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71.
Summary We used polarization spectroscopy to perform a high-resolution investigation of atomic oxygen in the visible and near-infrared
spectral region by means of dye and semiconductor diode lasers. We measured the fine structure of the highly excited 4d
5
D level and resolved the hyperfine structure of the metastable 3s
5
S
2 level of17O. Isotope shift values are also reported for several transitions of the three stable oxygen isotopes (16O,17O,18O). Polarization lineshapes are discussed and compared with those obtained in saturation techniques. 相似文献
72.
The isotopic exchange between hydrogen and methane over Ni catalyst has been studied as a function of temperature, isotopic substitution, and ratio of hydrogen to methane. The experimental results can be described by means of a model in which methane is adsorbed either as methyl or as methylene. The adsorbed species undergo one or several exchanges. The four required parameters are adjusted to the experimental results. The exchange of partially deuterated methane with H2 or D2 allowed us to study the isotopic effect on the adsorption and the exchange processes. 相似文献
73.
Gustavo?Garrigós Andreas?SeegerEmail author Tino?Ullrich 《Journal of Fourier Analysis and Applications》2018,24(5):1319-1339
We show that, for suitable enumerations, the Haar system is a Schauder basis in the classical Sobolev spaces in \({\mathbb R}^d\) with integrability \(1<p<\infty \) and smoothness \(1/p-1<s<1/p\). This complements earlier work by the last two authors on the unconditionality of the Haar system and implies that it is a conditional Schauder basis for a nonempty open subset of the (1 / p, s)-diagram. The results extend to (quasi-)Banach spaces of Hardy–Sobolev and Triebel–Lizorkin type in the range of parameters \(\frac{d}{d+1}<p<\infty \) and \(\max \{d(1/p-1),1/p-1\}<s<\min \{1,1/p\}\), which is optimal except perhaps at the end-points. 相似文献
74.
G. Rosenfeld K. Morgenstern M. Esser G. Comsa 《Applied Physics A: Materials Science & Processing》1999,69(5):489-496
Ultrathin metal films consisting of two-dimensional clusters are typically unstable: the cluster ensemble has the tendency
to reduce its total free energy via Ostwald ripening or dynamic coalescence of mobile clusters. In this paper we give an overview
of recent model experiments addressing these coarsening mechanisms. The experiments have been performed using STM on ensembles
consisting of adatom or vacancy clusters with typical diameters in the nanometer range on fcc(111)-metal surfaces. Agreement
with and deviations from conventional theories are discussed.
Received: 29 March 1999 / Accepted: 17 August 1999 / Published online: 30 September 1999 相似文献
75.
76.
77.
Denitsa Elenkova Rumen Lyapchev Julia Romanova Bernd Morgenstern Yana Dimitrova Deyan Dimov Martin Tsvetkov Joana Zaharieva 《Molecules (Basel, Switzerland)》2021,26(23)
New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu (III) complexes, Eu(PEP)2Cl3 and Eu(PEP)2(NO3)3, are synthesized and characterized. The synthetic procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single crystals obtained. The compounds [Eu(PEP)2Cl3]·2CH3CN and [Eu(PEP)2(NO3)3]∙2CH3CN crystalize in monoclinic space group P21/n and P21/c, respectively, with two acetonitrile solvent molecules. Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions in the inner coordination sphere, which allows exploring their influence on the stability, molecular and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition, molecular simulations are performed in order to explain the observed experimental behavior of the complexes. The discovered structure-properties relationships give insight on the role of the counter ions in the molecular design of new Eu (III) based luminescent materials. 相似文献
78.
Petter Dyverfeldt Roland Grdhagen Andreas Sigfridsson Matts Karlsson Tino Ebbers 《Magnetic resonance imaging》2009,27(7):913-922
Turbulent flow, characterized by velocity fluctuations, accompanies many forms of cardiovascular disease and may contribute to their progression and hemodynamic consequences. Several studies have investigated the effects of turbulence on the magnetic resonance imaging (MRI) signal. Quantitative MRI turbulence measurements have recently been shown to have great potential for application both in human cardiovascular flow and in engineering flow. In this article, potential pitfalls and sources of error in MRI turbulence measurements are theoretically and numerically investigated. Data acquisition strategies suitable for turbulence quantification are outlined. The results show that the sensitivity of MRI turbulence measurements to intravoxel mean velocity variations is negligible, but that noise may degrade the estimates if the turbulence encoding parameter is set improperly. Different approaches for utilizing a given amount of scan time were shown to influence the dynamic range and the uncertainty in the turbulence estimates due to noise. The findings reported in this work may be valuable for both in vitro and in vivo studies employing MRI methods for turbulence quantification. 相似文献
79.
Fernando Cobos Luz M. Fernández-Cabrera Thomas Kühn Tino Ullrich 《Journal of Functional Analysis》2009,256(7):2321-3722
We investigate the limit class of interpolation spaces that comes up by the choice θ=0 in the definition of the real method. These spaces arise naturally interpolating by the J-method associated to the unit square. Their duals coincide with the other extreme spaces obtained by the choice θ=1. We also study the behavior of compact operators under these two extreme interpolation methods. Moreover, we establish some interpolation formulae for function spaces and for spaces of operators. 相似文献
80.
V.S. Sistla Jan von Langermann H. Lorenz A. Seidel‐Morgenstern 《Crystal Research and Technology》2014,49(7):514-520
Differences in physical‐chemical properties of diaste‐reomeric salts allow the separation into the respective salts and subsequently into enantiomers by crystallization. Within this study unusual deviations in the cation‐/anion‐ratio of a diastereomeric salt pair were observed and characterized. While the n‐salt (L‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) crystallizes in a ratio of two cations and one anion, the p‐salt (D‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) consists of only one cation and one anion. Consequently the classical definition of a diastereomeric salt pair does not apply. In this contribution all differences in relevant thermodynamic properties of the unusual resulting diastereomeric salt pair are presented and discussed. 相似文献