高压烧结制备Tb掺杂n型(Bi1–xTbx)2(Te0.9Se0.1)3合金及其微结构和热电性能

采用高压烧结技术制备了稀土元素Tb掺杂的n型Bi2Te2.7Se0.3基纳米晶块体热电材料.将高压烧结成型的样品于633 K真空退火36 h.研究了Tb掺杂量对样品的晶体结构和热电性能的影响.结果表明,高压烧结制备的样品为纳米结构, Tb掺杂使样品的晶胞体积变大,功率因子增大,热导率降低,从而使ZT值提高.Tb掺杂量为x=0.004是最优的掺杂量,该掺杂量的高压烧结样品经退火处理后,于373 K时ZT值达到最大为0.99,并且在323-473 K范围内, ZT值均大于0.8,这对用于温差发电领域具有重要意义.     

Optimization of Active Sites via Crystal Phase,Composition, and Morphology for Efficient Low-Iridium Oxygen Evolution Catalysts

Reducing the amount of iridium in oxygen evolution electrocatalysts without compromising their catalytic performances is one of the major requirements in proton-exchange-membrane water electrolyzers. Herein, with the help of theoretical studies, we show that anatase-type TiO₂-IrO₂ solid solutions possess more active iridium catalytic sites for the oxygen evolution reaction (OER) than IrO₂, the benchmark OER catalyst. Note that the same is not observed for their rutile-type counterparts. However, owing to their thermodynamic metastability, anatase-type TiO₂-IrO₂ solid solutions are generally hard to synthesize. Our theoretical studies demonstrate that such catalytically active anatase-type solid-solution phases can be created in situ on the surfaces of readily available SrTiO₃-SrIrO₃ solid solutions during electrocatalysis in acidic solution as the solution can etch away Sr atoms. We experimentally show this with porous SrTiO₃-SrIrO₃ solid-solution nanotubes synthesized by a facile synthetic route that contain 56 % less iridium than IrO₂ yet show an order of magnitude higher apparent catalytic activity for OER in acidic solution.     

On a Predator–Prey System with Digestion Delay and Anti-predation Strategy

Journal of Nonlinear Science - Predator–prey interactions are among the most complicated interactions between biological species, in which there may be both direct effect (through predation)...     

真空条件下LiCl溶液蒸发量随浓度变化规律研究

除湿溶液再生是除湿空调系统的核心过程,为了提高除湿溶液再生效率,以蒸发量作为评价标准,在不同的真空度下对不同浓度LiCl溶液进行再生。对不同再生条件下,溶液的再生情况进行数学模拟及实验研究,并将模拟结果与实验结果进行对比分析,结果表明,实验结果同模拟结果具有相同的变化趋势。在6 kPa和8 kPa的压强下,LiCl溶液的蒸发量随浓度的增大先上升后下降,而在1 kPa的压强下,LiCl溶液的蒸发量随浓度的增大呈现出先下降再升高接着又下降的趋势。     

LIBS中药材石斛等级识别研究

石斛是一种常用的中药材,经常使用新鲜的或干燥的茎条入药,有益胃生津、滋阴清热的效果。近年来,药理学研究探索出石斛具有抗白内障、抗氧化、抗肿瘤、提高免疫力的作用,其在许多病例中疗效显著,引起了国内外学者的关注,然而不同时间采集的石斛中氨基酸、微量元素等含量各不同,其对应药用价值,价格也不同,因此石斛价格等级分辨的研究具有重要意义。为快速鉴别不同价格、不同药效的石斛,研究了随机森林分类模型结合激光诱导击穿光谱技术(LIBS)对石斛价格等级进行分析建模。选取5个等级的石斛样品进行建模,为了对样品进行精确稳定分析,所有石斛样品均通过粉碎压片减小实验误差。采用1 064 nm波长的Nd∶YAG脉冲激光器作为激发光源,设置激光脉冲能量50 mJ,探测延时1μs,采集五个等级石斛样本的光谱数据,每个等级的样本采集40组光谱,共200组数据,并采用归一化处理,使所有的光谱数据转换到-1~1之间。采用归一化处理后的光谱数据进行主成分分析,通过主成分分析获得前7个主成分的得分矩阵,其累计解释95.24%的光谱信息。将选取的7个主成分作为输入,建立波段为220~880 nm的随机森林鉴别模型。并将石斛样本编号打乱,任意选取50%的光谱数据作为训练集,剩下50%的光谱数据作为测试集,默认决策树个数ntree为500,分裂属性集中属性个数mtry为5,建立模型对不同等级的石斛进行分类。等级一、二、三、四、五的识别率分别为95.45%, 100%, 78.26%, 94.12%和85%,平均识别率为90.57%。为提高识别率,研究了不同的ntree和mtry对分类模型的影响,利用袋外数据误差率估计对随机森林的两个参数进行了优化。选择ntree为300,mtry为1,等级一、二、三、四、五的识别率分别为100%, 100%, 92.31%, 100%和90%,平均识别率为96.46%,识别率提高了5.89%。综上所述,采用LIBS技术结合优化后的随机森林模型鉴别石斛等级具有一定的可行性,为未来快速鉴定不同价格的石斛等级分类提供了可行性的判别系统。     

Quantitative 31P‐NMR spectroscopy for the determination of fosfomycin and impurity A in pharmaceutical products of fosfomycin sodium or calcium

A quantitative ³¹P‐NMR method for the determination of fosfomycin and impurity A in pharmaceutical products of fosfomycin sodium or calcium has been developed. In this method, coaxial inserts containing trimethyl phosphate are used as external standard. The method is convenient and robust, and gives both high accuracy and precision. It is shown that an accurate determination is possible using different probes and coaxial inserts. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Herbicidal Activities of 3‐(4‐Chloro‐2‐fluoro‐5‐substituted phenyl)benzo[d][1,2,3]triazin‐4(3H)‐one Derivatives

A series of 3‐phenyl benzo[d][1,2,3]triazin‐4(3H)‐one derivatives were synthesized through the condensation of phenol E and alkyl (alkenyl, alkynyl) chlorides (bromides, iodide) or alkyl chloroacetates or N‐alkyl chloroacetamides using K₂CO₃ as the acid acceptor in N,N‐dimethylformamide. Phenol E was prepared from starting material, 5‐amino‐2‐chloro‐4‐fluorophenyl ethyl carbonate, in four steps involving in amidation, reduction, diazotization, and deprotecting‐group reaction. The herbicidal activities of the title compounds were tested against two dicotyledonous plants and two monocotyledonous plants, in which some of them exhibited high herbicidal activities against two dicotyledonous plants in preemergence and postemergence treatments. Moreover, when the dosage was decreased to 180 and 90 g/ha, compounds F1 , F8 , and F9 showed highly selective inhibitory activities against amaranth pigweed, alfalfa, asteraceae, field sowthistle, morning glory, purslane, and velvetleaf in postemergence treatment but had no herbicidal efficacy on rape except F1 , suggesting that it be possible to find a kind of herbicides to inhibit dicotyledonous weeds in the field of dicotyledonous crops with the same genus as aforementioned weeds.     

A novel synthetic route to rac-(Z)-recifeiolide from cyclooctanone and acetaldehyde

A novel synthetic approach to (±)-Z-recifeiolide 6, a 12-membered-ring lactone which can be selectively isomerized into (E)-recifeiolide, a natural antibiotic product isolated from fungus (Cephalosporium recifei) is reported. The synthesis is accomplished in five steps starting from readily available cyclooctanone and acetaldehyde based on the Lewis acid-catalyzed TMS-directed oxy-2-oxonia-Cope rearrangement. The work represents a novel strategy to assemble related macrolides.