A web-based search system recommends and gives results such as customized image or video contents using information such as user interests, search time, and place. Time information extracted from images can be used as a important metadata in the web search system. We present an efficient algorithm to classify time period into day, dawn, and night when the input is a single image with a sky region. We employ the Mask R-CNN to extract a sky region. Based on the extracted sky region, reference color histograms are generated, which can be considered as the ground-truth. To compare the histograms effectively, we design the windowed-color histograms (for RGB bands) to compare each time period from the sky region of the reference data with one of the input images. Also, we use a weighting approach to reflect a more separable feature on the windowed-color histogram. With the proposed windowed-color histogram, we verify about 91% of the recognition accuracy in the test data. Compared with the existing deep neural network models, we verify that the proposed algorithm achieves better performance in the test dataset.
Malic acid is the active ingredient in many sour foods and found mostly in unripe fruits. The dicarboxylic acid is relatively inexpensive and commercially available in both enantiomeric forms. The application of malic acid derivatives as a chiral auxiliary is, however, not well known in the area of asymmetric synthesis.1 We herein report the first example of L-malate-mediated dynamic kinetic resolution of α-bromo esters in nucleophilic substitution with various arylamines. 2Treatment of diisopropyl L-malate with racemic α-bromo phenylacetic acid in the presence of DCC and DMAP provided α-bromo phenylacetate (αRS)-1 in 77% yield with about 50:50 diastereomeric ratio (dr). When the two diastereomeric mixture of (αRS)-1 was treated with p-anisidine (1.5 equiv), tetrabutylammonium iodide (TBAI, 1.0 equiv) and diisopropylethylamine (DIEA, 1.0 equiv) in CH 2 Cl 2 at room temperature for 12 h, N-aryl amino ester 2 was produced in 81% yield with 90:10 dr as shown in Scheme 1. Subsequent removal of diisopropyl L-malate with MeOH and Et 3 N gave N-aryl phenylglycinate (R)-3 in 71% yield with 89:11 enantiomeric ratio (er).3a,c The yield and stereoselectivity of the substitution imply that α-bromo stereogenic center is configurationally labile with respect to the rate of substitution and (αRS)-1 is dynamically resolved under the reaction condition.In order to understand the effect of additives and reaction pathway, we carried out a series of reactions as shown in Table 1. In the absence of both TBAI and DIEA, the substitution of 1 was very slow to provide 2 with 71:29 dr in 27% yield after 12 h (entry 1). Also, the rate of the substitution was substantially decreased in the absence of DIEA to provide 2 in 47% yield with 90:10 dr, whereas the reaction in the absence of TBAI gave 2 with both lower yield and stereoselectivity (entries 2-3). The results in entries 1-3 show the importance of the presence of halide ion and base for sufficient rate acceleration and selectivity. When the mixture of two diastereomers of 1 (70:30 dr) was allowed to reach thermodynamic equilibrium in the presence of TBAI and DIEA, the diastereomeric ratio of recovered 1 was analyzed by 1
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