约束端面对管内甲烷爆炸特性的影响

为研究不同约束端面下甲烷的爆炸特性,利用自行搭建的实验平台完成了多种约束端面下不同浓度甲烷的爆炸实验。研究表明:约束端面的性质对甲烷的爆炸特性有显著影响,约束端面的承压强度越高,甲烷的爆炸超压越大。单层PVC薄膜作用下,薄膜破裂,不会引起火焰与超压的振荡;而纸膜破裂后,管道内外气流的高速泄放和回流则会引起超压振荡,使火焰前锋波动并发生扭曲变形;两者共同作用时,PVC薄膜会阻碍气流的泄放与回流,加速超压衰减,抑制火焰和超压的振荡。然而,随着纸膜层数增加,破膜时管道内外形成的巨大压差会使约束端面完全破裂,降低PVC薄膜的抑制作用。当破膜难度达到一定程度时,约束端面作用下的泄压峰值成为不同浓度甲烷爆炸的最大超压峰值,且泄爆压力并不随甲烷浓度的改变而改变,因此不同浓度甲烷的爆炸超压在较高的泄爆压力下相同;此时,相同约束端面下不同浓度甲烷的压力振荡曲线在压力衰减的前半个周期内完全重合,管道内外的压差成为主导超压振荡的重要因素,而不同浓度甲烷的燃烧速率对超压振荡的影响则可以忽略不计。     

基于冠层尺度的枣树色素含量的高光谱估算模型

植物冠层色素含量与氮素含量具有高度的相关性,是农业遥感中的关键研究因素。本研究的主要目的是：(1)对比偏最小二乘回归和支持向量机两种建模方法对枣树冠层色素的预测精度;(2)构建基于高光谱数据的枣树冠层色素含量定量反演模型,为枣树冠层色素含量的快速、无损、廉价、环保的测定提供一定的理论依据和技术支持。相关性分析结果表明,枣树冠层色素与高光谱数据之间具有较好的相关性,但叶绿素、叶绿素a要优于叶绿素b和类胡萝卜素。独立样本对模型的预测性能检验结果表明,偏最小二乘回归和支持向量机均能有效的估算枣树色素含量,但不同色素的偏最小二乘回归模型和支持向量机模型的预测精度存在一定的差异,叶绿素和类胡萝卜素的支持向量机模型的预测精度要高于偏最小二乘回归模型,而叶绿素a和叶绿素b则相反。比较不同色素的最佳反演模型的预测精度表明,叶绿素、叶绿素a和类胡萝卜素的预测精度要优于叶绿素b,前三者的决定系数大于0.8,残余预测误差高于2.0,平均相对误差低于13%,而叶绿素b的对应值分别为0.60%,20.79%和1.79%。     

4-[(E)-2-(3, 4-二甲氧基苯基)乙烯基]苯氧基乙酸乙酯的合成及其NMR研究

以对硝基甲苯、3, 4-二甲氧基苯甲醛为起始原料,经过缩合,还原,重氮化水解,亲核取代反应,最终合成了新的化合物4-[(E)-2-(3, 4-二甲氧基苯基)乙烯基]苯氧基乙酸乙酯,用¹H 和¹³C NMR及多种二维核磁共振谱确定了该化合物的结构,完成了¹H 和¹³C NMR的归属,给出了分子中各氢,碳原子的准确化学位移.     

Nitrogen Dioxide Sensing Properties and Mechanism of Copper Phthalocyanine Film

Copper phthalocyanine film, a p-type organic semiconductor, is synthesized by vacuum sublimation and its surface morphology is characterized by SEM. A silicon-based copper phthalocyanine film gas sensor for NO2 detection is fabricated by MEMS technology. The results show that the resistance and sensitivity of copper phthalocyanine film decrease obviously as the NO2 concentration increases from Oppm to lOOppm. However, the sensitivity nearly keeps a constant of O. 158 between 30 ppm and 70 ppm. The best working temperature of the gas sensor is 90℃ for NO2 gas concentrations of lOppm, 20ppm and 30ppm, which is much lower than that of general metal oxide gas sensor.     

The existence and stability of bulk nanobubbles:a long-standing dispute on the experimentally observed mesoscopic inhomogeneities in aqueous solutions

In theory,nanobubbles can stably exist with a lifetime of microseconds at most,but numerous experimental observations demonstrate that nanobubbles in bulk solution can be stable from hours to weeks.Although various conjectures on the stability mechanism of bulk nanobubbles,such as the contaminant mechanism,skin mechanism,surface zeta potential mechanism,are proposed,there has not yet been a unified conclusion.Since bulk nanobubbles show great potential in a wide spectrum of applications and are relevant to a number of unsolved questions on cavitation and nucleation,the debate over their stability mechanisms has been active.In the past,extensive studies have been carried out to understand the mechanism of nanobubble stability,and important insights have already been provided.This paper will provide a brief overview of our current understanding of the unexpected stability of bulk nanobubbles.     

Examples of entropy generating sequence

We introduce the notion of entropy generating sequence for infinite words and define its dimension when it exists. We construct an entropy generating sequence for each symbolic example constructed by Cassaigne such that the dimension of the sequence is the same as its topological entropy dimension. Hence the complexity can be measured via the dimension of an entropy generating sequence. Moreover, we construct a weakly mixing example with subexponential growth rate.     

蓝青铜K0.3MoO3单晶Peierls相变研究

测量了蓝青铜K_0.3MoO₃单晶Ｒ-Ｔ曲线，发现曲线在２８０Ｋ左右有异常变化，计算得到１８０Ｋ以下的半导体能隙为１３２０Ｋ（０.１１ｅＶ）．液氮温度下测量了晶体的非线性导电性，得到电场阈值为０.1２９Ｖ／ｃｍ．样品ＤＳＣ研究表明，样品在２４０Ｋ处经历一新的Ｐｅｉｅｒｌｓ相变，且为一级相变，据此对相变的微观性质进行了定量计算．１８０Ｋ附近Δｃ_p-Ｔ曲线表明，１８０Ｋ处的相变为一个二级相变加一个一级相变 关键词：     

Diversifying vancomycin via chemoenzymatic strategies

[reaction: see text] The rapid diversification of glycopeptides via glycorandomization reveals that significantly diverse substitutions are tolerated and suggests there may be a synergistic benefit to the construction of mechanistically related natural product core scaffold fusions. This work also further highlights the utility of chemoenzymatic approaches to diversify complex natural product architectures.     

Alpha,beta-unsaturated imines from titanium hydroamination and functionalization by rhodium C-H activation

Titanium pyrrolyl complexes are effective catalysts for the synthesis of alpha,beta-unsaturated imines, which can be further functionalized using Rh-catalyzed alkene or alkyne insertion into the beta-C-H bond.     

Nanoscale aryleneethynylene molecular wires with reversible fluorenone electrochemistry for self-assembly onto metal surfaces

[structure: see text] Two rigid-rod conjugated molecules (11 and 12) of ca. 4 and 7 nm length, respectively, bearing protected terminal thiol groups have been synthesized via multistep Sonogashira coupling reactions and shown to possess reversible cathodic solution electrochemistry arising from reduction of the fluorenone units.