木材种类的近红外光谱和模式识别

木材的种类识别是木材加工和贸易的一个重要环节,传统的木材种类识别方法主要有显微检测法和木材纹理识别法,其操作繁琐,耗时长,成本高,不能满足当前需求。本研究利用木材的近红外光谱(NIRS)结合模式识别方法,以期实现木材种类的快速准确识别。采用近红外光谱结合主成分分析法(PCA)、偏最小二乘判别分析法(PLSDA)和簇类独立软模式法(SIMCA)三种模式识别对58种木材进行种类鉴别研究;5点平滑、标准正态变量变换(SNV)、多元散射校正(MSC)、Savitzky-Golay一阶导数(SG 1st-Der)和小波导数(WD)五种光谱预处理方法用于木材光谱的预处理;校正集和测试集样品的正确识别率(CRR)用于模型的评价。采用PCA方法,通过样品的前三个主成分空间分布图分辨木材种类的聚类情况。在建立PLSDA模型,原始光谱的正确识别率最高,分别为88.2%和88.2%;5点平滑处理的光谱校正集和测试集的CRR分别为88.1%和88.2%;SNV处理的光谱校正集和测试集的CRR分别为84.4%和84.5%;MSC处理的光谱校正集和测试集的CRR分别为83.1%和84.2%;SG 1st-Der处理的光谱校正集和测试集的CRR分别为81.8%和82.7%;WD(小波基为“Haar”,分解尺度为80)处理的光谱校正集和测试集的CRR分别为87.3%和87.2%。可知,在PLSDA模型中,木材光谱未经预处理种类识别效果最后好。在建立SIMCA模型过程中,原始光谱的校正集和测试集的CRR分别为99.7%和99.4%;5点平滑处理的光谱校正集和测试集的CRR分别为100%和100%;SNV处理的光谱校正集和测试集的CRR分别为99.5%和99.1%;MSC处理的光谱校正集和测试集的CRR分别为99.0%和98.4%;SG 1st-Der的光谱校正集和测试集的CRR分别为81.8%和82.7%;WD处理的光谱校正集和测试集的CRR分别为100%和100%。可知,在SIMCA模型中,木材光谱经平滑和小波导数处理后的识别效果最好,且光谱的校正集和测试集CRR都为100%。采用三种模式结合五种不同的预处理方法对木材近红外光谱进行定性建模识别时,由于木材样本属性复杂,主成分分布图相互交织,PCA无法识别出58种木材;原始光谱的PLSDA模型可以得到较好的判别模型,但校正集和测试集的CRR只有88.2%和88.2%;木材光谱经过5点平滑或WD预处理后的SIMCA模型可达到最好的识别效果,校正集和测试集的CRR均为100%,且WD-SIMCA模型因子数比5点平滑SIMCA模型小,模型更为简化,故WD-SIMCA为58种木材种类识别的最优模型。研究表明光谱预处理方法可以有效的提高木材种类识别精度,有监督模式识别方法SIMCA可以用来建立有效的木材识别模型,近红外光谱结合模式识别可以为木材种类的识别提供一种快速简便的分析方法。     

关注学科知识的职前化学教师自主研修——基于“化学师范生备课组”的活动个案

学科知识是师范生专业素质的重要组成部分,研究基于化学师范生备课组以学科知识强化为主题的研修活动,从备课选题、研修过程、问题批判等方面探讨化学师范生学科知识强化新途径,评析化学师范生备课组的价值。     

优化探究点, 渐进式推进学生自主探究实验的开展

在具体开展探究性实验教学时, 采取灵活多样的形式, 通过讨论、创设问题情境、反思等措施优化实验探究点, 渐进式推进学生自主探究实验的开展, 确保学生的思考能力、判断能力、分析能力及动手能力在探究活动中不断增强。     

Experimental investigation of liquid crystal director reorientation by mechanical vibrations

Reorientation of a nematic liquid crystal undergoing mechanical vibrations of one of cell walls was studied experimentally. Orientational structures have been revealed, which have interesting properties, their characteristics and formation processes were investigated. It was shown that these structures have parameters that do not depend on the intensity and frequency of mechanical vibrations.     

椭圆偏振光测不准原因分析

在光学实验中,用GSZF-3实验系统检测椭圆偏振光时,测得的振幅与角度在极坐标中画出的并不是椭圆,而是一个类肾脏线。本文分析了产生的原因,并提出了改进建议。     

一个风险模型的研究

研究了索赔到达过程为平稳无后效流,保单到达过程为平稳无后效流,并带扩散扰动项的盈余过程．讨论了该盈余过程的马尔科夫性和鞅性．然后用鞅方法得到其破产概率的表达式及其相应的Lundberg不等式．     

含有n个无关变元的离散不等式

对一些基本的不等式进行了推广,给出了含有n个无关变元的非线性的离散不等式.所得结果推广了已有的一些结论.     

Kruglov operator and operators defined by random permutations

The Kruglov property and the Kruglov operator play an important role in the study of geometric properties of r. i. function spaces. We prove that the boundedness of the Kruglov operator in an r. i. space is equivalent to the uniform boundedness on this space of a sequence of operators defined by random permutations. It is also shown that there is no minimal r. i. space with the Kruglov property.     

Hydrothermal Preparation of Photoluminescent Graphene Quantum Dots Characterized Excitation‐Independent Emission and its Application as a Bioimaging Reagent

Zero‐dimensional photoluminescent (PL) graphene quantum dots (GQDs) that can be used as the cell‐imaging reagent are prepared by a hydrothermal route using the graphene oxide (GO) as the carbon source. Under the optimized hydrothermal conditions, an initial hydrogen peroxide concentration of 0.5 mg mL^?1 at 180 °C for 120 min, the GO sheets can be cut into nanocrystals with lateral dimensions in the range of 1.5–5.5 nm and an average thickness of around 1.1 nm. The as‐prepared GQDs exhibit an abundance of hydrophilic hydroxy and carboxyl groups and emit bright blue luminescence with up‐conversion properties in a water solution at neutral pH. Most interestingly, they indicate excitation‐independent emission characteristics, and the surface state is demonstrated to have a key role in the PL properties. The fluorescence quantum yield of the GQDs is tested to be around 6.99% using quinine sulfate as a standard. In addition, the as‐prepared GQDs can enter into HeLa cells easily as a fluorescent imaging reagent without any further functionalization, indicating they are aqueous stability, biocompatibility, and promising for potential applications in biolabeling and solution state optoelectronics.