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Abstract The trans to cis photoisomerization of urocanic acid (UCA) in skin is considered to play an important role in the mechanism of immunosuppression. We have investigated the effects of skin type and various sunscreens with low sun protection factor (SPF) on the UV-induced cis -UCA formation in human skin after exposure to artificial IJV light. The rate of cis -UCA formation depends little on the skin type and is reduced by topical application of sunscreens. The rate of cis -UCA formation decreases with increasing SPF and only broad-spectrum, highly protective sunscreens offer protection against the UV-induced formation of cis -UCA, which accumulates in the stratum corneum after multiple UV exposures. A theoretical approach to estimate the distribution of cis -UCA after irradiation indicates that this compound may diffuse into the deeper layers of the epidermis with D ∼ 10−17 m2 /s, and that its elimination from the stratum corneum is mainly due to desquamation. 相似文献
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Queueing Systems - Donsker’s theorem is perhaps the most famous invariance principle result for Markov processes. It states that, when properly normalized, a random walk behaves... 相似文献
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Queueing Systems - A Markovian single-server queue is studied in an interactive random environment. The arrival and service rates of the queue depend on the environment, while the transition... 相似文献
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We present a comparison of the service disciplines in real time queueing systems (the customers have a deadline before which they should enter the service booth). We state that giving priority to customers having an early deadline minimizes the average stationary lateness. We show this result by comparing adequate random vectors with the Schur convex majorization ordering. 相似文献