基于严格α-双链对角占优矩阵的非奇H-矩阵的判定准则

研究了非奇H-矩阵的判定问题.先给出了几个判定严格α-双链对角占优矩阵的充要条件,进一步利用矩阵对角占优理论得到了判定非奇H-矩阵的一些充分条件,推广和改进了已有的相关结果,并用数值算例说明了这些判定方法的有效性.     

改进种群多样性的双变异差分进化算法

差分进化算法(DE)是一种基于种群的启发式随机搜索技术,对于解决连续性优化问题具有较强的鲁棒性.然而传统差分进化算法存在种群多样性和收敛速度之间的矛盾,一种改进种群多样性的双变异差分进化算法(DADE),通过引入BFS-best机制(基于排序的可行解选取递减策略)改进变异算子"DE/current-to-best",将其与DE/rand/1构成双变异策略来改善DE算法中种群多样性减少的问题.同时,每个个体的控制参数基于排序自适应更新.最后,利用多个CEC2013标准测试函数对改进算法进行测试,实验结果表明,改进后的算法能有效改善种群多样性,较好地提高了算法的全局收敛能力和收敛速度.     

On the stability of tangent bundle on double coverings

Let Y be a smooth projective surface defined over an algebraically closed field k with char k≠2, and let π : X →Y be a double covering branched along a smooth divisor. We show that y_X is stable with respect to π~*H if the tangent bundle y_Y is semi-stable with respect to some ample line bundle H on Y.     

层状复合氢氧化物的有机改性方法及应用研究进展

层状复合氢氧化物(LDHs)因其化学组成可调、比表面积大、生物相容性好等特点,目前在环境、能源和生物医药等领域广受关注.然而, LDHs在合成过程中由于其分子内作用力易发生团聚而导致其在基体中的分散不均匀,极大地限制了LDHs在实际中的应用.有机改性是改善LDHs分散性的有效方法,从表面改性和插层改性两个方面综述了近年来LDHs的有机改性方法,并介绍了其在阻燃、吸附、催化、气体阻隔、发光、储能和生物医药材料等领域的应用.最后对改性后LDHs未来的研究方向和应用领域进行了展望.     

Computational Mechanism Investigation of C=C Bond Hydrogenation Catalyzed by Rhodium Hydride

The hydrogenation of unsaturated carbons is a commonly used synthetic tool in pharmaceutical and industrial production. Recently, the Norton group realized highly selective hydrogenation of C=C bonds catalyzed by a rhodium hydride. Despite the great efforts made by experimentalists, details regarding the mechanism remained unclear. In this work, detailed DFT calculations were carried out to elucidate the principal features of this transformation. For enones we find that two possible competing mechanisms proposed by the experimental groups are computationally excluded, our proposed alternative mechanism with a total barrier of 20.0 kcal mol⁻¹ is theoretically feasible, solvent methanol to also plays a crucial role in assisting β-hydrogenation in addition to being the hydrogen source for α-hydrogenation, and the cross-polarization of the substrate enone-conjugated system to result in an enhanced charge density of the α-carbon, which favors being hydrogenated first. For isolated alkenes, neither of the two possible competing mechanisms can be excluded computationally and which carbon atom is first hydrogenated depends on the electronic properties of the substrate itself. The combination of rhodium and C=C bonds changes the electronic properties of H on the rhodium hydride and enhances its hydrogenation activity.     

Electronic and optical properties of quaternary selenides for optoelectronic applications: Insights from DFT+U-computations

The optical properties, electronic charge density, electronic structure of the new layered selenides materials, BaGdCuSe₃, CsUCuSe₃, CsZrCuSe₃, and CsGdZnSe₃ compounds have been calculated by using the full potential and linear augmented plane wave (FP-LAPW) methods as applied in the WIEN2k package, which is based on the density functional theory. The ALnMSe3 compound's structure of these was (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of (n = 1, 2) layers, which might be separated by A atoms. It is to be observed that there is strong hybridization between the s, p, and d states of Zr, Gd, and Cu atoms. Around the gadolinium atom, the charge density contours are completely circular, but the Gadolinium “Gd” atom shows an ionic nature. To calculate the refractive index, we used Kramer's Kronig correlations with the imaginary part dielectric function. The decrease in the refractive index is due to the lack of probability for direct excitation of the electrons, resulting in a loss of energy. The value of the static refractive index for all reference compounds is about 1.75–2.25, which is indication that the material used in optoelectronic devices.     

An Efficient Novel Electrochemical Sensor for Simultaneous Determination of Vitamin C and Aspirin Based on a PMR/Zn-Al LDH/GCE

A sensitive, low-cost, and simple electrochemical sensor based on Zn−Al layered double hydroxide (Zn−Al LDH) combined with a polymer film of methyl red (PMR) to modify a GCE has been created for the first time. Using cyclic voltammetry (CV), the electrochemical characteristics of the newly fabricated sensor were investigated. The characterised PMR/Zn−Al LDH/GCE shows high electro-catalytic activity towards the vitamin C (AA) and aspirin (ASA) oxidation. Schematic fabrication of PMR/Zn−Al LDH/GCE for the determination of AA or ASA was presented. The new sensor demonstrated superior analytical efficiency for the simultaneous identification of AA and ASA traces in well-spaced anodic peaks, even in the presence of certain intervening species. According to experimental results, the fabricated sensor represented two well-separated oxidation peaks for AA and ASA oxidation with potential difference of 799 mV (vs. Ag/AgCl). The linear dependences of the anodic peak currents of AA and ASA on their concentrations in the ranges of 0.10–53.17 μM are good. The detection limits of AA and ASA at the PMR/Zn−Al LDH/GCE were found to be 1.26 and 1.27 μM, respectively. Meanwhile, the quantification limits of AA and ASA were calculated as 4.21 and 4.25 μM, respectively. On other hand, the limit of detection (LODs) of AA and ASA oxidation were determined to be 0.47 and 0.21 μM, respectively, according to DPV method. The effect of scan rate (100 to 800 mV/s) on the anodic peak currents of AA and ASA was examined. A sensing model mechanism has been suggested and discussed in detail. Finally, the proposed sensor displayed a good reproducibility, stability and selectivity. The developed sensor was eventually used to successfully detect AA and ASA in urine samples.     

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH₄ + CO₂ hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH₄ + CO₂ hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.     

Toxicity of Zn-Fe Layered Double Hydroxide to Different Organisms in the Aquatic Environment

The application of layered double hydroxide (LDH) nanomaterials as catalysts has attracted great interest due to their unique structural features. It also triggered the need to study their fate and behavior in the aquatic environment. In the present study, Zn-Fe nanolayered double hydroxides (Zn-Fe LDHs) were synthesized using a co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption analyses. The toxicity of the home-made Zn-Fe LDHs catalyst was examined by employing a variety of aquatic organisms from different trophic levels, namely the marine photobacterium Vibrio fischeri, the freshwater microalga Pseudokirchneriella subcapitata, the freshwater crustacean Daphnia magna, and the duckweed Spirodela polyrhiza. From the experimental results, it was evident that the acute toxicity of the catalyst depended on the exposure time and type of selected test organism. Zn-Fe LDHs toxicity was also affected by its physical state in suspension, chemical composition, as well as interaction with the bioassay test medium.