时滞中立型神经网络全局渐近稳定性

针对具有时变时滞的中立型Hopfield神经网络,在对时变时滞的合理假设下,文中通过构造适当的Lyapunov泛函,提出了一种新的方法判定时变时滞中立型Hopfield神经网络系统的全局一致渐近稳定性。所得判据是建立在一个代数Riccati方程及其对应离散Lyapunov方程存在对称正定解之上的,并得出了易于计算机仿真实现的线性矩阵不等式的判据形式,仿真验证了结果的有效性。     

偕胺肟基功能高分子膜吸附铀量的测定

以偶氮氯膦Ⅲ(CPAⅢ)作为显色剂,研究可见光分光光度计测定含偕胺肟基功能高分子膜螯合电极对铀酰离子的吸附量的实验方法。确定了分光光度法测定的铀酰离子吸附量的实验条件:吸收光波长670 nm,CPAⅢ标准溶液(0.001 mol.L-1)的用量3mL,测定体系的最佳pH值1.0,室温下显色时间2 min。在此实验条件下,绘制了铀的工作曲线,并得到摩尔吸光系数为ε=29 750 mol-1.L.cm-1。对比电子能谱法所测定的脱附铀前后的螯合电极表面的铀含量(脱附前后亮区铀含量分别为38.12%和6.29%,暗区铀含量都为零),得到分光光度计法测定的铀含量并不是螯合电板表面的真实铀含量,但却是脱附下来的铀的真实量,这肯定了分光光度法测定铀的吸附量优势所在。     

用三元络合物萃取-火焰原子吸收法测定食品中痕量镉

建立了一种测定食品中痕量镉的新方法.以茜素黄R和邻菲罗啉为螯合剂,以甲基异丁基甲酮为萃取剂,直接以有机相进样测定,提高了测定的选择性和灵敏度.考察了介质酸度、缓冲溶液及螯合剂的用量等对测定的影响,优化了测定条件.详细研究了常见元素对镉元素测定的干扰情况,用酒石酸钾钠做掩蔽剂,可以消除大量共存组分的影响.在最佳工作条件下,镉离子质量浓度在3.0×10-3 ～0.25 μg·mL-1范围内线性关系良好,方法的检出限为1.7×10-3 μg· mL-1,对0.2 μg· mL-1的镉标准溶液进行9次平行测定,相对标准偏差为1.1％,检出限低,重现性好.该法用于食品中镉的测定,结果满意.     

Preparation of composite particles made from solid powders and wasted plastics by semichemical recycle method

Composite particles composed of solid powders and polymer were prepared by semichemical recycle of wasted plastics. Waste expanded polystyrene was used as raw materials of polymer matrix of composite particles. Both magnetite and silicon carbide powders were used as solid powders to give thermal and electric conductivity and magnetization, respectively. In the experiment, the oil‐phase dissolving expanded polystyrene was dispersed in fine droplets into the continuous water phase. Two kinds of powders were added at the same time or separately in the O/W dispersion. Composite particles were found to have the structure that polymer particle was covered with two kinds of solid powders. The mean diameter of composite particles and the content of each solid powder were strongly affected by the addition time when silicon carbide powder was added into the dispersion. Furthermore, it was found that the gradient adhesion layer due to two solid powders was able to be formed on the surface of polymer particle. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 483–488, 2003     

Silver catalysts supported over activated carbons for the selective oxidation of CO in excess hydrogen: effects of different treatments on the supports

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N₂ adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H₂ were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.     

Preparation of micron‐size monodispersed PS/P(St/MAA) microspheres by seeded dispersion polymerization

Uniform polystyrene (PSt) particles with the size of 1.9 μm were first prepared via dispersion polymerization, and then used as the seeds in a second‐stage dispersion copolymerization of styrene (St) and methacrylic acid (MAA) to produce carboxyl‐carrying microspheres. The PSt seed particles were swollen by monomer mixture of St and MAA, including an oil‐soluble initiator 2,2′‐azobisiso‐butyronitrile (AIBN), before polymerization. Finally, uniform PS/P(St/MAA) (polydispersity index, PDI = 1.02) microspheres with the size of 2.2 μm were obtained. The average particle size and size distribution of the final microspheres were investigated. MAA contents between 54 and 97 mg/g were detected from the PS/P(St/MAA) particles produced under different conditions. Dispersion medium has great influence on the kinetics of polymerization, due to its effect on the partitioning of monomers, solvents, and initiator in the particle phase, probably as well as on the conformation of the dispersion agent on the surface of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3586–3591, 2006     

具有“强积分小”系数的二阶泛函微分方程解的振动性质

本文研究下列二阶泛函微分方程解的振动性质: (r(t)x′(t))′+q(t)x′(t)+M(t,x(g(t)))=0给出了方程(*)存在非振动解的必要条件以及存在振动解的充分判据。     

Delay‐dependent stability of nonlinear hybrid neutral stochastic differential equations with multiple delays

In this article, we study the delay‐dependent stability of a class of hybrid neutral stochastic differential equations (NSDEs) with multiple delays which is highly nonlinear. Some novel stability criteria are investigated according to Lyapunov functions and generalized Itô's formula. In particular, we generalize and improve the results in Shen et al, Systems & Control Letters (2018) from a single delay to multiple delays.     

认知任务驱动的fMRI脑功能网络构建方法

针对脑功能网络的构建受到特定大脑图谱对兴趣点描述准确度及覆盖度的限制,提出了基于认知任务信息和神经影像数据的脑功能网络构建方法。首先计算fMRI体素对于认知任务的敏感度,然后在此基础上选取兼顾分布均衡和去中心化的大脑兴趣点,从而构建任务驱动的脑功能网络。实验通过在人脸情绪识别认知任务相关的梭状回构造任务驱动的脑功能网络,其度中心性、聚类系数、全局效率、局部效率这四个复杂网络指标均优于典型大脑图谱梭状回中兴趣点构成的网络。结果表明,计算得到的大脑兴趣点具有更强的整合性,更适合用于表征特定认知任务下的脑功能网络。     

Broadband terahertz spectroscopy of amino acids

Broadband spectra of 20 L-amino acids were obtained at room temperature by terahertz time-domain and infrared spectroscopy. The intensity of terahertz absorption peaks varied with the concentrations of amino acids, and the optimum proportion for each amino acid was obtained. An absorption spectral database of 20 L-amino acids was established from 0 to 6 THz. The associations between terahertz absorption peaks and molecular structures of amino acids were analyzed. The terahertz spectra for L-alanine were compared with the calculated results based on density functional theory using two basis sets that were reliably consistent.