电流退火铁基薄带巨磁阻抗效应的影响

研究了电流退火工艺对铁基非晶合金Fe₈₄Zr₈Nb_3.5B_3.5Cu_{1〈/sub>薄带巨磁阻抗效应的影响.实验结果表明,该铁基合金的巨磁阻抗ΔZ/Z随退火电流的增加而增强,当电流为820mA时,ΔZ/Z达到最大值62％,阻抗变化灵敏度可达约0.23％（A/m)^-1.结合此合金在电流退火燧后电性能和软磁性能的演变,讨论了材料的巨磁阻抗效应借助趋肤效应与交流频率和外加纵向磁场的关系. 关键词：}     

卟啉基超交联聚合物的合成及其对二氧化碳和汞(Ⅱ)离子的吸附北大核心CSCD

超交联聚合物(HCPs)具有较高的比表面积和独特的孔结构,且制备方法简单、合成原料广泛,是多孔有机聚合物的研究热点之一。卟啉是一类由4个吡咯类亚基的α-碳原子通过次甲基桥互联形成的大分子杂环化合物,可与多种金属形成稳定的配合物,在重金属的吸附与检测、气体的吸附与分离等方面具有很好的应用。卟啉结构的HCPs也有了较多的报道,然而当前报道的卟啉结构HCPs几乎均是通过Friedel-Crafts烷基化反应构筑的。Friedel-Crafts酰基化反应在卟啉结构HCPs上报道较少。而通过Friedel-Crafts酰基化反应制备的聚合物表面含大量羰基,为其进一步功能化提供了可能。但是,这类聚合物的比表面积低、孔结构差,而其优良孔结构的构建是亟待解决的问题。为此,本文在四苯基卟啉与1,2,4,5-苯四甲酸酐通过Friedel-Crafts酰基化反应制备的聚合物的基础上,进一步通过席夫碱反应,用含刚性三嗪环的三聚氰胺将其进一步交联,合成了三聚氰胺修饰的卟啉基超交联聚合物。结果发现,三聚氰胺的引入不仅实现了超交联聚合物孔结构的支撑,使得聚合物比表面积极大增长(从2 m^(2)/g增加到118 m^(2)/g),且具有优良的多级孔结构。三聚氰胺修饰卟啉基超交联聚合物的高氮质量分数(46.28%)和多级孔结构使其对CO_(2)(93 mg/g,273 K,101 kPa)和Hg^(2+)(494.1 mg/g,298 K)具有较好的吸附。     

宇宙中的暗物质及大尺度结构的形成——暗物质成分及成团图景

宇宙间的物质绝大部分是不可视的。这些暗物质成分不是单一的,对大尺度结构的形成起着关键的作用。在含有多种成分的宇宙中,一种重要的成团特性是:若成分1和2的密度和Jeans长度满足ρ₁《ρ₂,λ_1J《λ_2J,则非主导成分1中尺度小于λ_2J的非均匀性,无论初始如何,最终总是强于主导成分中的相应非均匀性。利用这一机制可以推断,暗物质至少含有两种成分,一是静质量较小的弱粒子,构成主导成分,一是质量较大的超弱粒子,构成非主导成分。含有两种暗物质的宇宙,可以统一地解释大尺度结构的主要特征:1.超星系团和巨洞构成的100Mpc非均匀性;2.存在红移z>2的可视天体;3.在小于超星系团尺度上,暗物质分布较可视天体均匀;4.由矮球星系数据所推知的可能存在两种质量不同的微子。     

黑洞吸积盘中的迅速冷却区及受激复合发射

本文提出了在黑洞吸积盘中有可能存在受激复合发射机制,这种机制将出现于具有迅速冷却区的吸积盘中.这种盘将有相干的H及HeI的线发射.这一模型可以用来自恰地解释所有迄今得到的关于SS433的观测事实.     

Stability Analysis of Gradient-Based Neural Networks for Optimization Problems

The paper introduces a new approach to analyze the stability of neural network models without using any Lyapunov function. With the new approach, we investigate the stability properties of the general gradient-based neural network model for optimization problems. Our discussion includes both isolated equilibrium points and connected equilibrium sets which could be unbounded. For a general optimization problem, if the objective function is bounded below and its gradient is Lipschitz continuous, we prove that (a) any trajectory of the gradient-based neural network converges to an equilibrium point, and (b) the Lyapunov stability is equivalent to the asymptotical stability in the gradient-based neural networks. For a convex optimization problem, under the same assumptions, we show that any trajectory of gradient-based neural networks will converge to an asymptotically stable equilibrium point of the neural networks. For a general nonlinear objective function, we propose a refined gradient-based neural network, whose trajectory with any arbitrary initial point will converge to an equilibrium point, which satisfies the second order necessary optimality conditions for optimization problems. Promising simulation results of a refined gradient-based neural network on some problems are also reported.     

双二茂铁甲氨基醇的合成及其硅烷基化

;双二茂铁甲醇;硅基化;双二茂铁甲氨基醇的合成及其硅烷基化     

Preparation of Gd-Ni Film Alloy in Urea-NaBr Melt

Gd in 4f lanthanon has ferromagnetic-paramagnetism transform temperature (Curie point) and the highest magnetic thermal entropy change at room temperature. So far, it is still the best magnetic refrigeration working substance material. The systems of urea with some alkali metal salts have lower melting point (301~389 K)^[1], greater solubility of metal chloride and higher conductivity^[2]. In this paper, the electrode processes of Ni (Ⅱ) reduced in urea-NaBr melt, electrodeposition of nickel with gadolinium, and the surface morphology and the structural states of electrodeposited films and films after heat treatment have been investigated.     

A Study of the Dual Affine Scaling Continuous Trajectories for Linear Programming

In this paper, a continuous method approach is adopted to study both the entire process and the limiting behaviors of the dual affine scaling continuous trajectories for linear programming. Our approach is different from the method presented by Adler and Monteiro (Adler and Monteiro, Math. Program. 50:29–51, 1991). Many new theoretical results on the trajectories resulting from the dual affine scaling continuous method model for linear programming are obtained.     

新型锂离子电池正极材料LiVOPO4的制备与表征

Novel lithium-ion battery cathode material LiVOPO₄ was synthesized by sol-gel method using lithium hydroxide, ammonium metavanadate, phosphoric acid and citric acid as raw materials. The microstructure, surface morphology and electrochemical properties were characterized by various electrochemical methods in combination with thermogravimertric (TG) analysis and differential thermal analysis (DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscope (SEM). Results show that the sample obtained by calcinating at 650 ℃ for 6 h is made up of uniform particles with size of 2～3 μm. The first discharge, charge capacity and columbic efficiency of LiVOPO₄ is 137.1 mAh·g^-1, 146.1 mAh·g^-1 and 93.8%, respectively. After 80 cycles the discharge capacity is kept at 130.4 mAh·g^-1, which is 95.1% of the first discharge capacity, and the capacity loss per cycle was only 0.061%, suggesting the LiVOPO₄ derived by this method is a promising cathode material for lithium ion batteries.     

{[Nd4(ox)4(NO3)2(OH)2(H2O)2].5H2O}n: a porous 3D lanthanide-based coordination polymer with a special luminescent property

Unique bridging modes of oxalates and nitrates have unexpectedly caused a porous 3D lanthanide-based coordination polymer, which has 1D channels and displays a special luminescent property.