改进的PNC方法及其在非线性偏微分方程多解问题中的应用

2017年，李昭祥等提出了一种偏牛顿-校正法（Partial Newton-Correction Method，简记为PNC方法），并利用它成功地计算出了三类非线性偏微分方程的多重不稳定解.本文在PNC方法的基础上，提出并发展了一种改进的PNC方法.首先，利用Nehari流形$\mathcal{N}$与零平凡解的可分离性，建立并证明了$\mathcal{N}$的某特殊子流形$\mathcal{M}$上的全局分离定理及其推广（即局部分离定理）.全局分离定理只跟非线性偏微分算子或相应的非线性泛函本身有关，而与具体的计算方法无关.对一些典型的非线性偏微分方程多解问题（比如，Henon方程问题），该全局分离定理的分离条件，经验证是成立的.另一个方面，通过修改或补充原辅助变换的定义，去掉了原辅助变换的奇异性；接着建立并证明了某些非线性偏微分方程问题的新未知解与该非线性偏微分算子零核空间的密切关系；在证明中，去掉了在原奇异变换下所需的标准收敛（standard convergence）假设.最后，计算实例与数值结果验证了改进的PNC方法的可行性和有效性；同时表明子流形$\mathcal{M}$与已知解的可分离性是PNC方法和本文新方法能成功找到多解的关键.     

两个基于2,5-二甲氧基对苯二甲酸和咪唑衍生物的超分子钴配位聚合物的结构及光催化反应

本文以咪唑衍生物为配体,通过水热合成法与钴离子制备出两个配位聚合物:{[Co(DTA)(1,4-DIB)(H₂O)]·H₂O}_n(1)和[Co(DTA)(1,3-BMIB)]_n(2)(1,4-DIB=1,4-二(1H-咪唑-1-基)苯; 1,3-BMIB=1,3-二(4-甲基-1H-咪唑-1-基)苯;H₂DTA=2,5-二甲氧基对苯二甲酸)。利用X射线单晶衍射、粉末衍射、热失重、元素分析、红外光谱以及固体紫外-可见光谱等对两个配合物进行了表征。结构分析证实配合物1和2是通过二维结构堆积成的三维超分子化合物。粉末衍射测试则显示两个配合物在水中有很好的稳定性。固体紫外-可见光谱显示两个配合物属半导体材料,对紫外-可见光有很强的吸收作用。在光催化实验中,配合物1和2可加快亚甲基蓝的降解速度。     

超导磁共振仪器设备国产化现状及挑战

磁共振在化学分析和医学影像等领域发挥着不可或缺的作用，而磁共振仪器设备是开展磁共振研究的必要前提.长期以来，国外仪器厂商在我国磁共振仪器市场居于垄断地位.近年来，随着我国在磁共振仪器研发和产业化方面不断取得进展，市场份额为外商垄断的局面已大为改观.本文调研综述了我国磁共振仪器设备研制的现状，以及面临的若干挑战.     

移动加热器法生长碲锌镉晶体的组分输运与界面形貌研究

移动加热器法(THM)生长碲锌镉晶体时,界面稳定性对晶体生长的质量有很大影响。本文基于多物理场有限元仿真软件Comsol建立了THM生长碲锌镉晶体的数值模拟模型,讨论了Te边界层与组分过冷区之间的关系,对不同生长阶段的物理场、Te边界层与组分过冷区进行仿真研究,最后讨论了微重力对物理场分布的影响,并对比了微重力与正常重力下的生长界面形貌。模拟结果表明,Te边界层与组分过冷区的分布趋势是一致的,在不同生长阶段,流场中次生涡旋的位置会发生移动,从而导致生长界面的形貌随着生长的进行发生变化,同时微重力条件下形成的生长界面形貌最有利于单晶生长。因此,在晶体生长的中前期,对次生涡旋位置的控制和对组分过冷的削弱,是THM生长高质量晶体的有效方案。     

Catalytic Chemosensing Assay for Selective Detection of Methyl Parathion Organophosphate Pesticide

Herein, a catalytic chemosensing assay (CCA), based on a bimetallic complex, [Ru^II(bpy)₂(CN)₂]₂(Cu^II)₂ (bpy=2,2′-bipyridine), is described. This complex integrates a task-specific catalyst (Cu^I-catalyst) and a signaling unit ([Ru^II(bpy)₂(CN)₂]) to specifically hydrolyze methyl parathion, a highly toxic organophosphate (OP) pesticide. The bimetallic complex catalyzed the hydrolysis of the phosphate ester to generate o,o-dimethyl thiophosphate (DTP) anion and 4-nitrophenolate. Intrinsically, 4-nitrophenolate absorbed UV/Vis light at λ_max=400 nm, creating the first level of the chemosensing signal. DTP interacted with the original complex to displace the chromophore, [Ru^II(bpy)₂(CN)₂], which was monitored by spectrofluorometry; this was classified as the second level of chemosensing signal. By integrating both spectroscopic and spectrofluorometric signals with a simple AND logic gate, only methyl parathion was able to provide a positive response. Other aromatic and aliphatic OP pesticides (diazinon, fenthion, meviphos, terbufos, and phosalone) and 4-nitrophenyl acetate provided negative responses. Furthermore, owing to the metal-catalyzed hydrolysis of methyl parathion, the CCA system led to the detoxification of the pesticide. The CCA system also demonstrated its catalytic chemosensing properties in the detection of methyl parathion in real samples, including tap water, river water, and underground water.     

C−C Bond Formation of Benzyl Alcohols and Alkynes Using a Catalytic Amount of KOtBu: Unusual Regioselectivity through a Radical Mechanism

We report a C?C bond‐forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO^tBu to form α‐alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.     

Enantioselective C−H Activation with Earth‐Abundant 3d Transition Metals

Molecular syntheses largely rely on time‐ and labour‐intensive prefunctionalization strategies. In contrast, C?H activation represents an increasingly powerful approach that avoids lengthy syntheses of prefunctionalized substrates, with great potential for drug discovery, the pharmaceutical industry, material sciences, and crop protection, among others. The enantioselective functionalization of omnipresent C?H bonds has emerged as a transformative tool for the step‐ and atom‐economical generation of chiral molecular complexity. However, this rapidly growing research area remains dominated by noble transition metals, prominently featuring toxic palladium, iridium and rhodium catalysts. Indeed, despite significant achievements, the use of inexpensive and sustainable 3d metals in asymmetric C?H activations is still clearly in its infancy. Herein, we discuss the remarkable recent progress in enantioselective transformations via organometallic C?H activation by 3d base metals up to April 2019.     

Heterogeneous copper‐catalyzed oxidative coupling of oxime acetates with sodium sulfinates: An efficient and practical synthesis of β‐keto sulfones

An efficient and practical route to β‐keto sulfones has been developed through heterogeneous oxidative coupling of oxime acetates with sodium sulfinates by using an MCM‐41‐supported Schiff base‐pyridine bidentate copper (II) complex [MCM‐41‐Sb,Py‐Cu (OAc)₂] as the catalyst and oxime acetates as an internal oxidant, followed by hydrolysis. The reaction generates a variety of β‐keto sulfones in good to excellent yields. This new heterogeneous copper (II) catalyst can be easily prepared via a simple procedure from readily available and inexpensive reagents and exhibits the same catalytic activity as Cu (OAc)₂. MCM‐41‐Sb,Py‐Cu (OAc)₂ is also easy to recover and is recyclable up to eight times with almost consistent activity.     

Synergistic Effects of Pseudocolor Imaging,Differentiation, and Square and Logarithmic Conversion on Accuracy of Quantification of Chemical Characteristics Using Test Strips and Similar Products

Test strips and similar products are highly feasible tools for the rapid and approximate determination of chemical characteristics. Although the application of both the quantitative observation of coloration and regression modeling has recently enabled these products to become quantitative tools, their precision and accuracy may be further improved. In this study, the pseudocolor imaging of the coloration image, derivative spectrophotometry-like differentiation of the coloration values, and logarithmic conversion of the raw and derivative values were compared in terms of the precision and accuracy of the quantitative determination of corrosiveness, glucose, nitrate, and pH using the products. The best regression models for the determination were provided by the combination of pseudocolor imaging and differentiation (nitrate and pH); pseudocolor imaging, differentiation, and square-conversion (corrosiveness); or all of the techniques (glucose). When compared to the use of the original 10 raw coloration variables of red-green-blue, cyan-magenta-yellow-key black, and L*a*b* color models only, the above combinations improved the normalized mean absolute error from 14.8% to 3.09% (corrosiveness), 6.33% to 3.15% (glucose), 7.46% to 4.56% (nitrate), and 3.22% to 0.94% (pH). These achievements were largely attributed to the combination of multiple variables that have non-linear and nonmonotonic relationships with the chemical characteristics.