“蜡烛火焰划分”实验的局限成因分析及改进研究

人教版初中化学首个探究性实验"蜡烛及其燃烧"明确指出火焰的划分方法，但在实际教学中肉眼观察法和火柴梗燃烧法对蜡烛火焰的划分存在一定的局限性。采用文献研究法和实验验证法分析其局限性的成因——燃料的析炭能力强弱、材料结构的不同等，并提出相应的改进建议。     

级联光栅结合Sagnac环的可调谐光纤激光器

提出并验证了一种单-双波长可调谐掺铒光纤激光器。利用级联光纤布拉格光栅(Cascaded Fiber Bragg gratings,Cascaded FBGs)结合Sagnac环结构所产生的复合滤波效应,实现较高精细度滤波,并通过调节环内偏振控制器(Polarization Controller,PC),引入双折射效应,得到波长可调谐的光纤激光器。基于耦合模理论并使用传输矩阵法对该结构的传输特性进行了分析,在此基础上搭建实验系统,验证了理论分析的正确性。实验结果表明:通过调节PC,激光器输出激光的波长范围约为1 555.644～1 556.112 nm,双波长间隔的可调范围约为0.108～0.452 nm,单-双波长的边模抑制比(SMSR)均高于40 dB;在稳定性测试中,输出单-双波长激光的波长最大漂移量小于0.008 nm。该方法具有结构简单、调谐方便、易于实现且精细度较高的优点,可应用于密集波分复用及全光通信系统等领域。     

星载海洋激光雷达最佳工作波长分析

星载激光雷达是实现海洋垂直剖面探测的有效工具,也是目前迫切需求的海洋光学遥感手段。对星载海洋激光雷达的波长参数进行评估对保证探测有效性具有重要意义。本文从探测深度和信噪比两方面分析了星载海洋激光雷达探测全球海洋的最佳波长。利用MODIS 10个波段的水体光学特性数据,估算全球海水探测深度及相应的最优波长;并根据太阳夫琅禾费暗线特性,对信号信噪比进行优化。结果表明:在探测深度方面,最优探测波长在488 nm波段的海洋占全球海洋面积的70%左右,并且全球95%以上的海域在488 nm波段的探测深度优于0.8倍的真光层深度;在信噪比方面,相对于488 nm波段,486.134 nm夫琅禾费暗线处采用0.1 nm带宽的滤光片可以将背景光强度降低70%,相应地回波信噪比整体提升了约5.0%。就全球海洋探测来说,使用486.134 nm作为探测波长可以提高探测深度,有效抑制太阳背景光,提高信噪比,因此,486.134 nm是星载海洋激光雷达的最佳工作波长。     

Guest-Reaction Driven Cage to Conjoined Twin-Cage Mitosis-Like Host Transformation

We report here a guest-reaction-induced mitosis-like host transformation from a known Pd₄L₂ cage 1 to a conjoined Pd₆L₃ twin-cage 2 featuring two separate cavities. The encapsulation of 1-hydroxymethyl-2-naphthol ( G1 ), a known ortho-quinone methide (o-QMs) precursor, within the hydrophobic cavity of cage 1 is found crucial to realize the cage to twin-cage conversion. Confined G1 molecules within the nanocavity undergo self-coupling dimerization reaction to form 2,2′-dihydroxy-1,1′-dinaphthylmethane ( G2 ) which then triggers the cage to twin-cage mitosis. The same conversion also proceeds, in a much faster rate, via the direct templation of G2 , confirming the induced-fit transformation mechanism. The structure of the ( G2 )₂⊂ 2 host–guest complex has been established by X-ray crystallographic study, where cis- to trans- conformational switch on one bridging ligand is revealed.     

Tuning the Upconversion Luminescence Lifetimes of KYb2F7:Ho3+ Nanocrystals for Optical Multiplexing

Conventional luminescent color coding is limited by spectral overlap and the interference of background fluorescence, thus restricting the number of distinguishable identities that can be used in practice. Here, we demonstrate the possibility of generating diverse time‐domain codes, specially designed for a single emission band, using lanthanide‐doped upconversion nanocrystals. Based on the knowledge of concentration quenching, the upconversion luminescence kinetics of KYb₂F₇: Ho³⁺ nanocrystals can be precisely controlled by modifying the dopant concentration of Ho³⁺ ions, resulting in a tunable emission lifetime from 75.8 to 1944.5 μs, which suggests the practicality of these time‐domain codes for optical multiplexing.     

Wavelength selection framework for classifying food and pharmaceutical samples into multiple classes

Near infrared (NIR) spectroscopy is an efficient, low‐cost analytical technique widely applied to identify the origin of food and pharmaceutical products. NIR spectra‐based classification strategies typically use thousands of equally spaced wavelengths as input information, some of which may not carry relevant information for product classification. When that is the case, the performance of predictive and exploratory multivariate techniques may be undermined by such noisy information. In this paper, we propose an iterative framework for selecting subsets of NIR wavelengths aimed at classifying samples into categories. For that matter, we integrate Principal Components Analysis (PCA) and three classification techniques: k‐Nearest Neighbor (KNN), Probabilistic Neural Network (PNN) and Linear Discriminant Analysis (LDA). PCA is first applied to NIR data, and a wavelength importance index is derived based on the PCA loadings. Samples are then categorized using the wavelength with the highest index and the classification accuracy is calculated; next, the wavelength with the second highest index is inserted into the dataset and a new classification is performed. This forward‐based iterative procedure is carried out until all original wavelengths are inserted into the dataset used for classification. The subset of wavelengths leading to the maximum accuracy is chosen as the recommended subset. Our propositions performed remarkably well when applied to four datasets related to food and pharmaceutical products. Copyright © 2016 John Wiley & Sons, Ltd.     

Intelligent resource allocation for transmission security on IRS-assisted spectrum sharing systems with OFDM

In this paper, intelligent reflecting surface (IRS) technology is employed to enhance physical layer security (PLS) for spectrum sharing communication systems with orthogonal frequency division multiplexing (OFDM). Aiming to improve the secondary users’ secrecy rates, a design problem for jointly optimizing the transmission beamforming of secondary base station (SBS), the IRS’s reflecting coefficient and the channel allocation is formulated under the constraints of the requirements of minimum data rates of primary users and the interference between users. As the scenario is highly complex, it is quite challenging to address the non-convexity of the optimization problem. Thus, a deep reinforcement learning (DRL) based approach is taken into consideration. Specifically, we use dueling double deep Q networks (D3QN) and soft Actor–Critic (SAC) to solve the discrete and continuous action space optimization problems, respectively, taking full advantage of the maximum entropy RL algorithm to explore all possible optimal paths. Finally, simulation results show that our proposed approach has a great improvement in security transmission rate compared with the scheme without IRS and OFDM, and our proposed D3QN-SAC approach is more effective than other approaches in terms of maximum security transmission rate.     

基于改进免疫遗传算法的近红外光谱变量选择方法

该文在免疫遗传算法（IGA）的基础上,提出一种改进免疫遗传算法（iIGA）用于近红外光谱波长变量的选择。该算法舍去了原算法中固定抗体相似度阈值的思想,取而代之的是抗体相似度阈值自适应,同时引入精英保留策略和贪心算法思想,使得算法朝着正确的方向进行局部性探优。将该算法在玉米的淀粉和蛋白质含量数据集上进行实验测试,建立偏最小二乘（PLS）分析模型,并与IGA、遗传算法（GA）以及全谱方法进行了对比。结果表明,在玉米淀粉含量的预测上,iIGA相较于原IGA算法,预测集均方根误差（RMSEP）从0.312 0降至0.298 0,预测集预测精度提升4.5%;在玉米蛋白质含量的预测上,RMSEP从0.124 4降至0.110 3,预测集预测精度提升11.3%。分别对预测淀粉和蛋白质模型的RMSEP值进行显著性检验,F值分别为165.22和182.05,P值分别为9.5 × 10－23和4.5 × 10－24,P值均小于0.05,因此,iIGA能显著提升模型预测精度。     

A novel water-soluble AIE-based fluorescence probe with red emission for the sensitive detection of heparin in aqueous solution and human serum samples

Heparin is widely used to anticoagulation treatment in clinic, while the overdoses of heparin can cause potentially catastrophic complications. Thus, the selective and sensitive detection of heparin is of great importance. Herein, a novel water-soluble AIE-based fluorescent probe (TIBI) with red emission (650 nm) has been rationally developed to detect heparin by the electrostatic-interaction and ion replacing strategy. TIBI exhibited excellent selectivity and low detection limit (0.08 μM) for detection of heparin. Moreover, TIBI was successfully applied to detect heparin in complicated serum samples with satisfactory results. This study holds great promise for real time monitoring heparin in clinical application.     

交换L*-环

我们证明一个交换整环或交换局部环是一个L*-环当且仅当它是一个O*-环.文中还证明了一些一般性的条件使之一个交换环不是L*.