基于水面光谱数据的官厅水库有色可溶性有机物反演

有色可溶解性有机物(简称CDOM,又称为黄色物质),存在于所有自然水体中,可以用于指示水体有机物污染的状况。相比于常规采样监测方法,基于遥感数据反演CDOM具有重要优势。但是遥感数据反演CDOM的方法通常具有区域局限性,因此需要对不同区域水体进行反演方法的检验和完善。我国北方水体CDOM遥感反演的相关研究较少,选择位于河北省张家口市和北京市延庆区交界的官厅水库为研究区,利用2013年10月26日获取的水面遥感反射率光谱(R_rs(λ))和实验室测得的CDOM吸收系数(a_CDOM(λ))数据,首次进行了CDOM浓度(以440 nm处CDOM的吸收系数(a_CDOM(440))表示)反演。对半解析方法即QAA-CDOM方法进行了检验和改进,并建立了CDOM反演的经验模型。QAA-CDOM方法反演结果的均方根误差RMSE为0.10,平均相对误差σ为10.8%。通过实测数据计算了每个波段的水面以下上行辐照度与辐亮度的比值Q,代替了QAA-CDOM方法中的固定Q值,对QAA-CDOM方法进行改进,反演结果精度仅略有提升,RMSE=0.09, σ=10.2%。同时,用四个遥感反射率的比值与a_CDOM(440)进行回归分析,建立了CDOM反演的经验模型。结果显示R_rs(531)/R_rs(551)与CDOM浓度的相关性最大,决定系数为0.63;基于该波段比值建立的CDOM反演经验模型的反演结果的均方根误差RMSE为0.08,平均相对误差σ为8.8%。经验方法反演结果的精度更高,但需要同步实测数据进行所选波长和模型系数的标定;半解析方法不需要标定,更易于推广。     

厚朴酚近红外光谱的2D-COS解析及其在藿香正气口服液模型中应用

以氘代氯仿为溶剂,以中药化学标准品厚朴酚为载体,采用二维相关光谱(Tow-dimensional correlation spectroscopy, 2D-COS)技术,采集近红外光谱(near infrared spectroscopy, NIR),由氘代氯仿纯溶剂与厚朴酚原始光谱的二维相关同步谱可知,厚朴酚在1 365～1 455, 1 600～1 720, 2 000～2 181和2 275～2 465 nm处有特征吸收,其中1 440 nm为酚基O—H伸缩振动基频的一级倍频谱带,1 679 nm为芳基C—H及与芳基相连的甲基C—H伸缩振动一级倍频谱带,2 117, 2 304, 2 339和2 370 nm为芳基C—H伸缩振动、弯曲振动和变形振动的组合频,2 445 nm为芳基相连的甲基C—H弯曲振动基频二级倍频谱带,这些波段为厚朴酚的特征归属。以藿香正气口服液复杂体系为载体,以厚朴酚光谱解析的特征波段与间隔偏最小二乘(interval partial least squares, iPLS)和组合间隔偏最小二乘(synergy interval partial least squares, SiPLS)筛选的特征波段分别建立偏最小二乘(partial least squares, PLS)定量模型,模型的决定系数R2_cal 和R2_pre均大于0.99,校正均方根误差(root mean of square error of calibration, RMSEC),交叉验证均方根误差(root mean of square error of cross validation, RMSECV)和预测均方根误差(root mean of square error of prediction, RMSEP)均较小。结果表明,2D-COS技术解析厚朴酚所得波段建立的定量模型与iPLS和SiPLS波段筛选的模型均相对稳定,这使定量模型的波段选择更具有解释性。该研究为中药化学成分NIR光谱解析特征波段的归属提供方法参考,同时为NIR建模波段筛选提供借鉴和指导。     

基于中温黑体的近红外光纤光谱仪辐射定标的方法研究

中温黑体是红外谱段常用的高精度辐射标尺设备,而近红外是处于其有效辐射范围边缘的谱段,所以该谱段的定标研究相对较少。研究了基于中温黑体的近红外光纤光谱仪辐射定标方法,主旨是探讨定标精度如何受定标模型的结构参数选择的影响,进而为近红外光谱辐射计量溯源提供技术参考。采用50～1 050 ℃的可调中温黑体对近红外光纤光谱仪(950～1 700 nm)进行辐射定标。针对定标的关键环节重点讨论了两个内容,首先是辐射传输模型的几何因子匹配问题,比较分析了传统的双圆盘辐射传输模型和光纤直接耦合模型。对于光纤光谱仪的辐射定标来讲,采用光纤直接耦合形式的辐射传输模型,结构上更简单,耦合效率更高。其次重点分析了辐射定标中模型的结构参数对定标精度的影响,其影响的原因是定标数据本身属性中的尺度结构特征,即通常所说的非线性问题。因此对于定标精度要求较高时,需要采用非线性定标模型进行校正,并尽可能保证测试点采样的尺度均衡,这是小样本数据解释非线性结构关系时无法回避的样本选择问题。数据分析结果表明,定标方程的不同结构参数的选择策略对定标精度有显著影响,校正方程的样本残差标准差带变化范围为±0.1%～±1%。     

两种国产新型掺Yb氟化物激光晶体的光谱特性研究

掺Yb氟化物激光材料是继掺Yb氧化物激光材料之后的另一类重要的掺Yb激光材料,已经成为可调谐激光和超快激光领域中研究的热点之一。针对两种国产新型掺Yb的氟化物激光材料：混晶材料Yb∶CaF₂-SrF₂和共掺离子型的单晶材料Yb, Y∶CaF₂,进行了详细的光谱特性比对实验研究。通过荧光比对实验,发现这两类激光材料的荧光光谱完全不同,并分析了不同荧光产生的物理机制。通过吸收率比对实验,讨论了两类材料中的激活离子Yb或共掺离子Y的掺杂浓度对晶体吸收特性的影响,得到了最佳掺Yb离子或共掺Y离子的浓度。利用激光二极管作为泵浦源,实现了这两类新型材料在折叠腔型下的连续激光输出运转,其中对于共掺离子型Yb, Y∶CaF₂晶体是首次实现连续激光运转。通过激光对比实验,获得了两类激光材料(四种样品)的激光输入—输出关系曲线,测量了各自的斜效率和激光光谱特征。通过系统地比较两类激光晶体的吸收率、荧光光谱特性、激光光谱特性以及连续激光运转的阈值功率和斜效率等参数得出以下结论：在四种实验样品中,共掺离子型单晶材料中的3at%Yb, 6at% Y∶CaF₂晶体具有最好的光谱和激光特性,具有良好的应用前景。这些实验结果为进一步提升此类激光材料的性能提供了有益的参考。     

基于优化光谱指数的牧草生物量估算

牧草生物量是天然和人工草场产出的一个重要指标,能直接反映牧草的长势,它的实时监测是制定合理的草地管理和放牧制度的前提。然而,传统的样方法费时、费力很难满足草地生物量监测的实时性要求。近年来,随着高光谱遥感的发展,为草地的快速、无损的监测提供了可能。通过对内蒙古天然和人工草地生物量及其冠层光谱数据分析,探讨了不同类型光谱指数在估算牧草生物量的鲁棒性。研究表明,由于冠层结构和生物量的影响,不同类型草地冠层的光谱反射存在巨大的差异,从而使现有光谱指数对天然草地和不同品种人工草地牧草生物量的预测能力存在显著的差异(R2=0.00～0.65)。在荒漠草原低生物量的条件下,受土壤背景影响不同光谱指数预测能力较小,而在青贮玉米高生物量条件下,基于红光的光谱指数容易发生饱和失去敏感性。把不同草地类型的数据结合后进行简单比率和归一化窄波段光谱指数的波段优化,与出版的光谱指数相比优化后的归一化光谱指数(normalized difference spectral index, NDSI）显著提高了牧草生物量的预测能力,预测生物量模型的决定系数最高(R2=0.72)。敏感性分析进一步证明了基于波段优化算法的优化光谱指数NDSI,(ration spectral index, RSI）有最低的噪声,从而能更好的预测牧草生物量。波段优化算法可以有效提高遥感估算草地牧草生物量的精度,光谱指数及其优化波段的选择会直接影响模型的预测能力。     

Paraconductivity for a d-wave superconductor in short-wavelength fluctuation regime

A theoretical study of the fluctuation conductivity above T_c (paraconductivity) is reported for a d-wave superconductor with resonant scattering impurities. A d-wave system is modeled by tight-binding electrons in the two-dimensional squared lattice, and the impurity scattering is treated in the T-matrix approximation in a unitary limit. In calculating the Aslamazov–Larkin (AL) and the Maki–Thompson (MT) terms, we also consider effects of a short-wavelength cutoff in the fluctuation spectrum. The d-wave character in the AL and MT terms manifests itself to renormalization effects on the fluctuation amplitude and reduced temperature, whereas an anomalous-MT term is absent. The present calculations can describe fairly well experiments on the paraconductivity in zinc-doped cuprate superconductors provided that effects of a total-energy cutoff are taken into account.     

Generalized biaxial shearing of MQMAS NMR spectra

Two dimensional multiple quantum (MQ) MAS NMR experiments have become popular due to the wide applicability of this technique to structural questions in materials science, the abundance of half-integer spin nuclei in the periodic table, and the ease of implementation on typical solid state NMR instruments. In spite of the high-resolution theoretically possible from such experiments, the homogeneous and inhomogeneous broadening factors inherent in many samples of interest can make spectral analysis challenging. We present several possible spectral shearing schemes that may be useful for spectral analysis, and in particular we introduce shearing in the directly detected dimension. We suggest that for amorphous or disordered samples that give broad spectral features, shearing may be used as a general tool for optimal positioning of these features relative to one another and for the characterization of isotropic chemical and quadrupolar shifts.     

Evaporation of an emulsion trapped in a yield stress fluid

The present work deals with emulsions of volatile alkanes in an aqueous clay suspension, Laponite, which forms a yield stress fluid. For a large enough yield stress (i.e. Laponite concentration), the oil droplets are prevented from creaming and the emulsions are thus mechanically stabilized. We have studied the evaporation kinetics of the oil phase of those emulsions in contact with the atmosphere. We show that the evaporation process is characterized by the formation of a sharp front separating the emulsion from a droplet-free Laponite phase, and that the displacement of the front vs. time follows a diffusion law. Experimental data are confronted to a diffusion-controlled model, in the case where the limiting step is the diffusion of the dissolved oil through the aqueous phase. The nature of the alkane, as well as its volume fraction in the emulsion, has been varied. Quantitative agreement with the model is achieved without any adjustable parameter and we describe the mechanism leading to the formation of a front.     

Heteroepitaxial growth of thin InAs layers on GaAs(1 0 0) misoriented substrates: A structural and morphological comparison

Thin InAs epilayers were grown on GaAs(1 0 0) substrates exactly oriented and misoriented toward [1 1 1]A direction by atmospheric pressure metalorganic vapor phase epitaxy. InAs growth was monitored by in situ spectral reflectivity. Structural quality of InAs layers were studied by using high-resolution X-ray diffraction. No crystallographic tilting of the layers with respect to any kind of these substrates was found for all thicknesses. This result is discussed in terms of In-rich growth environment. InAs layers grown on 2° misoriented substrate provide an improved crystalline quality. Surface roughness of InAs layers depend on layer thickness and substrate misorientation.