表面粗糙度对近红外光谱分析木材密度的影响

近红外(NIR)光谱技术是一种基于多元统计分析建立预测模型的定量分析技术,应用十分广泛,然而,近红外光谱分析结果的准确性会受到多种因素的影响。文章分析了木材表面粗糙度对近红外光谱预测木材密度的影响。结果表明,当待预测样品的粗糙度和建模样品的粗糙度一致时,分析结果较好;二者不一致时,分析误差较大。采用不同粗糙度样品建立混合预测模型,可以显著提高模型对粗糙度的适应性和稳健性。     

Cocondensation of urea with methylolphenols in acidic conditions

The reactions of urea with methylolphenols under acidic conditions were investigated using 2- and 4-hydroxybenzyl alcohol and crude 2,4,6-trimethylophenol as model compounds. The reaction products were analyzed with ¹³C-NMR spectroscopy and GPC. From the reaction of urea with 4-hydroxybenzyl alcohol, the formations of 4-hydroxybenzylurea, N,N′-bis (4-hydroxybenzyl) urea, and tris(4-hydroxybenzyl) urea were confirmed and the formations of N,N-bis(4-hydroxybenzyl) urea and tetrakis (4-hydroxybenzyl) urea were suggested. From the reaction of urea and 2-hydroxybenzyl alcohol, 2-hydroxybenzylurea and N,N′-bis(2-hydroxybenzyl) urea were identified. Further, the alternative copolymer of urea and phenol could be synthesized by the reaction of urea with 2,4,6-trimethylophenol. It was also found that the cocondensation between p-methylol group and urea prevails against the self-condensation of the methylolphenol even at the low pH below 3.0, and that p-methylol group has the stronger reactivity to urea than o-methylol group. © 1992 John Wiley & Sons, Inc.     

Saturation spectroscopy of CO2 and frequency stabilization of an optical parametric oscillator at 2.77 μm

We report the frequency stabilization of a CW single-frequency, singly resonant optical parametric oscillator (OPO) to the saturation absorption center of the (12)C(16)O2[10°1,02°1](II)>←00°0 P(14) line at 2.77 μm. The CO2 molecules were excited by the OPO idler wave, and the absorption signal was monitored through the fluorescence at 4.3 μm using a gold-coated longitudinal cell. The idler frequency was stabilized onto the line center by wavelength modulation method. The linewidth of the saturation dip was estimated to be 4.7 MHz, and the achieved frequency stability was 3.9 kHz (3.6×10(-11)).