比光谱-导数-紫外分光光度法同时测定水中硝酸根和亚硝酸根

利用二元混合物的混合光谱与其中某一组分光谱的比值对波长求导，可达到分辨重叠光谱的目的。本文研究了用比光谱-导数-紫外分光光度法同时测定水样中NO3-和NO2-，以“减法技术”求导，兼具导数光度法能消除低频背景和高频噪声干扰及线性回归法分辨能力强的优点。方法避免了一般光度法需加入试剂而可能引起的误差。在pH7～9条件下测量203um～219um的光吸收值，用比光谱-导数技术处理，同时测定合成试样中0～4mg／L的NO3-和NO2-，6次测定相对标准偏差＜7％，加入回收率在95％～101％之间。讨论了干扰离子的影响及消除，并与P-矩阵法作了比较。方法已用于井水、雨水及湖水中NO3-和NO2-的同时测定。     

计算机法选择混合固定相最佳配比的研究

本文设计了1个BASIC计算程序，可以对任一混合物进行N种固定液最佳混合配比的计算，同时给出了26种物在4种常用固定液上的实验数据，并进行了2个实际样品的分离实验，证明通过计算机所选择的混合固定相的最佳配比是令人满意的。     

比值光谱—导数分光光度法同时测定纤维上的二组分混合染料

研究了用比值光谱－导数分光光度法同时测定两组分混合染料体系中分散大红ＢＷＦＬ和分散红玉ＺＧＦＬ的方法。回收率在９５．６％～１０７．５％。方法已用于分析纺织纤维上分散大红和分散红玉二元混染体系。     

Improved performance analysis of Gigabit passive optical networks

Gigabit passive optical networks (GPON) provide a capacity boosts in both the total bandwidth and bandwidth efficiency through the use of larger variable-length packets in Passive Optical Networks technology. In this paper, we have described a purely-passive GPON compatible reach extender using distributed Raman amplification and reported the improved investigation through implementation of a square root module by a distance of 60 km at data rate of 2.5 Gbps. An efficient improvement in Q factor is achieved with square root module, which further helps in increasing the length of GPON.     

监测小麦叶片氮积累量的新高光谱特征波段及比值植被指数

实时、快速、无损监测作物氮素状况对于精确氮肥管理具有重要意义。传统的氮素估测方法在时间或空间上难以满足要求,新兴的高光谱遥感技术为作物氮素监测提供了有效手段和技术途径。本研究的目的是基于三个田间试验的系统观测资料,探索可用于小麦叶片氮素监测的新的高光谱敏感波段及比值指数。利用减量精细采样法,系统构建了350～2 500 nm范围内所有两两波段形成的比值光谱指数RSI(ratio spectral index),综合分析了小麦叶片氮积累量LNA(leaf nitrogen accumulation)(g N·m-2)与RSI的定量关系,发现了监测叶片氮积累量的新高光谱特征波段(990, 720)和光谱指数RSI(990, 720),建立了相应的监测模型y=5.095x-6.040,模型的决定系数(R2)为0.814。利用独立试验资料检验模型,决定系数(R2)为0.847,相对根均方差(RRMSE)为24.70%,表明模型预测值与观察值之间的符合度较高。因此,利用高光谱比值指数RSI(990, 720)来估算小麦叶片氮积累量是精确可行的。该结果为便携式小麦氮素监测仪的研制开发及遥感信息的快速提取提供了适用可行的波段选择与技术依据。     

Identifying and supporting teachers’ robust understanding of proportional reasoning

This case study uses the Framework for Teachers’ Robust Understanding of Proportional Reasoning for Teaching (Weiland et al., 2020) to characterize how 51 mathematics teachers solved a comparison proportional problem. We found 50 of the 51 teachers productively drew upon four knowledge resources: (1) proportional situation, (2) ratios as part: part or part: whole, (3) unit rates, and (4) ratio as measure. This study details these and teachers’ less commonly used knowledge resources, as well as counterproductive statements related to the knowledge resources. We analyze the structure of the comparison proportion problem and suggest why teachers drew on particular knowledge resources. Lastly, we highlight how counterproductive statements highlight areas of focus for mathematics teacher educators and extends the operationalizing of the robust proportional reasoning framework for mathematics education researchers.     

The moment function for the ratio of correlated generalized gamma variables

The moment function for the ratio of correlated generalized gamma variables is expressed in terms of special functions. The expression presented generalizes the known moment expression for the integer valued moments to the real valued moments. Approximate formulas, in terms of elementary functions, are provided for low and high correlation regions and some application examples are given.     

Conformational Switches: Controlling the Carbamate C-N Rotamer Equilibrium

The syn / anti rotamer ratio for tert -butyl N -(2-thiazyl)carbamate 3 was measured by solution-state NMR in the presence and absence of a donor-acceptor-donor hydrogen bonding template. The template is able to switch the conformation of carbamate 3 from >95% anti to >70% syn making it the most effective carbamate conformational switch yet reported. B3LYP calculations provide insight into the factors that produce this result.     

Electroanalytical Studies and Simultaneous Determination of Amlodipine Besylate and Atorvastatine Calcium in Binary Mixtures Using First Derivative of the Ratio‐Voltammetric Methods

The electrochemical behavior of atorvastatin and amlodipine at a glassy carbon electrode has been studied using different voltammetric techniques. First derivative of the ratio voltammetric methods for determination of amlodipine and atorvastatin in tablets in the presence of the other compound has been described. This technique depends on the measuring of first derivative of the ratio voltammograms of each concentration as a function of the increased concentrations. DP and SW voltammetric methods depend on first derivative of the ratio‐voltammetry by measurements of the selected potentials for amlodipine and atorvastatin. The linear response was within the range of 4×10^?6–1×10^?4 M for amlodipine and 2×10^?6–1×10^?4 M for atorvastatin. The proposed methods have been extensively validated.     

Theoretical optimisation of the side-wall of micropillar array columns using computational fluid dynamics

The present study provides an overview of the ideal side-wall position in micro-pillar array columns for the case of semi-embedded side-walls. The position has been determined using computational fluid dynamics simulations of the flow field in flow domains with different side-wall shifts. Optimal side-wall shift values are presented for a wide range of shapes (cylinders, and diamonds and hexagons with different aspect ratios) and packing densities. Simple linear correlations that allow calculating the optimised side-wall geometries for the different considered variety of shapes and packing densities could be established. Interestingly, only two correlations are needed to represent all investigated cases: one correlation for all diamonds, and one correlation for the cylinders and all hexagons. Compared to the case of a flat side-wall, the minimal feature size on the mask can be increased by a factor of 2.5 in the case of cylindrical pillar bed with external porosity ? = 0.4, implying that that much smaller pillar diameters can be used in the bulk of the bed before the minimal feature size on the mask falls below the lithography resolution.