1,083 Works

High-resolution 27Al MAS NMR spectroscopic studies of the response of spinel aluminates to mechanical action

Vladimir Šepelák, Ingo Bergmann, Sylvio Indris, Armin Feldhoff, Horst Hahn, Klaus-Dieter Becker, Clare P. Grey & Paul Heitjans
The response of the local structure of various types of spinel aluminates, ZnAl2O4 (normal spinel), MgAl2O4 (partly inverse spinel), and Li0.5Al2.5O4 (fully inverse spinel), to mechanical action through high-energy milling is investigated by means of 27Al MAS NMR. Due to the ability of this nuclear spectroscopic technique to probe the local environment of Al nuclei, valuable quantitative insight into the mechanically induced changes in the spinel structure, such as the local cation disorder and the...

Formation of ultracold Rb 2 molecules in the v′′ = 0 level of the a 3Σ + u state via blue-detuned photoassociation to the 1 3Π g state

M.A. Bellos, D. Rahmlow, R. Carollo, J. Banerjee, O. Dulieu, A. Gerdes, E.E. Eyler, P.L. Gould & W.C. Stwalley
We report on the observation of blue-detuned photoassociation in Rb2, in which vibrational levels are energetically above the corresponding excited atomic asymptote. 85Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 13Πg state at a rate of approximately 5 × 104 molecules s−1. We have observed most of the predicted vibrational levels for all four spin–orbit components; 0+g, 0−g, 1g, and 2g, including levels of the 0+g outer well....

Formate modulated solvothermal synthesis of ZIF-8 investigated using time-resolved in situ X-ray diffraction and scanning electron microscopy

Janosch Cravillon, Christian A. Schröder, Helge Bux, André Rothkirch, Jürgen Caro & Michael Wiebcke
Time-resolved investigations using in situ energy-dispersive X-ray diffraction in tandem with ex situscanning electron microscopy revealed that solvothermal crystallisation of ZIF-8 in methanol solvent and in the presence of sodium formate as a simple monodentate ligand (modulator) is a rapid process yielding big, high-quality single crystals in short time (<4 h). Kinetic analysis of crystallisation curves was performed by applying the Avrami–Erofe'ev and Gualtieri models. The analyses revealed that the weakly basic formate modulator acts...

Li self-diffusion in lithium niobate single crystals at low temperatures

Johanna Rahn, Erwin Hüger, Lars Dörrer, Bernhard Ruprecht, Paul Heitjans & Harald Schmidt
Li self-diffusion in Li 2O-deficient LiNbO 3 single crystals is investigated in the temperature range between 423 and 773 K (150-500 °C) by secondary ion mass spectrometry. A thin layer of ion-beam sputtered isotope enriched 6LiNbO 3 was used as a tracer source, which allows one to study pure isotope interdiffusion. The diffusivities can be described by the Arrhenius law with an activation enthalpy of (1.33 ± 0.03) eV, which is in acceptable agreement with...

Comparison of the photoelectrochemical oxidation of methanol on rutile TiO 2 (001) and (100) single crystal faces studied by intensity modulated photocurrent spectroscopy

Amira Y. Ahmed, Torsten Oekermann, Patrick Lindner & Detlef W. Bahnemann
The photooxidation of methanol as a model substance for pollutants on rutile TiO 2 (001) and (100) surfaces was investigated using intensity modulated photocurrent spectroscopy (IMPS). The results are analyzed in view of the influence of the surface structure, the methanol concentration and the electrode potential on the rate constants of charge transfer and recombination. The obtained results have been explained with a model combining the theory of IMPS for a bulk semiconductor surface and...

Investigation of ion-ion-recombination at atmospheric pressure with a pulsed electron gun

Andre Heptner, Philipp Cochems, Jens Langejuergen, Frank Gunzer & Stefan Zimmermann
For future development of simple miniaturized sensors based on pulsed atmospheric pressure ionization as known from ion mobility spectrometry, we investigated the reaction kinetics of ion-ion-recombination to establish selective ion suppression as an easy to apply separation technique for otherwise non-selective ion detectors. Therefore, the recombination rates of different positive ion species, such as protonated water clusters H +(H 2O) n (positive reactant ions), acetone, ammonia and dimethyl-methylphosphonate ions, all recombining with negative oxygen clusters...

Colloidal Cu 2-x(S ySe 1-y) alloy nanocrystals with controllable crystal phase: Synthesis, plasmonic properties, cation exchange and electrochemical lithiation

Enrico Dilena, Dirk Dorfs, Chandramohan George, Karol Miszta, Mauro Povia, Alessandro Genovese, Alberto Casu, Mirko Prato & Liberato Manna
We report synthetic routes to both cubic and hexagonal phase Cu 2-x(S ySe 1-y) alloy nanocrystals exhibiting a well-defined near-infrared valence band plasmon resonance, the spectral position of which is dependent mainly on x, i.e. on Cu stoichiometry, and to a lesser extent on the crystal phase of the NCs. For cubic Cu 2-x(S ySe 1-y) nanocrystals y could be varied in the 0.4-0.6 range, while for hexagonal nanocrystals y could be varied in the...

Extremely slow Li ion dynamics in monoclinic Li 2TiO 3 - Probing macroscopic jump diffusion via 7Li NMR stimulated echoes

Bernhard Ruprecht, Martin Wilkening, Reinhard Uecker & Paul Heitjans
A thorough understanding of ion dynamics in solids, which is a vital topic in modern materials and energy research, requires the investigation of diffusion properties on a preferably large dynamic range by complementary techniques. Here, a polycrystalline sample of Li 2TiO 3 was used as a model substance to study Li motion by both 7Li spin-alignment echo (SAE) nuclear magnetic resonance (NMR) and ac-conductivity measurements. Although the two methods do probe Li dynamics in quite...

Factors affecting the selectivity of the photocatalytic conversion of nitroaromatic compounds over TiO2 to valuable nitrogen-containing organic compounds

Amer Hakki, Ralf Dillert & Detlef W. Bahnemann
The photocatalytic conversion of various nitroaromatic compounds in alcohols employing four different types of TiO2 (Sachtleben Hombikat UV100 as anatase, Crystal Global R34 as rutile, Evonik-Degussa Aeroxide P25 as an anatase-rutile mixture, and home-made mesoporous anatase) has been studied. The effect of platinization of these different types of TiO2 on the reaction sequence has also been investigated. Upon irradiation of an ethanolic solution of m-nitrotoluene, as a model reaction, in the presence of the bare...

Access to metastable complex ion conductors via mechanosynthesis: Preparation, microstructure and conductivity of (Ba,Sr)LiF3 with inverse perovskite structure

A. Düvel, S. Wegner, K. Efimov, A. Feldhoff, Paul Heitjans & Martin Wilkening
Highly metastable Ba1−xSrxLiF3 (0 < x ≤ xmax ≈ 0.4) with an inverse perovskite structure analogous to that of BaLiF3 was synthesized by soft mechanical treatment of BaF2 and LiF together with SrF2 at ambient temperature. Ex as well as in situX-ray powder diffraction (XRPD) measurements show that heat treatment at 393 K initiates the decomposition of the mixed phase into BaLiF3, LiF and (Sr,Ba)F2. Structural details of the metastable compound (Ba,Sr)LiF3 were investigated by...

Bioorthogonal metal-free click-ligation of cRGD-pentapeptide to alginate

Andreas Krause, Andreas Kirschning & Gerald Dräger
Click reactions have become very common and powerful ligation techniques, of which 1,3-dipolar cycloadditions have most frequently been employed. Since metal-mediated cycloadditions are incompatible in biomedical applications due to toxicity issues associated with transition metals like copper, metal-free variants provide important alternatives. The metal-free conjugation process is studied in detail with special emphasis put on the reaction progress. This report unfolds the first aqueous metal-free "click" conjugation of a cyclic RGD-pentapeptide with the biomacromolecule alginate,...

Brookite versus anatase TiO2 photocatalysts: Phase transformations and photocatalytic activities

Tarek A. Kandiel, Lars Robben, Ayad Alkaim & Detlef W. Bahnemann
Titanium dioxide nanoparticles consisting of pure anatase, anatase-rich, brookite-rich, and pure brookite modifications were synthesized and characterized by X-ray diffraction, field emission-scanning electron microscopy and nitrogen adsorption. The phase transformations among the three modifications of TiO2 (anatase, brookite, and rutile) and the photocatalytic activities of these nanoparticles were investigated by heat treatment over the temperature range from 400 to 800 °C and by the photooxidation of methanol, respectively. Direct transformation of anatase and brookite to...

In situ static and dynamic light scattering and scanning electron microscopy study on the crystallization of the dense zinc imidazolate framework ZIF-zni

Todor Hikov, Christian A. Schröder, Janosch Cravillon, Michael Wiebcke & Klaus Huber
The kinetics and mechanism of crystallization of the dense zinc imidazolate framework with zni topology, from comparatively dilute methanol solutions containing Zn(NO3)·6H2O and imidazole with variation of the zinc-to-imidazole ratio, were followed in situ by time-resolved static and dynamic light scattering. The light scattering data revealed that metastable primary particles of about 100 nm in diameter form rapidly upon mixing the component solutions. After a lag time that is dependent on the imidazole concentration, the...

AsS2Cl - An arsenic(V) compound? Formation, stability and structure of gaseous AsSCl and AsS2Cl - A combined experimental and theoretical study

E. Milke, R. Köppe & Michael Binnewies
By reaction of solid As4S4 with gaseous Cl2 at a temperature of 410 K gaseous AsSCl and AsS2Cl are formed. Unexpectedly in AsS2Cl the arsenic is not of formal oxidation state +V but +III: the molecular structure of AsS2Cl is arranged as a 1-chloro-dithia-arsirane and comprises an hitherto unknown AsS2 three-membered ring. Thermodynamic data on AsSCl and AsS2Cl are obtained by mass spectrometry (MS). The experimental data are extended and confirmed by ab initio quantum...

A computational model for previtamin D 3 production in skin

Merve Meinhardt-Wollweber & Ronald Krebs
Low levels of vitamin D have been implicated in a wide variety of health issues from calcemic diseases to cancer, diabetes and cardiovascular disease. For most humans, the majority of vitamin D 3 is derived from sunlight. How much vitamin D is produced under given exposure conditions is still widely discussed. We present a computational model for the production of (pre-)vitamin D within the skin. It accounts for spectral irradiance, optical properties of the skin...

A practical synthesis of Rho-Kinase inhibitor Y-27632 and fluoro derivatives and their evaluation in human pluripotent stem cells

Jiri Paleek, Robert Zweigerdt, Ruth Olmer, Ulrich Martin, Andreas Kirschning & Gerald Dräger
A practical synthesis of the Rho-Kinase inhibitor Y-27632 and two new fluoro derivatives was achieved in seven steps and with a good overall yield of 45% starting from commercially available (R)-1-phenylethylamine. Compared to Y-27632 the new fluoro derivatives showed reduced or no effect on hPSC vitality and expansion after dissociation in human pluripotent stem cells. © 2011 The Royal Society of Chemistry.

1H-NMR measurements of proton mobility in nano-crystalline YSZ

Judith Hinterberg, Alina Adams, Bernhard Blümich, Paul Heitjans, Sangtae Kim, Zuhair A. Munir & Manfred Martin
We report nuclear magnetic resonance (NMR) results on water saturated, dense, nano-crystalline YSZ samples (9.5 mol% yttria doped zirconia) which exhibit proton conductivity at temperatures as low as room temperature. 1H-NMR spectra recorded under static and magic angle spinning conditions show two distinct signals. Their temperature-dependent behavior and their linewidths suggest that one can be attributed to (free) water adsorbed on the surface of the sample and the other one to mobile protons within the...

Anforderungen an Open-Access-Publikation von Forschungsdaten - Empfehlungen für einen offenen Umgang mit Forschungsdaten

Janna Neumann, Elke Brehm & Frauke Ziedorn
Die Publikation von Forschungsdaten wird vor allem im Rahmen der Forschungsförderung verstärkt eingefordert, auch um Forschungsergebnisse nachvollziehbar, reproduzierbar und nachnutzbar zu machen. Im Kontext des Umgangs mit Forschungsdaten im gesamten Forschungsprozess gibt es eine Reihe von rechtlich relevanten Regelungen und Vereinbarungen mit unterschiedlich beteiligten Akteuren. In der Regel werden diese unabhängig voneinander vereinbart und wenig aufeinander abgestimmt. Auch im Rahmen von Datenmanagementplänen werden Regelungen zum Umgang mit Forschungsdaten getroffen, die Datenpublikationen mitunter verhindern bzw. erschweren...

Lizenzierung von AV-Medien in Deutschland

Elke Brehm
Zunehmend werden auch im wissenschaftlichen Kontext Filme publiziert. Damit müssen Möglichkeiten geschaffen werden diese Filme auch in wissenschaftlichen Online-Portalen anzubieten. Ziel des Kompetenzzentrums für nichttextuelle Materialien der TIB ist es unter anderem, wissenschaftliche audiovisuelle Medien zu sammeln, zu archivieren und über das TIB AV Portal Nutzern online zur Verfügung zu stellen. Die Filme werden inhaltlich erschlossen und durch Vergabe von DOIs sekundengenau referenzierbar gemacht. Die Sammlung und der Erwerb der notwendigen Rechte ist im Hinblick...

Gerhart Hauptmanns Erzählung Mignon. Mit Erstdruck der ersten Fassung und Materialien

Bernhard Tempel
Die Erzählung Mignon – zwischen 1939 und 1944 entstanden und 1947 posthum veröffentlicht – ist ein bislang unterschätztes Zeugnis für Gerhart Hauptmanns Goethe-Rezeption. Die vorliegende Studie rekonstruiert zunächst die Entstehungsgeschichte des Werks und legt eine Interpretation vor, die vor allem das Spannungsfeld von intertextuellen und autobiographischen Bezügen berücksichtigt Von den Entwurfsnotizen und der ersten Niederschrift, der sogenannten 'Stresa-Novelle', bis zur Endfassung ändert sich die Konzeption gravierend. Die Erzählung, die als „Biographie einer Geistererscheinung“ noch ganz...

The effect of degassing and volatile exsolution on the composition of a trachybasaltic melt decompressed at slow and fast rates

Silvio Mollo, Francesco Vetere, Harald Beherens, Vanni Tecchiato, Antonio Langone, Piergiorgio Scarlato & Diego Perugini
It is widely accepted that, for the correct interpretation of bulk rock compositions, degassing process controlling both loss of magmatic volatiles and significant changes in the contents of volatile chemical species must be considered. The continuous degassing experiments presented in this study attempt to determine the absolute and relative change in abundances of volatile components in the melt at shallow levels, simulating what might occur during slow and fast ascent of magma from depth without...

Properties of geopolymer binders prepared from milled pond ash

J. Temuujin, A. Minjigmaa, U. Bayarzul, D.S. Kim, S.-H. Lee, H.J. Lee, C.H. Ruescher & K.J.D. MacKenzie
Alkali-activated materials were prepared from pond ash from the Darkhan city (Mongolia) thermal power station. This ash contains about 60 wt % X-ray amorphous material in addition to quartz, mullite, hematite and magnesioferrite, and presents significant storage problems since it is accumulating in large amounts and is a hazardous waste, containing 90-100 ppm of the heavy metals As, Pb and Cr, and about 800 ppm Sr. Alkali-activated materials synthesized from the as-received pond ash achieved...

Population density gratings induced by few-cycle optical pulses in a resonant medium

R.M. Arkhipov, A.V. Pakhomov, M.V. Arkhipov, I. Babushkin, A. Demircan, Uwe Morgner & N.N. Rosanov
Creation, erasing and ultrafast control of population density gratings using few-cycle optical pulses coherently interacting with resonant medium is discussed. In contrast to the commonly used schemes, here the pulses do not need to overlap in the medium, interaction between the pulses is mediated by excitation of polarization waves. We investigate the details of the dynamics arising in such ultrashort pulse scheme and develop an analytical theory demonstrating the importance of the phase memory effects...

Instantons on the six-sphere and twistors

Olaf Lechtenfeld & Alexander D. Popov
We consider the six-sphere S6 = G2/SU(3) and its twistor space Z=G2/U(2) associated with the SU(3)-structure on S6. It is shown that a Hermitian Yang-Mills connection (instanton) on a smooth vector bundle over S6 is equivalent to a flat partial connection on a vector bundle over the twistor space Z. The relation with Tian's tangent instantons on ℝ7 and their twistor description are briefly discussed. © 2012 American Institute of Physics.

Orbifold instantons, moment maps, and Yang-Mills theory with sources

T.A. Ivanova, Olaf Lechtenfeld, Alexander D. Popov & R.J. Szabo
We revisit the problem of constructing instantons on ADE orbifolds R4/Γ and point out some subtle relations with the complex structure on the orbifold. We consider generalized instanton equations on R4/Γ which are BPS equations for the Yang-Mills equations with an external current. The relation between level sets of the moment maps in the hyper-Kähler quotient construction of the instanton moduli space and sources in the Yang-Mills equations is discussed. We describe two types of...

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