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  • 1
    Digitale Medien
    Digitale Medien
    Two-photon absorption and resonant non-phase-matched second-harmonic generation in CdSe (1990)
    Springer
    Optical and quantum electronics 22 (1990), S. 351-367 
    Details
    ISSN: 1572-817X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Exciting a hexagonal CdSe crystal with picosecond Nd: glass laser pulses, two-photon absorption and resonant non-phase-matched second-harmonic generation occur simultaneously. Using different crystal orientations, all components of the secondharmonic susceptibility tensor (non-vanishing components ared 31,d 33 andd 15) and some components of the two-photon absorption susceptibility tensor χ ijkl (3)′′ (−ωL; ωL, ωL, −ωL) are determined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02189218
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  • 2
    Digitale Medien
    Digitale Medien
    On the nature of the active state of silver during catalytic oxidation of methanol (1993)
    Springer
    Catalysis letters 22 (1993), S. 215-225 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Ion-scattering spectroscopy (ISS) ; methanol oxidation ; oxygen ; Raman spectroscopy ; reflection electron microscopy (REM) ; silver ; X-ray photoelectron spectroscopy (XPS)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Under the applied high reaction temperatures (∼900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (Oγ) apart from O atoms dissolved in the bulk (Oβ). Methanol oxidation to formaldehyde proceeds through this Oγ species as demonstrated by application of a variety of spectroscopic techniques.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00810368
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  • 3
    Digitale Medien
    Digitale Medien
    Oxidative coupling of methane on silver catalysts (1995)
    Springer
    Catalysis letters 32 (1995), S. 185-194 
    Details
    ISSN: 1572-879X
    Schlagwort(e): methane ; silver ; oxidative coupling ; C2 selectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Bulk silver catalysts were found to be active for the oxidative coupling of methane to ethane and ethylene if operated under oxygen-limited conditions at atmospheric pressure and at temperatures above 1020 K. The addition of small amounts of sodium phosphate as promoter increases markedly the C2 selectivity (to values above 90%) and yield (〉10%) by efficient suppression of reaction steps leading to total oxidation. Further improvement of the yields might be achieved by more appropriate reactor design.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00806113
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  • 4
    Digitale Medien
    Digitale Medien
    The effect of water on the formation of strongly bound oxygen on silver surfaces (1995)
    Springer
    Catalysis letters 32 (1995), S. 171-183 
    Details
    ISSN: 1572-879X
    Schlagwort(e): oxygen ; partial oxidation ; reconstruction ; reflection electron microscopy ; Raman spectroscopy ; silver ; water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Interaction of water with an oxygenated Ag(111) surface leads to an enhancement of the surface restructuring and an activated formation of hydroxyl groups (OH) located stably on the surface and incorporated in the subsurface region, as evidenced by means of reflection electron microscopy (REM) and in situ Raman spectroscopy. Dehydroxylation of OHads at elevated temperatures releases the strongly bound oxygen species labelled Oγ at the surface, and offers an alternative to the energetically less favorable pathway for the direct formation of the Oγ species from molecular oxygen.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00806112
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  • 5
    Digitale Medien
    Digitale Medien
    On the relation between catalytic performance and microstructure of polycrystalline silver in the partial oxidation of methanol (1995)
    Springer
    Catalysis letters 33 (1995), S. 305-319 
    Details
    ISSN: 1572-879X
    Schlagwort(e): methanol oxidation ; conversion to formaldehyde ; silver ; surface oxygen ; STM ; IMR-MS ; adsorption-induced restructuring ; atomic structure ; texture ; X-ray diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Electrolytic silver was investigated as partial oxidation catalyst for the conversion of methanol to formaldehyde. Using the mass spectrometric technique as on-line detector the relation between feed composition and temperature was determined allowing us to conclude that two simultaneous reaction pathways operate under steady state conditions. The microstructure was analysed by XRD and STM. A pronounced restructuring of the surface on the mesoscopic scale was detected. The atomic structure of the γ oxygen phase was determined on the (111) face of facets grown during reaction. The two reaction pathways find their counterparts in two distinctly different surface microstructures providing different geometries for the respective active sites. After prolonged time on stream the high surface mobility of the silver atoms removes all mesoscopic restructuring without changing the conversion characteristics. The observed restructuring is thus considered as a frozen large scale image of the continuously changing surface under reaction conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00814233
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  • 6
    Digitale Medien
    Digitale Medien
    Stability constant of Fe2+ chelates with soluble ligands from incubated soils (1987)
    Springer
    Biology and fertility of soils 5 (1987), S. 88-92 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Ferrous iron ; Fe2+ chelates ; Stability constants ; Anearobic decomposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Summary The stability constants (log K) of Fe2+ chelates were determined on the basis of the shift in peak potential during the reduction of Fe2+ by a consortium of soluble ligands from incubated soils. Log K values ranged from 2.6 to 4.5. On average a change in pH of 1 unit induced a change in log K of 0.92 units. Aeration of the anaerobic decomposition products increased log K. The log K for Fe2+ chelates was about 0.8 units larger than that for Mn2+ chelates. It is considered that the chelation of ferrous iron plays an important role in the mobility and availability of iron to plants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00264352
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  • 7
    Digitale Medien
    Digitale Medien
    Voltage-controlled electroluminescence from SiO2 films containing Ge nanocrystals and its mechanism (2000)
    Springer
    Applied physics 71 (2000), S. 299-303 
    Details
    ISSN: 1432-0630
    Schlagwort(e): PACS: 78.60.Fi; 78.66Jg; 78.66Db
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract. Luminescent SiO2 films containing Ge nanocrystals are fabricated by using Ge ion implantation, and metal–oxide–semiconductor structures employing these films as the active layers show yellow electroluminescence (EL) under both forward and reverse biases. The EL spectra are strongly dependent on the applied voltage, but slightly on the mean size of Ge nanocrystals. When the forward bias increases towards 30 V, the EL spectral peak shifts from 590 nm to 485 nm. It is assumed that the EL originates from the recombination of injected electrons and holes in Ge nanocrystals near the Si/SiO2 interface, or through luminescent centers in the SiO2 matrix near the SiO2/metal interface. The mismatch of the injection amounts between holes and electrons results in the low EL efficiency.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003390000518
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  • 8
    Digitale Medien
    Digitale Medien
    Expression of different levels of enzymes from the Pichia stipitis XYL1 and XYL2 genes in Saccharomyces cerevisiae and its effects on product formation during xylose utilisation (1997)
    Springer
    Applied microbiology and biotechnology 48 (1997), S. 218-224 
    Details
    ISSN: 1432-0614
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Saccharomyces cerevisiae was transformed with the Pichia stipitis CBS 6054 XYL1 and XYL2 genes encoding xylose reductase (XR) and xylitol dehydrogenase (XDH) respectively. The XYL1 and XYL2 genes were placed under the control of the alcohol dehydrogenase 1 (ADH1) and phosphoglycerate kinase (PGK1) promoters in the yeast vector YEp24. Different vector constructions were made resulting in different specific activities of XR and XDH. The XR:XDH ratio (ratio of specific enzyme activities) of the transformed S. cerevisiae strains varied from 17.5 to 0.06. In order to enhance xylose utilisation in the XYL1-, XYL2-containing S. cerevisiae strains, the native genes encoding transketolase and transaldolase were also overexpressed. A strain with an XR:XDH ratio of 17.5 formed 0.82 g xylitol/g consumed xylose, whereas a strain with an XR:XDH ratio of 5.0 formed 0.58 g xylitol/g xylose. The strain with an XR:XDH ratio of 0.06, on the other hand, formed no xylitol and less glycerol and acetic acid compared with strains with the higher XR:XDH ratios. In addition, the strain with an XR:XDH ratio of 0.06 produced more ethanol than the other strains.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002530051041
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  • 9
    Digitale Medien
    Digitale Medien
    Synthesis of silicon carbide foams from polymeric precursors and their blends (1999)
    Springer
    Journal of materials science 34 (1999), S. 2495-2505 
    Details
    ISSN: 1573-4803
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Several polysilanes with different overall functionalities have been synthesized and pyrolyzed to produce porous silicon carbide. The polysilanes and their ceramic products have been characterized using gel permeation chromatography, Fourier transform-infrared spectroscopy, thermogravimetry, X-ray diffractometry and microscopy. Some products were foams while others were micro-porous ceramics. The effect of the final pyrolytic yield on the Type of ceramic produced, its pore structure and shape retention are discussed. Two polysilanes were blended in various ratios to control the pyrolysis process more precisely. This allowed the Type, shape and pore-structure of the silicon carbide produced to be controlled more efficiently. There exists a relationship between the composition and structure of the precursors and their final pyrolytic yield and this determines the Type, shape retainability and pore structure of the ceramics produced. In this work, precursors or their blends which gave a final pyrolytic yield of 50–60 wt % produced the best silicon carbide foams.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004666326039
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  • 10
    Digitale Medien
    Digitale Medien
    Stability of the low-temperature tetragonal phase in La2−x Ba x CuO4 and related compounds (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 33-35 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Low-temperature tetragonal (TLT) phase ; La2−x Ba x−y M y CuO4 (M=Sr or Ca) ; La2−x−y Nd y Ba x CuO4 ; ionic size
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract In La2−x Ba x CuO4 (LBCO), the structural transition to a low-temperature tetragonal phase below 60 K and suppression of superconductivity are observed when the carrier density isp ∼ 1 /8 per copper. The replacement by divalent ions smaller than Ba2+ suppresses the static deformation of the lattice. We have found that the variationsT d2 and superconducting transition temperatureT c are quantitatively characterized by the averaged ionic radius at the La site or lattice parameters. This aspect of substitution could be regarded as the effect of chemical pressure, since similar variations have been reported on applying hydrostatic pressure. In La2−x−y Nd y (Ba, Sr) x CuO4,T d2 increases with increasingy in a wide range ofp whileT c is suppressed only at p∼ l /8. The structural transition atT d2 here should be ascribed mainly to the crystallochemical origin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00730363
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