Epitaxial films of perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) on graphite (0001) were investigated by scanning tunneling microscopy. Molecular image contrast of PTCDA was found to depend strongly upon the molecular orientation and the position on graphite. In particular, the periodic discrepancy between PTCDA and graphite lattice points results in a modulation of contrast, which can be used to determine the epitaxial relation of PTCDA relative to the substrate accurately. By analyzing this modulation of contrast, we determined two kinds of epitaxial orientation of PTCDA. These orientations have no exact commensurate relation with graphite, but every lattice point of PTCDA lies on a lattice line parallel to the a axis (or b axis) of graphite. This specific feature contributes to decreasing the interfacial energy. The contrast mechanism of adsorbed molecules is also discussed.

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Rice reflectance was measured to determine the spectral regions most sensitive to panicle blast infection. Reflectance increased in the 430- to 530-, 580- to 680-, and 1,480- to 2,000-nm regions at the dough stage both in the laboratory and the field as the percentage of diseased spikelets increased. The wavebands of the greatest sensitivity were in the visible region, located near 485 and 675 nm. After the yellow-ripe growth stage, near-infrared rather than visible reflectance responded to panicle blast infections. Ratios of rice reflectance were evaluated as indicators of panicle blast. R470/R570 (reflectance at 470 nm divided by reflectance at 570 nm), R520/R675, and R570/R675 decreased significantly as the incidence of panicle blast increased at the dough stage. At the yellow-ripe stage, R550/R970 and R725/R900 were used to estimate panicle blast severity as measured in terms of the percentage of diseased spikelets. According to the simulation that uses ground-based sensor data, airborne multispectral scanners may be effective in detecting the occurrence of panicle blast using a band combination of 530- to 570- and 650- to 700-nm regions at the dough stage.