溶液样品温度对ICP光源发射强度的影响

通过光电检测法研究了溶液样品温度在20,40和60 ℃条件下,对电感耦合等离子体(ICP)光源发射强度的影响。实验结果表明,随着溶液温度的提高,元素钡、铜和锌的谱线强度有明显的增强。观察了在不同溶液温度下,谱线强度随光源观察高度和载气压力的变化规律, 发现温度的提高使最佳观测高度位置降低,而最佳载气压力升高。     

外场下压力及屏蔽对无限深量子阱中施主结合能的影响

考虑外加磁场、压力及屏蔽效应,利用变分方法数值计算GaN/AlxGa1-xN无限深量子阱系统中的杂质态结合能。给出结合能随磁场和阱宽的变化关系,同时讨论了有无屏蔽时的区别。结果表明:在磁场和压力作用下,结合能随阱宽的增大而减小;阱宽和压力一定时,结合能随磁场的增大而增大。屏蔽效应使得有效库仑吸引作用减弱而导致杂质态结合能显著下降。屏蔽效应对结合能的影响随压力增大而增强,随磁场强度增大而减弱。     

若丹明B荧光增强二硫化碳高阶受激喇曼散射

 利用若丹明B乙醇溶液的荧光改变了二硫化碳的一至三阶Stokes喇曼谱线的强度分布,选择性地增强了三阶Stokes喇曼谱线。在泵浦功率密度为~560MW^.cm^-2时,对染料摩尔浓度分别为~10^-5、cm^-5散射池和~10^-4、1cm散射池进行实验,观察到二硫化碳的三阶Stokes喇曼谱线与染料激光形成的共振增强现象及、二阶Stokes喇曼谱线的部分或完全耗尽。     

分光光度法测定蒙药卷柏中总黄酮含量

采用分光光度法 ,测定了蒙药卷柏中总黄酮的含量 ,检测波长为 5 0 0 nm,校准曲线相关系数为 0 .9996 ,相对标准偏差为 1 .0 1 %,平均加样回收率为 1 0 1 .6 1 %。此法准确度较高 ,为卷柏中黄酮含量测定提供了一种切实可行的方法。     

Coinage metal aluminyl complexes: probing regiochemistry and mechanism in the insertion and reduction of carbon dioxide

The synthesis of coinage metal aluminyl complexes, featuring M–Al covalent bonds, is reported via a salt metathesis approach employing an anionic Al(i) (‘aluminyl’) nucleophile and group 11 electrophiles. This approach allows access to both bimetallic (1 : 1) systems of the type (^tBu₃P)MAl(NON) (M = Cu, Ag, Au; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and a 2 : 1 di(aluminyl)cuprate system, K[Cu{Al(NON)}₂]. The bimetallic complexes readily insert heteroallenes (CO₂, carbodiimides) into the unsupported M–Al bonds to give systems containing a M(CE₂)Al bridging unit (E = O, NR), with the μ-κ¹(C):κ²(E,E′) mode of heteroallene binding being demonstrated crystallographically for carbodiimide insertion in the cases of all three metals, Cu, Ag and Au. The regiochemistry of these processes, leading to the formation of M–C bonds, is rationalized computationally, and is consistent with addition of CO₂ across the M–Al covalent bond with the group 11 metal acting as the nucleophilic partner and Al as the electrophile. While the products of carbodiimide insertion are stable to further reaction, their CO₂ analogues have the potential to react further, depending on the identity of the group 11 metal. (^tBu₃P)Au(CO)₂Al(NON) is inert to further reaction, but its silver counterpart reacts slowly with CO₂ to give the corresponding carbonate complex (and CO), and the copper system proceeds rapidly to the carbonate even at low temperatures. Experimental and quantum chemical investigations of the mechanism of the CO₂ to CO/carbonate transformation are consistent with rate-determining extrusion of CO from the initially-formed M(CO)₂Al fragment to give a bimetallic oxide that rapidly assimilates a second molecule of CO₂. The calculated energetic barriers for the most feasible CO extrusion step (ΔG^‡ = 26.6, 33.1, 44.5 kcal mol⁻¹ for M = Cu, Ag and Au, respectively) are consistent not only with the observed experimental labilities of the respective M(CO)₂Al motifs, but also with the opposing trends in M–C (increasing) and M–O bond strengths (decreasing) on transitioning from Cu to Au.

The differential reactivity of copper, silver and gold aluminyl compounds towards CO₂ and other heteroallenes are probed by experimental and quantum chemical methods.     

Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation

This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni-photoredox amide arylation, which contrasts with other Ni-photoredox C-heteroatom couplings that operate via Ni(I/III) self-sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)-mediated oxidative addition into the aryl bromide. Using NiCl₂ as the precatalyst resulted in an observable induction period, which was found to arise from a photochemical activation event to generate Ni(0) and to be prolonged by unproductive comproportionation between the Ni(II) precatalyst and the in situ generated Ni(0) active species. Ligand exchange after oxidative addition yields a Ni(II) aryl amido complex, which was identified as the catalyst resting state for the reaction. Stoichiometric experiments showed that oxidation of this Ni(II) aryl amido intermediate was required to yield functionalized amide products. The kinetic data presented supports a rate-limiting photochemically-mediated Ni(II/III) oxidation to enable C−N reductive elimination. An alternative Ni(I/III) self-sustained manifold was discarded based on EPR and kinetic measurements. The mechanistic insights uncovered herein will inform the community on how subtle changes in Ni-photoredox reaction conditions may impact the reaction pathway, and have enabled us to include aryl chlorides as coupling partners and to reduce the Ni loading by 20-fold without any reactivity loss.     

How Do Cultural Classes Emerge from Assimilation and Distinction? An Extension of the Cucker-Smale Flocking Model

When cultural tastes are not neutral but hierarchically matched to social status, people assimilate themselves to higher status by consuming cultural goods while distinguishing themselves from lower status by developing new tastes. Extending the Cucker-Smale model for mutual influence among agents, we examine when and how many cultural classes emerge from continuous distributions of tastes and what conditions those classes satisfy, through the assimilation-distinction mechanism. We simulate the models with different initial distributions of tastes (uniform, normal, and chi-square), given various ranges of 2 parameters: (a) the strength and (b) the range of distinction relative to assimilation. Tastes are flocking and cultural classes emerge when the range of assimilation is much larger than that of distinction. The number of classes increases with the strength of distinction, whereas the distance between classes equals the range of distinction. Some properties of emergent classes are mathematically proved. First, in a two-class system, the stronger distinction, the larger the upper class. Second, in a three-class system, the middle class is necessarily larger than the lower class and likely larger than the upper class. Third, a 3-class system cannot emerge if distinction is weaker than assimilation. These properties are universal and do not depend on the initial distribution of cultural tastes. This independence predicts homogeneous cultural classes emerging across different social conditions. Also, the cultural middle class as the largest group may explain why subjective class consciousness is often higher than objective position. Unless assimilating efforts can reach an infinite range, there emerges a cultural outcast at the lowest end of the cultural hierarchy.     

分数阶模糊时滞神经网络模型解的存在唯一性和有限时间稳定性

本文介绍了一类分数阶模糊时滞神经网络模型.利用压缩映射原理,讨论了带时滞的分数阶神经网络模型解的存在性和唯一性,并根据Gronwall不等式结合分数阶微分方程的性质,证明了分数阶神经网络模型平衡点的有限时间稳定性,给出了有限时间稳定性的判断准则.最后,给出数值仿真说明了理论结果的正确性.     

不确定信息处理及在归纳学习中的应用

信息的不确定性是由于模糊性、随机性、不完全性、不精确性等因素造成的,不确定性信息在现实世界中广泛存在.关于这方面的研究主要集中在模糊性这种不确定性上.我们课题组在此领域的研究已经持续20余年,概括起来讲,早期的研究兴趣在于模糊(非可加)测度与积分的理论建立,主要研究了传统的可加测度与积分理论到非可加情况的推广;尔后的兴趣转向为如何用数值方法确定非可加测度;近期的研究兴趣在于从已有数据中获取模糊控制规则以及具有模糊表示的归纳学习问题.近10年的研究曾得到了多项基金项目资助,出版专著3部,发表学术论文100余篇,30余篇被SCI收录,20余篇被EI收录,省级以上奖励3项.以下是我们近期研究工作的一个总结,主要包括模糊决策树归纳;基于模糊信息的决策表简化;产生模糊规则的扩张矩阵算法;模糊归纳学习在其他领域中的应用;基于示例学习的模糊控制等.