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  • 1
    Electronic Resource
    Electronic Resource
    Porous silicon photoluminescence: Implications from in situ studies (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 7009-7017 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence and Raman measurements have been performed on an anodized silicon surface in an HF/ethanol anodization solution and after replacement of this solution with water. Immediately after anodization and while resident in HF/ethanol, the porous silicon produced does not exhibit intense photoluminescence. Intense photoluminescence develops spontaneously in HF/ethanol after 18–24 h or with replacement of the HF/ethanol with water. The results are consistent with a quantum confinement mechanism in which electron-hole pair migration to traps and nonradiative recombination dominates the de-excitation pathways until silicon nanocrystals are physically separated and energetically decoupled by hydrofluoric acid etching or surface oxidation. Raman spectra show the development of nanometer-size silicon crystals concurrent with intense photoluminescence. Illumination of the silicon surface during anodization tends to inhibit the formation of nanocrystalline silicon, but even very thin layers (tens of nanometers or less) exhibit photoluminescence. As produced by anodization, the porous silicon surface is apparently inhomogeneous on the millimeter scale, showing large variations in photoluminescence intensity and peak wavelength. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363813
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  • 2
    Electronic Resource
    Electronic Resource
    Energy transfer and relaxation in europium-activated Y2O3 after excitation by ultraviolet photons (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4053-4064 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present persistence data from the 5D manifolds of europium (3+)-activated Y2O3, after excitation by ultraviolet photons. For europium concentrations below 1 at. %, the persistence is largely consistent with multiphonon relaxation. For europium concentrations at and above 1 at. %, the persistence shows evidence for energy transfer interactions between europium activators. Interactions involving one activator in an upper (5D3, 5D2 or 5D1) manifold and another in a ground state (7F) manifold affect the kinetics of the relaxation of the upper 5D manifolds but do not degrade phosphor efficiency. Interactions involving two activators in excited manifolds ultimately dissipate, by phonon emission, excitation that might be emitted as photons. The interactions involving two activators in excited manifolds appear to be related to both concentration quenching and the reduction of phosphor efficiency at high excitation density. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1452770
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  • 3
    Electronic Resource
    Electronic Resource
    Bonding topologies in diamondlike amorphous-carbon films (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2047-2049 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces; their thicknesses increase with deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies 〈60 eV and increases for films grown using ion energies 〉160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of σ- to π-bonded carbon atoms. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126250
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrahard carbon nanocomposite films (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3052-3054 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modest thermal annealing to 600 °C of diamondlike amorphous-carbon (a-C) films grown at room temperature results in the formation of carbon nanocomposites with hardness similar to diamond. These nanocomposite films consist of nanometer-sized regions of high density a-C embedded in an a-C matrix with a reduced density of 5%–10%. We report on the evolution of density and bonding topologies as a function of annealing temperature. Despite a decrease in density, film hardness actually increases ∼15% due to the development of the nanocomposite structure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126576
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  • 5
    Electronic Resource
    Electronic Resource
    Turbulent Boundary-Layer Separation (1989)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 21 (1989), S. 205-232 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.21.010189.001225
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  • 6
    Electronic Resource
    Electronic Resource
    Signal-processing techniques for low signal-to-noise ratio laser Doppler velocimetry signals (1992)
    Springer
    Experiments in fluids 12 (1992), S. 319-328 
    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 A variety of methods have been developed to obtain acurate frequency estimates from laser Doppler velocimetry (LDV) signals. Rapid scanning and fiber optic LDV systems require robust methods for extracting accurate frequency estimates with computational efficiency from data with poor signal-to-noise ratios. These methods typically fall into two general categories, time domain parametric techniques and frequency domain techniques. The frequency domain approach is initiated by transforming the Doppler bursts into the frequency domain using the fast Fourier transform (FFT). From this basic transformation a variety of interpolation procedures (parabolic, Gaussian, and centroid fits) have been developed to optimize the frequency estimation accuracy. The time domain approaches are derived from the parametric form of a sinusoid. The estimation of constants in this relationship is performed to satisfy specific constraints, typically a minimization of a variance expression. A comparison of these techniques is presented using simulated signals and additive Gaussian and Poisson white noise. The statistical bias and random errors for each method are presented from 200 signal simulations at each condition. Frequency estimation via the FFT with zero-padding and a Gaussian interpolation scheme was found to produce the lowest bias and random errors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00187310
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  • 7
    Electronic Resource
    Electronic Resource
    An experimental study of a turbulent wing-body junction and wake flow (1993)
    Springer
    Experiments in fluids 14 (1993), S. 366-378 
    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 Extensive measurements were conducted in an incompressible turbulent flow around the wing-body junction formed by a 3∶2 semi-elliptic nose/NACA 0020 tail section and a flat plate. Mean and fluctuating velocity measurements were performed adjacent to the wing and up to 11.56 chord lengths downstream. The appendage far wake region was subjected to an adverse pressure gradient. The authors' results show that the characteristic horseshoe vortex flow structure is elliptically shaped, with ∂ (W)/∂Y forming the primary component of the streamwise vorticity. The streamwise development of the flow distortions and vorticity distributions is highly dependent on the geometry-induced pressure gradients and resulting flow skewing directions. The primary goal of this research was to determine the effects of the approach boundary layer characteristics on the junction flow. To accomplish this goal, the authors' results were compared to several other junction flow data sets obtained using the same body shape. The trailing vortex leg flow structure was found to scale on T. A parameter known as the momentum deficit factor (MDF = (Re T)2 (θ/T)) was found to correlate the observed trends in mean flow distortion magnitudes and vorticity distribution. Changes in δ/T were seen to affect the distribution of u′, with lower ratios producing well defined local turbulence maxima. Increased thinning of the boundary layer near the appendage was also observed for small values of δ/T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189496
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  • 8
    Electronic Resource
    Electronic Resource
    Full three-dimensional measurements of the cross-flow separation region of a 6:1 prolate spheroid (1994)
    Springer
    Experiments in fluids 17 (1994), S. 68-74 
    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 The flow in the cross-flow separation region of a 1.37 m long, 6:1 prolate spheroid at 10° angle of attack was investigated with a novel 3-D fiber-optic Laser Doppler Velocimeter (LDV). The probe was used to measure three simultaneous, orthogonal velocity components from within the model. The design and operation of this LDV probe is described and velocity, Reynolds stress, and velocity triple-product measurements are presented from the inner boundary layer through the boundary-layer edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02412805
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis, Properties and Performance of the High Explosive ANTA (1994)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 19 (1994), S. 174-179 
    Details
    ISSN: 0721-3115
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 3-Amino-5nitro-1,2,4-triazole(ANTA) was prepared and evaluated in terms of insensitivity and performance. The material is very insensitive to impact and moderately so to thermal stimuli. Performance was found to be inferior to 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The best synthesis of ANTA is a three-step route using commercially available 3,5-diamino-1,2,4-triazole.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prep.19940190405
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  • 10
    Electronic Resource
    Electronic Resource
    CL-20 performance exceeds that of HMX and its sensitivity is moderate (1997)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 22 (1997), S. 249-255 
    Details
    ISSN: 0721-3115
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The explosive performance of ∊-CL-20 was found to be approximately 14% greater than HMX as determined by cylinder expansion and tantalum plate acceleration experiments. This makes it the most powerful explosive ever tested at small volume expansions of the detonation products. In general CL-20 is more sensitive than HMX. However, the sensitivity of CL-20 to one-dimensional shock loading was found to be similar to HMX.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prep.19970220502
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