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1.
Becker Otwin Leopold-Wildburger Ulrike 《Central European Journal of Operations Research》2020,28(2):425-440
Central European Journal of Operations Research - This paper combines work to use a decision support tool for sustainable economic development, while acknowledging interdependent dynamics of... 相似文献
2.
W. Potzel J. Moser Ulrike Potzel F. J. Litterst G. M. Kalvius J. Gal M. Boge J. Chappert J. Spirlet 《Hyperfine Interactions》1987,34(1-4):391-405
Due to the wider radial extent of 5f electrons when compared to their 4f counterparts, intermetallics of the light actinides show a broad spectrum of magnetic properties ranging from the localized magnetism of the lanthanides to the itinerant magnetism often found in transition metal compounds. One parameter which strongly influences the magnetic character of the compound is the actinide-actinide separation which can experimentally be varied by the application of high pressure. The question of 5f electron delocalization will be reviewed with respect to Moesshauer high pressure data on NpCo2si2, NpAl2, NpOs2 and new results will be presented of NpAs. The connection of hyperfine parameters with results of X-ray diffraction studies will be discussed.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany 相似文献
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5.
F. Henneberger U. Woggon J. Puls Ch. Spiegelberg 《Applied physics. B, Lasers and optics》1988,46(1):19-25
We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1m slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm2 range. 相似文献
6.
β-Aminocrotonic esters are of great importance as stabilizers for the production of clearly transparent food packaging of PVC. For the purpose of studying the migration into foods a thin-layer Chromatographic and a polarographic method were elaborated. The TLC method consists of the visual comparison of the intensity of the spots after treatment with Fast Blue B salt. The polarographic determination is carried out after nitrosation of the stabilizer. By the TLC method 10?7 g of ester per spot are still detectable; the concentration which is still determinable by cathode-ray polarography is 5×10?7 g of ester and by conventional d.c. polarography 5×10?6g of ester per ml of final solution. After extraction with acetonitrile traces of the stabilizer which are migrated into edible oil are still determinable down to 2 ppm by the methods described. 相似文献
7.
Karl Grubmayr Ulrike Gabriella Wagner 《Monatshefte für Chemie / Chemical Monthly》1988,119(6-7):793-812
1H NMR-spectroscopic investigations of the acid catalyzed addition of methanol to dihydrodipyrrinones (Z)-2, (E)-2, and4 show the C-protonation of their enamide parts to be the first and rate determining step forming the key intermediate, the N-acyl-immonium ion N+. Its ability to add nucleophiles diastereoselectively can be used to prepare the adductsl-3 andl-5. Exclusive formation of thelike-isomer can be explained by a stereoelectronically favoured approach of the nucleophile and by the thermodynamically favoured arrangement of the bulky ring substituents. Both explanations are based on low temperature X-ray crystal structure determinations: in the first place, the orientation of the added nucleophile could be found to be nearly parallel to the -plane of the lactam unit and quasi-axial with respect to theenvelope-like conformation of the five-ring lactam; in the second place, the relative orientation of the methoxycarbonyl-metyl-group at C-3 and the pyrrolylmethyl-substituent at C-4 could be found to be atrans-quasi-diequatorial one. 相似文献
8.
The surface and materials science of tin oxide 总被引:3,自引:0,他引:3
The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO2 surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn4+ surface cations into a reduced surface with Sn2+ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO2. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO2 are discussed and the few surface science studies of doped SnO2 are reviewed. Epitaxial SnO2 films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO2 surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized. 相似文献
9.
C. Etzlstorfer H. Falk N. Müller W. Schmitzberger Ulrike G. Wagner 《Monatshefte für Chemie / Chemical Monthly》1993,124(6-7):751-761
Summary Stereochemistry and tautomerism of hypericin, pseudohypericin, and several of their partial structure models were investigated using an MM2 derived force field method. Besides the propeller type conformer, which was also found by the X-ray crystallographic study, the complicated energy hypersurface was shown to contain a novel double-butterfly conformer of similar stability. The upper limit interconversion barrier between these conformers and their enantiomers was found to be in the order of 115 kJ/mol.1H-NMR experiments suggested a lower limit interconversion barrier of at least 80 kJ/mol. From the ten tautomers possible in principle, the 7,14-species was derived to be the most stable one by at least 48 kJ/mol.
Tautomerie und Stereochemie von Hypericin: Untersuchungen mit Hilfe der Kraftfeld-Methodik, NMR-Spektroskopie und Röntgenstrukturanalyse
Zusammenfassung Die Stereochemie von Hypericin, Pseudohypericin und einigen seiner Partialstrukturmodelle wurde mit Hilfe einer von MM2 abgeleiteten Kraftfeldmethodik untersucht. In der komplizierten Energiehyperfläche wurde neben dem auch durch Röntgenstrukturanalyse gefundenen Propeller-Konformeren ein neues Doppelschmetterling-Konformer ähnlicher Stabilität aufgefunden. Die obere Grenze für die Interkonversionsbarrieren zwischen diesen Konformeren und ihren Enantiomeren sind in der Größenordnung von 115 kJ/mol. Aus1H-NMR-Experimenten konnte eine untere Grenze von wenigstens 80 kJ/mol abgeleitet werden. Es wurde gefunden, daß von den zehn prinzipiell möglichen Tautomeren die 7,14-Spezies die um wenigstens 48 kJ/mol stabilste ist.相似文献
10.
S. Jakobs Ulrike Schulz Angela Duparré Norbert Kaiser 《Analytical and bioanalytical chemistry》1997,358(1-2):242-244
SiO2 protective coatings have been deposited on polycarbonate substrates by plasma ion assisted deposition. The influence of ion energy on the water permeability and the surface topography of the coatings was studied by infrared spectroscopy and atomic force microscopy. Coatings deposited at sufficiently high ion energies show a barrier effect against moisture uptake and considerably reduced film roughness. Both effects are attributed to an increase of the packing densities of the coatings. 相似文献