Chlorophyll Fluorescence Detected Passively by Difference Reflectance Spectra of Wheat （Triticum aestivum L.） Leaf

The chlorophyll fluorescence （CF） signature emitted from vegetation provides an abundance of information regarding photosynthetics activity and has been used as a powerful tool to obtain physiological information of plant leaves in a non-invasive manner. CF is difficult to quantify because the CF signal is obscured by reflected light. In the present study, the apparent reflectance spectra of wheat （Triticum aestivum L.） leaves were measured under illuminations with and without filtering by three specially designed long-wave pass edge filters; the cut-off wavelengths of the three filters were 653.8, 678.2, and 694. l nm at 50% of maximum transmittance. The CF spectra could be derived as the reflectance difference spectra of the leaves under illuminations with and without the long wave pass edge filters. The ratio of the reflectance difference at 685 and 740 nm （Dif685/Dif740） was linear correlated with the CF parameters （maximal photochemical efficiency Fv/Fm, and the yield of quantum efficiency） measured by the modulated fluorometer. In addition, the ratio reflected the water stress status of the wheat leaf, which was very high when water deficiency was serious. This method provides a new approach for detecting CF and the physiological state of crops.

Hot Rolled Strip Re-reddening Temperature Changing Law during Ultra-fast Cooling

Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling （UFC）. Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained： UFC re-reddening temperature and laminar cooling （LC） re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.