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  • 1
    Electronic Resource
    Electronic Resource
    The evolution of initially uniform shear flow through a nearly two-dimensional 90° curved duct (1995)
    Springer
    Experiments in fluids 19 (1995), S. 173-187 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental study has been made in a nearly two-dimensional 90° curved duct to investigate the effects of interaction between streamline curvature and mean strain on the evolution of turbulence. The initial uniform shear at the entrance to the curved duct was varied by an upstream shear generator to produce five different shear conditions; a uniform flow (UF), a positive weak shear (PW), a positive strong shear (PS), a negative weak shear (NW) and a negative strong shear (NS). The variations of surface pressure and the mean velocity profiles along the downstream direction under different initial shears are carefully measured. The responses of turbulent Reynolds stresses and triple velocity products to the curvature and the mean strain are also investigated. The evolution of turbulence under the curvature with the different shear conditions is described in terms of the turbulent kinetic energy and the various length scales vs the angular distance θ or a curvature parameters S c which is defined by S c = (U/R)/(dU/dy- U/R). The results show that the turbulent kinetic energy and the integral length scale are augmented when S c 〈 0.054 whereas they are suppressed when S c 〉 0.054. It is also observed that the micro-length scales of Taylor and Kolmogoroff are relatively insensitive to the curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189706
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Study of defects in GaAs by differential thermal analysis (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2738-2741 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differential thermal analysis is applied to the measurement of defect total energies in GaAs. First, the technique is used to determine the energy liberated in the recombination of an As vacancy-interstitial pair; the result, in agreement with the theoretical estimate of the energy stored in such defect, allows the demonstration of the validity of the technique as well as its limitations. Then, the technique is used to evaluate the introduction rate of such defects by electron irradiation in a semi-insulating material in which electrical techniques cannot be applied. Finally, a characterization of native defects is attempted; it shows that recombination of native vacancies, with interstitials liberated when the movement of α dislocations takes place, occurs around 450 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339847
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  • 3
    Electronic Resource
    Electronic Resource
    Optical absorption of Co^2^+ ions in HgGa"2"-"xIn"xSe"4 (0.0 =〈 X =〈 2.0) solid solution
    Amsterdam : Elsevier
    Solid State Communications 85 (1993), S. 883-886 
    Details
    ISSN: 0038-1098
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0038-1098(93)90197-U
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  • 4
    Electronic Resource
    Electronic Resource
    Oxidation Behavior of Nanocrystalline Al Alloys Containing 5 and 10 at.% Ti (1999)
    Springer
    Oxidation of metals 51 (1999), S. 79-95 
    Details
    ISSN: 1573-4889
    Keywords: HIGH-TEMPERATURE OXIDATION ; PROTECTIVE OXIDE LAYER ; Al-Ti ALLOYS ; NANOCRYSTALLINE ; MECHANICAL ALLOYING
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of mechanically alloyed(MA) Al-Ti alloys containing 5 and 10 at.% Ti wereinvestigated at 500-600°C under 1 atm of oxygen. Ateach temperature, alloys oxidized linearly during the initial stage and later followed the parabolicrate law. During the initial stage, the oxidation ratesof nanocrystalline (≤50 nm) Al-Ti alloys were fasterthan those of conventional (≤200 nm) alloys. It is suggested that more grain boundaries innanocrystalline alloys provide more nucleation sites foroxides, so that the oxide scales grew faster as denseprotective layers. During the parabolic stage, the nanocrystalline alloys had greater oxidationresistance than conventional alloys because of the denseprotective layer. Oxide scales on both alloys consistedof a mixture of γ-Al2O3 andTiO2 in the outer layer andγ-Al2O3 near the alloy as aprotective layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018802218912
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of particle size of alumina dispersions on the oxidation resistance of Ni-Cr alloys (1997)
    Springer
    Oxidation of metals 48 (1997), S. 391-415 
    Details
    ISSN: 1573-4889
    Keywords: high-temperature oxidation ; Ni-Cr alloy ; oxidation rate ; protective Cr2O3 layer ; Al2O3 dispersion ; selective oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of Ni-Cr alloys with various chromium concentrations and particle sizes of a dispersion of 10 vol.% Al2O3 was observed in 1 atm of oxygen at 1000°C. This study was intended to determine the critical chromium concentration to form a protective Cr2O3 oxide layer for different Al2O3 particle sizes. The oxidation rate of Ni-Cr alloys containing 10 vol.% Al2O3 followed a parabolic rate law and a Cr2O3 protective layer continuously formed when the oxidation rate decreased rapidly. Times to form a continuous and protective Cr2O3 layer during the initial oxidation shortened as the size of the dispersion decreased. The critical chromium concentration to form a protective Cr2O3 layer in the oxide scale was 6∼9 wt.% and was related strongly to the particle size of the Al2O3 dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153458
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  • 6
    Electronic Resource
    Electronic Resource
    Separation of positional isomers on polymeric calix[4]arene-siloxane stationary phases in capillary GC (1998)
    Springer
    Chromatographia 48 (1998), S. 422-426 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Calix[4]arene-tetramethyldisiloxane stationary phases ; Geometric and positional isomer separations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Poly(p-tert-butyldimethoxydipropyloxycalix[4]arene-tetramethyldisiloxane) (TBCX-TMDS) and poly(dimethoxydipropyloxycalix[4]arene-tetramethyl-disiloxane) (CX-TMDS), have been prepared and used as stationary phases for isothermal capillary gas chromatographic separations of positional isomers. Retention factors and separation factors for the isomers were measured. The isomers investigated were well-resolved on the two phases. Retention of all the solutes investigated is greater on TBCX-TMDS than on CX-TMDS, probably because of extra dispersive interactions of the solutes with thetert-butyl groups of the phase. Separation factors for closely-eluting isomer pairs are similar on the two phases. This seems to indicate either that the solutes are retained by non-inclusion processes or that if the isomer molecules do enter the cavity of the calixarene, i.e. the solute is retained by inclusion, thetert-butyl groups do not play a role in discriminating between the isomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467714
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of triethylamine in the mobile phase on the retention properties of conventional polymeric and horizontally polymerized octadecylsilica in RPLC (1999)
    Springer
    Chromatographia 49 (1999), S. 635-642 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Interaction of mobile and stationary phases ; Linear solvation energy relationships ; Triethylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of triethylamine (TEA) in the mobile phase on the RPLC retention behavior of small organic solutes has been studied on a conventional polymeric octadecylsilica (ODS) and on a horizontally polymerized ODS. Retention factors for a set of solutes were measured on the two phases with methanol-water mobile phases containing triethylamine at different concentrations and analyzed by use of linear solvation energy relationships (LSER). Variation of the resulting LSER coefficients—v (hydrophobicity),r (polarizability),s (dipolarity),b (hydrogen-bond (HB) donating acidity), anda (HB accepting strength)—were examined to see how TEA affects the intermolecular interaction properties of the mobile and stationary phases and hence the retention of the solutes. Addition of TEA to the mobile phase changes the interaction properties of both conventionally polymerized and horizontally polymerized ODS; the effect is greater for the conventional phase. The HB donating acidity (b) of conventional polymeric ODS is significantly reduced by addition of TEA. For the mobile phases studied the magnitudes of theb andv coefficients for the horizontally polymerized ODS phase are greater than for the conventional phase. The different interaction properties of the two polymeric phases arise mainly as a result of differential adsorption of TEA, because of the very different amounts of surface silanol groups present on the two phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02466905
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