CARBON NANOTUBES VIA METHANE DECOMPOSITION ON AN ALUMINA SUPPORTED COBALT AEROGEL CATALYST

An alumina-supported cobalt aerogel catalyst prepared from a sol-gel and a supercritical drying method was used in the catalytic decomposition of methane.The physical-chemical properties of the catalyst were characterized and its activity for methane decomposition was investigated.The effects of calcination and reaction temperatures on the activity of the catalyst and the morphology of the carbon nanotubes produced were discussed.A COAl2O4 spinel structure formed in the calcined catalyst.The quantity of the nanotubes produced in the reaction increases with the amount of cobalt in the reduced catalyst.A higher reaction temperature leads to a higher reaction rate,though faster deactivation of the catalyst occurs with the change.The carbon nanotubes grown on the catalyst have smooth walls and uniform diameter distribution.     

ANALYSIS OF FRICTION INDUCED VIBRATION UNDER THE ACTIVE DISTURBANCE REJECTION CONTROL FRAMEWORK 1)

自抗扰控制(active disturbance rejection control, ADRC)是一种具有两自由度控制结构的工程化方法, 由于其能够直观有效地处理多种扰动, 近些年来在许多机电系统上得到了成功应用. 当采用ADRC对带有摩擦力的机电系统进行调节时, 可能会产生极限环振动. 目前, 还没有ADRC框架下摩擦力振动精确分析的相关工作. 因此, 本文采用非线性动力学系统的分析工具对这一问题进行研究. 首先, 考虑两种典型摩擦力模型, 静态切换模型和动态LuGre 模型, 对一类二阶运动系统设计不同阶次的ADRC, 得到控制器的等效形式, 并揭示出与比例积分微分(proportional-integral-derivative, PID)控制之间的联系. 然后, 采用打靶法结合拟弧长延拓方法求解系统中的极限环, 并根据Floquet理论判断极限环的稳定性、可能出现的分岔以及分岔类型. 此外, 通过雅克比矩阵和近似数值方法对系统平衡点集的局部稳定性进行了分析. 最后, 通过数值计算研究了摩擦力模型和参数、ADRC阶次和参数对极限环和平衡点集的影响. 计算结果表明, 决定摩擦力Stribeck效应负斜率的参数$\beta$作用较大. 当$\beta>1$时, 两种摩擦力模型下的闭环系统呈现出相同的特性, 极限环会出现环面折叠分岔(cyclic fold bifurcation, CFB)且平衡点集是局部稳定的. 然而当$\beta<1$时, 两种闭环系统呈现出完全不同的特性. 此外, 不同阶次的ADRC在极限环的存在性和稳定性、平衡点集的稳定性上面的结论是相同的, 而低阶次的ADRC能够更好地解决摩擦力补偿和稳定鲁棒性之间的矛盾问题. 这些结论对实际现象的理解、ADRC阶次的选择以及参数整定提供了一定指导.     

地表反照率对短波红外探测大气CO2的影响

在卫星短波红外遥感二氧化碳的过程中, 表征地表特征的地表反照率是影响探测精度的重要参数之一. 针对温室气体二氧化碳高精度探测的需求, 本文研究了地表反照率对正演模拟光谱和反演近地面二氧化碳平均柱浓度XCO₂的影响. 模拟计算结果显示, 地表反照率数值增大时, 观察的光谱强度也相应增大, 并且在O₂-A波段造成的光谱差异比1.6 μm波段高出一个数量级, 即地表反照率在O₂-A波段的影响比较大. 选取了两个不同地表类型的实际观测光谱, 仅改变O₂-A波段和1.6 μm波段地表反照率数值, 得出草地点在O₂-A波段地表反照率达到0.25的误差时, 会给XCO₂的反演结果造成大于1%的相对误差, 而1.6 μm波段的地表反照率变化对XCO₂的反演结果造成的误差可以忽略不计, 说明了地表反照率在反演XCO₂过程中的重要性主要来自对O₂-A波段的影响. 此研究表明了地表反照率在卫星遥感温室气体过程中的重要性, 为提高遥感探测二氧化碳的精度提供了重要的理论依据和指导.     

Gas purge microsyringe extraction for quantitative direct gas chromatographic-mass spectrometric analysis of volatile and semivolatile chemicals

Sample pretreatment before chromatographic analysis is the most time consuming and error prone part of analytical procedures, yet it is a key factor in the final success of the analysis. A quantitative and fast liquid phase microextraction technique termed as gas purge microsyringe extraction (GP-MSE) has been developed for simultaneous direct gas chromatography-mass spectrometry (GC-MS) analysis of volatile and semivolatile chemicals without cleanup process. Use of a gas flowing system, temperature control and a conventional microsyringe greatly increased the surface area of the liquid phase micro solvent, and led to quantitative recoveries of both volatile and semivolatile chemicals within short extraction time of only 2 min. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and alkylphenols (APs) determined were 85-107%, and reproducibility was between 2.8% and 8.5%. In particular, the technique shows high sensitivity for semivolatile chemicals which is difficult to achieve in other sample pretreatment techniques such as headspace-liquid phase microextraction. The variables affecting extraction efficiency such as gas flow rate, extraction time, extracting solvent type, temperature of sample and extracting solvent were investigated. Finally, the technique was evaluated to determine PAHs, APs and OCPs from plant and soil samples. The experimental results demonstrated that the technique is economic, sensitive to both volatile and semivolatile chemicals, is fast, simple to operate, and allows quantitative extraction. On-site monitoring of volatile and semivolatile chemicals is now possible using this technique due to the simplification and speed of sample treatment.     

混合区间多尺度分解的区间时间序列组合预测

鉴于传统预测方法一直基于“点”来衡量时间序列数据,然而现实生活中在给定的时间段内许多变量是有区间限制的,点值预测会损失波动性信息。因此,本文提出了一种基于混合区间多尺度分解的组合预测方法。首先,建立区间离散小波分解方法(IDWT)、区间经验模态分解方法(IEMD)和区间奇异普分析方法(ISSA)。其次,用本文构建的IDWT、IEMD和ISSA对区间时间序列进行多尺度分解,从而得到区间趋势序列和残差序列。然后,用霍尔特指数平滑方法(Holt's)、支持向量回归(SVR)和BP神经网络对区间趋势序列和残差序列进行组合预测得到三种分解方法下的区间时间序列预测值。最后,用BP神经网络对各预测结果进行集成得到区间时间序列最终预测值。同时,为证明模型的有效性进行了AQI空气质量的实证预测分析,结果表明,本文所提出基于混合区间多尺度分解的组合预测方法具有较高的预测精度和良好的适用性。     

Friedländer reaction of 3-acetyltropolones: Synthesis of naphthyridinyl- and allied heterocyclic-substituted tropolones

Five 3-acetyltropolones reacted with 2-amino-3-pyridinecarbaldehyde to afford the corresponding 3-(1,8-naphthyridin-2-yl)tropolones in excellent yields. In a similar manner, 1,6-naphthyridin-2-yl-,1,7-naphthyridin-2-yl-, 6-pyrido[2,3-b]pyrazinyl-, and 1-methyl-6-pyrazolo[5,4-b]pyridyl-substituted tropolones were prepared. Reactivities of amino-substituted heteroarenecarbaldehydes in these reactions and properties of the products are also discussed.     

超微粒金刚石砂轮精密修整技术

金刚石砂轮的精密修整是脆硬材料镜面磨削的关键技术之一，为了保证磨轮起到足够数量微小磨削刃的作用，以使脆硬材料镜面磨削得到较好的面形精度，超微粒金刚石砂轮精密修整技术是目前国内外研究的一个课题。这里介绍了目前国内外修整金刚石砂轮的各种技术方法，并提出采用碗形碳化硅修整器和在线电解修整法，可获得较理想的修整效果。     

Strontium‐based initiator system for ring‐opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by ¹H NMR, ¹³C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, ¹H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003     

一种求解虚波长路径光网络波长资源优化问题的启发式算法

本文提出了一种虚波长路径光网络的启发式路由选择算法,它可以用来解决以最小化网络所需波长数目为目标的资源优化问题.该算法应用了基于最大概率路径的选路优化策略.对一个样例网络的数值分析结果表明该算法是有效的.     

双孤子压缩态的特性

在线性近似条件下,量子化了非线性薛定谔方程,用后向传播法数值求解了双孤子压缩态的特性.数值结果表明,在碰撞距离附近,压缩比显著增加.减小孤子间相互作用,可以降低压缩比.