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  • 11
    Digitale Medien
    Digitale Medien
    Absolute photoabsorption cross-section measurements of simple molecules in the core-level region : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1531-1533 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Absolute inner-shell photoabsorption cross-section measurements were obtained from a variety of simple gas-phase molecules containing low Z elements (C, N, O, F), independent of the effects of stray light, high-order light, and photoabsorption from the various optical elements. The experimental apparatus consists of (1) a compact high-order light suppressor based on the photon energy dependence of the grazing angle reflectivity of various materials which provides an adjustable cut-off energy, and (2) a gas-phase absorption cell which monitors the photon flux before and after the gas cell to yield measurements independent of the absorptions of various optical elements, response functions of the photon detectors used, and variations of the photon flux during the scans. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1145900
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  • 12
    Digitale Medien
    Digitale Medien
    Photoluminescence of Cd1−xMnxTe films grown by metalorganic chemical vapor deposition (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1711-1716 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cd1−x Mnx Te (CMT) films grown by metalorganic chemical vapor deposition on GaAs, CdTe/GaAs, and CdS/SnO2 /glass (CSG) have been studied at 2 and 80 K by photoluminescence (PL). Analysis of the CMT bandedge peak yields Mn concentration x and indicates the degree of stress in the films due to lattice mismatch with the substrates, which also causes a blue shift of the PL band with temperature. A CdTe buffer layer greatly reduces stress and resulting defects. PL spectra from polycrystalline CMT films on commercial CSG wafers, reported for the first time, show a strong band near 1.62 eV which may represent states at the CMT-CdS interface. In CMT/CdTe/GaAs, we see evidence of front-to-back inhomogeneity in the CMT film which may appear in layered form.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.344391
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  • 13
    Digitale Medien
    Digitale Medien
    Magnetic tape recovery and rerecording of data (invited) (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4004-4006 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Degraded magnetic tapes and data were recovered from damaged reels through a series of chemical, mechanical, and rerecording processes. This paper describes the procedures used on three reels recovered from the space shuttle Challenger after being immersed in the ocean for six weeks.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.338560
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  • 14
    Digitale Medien
    Digitale Medien
    Characterization of GaAs/AlGaAs graded index-separate confinement heterostructure lasers by Raman scattering (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 358-361 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the first use of Raman scattering to study GaAs/AlGaAs graded index-separate confinement heterostructure quantum-well lasers. We have used a forward scattering geometry in which the waveguide is endfired, and the light emerging from the opposite end facet is collected and spectrally analyzed. The probe is confined by the waveguide and thus interacts with the entire laser cavity. Because Raman scattering occurs in all regions of the heterostructure to which the optical mode is confined, this technique is a useful indication of the mode profile in waveguide heterostructures. We observe inhomogeneously broadened longitudinal and transverse optical phonons in the graded region.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347143
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  • 15
    Digitale Medien
    Digitale Medien
    Characterization by Raman scattering, x-ray diffraction, and transmission electron microscopy of (AlAs)m(InAs)m short period superlattices grown by migration enhanced epitaxy (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 308-310 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report growth of (InAs)1(AlAs)1 and (InAs)2(AlAs)2 strained layer superlattices by migration enhanced epitaxy. The samples were grown on InP (001) substrates and characterized by Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Satellite peaks in the x-ray data confirm the intended periodicity and indicate the presence of some disorder in the monolayer sample. The energies of the zone folded and quantum confined optic phonons are in reasonable agreement with calculations based on one-dimensional elastic continuum and linear chain models.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352139
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  • 16
    Digitale Medien
    Digitale Medien
    A laboratory-scale arc furnace for melting volatile metals under elevated inert gas pressures (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5459-5463 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A laboratory-scale arc furnace encompassing a nonconsumable electrode and a cold hearth and operating at inert gas pressures of up to 20 bar is described. Using this equipment, weight losses due to volatilization when melting high vapor pressure metallic materials have been reduced to about 20% of those encountered with a conventional arc furnace operating at 1 bar. The arc furnace has been designed to be evacuable to high vacuum levels, as well as attaining high pressures, so that specimen purity can be retained by thoroughly evacuating and degassing the system prior to admitting inert gas and melting. Increases in gas pressure have been found to have a pronounced effect on the stability of the arc, especially at low arc currents, and to achieve minimum volatilization losses a balance is required between pressure and arc current for a particular sample.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1143418
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  • 17
    Digitale Medien
    Digitale Medien
    Term-by-term tests of stress-transport turbulence models in a three-dimensional boundary layer (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 986-998 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Current Reynolds-averaged turbulence models for use in three-dimensional flows have mostly been derived by straightforward generalization of two-dimensional models; the results are rather unsatisfactory. Reynolds-stress transport methods perform better than methods based on an (isotropic) eddy viscosity. One approach to the problem is a term-by-term check of Reynolds-stress transport models against experiments or simulation data in representative three-dimensional flows. In this paper a comparison of four models for the turbulent-transport "diffusion'' terms, and four models for the pressure–strain "redistribution'' terms, with measurements (including all six Reynolds stresses and all ten triple products) in the thin boundary layer on the flat floor of a duct with a 30° bend in the horizontal plane is presented. The conclusion is that the pressure–strain models perform remarkably well, and that although the triple-product models often perform badly, they represent rather small terms and therefore do not cause large errors in Reynolds-stress predictions. The implication is that inadequate modeling of the dissipation must be the main cause of errors in predictions of three-dimensional boundary layers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.868330
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  • 18
    Digitale Medien
    Digitale Medien
    A note on "critical roughness height" and "transitional roughness" (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 1611-1614 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An unrigorous but plausible analysis suggests that the concept of a critical roughness height, below which roughness does not affect a turbulent wall flow, is erroneous. The Oseen approximation implies that the effect of roughness on the additive constant in the logarithmic law of the wall should vary as the square of the roughness Reynolds number (specifically the roughness height in "wall units"). This is an important point in determining whether surfaces used in experiments at high unit Reynolds number can be regarded as hydraulically smooth. Attention is also called to the qualitative difference between Nikuradse's measurements of friction factor in pipe flow with uniform-size sand-grain roughness in the "transitional" range of Reynolds number and the data correlation in the Moody chart of 1944; the latter was derived from tests on miscellaneous real-life rough surfaces in the 1930s. Nearly all textbooks on elementary fluid dynamics present, but practically none discuss, this difference. Nikuradse's monodisperse roughness is a very rare case with untypical behavior in the transitional range. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.870410
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  • 19
    Digitale Medien
    Digitale Medien
    Scaling the near-wall axial turbulent stress in the zero pressure gradient boundary layer (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 1819-1821 
    Details
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Based upon high resolution LDA measurements over a range of momentum deficit thickness Reynolds numbers (Rθ=U∞θ/ν) from 1430 to 31 000, DeGraaff and Eaton [J. Fluid Mech. 422, 319 (2000)] propose a new mixed scaling for the near-wall region profile of the axial turbulent stress, u2. The present results support the validity of this scaling over an extended Reynolds number range 1000≤Rθ≤5×106. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1368852
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  • 20
    Digitale Medien
    Digitale Medien
    The photon-induced reactions of chemisorbed CH3Br on Pt{111} (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3930-3938 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The photochemistry of chemisorbed CH3Br on Pt{111} has been investigated using high resolution electron energy loss spectroscopy (HREELS) and thermal desorption. The primary photon-induced reaction involves the cleavage of the C–Br bond, giving rise to chemisorbed CH3 and Br, both of which can be identified in HREELS. From the angular dependence of the loss peaks, the symmetry of the CH3 surface complex is shown to be C3v. HBr can also be identified in subsequent thermal desorption. Experiments performed directly with HBr on Pt{111} indicate that molecular HBr adsorbs dissociatively on this surface. This result, in combination with observations of the C–H vibrational mode as a function of temperature, shows that the production of HBr arises from a secondary surface reaction between Br and CHx fragments. Based on the wavelength dependence of the fragmentation cross section and the photoemission spectrum of adsorbed CH3Br the primary photon-induced reaction to a charge transfer excitation is ascribed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460799
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