical environment via the oxygen partial pressure or ion irradiation; changes induce stoichiometry deviations, which cause conductivity changes and modify the ferroic characteristics. Ternary and quaternary compounds from the perovskite family will be discussed as examples, which correlate local changes due to point and planar defects with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional calculations, which yield the basis for more large-scale simulations with effective Hamiltonian approaches. Under oxygen-poor conditions, oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. In an Sr/O-rich environment the phases SrO(SrTiO3)n are formed, which yield a distinct change of the X-ray reflectivity due to the regular arrangement of extrinsic SrO(001) stacking faults. YMn2O5 has a series of complex antiferromagnetic phases in coexistence with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found and ferroelectricity is absent. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the Fe-substituted and the mangenese-only compounds and relates them to crystal-field interactions. Finally, BiFeO3 will be addressed, which is a rhombohedral multiferroic with several domain wall configurations, which exhibit specific magnetic and conductance properties.

Keywords: oxide; DFT; density-functional; multiferroic; bismuth ferrite; manganite; titanate

  • Invited lecture (Conferences)
    MRS Spring Meeting, 09.-13.04.2012, San Francisco, U.S.A.

Publ.-Id: 17342

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