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We develop a superficial diffusing probe with a 3 mm source-detector separation that can be used in combination with diffuse optical spectroscopic (DOS) methods to noninvasively determine full-spectrum optical properties of superficial in vivo skin in the wavelength range from 650 to 1000 nm. This new probe uses a highly scattering layer to diffuse photons emitted from a collimated light source and relies on a two-layer diffusion model to determine tissue absorption coefficient mu a and reduced scattering coefficient mu's. By employing the probe to measure two-layer phantoms that mimic the optical properties of skin, we demonstrate that the probe has an interrogation depth of 1 to 2 mm. We carry out SSFDPM (steady state frequency-domain photon migration) measurements using this new probe on the volar forearm and palm of 15 subjects, including five subjects of African descent, five Asians, and five Caucasians. The optical properties of in vivo skin determined using the superficial diffusing probe show considerable similarity to published optical properties of carefully prepared ex vivo epidermis+dermis.

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Today, many products are designed and manufactured to function for a long period of time before they fail. Determining product reliability is a great challenge to manufacturers of highly reliable products with only a relatively short period of time available for internal life testing. In particular, it may be difficult to determine optimal burn-in parameters and characterize the residual life distribution. A promising alternative is to use data on a quality characteristic (QC) whose degradation over time can be related to product failure. Typically, product failure corresponds to the first passage time of the degradation path beyond a critical value. If degradation paths can be modeled properly, one can predict failure time and determine the life distribution without actually observing failures. In this paper, we first use a Wiener process to describe the continuous degradation path of the quality characteristic of the product. A Wiener process allows nonconstant variance and nonzero correlation among data collected at different time points. We propose a decision rule for classifying a unit as normal or weak, and give an economic model for determining the optimal termination time and other parameters of a burn-in test. Next, we propose a method for assessing the product's lifetime distribution of the passed units. The proposed methodologies are all based only on the product's initial observed degradation data. Finally, an example of an electronic product, namely contact image scanner (CIS), is used to illustrate the proposed procedure.

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The conventional burn-in test, which only collects go/no go (or time-to-failure) data over short testing periods becomes rather ineffective for highly reliable products. This decision problem can be solved if there exists a suitable quality characteristic whose degradation over time can be related to the product's lifetime. An innovative approach to determine the burn-in policy by using a suitable degradation model has been suggested in the literature. However, a major disadvantage of this procedure is that it only uses information contained in current degradation data, and it ignores any information given by the entire sequence of observations. Thus, it becomes relatively insensitive to detecting weak items if the degradation path of the product degrades very slowly. To remedy this weakness, similar to the CUSUM control charting scheme in statistical process control, we propose an integrated Wiener process to model the cumulative degradation path of the product's quality characteristic. Then the optimal burn-in policy can be easily obtained.In addition, we also use an analytic approach to compare the efficiency of our proposed procedure with the method that is previously reported in the literature.