Four pyridinium ionic liquid cations (N-ethylpyridinium, N-butyl-pyridinium, N-butyl-4-methyl-pyridinium, N-hexyl-pyridinium) were separated and determined by reversed phase ion-pair chromatography with ultraviolet-visible detection. The effects of ion-pair reagent, acetonitrile concentration and column temperature on the retention and separation of the cations were evaluated. Then the four pyridinium cations could be separated at baseline within 13 min. The detection limits (S/N = 3) were 0.30-0.70 mg L -1 , and relative standard deviations (n = 5) for peak areas were 0.18-0.58%. The method was applied to analyze surface water with recoveries of 99.5-104.0%, which is accurate, reliable and practical.
In this paper, we present a novel approach for frontal face detection in gray-scale images. We represent both faces and clutter by using two-dimensional wavelet decomposition. To characterize the statistical dependency between different levels of wavelet, we introduce a Hidden Markov Model (HMM), in which a number of discrete states at each level capture the diversity of faces as well as clutter. Our experiments indicate that the proposed algorithm outperforms conventional templatebased methods such as matched filter and eigenface methods.
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