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111.
Green leaf area index (LAI) is a measure of vegetative growth and development and is frequently used as an input parameter in yield estimation and evapotranspiration models. Extensive destructive sampling is usually required to achieve accurate estimates of green LAI in natural situations. In this investigation, a statistical modeling approach was used to predict the green LAI of oats from bidirectional reflectance data collected with multiband radiometers. Stepwise multiple regression models based on two sets of spectral reflectance factors accounted for 73% and 65% of the variance in green LAI of oats. Exponential models of spectral data transformations of greenness, normalized difference, and near-infrared/red ratio accounted for more of the variance in green LAI than the multiple regression models. 相似文献
112.
The effect of volatilization on the conduction behavior of Li- or Mg-doped Cr2 O3 was studied. The P o2 dependence on conduction changed from 1/4 to 3/8 when volatilization occurred. The high-temperature conduction mechanism of Cr2 O3 may be dominated by the formation of Cr vacancies due to the volatilization effect. 相似文献
113.
Harlan J. Brown-Shaklee Eric W. Neuman William G. Fahrenholtz Gregory E. Hilmas 《Journal of the American Ceramic Society》2023,106(3):1932-1944
Boron carbide powders were synthesized from elemental powders and studied using X-ray diffraction (XRD) and UV–visible diffuse reflectance, Raman, and diffuse reflectance IR spectroscopies. Following reaction at 1400°C for 6 h, synthesized powders exhibited possible faulting as suggested by XRD patterns. B3C, B4.3C, and B5C powders contained graphitic carbon whereas the boron carbides with higher B/C ratios contained no residual carbon, suggesting that the carbon rich phase boundary is likely temperature dependent. Analysis by Raman and IR spectroscopy suggested that Raman spectra are influenced by excitation frequency due to resonance. We suggest that measurement of boron carbides with resonant Raman lifts the selection rules to allow measurement of Raman silent modes that are present in the IR spectra. Optical reflectance of the boron carbide powders revealed that the B/C ratio governed the indirect and direct optical band gaps of the faulted powders. B3C and B4.3C powders were light gray in spite of the presence of the carbon, whereas B5C, B6.5C, B10C, and B12C were gray, green, brown, and dark brown, respectively. Increasing carbon content increased the optical indirect band gap from 1.3 eV for B12C to 3.2 eV for B3C, causing the observed color changes. 相似文献