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β-胡萝卜素广泛存在于植物体中,是典型的线性多稀分子,具有重要的生物功能。由于β-胡萝卜素是碳碳单、双键(C-C,C=C)交替的短链共轭多稀分子,含有大量离域的π电子,具有重要的光电特性。根据Andreas等对拉曼散射强度的研究,当激发光波长落在分子的电子吸收带时,会产生共振拉曼效应,能使拉曼光谱强度提高106倍。利用共振拉曼光谱技术,测量了β胡萝卜素分子及胡萝卜、青萝卜、白萝卜肉质直根不同部位其拉曼光谱,发现含β-胡萝卜素较高的胡萝卜的拉曼光谱与β-胡萝卜素的吻合很好。Gellerman等研究表明,样品浓度与拉曼峰强成正比关系,从拉曼光谱中容易发现三种萝卜的光谱强度纵向根头到主根及横向表皮到根芯逐渐降低,且青萝卜和白萝卜拉曼光谱强度都很低,并在碳碳单键的振动峰处发生峰劈裂。分别计算了碳碳单键和碳碳双键与碳氢键拉曼强度比,三种萝卜的ICC/IC-H随着测量部位(横向和纵向)的不同变化幅度接近:胡萝卜的表皮和根芯纵向的变化率分别为A1=0.213 3和A2=0.215 9,青萝卜表皮外和里的变化率分别为B1=0.219 1和B2=0.211 4,白萝卜表皮外和里分别为D1=0.223 9和D2=0.224 1;而对于IC-C/IC-H随着测量部位不同其变化率相差很大:胡萝卜的变化率a1=0.212 1和a2=0.232 4,青萝卜的变化率b1=0.263 5和b2=0.268 7,白萝卜的变化率d1=0.369 0和d2=0.304 9。对比发现三种萝卜的碳碳单键与碳氢键振动强度比随着测量部位的不同变化幅度相差很大,而从碳碳双键与碳氢键振动强度比发现三种萝卜中不同部位的β胡萝卜含量有相似的分布。这是由于青萝卜和白萝卜中β-胡萝卜素的含量少, 随着测量部位的不同C-C伸缩振动峰发生峰劈裂, 即在1 130和1 156 cm-1处出现两个振动峰, 经过计算和分析这两个峰都属于碳碳单键的伸缩振动峰, 且随着β-胡萝卜素含量的减少C-C整体的强度降低, 劈裂的新峰峰强度却有增加的趋势, 这使得原峰位的峰强度大幅度降低, 这与计算IC-C/IC-H的结果一致,不同品种的萝卜中β-胡萝卜素含量随测量部位的不同变化幅度截然不同。因此, 当样品中β-胡萝卜含量较少时,利用C=C振动峰峰强度同时分析样品不同部位的β-胡萝卜素含量分布变化会更准确。同时,研究和了解萝卜中不同部位β-胡萝卜素的含量为日常消费和膳食营养提供了很好的理论依据。 相似文献
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The Debye series of light scattering by an infinite multi-layered cylinder in an off-axis 21) Gaussian beam is studied. A simplified but rigorous iterative formula for scattering coefficients is presented. The numerical calculations of scattering intensity by a cylinder in on-axis and off-axis beams are developed. It is indicated that the results of Debye series reach an agreement with those of generalized Lorenz-Mie theory and the off-axis distances vary the results to a great extent. The Debye series components of a two-layered cylinder are further discussed. The relations between them with rainbow phenomena are analysed. 相似文献
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城市生活垃圾焚烧产物中二噁英检测方法 总被引:3,自引:1,他引:2
为研究城市生活垃圾焚烧产生的二噁英污染检测问题,介绍了垃圾焚烧过程中二噁英类的生成机理及其检测方法。色谱法、免疫法、生物法、激光质谱法是目前检测二噁英类的主要手段,其中高分辨气相色谱-高分辨质谱(HRGC-HRMS)法、虫荧光素酶报告基因(CALUX)法及酶免役分析(EIA)法等在实践中取得了很好的检测效果,但各种方法适应范围有很大差别。色谱法可有效分离各种二噁英类成分,但对仪器精度和操作水平要求较高,测试周期较长,费用较高,适于准确对各种成分定量检测,不需计算总量的场合;生物法测试周期短,可平行测试大量样品,适于快速、大规模样品的筛选,但只能测定总毒性当量;激光质谱法具有高选择性、高灵敏度、多组分测定、可实现在线检测等优势,但需要预先了解污染物的光谱结构。 相似文献
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The approximate point spectrum properties of p-ω-hyponormal operators are given and proved.In fact,it is a generalization of approximate point spectrum properties of ω-hyponormal operators.The relation of spectra and numerical range of p-ω-hyponormal operators isobtained.On the other hand,for p-ω-hyponormal operators T,it is showed that if is normal,then T is also normal. 相似文献
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Scattering of a high-order Hermite-Gaussian beam by a multi-layered sphere is analyzed. The incident high- order Hermite-Gaussian beam field is expressed by the complex-source-point method and expanded in terms of spherical vector wave functions. The beam shape coefficients of the Hermite-Gaussian beam are obtained. Under electromagnetic field boundary conditions, coefficients in the expressions of scattering fields are derived. Results of the numerical calculation of scattering intensity are presented. The effects of the particle parameters and beam parameters on scattering intensity are discussed in detail. 相似文献
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Xiaojin Yang 《中国物理 B》2022,31(7):74202-074202
The reflection and transmission of a finite-power Airy beam incident on a dielectric slab are investigated by an analytical method. Based on the plane-wave angular spectrum expansion and Fresnel approximation, the analytical expressions of the reflected field, internal field as well as transmitted field in each region are obtained. Through numerical simulations, the intensity distributions of the incident beam, reflected beam, internal beam as well as transmitted beam are presented at oblique incidence. Besides, we also compare the intensity distributions of the geometrical-optics beam field, the first order beam mode field and the actual beam field, which indicates that the contribution of each order beam mode field to the actual beam field is related to the refractive index of the dielectric slab. Meanwhile, the reflection characteristics of the Airy beams in the special cases of Brewster incidence and total reflection are investigated. Finally, the effects of the optical thickness and refractive index of the dielectric slab on the peak intensity distributions and beam shifts of the reflected and transmitted beams are also discussed in detail. The analytical and numerical results will be useful to analyze the propagation dynamics of Airy beam in the dielectric slab and provide some theoretical supports to the design of optical film. 相似文献