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  • 1
    ISSN: 1432-0630
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The adsorption of oxygen and hydrogen on a Pt(111) surface has been studied with phase-sensitive Second-Harmonic Generation (SHG) signal detection. The SHG-signal change measured with p-in, p-out polarization during the adsorption of oxygen and hydrogen was found to be different in amplitude and phase for the two adsorbates. At the wavelength used (1064 nm), only a localized interaction between adsorbate and substrate is seen, leading to a linear dependence of the susceptibility on the coverage. Sticking coefficients, $s_\theta$ , and their coverage dependence were determined. For hydrogen, a linear decrease in $s _\theta$ with coverage was found; the initial sticking coefficient being $s_0= 0.06$ at a temperature of $T = 130$ K. For oxygen, $s_\theta$ shows a quadratic decrease with coverage, strongly dependent on temperature, with $s_0=0.05$ at $T = 350$ K. A method based on these results is proposed, which would allow the determination of adsorbate coverages of coadsorption systems with SHG using phase-sensitive signal detection. PACS68.35; 82.20; 42.65
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  • 2
    ISSN: 1432-0630
    Keywords: 68.35 ; 82.20 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The adsorption of oxygen and hydrogen on a Pt(111) surface has been studied with phase-sensitive Second-Harmonic Generation (SHG) signal detection. The SHG-signal change measured with p-in, p-out polarization during the adsorption of oxygen and hydrogen was found to be different in amplitude and phase for the two adsorbates. At the wavelength used (1064 nm), only a localized interaction between adsorbate and substrate is seen, leading to a linear dependence of the susceptibility on the coverage. Sticking coefficients,sθ, and their coverage dependence were determined. For hydrogen, a linear decrease insθ with coverage was found; the initial sticking coefficient beings 0=0.06 at a temperature ofT=130 K. For oxygen,sθ whows a quadratic decrease with coverage, strongly dependent on temperature, withs 0=0.05 atT=350 K. A method based on these results is proposed, which would allow the determination of adsorbate coverages of coadsorption systems with SHG using phase-sensitive signal detection.
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  • 3
    ISSN: 1432-0630
    Keywords: 42.85Fe ; 61.80Ba ; 42.20Ji
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The energy of the acoustic pulse generated by laser-surface interactions and measured by probe beam deflection was used to investigate laser surface damage thresholds of fluoride crystals with optical quality. It was found that damage thresholds decrease with increasing density of surface states. The defect density also controls the energy absorption mechanism: for surfaces with few defects, like polished MgF2 and CaF2, avalanche breakdown occurs at above 1 GW/cm2, whereas for materials with lower damage thresholds, such as LiF, BaF2, and roughened or incubated surfaces of CaF2, multiphoton absorption across the band gap is observed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 64 (1997), S. 573-578 
    ISSN: 1432-0649
    Keywords: PACS: 33.80K, 07.75, 82.65J
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 2 +½ O2→H2O on polycrystalline Pt foils has been studied by detection of desorbing OH radicals using the Resonance Enhanced Multiphoton Ionization, REMPI, technique. The measurements were performed at catalyst temperatures of 1000–1400 K and a total pressure below 10-4 mbar. The studies of OH desorption by REMPI were achieved using a two-photon excitation D2Σ-–X2Π (1–0), followed by one-photon ionization. The ions were detected in a time-of-flight mass spectrometer, TOF-MS, in order to avoid interference from non-resonantly ionized molecules. By applying TOF-MS, a simultaneous non-resonant ionization and detection of H2, O2 and H2O was achieved. Recorded REMPI spectra were compared with spectra simulated using known molecular constants. The kinetics of the reaction derived from the measurements were compared with what was obtained in earlier LIF detection of OH, performed at higher total reactant pressure using the A–X transition. REMPI TOF-MS is shown to be a complement to LIF for reaction studies below 5×10-4 mbar total pressure, where LIF is too insensitive for quantification. The reaction kinetics was found to be in agreement with a theoretic model and previous LIF studies.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 101 (1936), S. 113-116 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Die Gitterkonstante von Topas parallel der Spaltfläche ist in den drei ersten Ordnungen mit Cu K α1 gemessen. Aus diesen gefundenen Werten sind die Gitterkonstantenwerte höherer Ordnung berechnet. Der Brechungsindex von Topas für die betreffende Wellenlänge ist ebenfalls ausgewertet.
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  • 6
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Zusammenfassung Die Gitterkonstante von Quarz (Ebene 0001) ist in den drei ersten Ordnungen mit MoKα1 bestimmt worden. Weiter sind die Kα2 und Kα1-Linien der Elemente 45 Rh, 46 Pd und 47 Ag in den zwei ersten Ordnungen gemessen worden. Der Brechungsindex von Quarz für die betreffenden Wellenlängen wurde ebenfalls ausgewertet.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2005-2007 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The technique of intensity dependent photoacoustic probe beam deflection has been applied to the determination of surface damage thresholds. We take advantage of an unambiguous correlation between the degree of laser damage and the energy in the generated acoustic pulse. The high sensitivity of this method, cross checked by measuring scatter losses in reflection, is independent of any surface optical properties. As an example for optical materials, damage thresholds for MgF2 and CaF2 have been determined to be about 1.4 GW/cm2 , and for LiF to be about 0.2 GW/cm2 .
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The desorption of OH radicals from Pt(111) at high temperature, (approximately-greater-than)1000 K, during the water formation (H2+1/2 O2→H2O) and water decomposition reactions, respectively, was investigated using the laser-induced fluorescence technique. The results are compared with corresponding data from our laboratory for polycrystalline Pt. The OH desorption rate in H2+O2 at 1–100 mTorr total pressure has its maximum at 8%–9% relative H2 concentration for surface temperatures between 1100 and 1400 K. With H2 replaced by D2, the OD desorption rate maximizes at somewhat higher relative hydrogen content. The apparent activation energy for OH desorption increases from about 1.4 eV at low relative hydrogen concentration to about 2.0 eV at hydrogen contents of 25% or more. For the water decomposition reaction, the apparent activation energy for OH desorption was found to be 1.7±0.2 eV at 0.5 Torr and 1.9±0.2 eV at 1 Torr. These differences in apparent activation energies are primarily due to kinetic effects. The results are analyzed within a kinetic model previously developed by Hellsing et al. [J. Catal. 132, 210 (1991)], and are also compared with previous data for polycrystalline Pt. The kinetic model calculations give good overall agreement with the measured OH desorption rates as functions of temperature, H2/O2 mixture and H2O pressure, respectively. A nonuniqueness problem, with respect to the choice of kinetic parameters, is encountered in the simulation of the measured data; quite different sets of two of the kinetic constants, namely the activation energy for water formation (via OH+H→H2O) and the activation energy for OH desorption can reproduce the data as long as their difference is constant.This nonuniqueness problem, which is a consequence of the steady-state nature of the measurements, is analyzed and discussed in some detail, as are some apparent contradictions in the absolute values of reported kinetic constants in the literature. From this analysis two important conclusions are drawn. (i) The apparent contradictions in the literature about absolute values of activation energies for the water formation reaction and for OH-desorption may be less severe than believed or nonexistent. (ii) Coverage dependent activation energies must be considered and experimental exploration of such coverage dependencies are needed to create a firmer base for the kinetic modeling of the H2/O2 reaction on Pt. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    European journal of marketing 30 (1996), S. 61-74 
    ISSN: 0309-0566
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Economics
    Notes: Managing a set of relationships to other firms is a complex task, since each relationship is likely to have consequences on the other ones. Highlights the co-ordination of interorganizational ties during a process of internationalization, and the consequences that different types of relationships have on a firm's overall relational marketing opportunities. Systematizes the relational issues that face a firm when the boundaries surrounding its home market network dissolve. Presents a framework which stresses four types of relationships and the interplay between them. Based on the notion that a firm must co-ordinate the management of horizontal and vertical dependencies, and pursue new marketing opportunities while simultaneously safeguarding its original relations. Illustrates the significance of the framework and the interplay between the four relational issues, by the alliances presently developed by two Swedish food companies to organizations in other EU countries.
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  • 10
    Electronic Resource
    Electronic Resource
    Bingley : Emerald
    ISSN: 0959-0552
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Economics
    Notes: Existing market orientation frameworks are based mostly on studies of manufacturers. Therefore, there is a need of a modified approach that acknowledges the special conditions for retailers. A framework is presented that includes both internal and relational aspects. Inter-firm market orientation is presented as especially relevant for retailers. Antecedents to market orientation on a relationship level are also considered. Kohli and Jaworski's three basic components are used, but the paper then discusses indicators that are especially useful in order to capture market orientation in a retail context. The suggested framework is further developed using a case study of a major British food retailer.
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