spectral hardening

例句：

1. 1. Spectral analysis is a method used to analyze the properties of materials by measuring their absorption and emission spectra.
   光谱分析是一种通过测量材料的吸收和发射光谱来分析其性质的方法。
2. 2. The researcher studied the spectral characteristics of different types of stars.
   研究者研究了不同类型恒星的光谱特征。
3. 3.The spectral lines in the spectrum are used to determine the temperature and composition of the gas.
   光谱线在光谱中用于确定气体的温度和组成。