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Backscattering from a cloaked submerged spherical shell is analyzed in the low, mid, and high frequency regimes. Complex poles of the scattered pressure amplitudes using Cauchy residue theory are evaluated in an effort to explain dominant features of the scattered pressure and how they are affected by the introduction of a cloak. The methodology used is similar to that performed by Sammelmann and Hackman [J. Acoust. Soc. Am. 85, 114-124 (1989); J. Acoust. Soc. Am. 89, 2096-2103 (1991); J. Acoust. Soc. Am. 90, 2705-2717 (1991)] in a series of papers written on scattering from an uncloaked spherical shell. In general, it is found that cloaking has the effect of diminishing the amplitude and shifting tonal backscatter responses. Extreme changes of normal and tangential fluid phase velocities at the fluid-solid interface when cloaking is employed leads to elimination of the 'mid-frequency enhancement' near the coincidence frequency for even modestly effective cloaks, while reduction of the 'high-frequency enhancement' resulting from the 'thickness quasi-resonance' near the cut-off frequency of the symmetric (S2B) mode requires more effective cloaking, but can be practically eliminated by employing a cloak that creates tangential acoustic velocities in excess of the S2B mode phase speed near cutoff. [ABSTRACT FROM AUTHOR]

Forensic age progression for the purpose of ageing a missing child is a discipline currently dominated by artistic methodologies. In order to improve on these techniques, a statistically rigorous approach to the ageing of the human face is presented. The technique is based upon a principal component analysis and involves the definition of an ageing direction through the model space, using an age-weighted combination of model parameters. Pose and expression compensation methods are also incorporated, allowing faces at a wide variety of pose orientations and expressions to be aged accurately. Near photo-quality images are obtained quickly and the resultant ageing effects are realistic and plausible. As a quantitative check of the results, the root mean square error is calculated between the shape vector of the aged face and that of the target face, as well as between the aged face and faces of different identity at the target age. In general, this error is found to be smaller between the aged face and the target face, indicating that the face successfully retains its identity as it is aged. As a further test of the basic plausibility of our results, a regression analysis is performed between the shape model parameters and the age of each subject, assuming a linear relationship. The coefficient of determination is calculated to be r2=0.68 and the relationship between the variables is found to be significant at a level >0.99 upon performance of a standard F-test. [ABSTRACT FROM AUTHOR]

Direct imaging of minority electron transport via the spatially resolved recombination luminescence signature has been used to determine carrier diffusion lengths in GaInP as a function of doping. Minority electron mobility values are determined by performing time resolved photoluminescence measurements of carrier lifetime on the same samples. Values at 300K vary from 2000 to 400 cm²/Vs and decrease with increasing doping. Anisotropic diffusion lengths and strongly polarized photoluminescence are observed, resulting from lateral composition modulation along the [110] direction. We report anisotropic mobility values associated with carrier transport parallel and perpendicular to the modulation direction. [ABSTRACT FROM AUTHOR]

An all-optical technique has been used to provide the first direct measurement of anisotropic minority-carrier diffusion in an ordered alloy of GaInP. Direct imaging of the minority-carrier diffusion distribution resulting from generation at a quasipoint source is obtained using an optical microscope coupled to a scanning electron microscope. Minority-carrier diffusion lengths ranging from 3 to 60 μm are measured by this technique in double heterostructures of GaInP, GaAs, and GaInAs, providing a key parameter of interest to the performance of state-of-the-art triple junction solar cells. Here we show a direct measurement of anisotropy in minority-carrier mobility in ordered GaInP, which is evident in the oval-shaped distribution of the recombination luminescence. A factor of 1.6 increase in minority electron mobility along the [110] major axis is reported. [ABSTRACT FROM AUTHOR]

Abstract: An optical technique is used to measure local variations in minority carrier diffusion length associated with dislocation networks in ordered GaInP. Two-dimensional images of the luminescence resulting from carrier generation along a line source are obtained using an optical microscope coupled to a scanning electron microscope. Minority carrier diffusion lengths are determined from the spatial distribution of the recombination luminescence. The use of double heterostructures of AlGaInP/GaInP/AlGaInP restricts diffusion to the plane of the epilayer. Because the technique offers high spatial resolution, it is possible to measure variations in carrier transport associated with the dislocation bands produced due to lattice mismatch with the substrate. Minority carrier diffusion lengths have been correlated to the intensity fluctuations commonly observed in cathodoluminescence across several light and dark bands. In multiple regions of the sample, increased cathodoluminescence intensity occurs in areas of decreased diffusion length. Modeling shows that increased luminescence intensity can correspond to regions of decreased effective minority carrier lifetime, due to the combined effect of variations in non-radiative and radiative recombination rates. [Copyright &y& Elsevier]

A contact-free optical technique is developed to enable a spatially resolved measurement of minority carrier diffusion length and the associated mobility-lifetime (μτ) product in bulk semiconductor materials. A scanning electron microscope is used in combination with an internal optical microscope and imaging charge-coupled device (CCD) to image the bulk luminescence from minority carrier recombination associated with one-dimensional excess carrier generation. Using a Green's function to model steady-state minority carrier diffusion in a three-dimensional half space, non-linear least squares analysis is then applied to extract values of carrier diffusion length and surface recombination velocity. The approach enables measurement of spatial variations in the μτ product with a high degree of spatial resolution. [ABSTRACT FROM AUTHOR]