Y2O3修饰Ni/SiO2催化剂在甲烷部分氧化制合成气反应中的催化性能及稳定性

采用常规浸渍法制备Y₂O₃修饰的Ni/SiO₂催化剂,并考察其催化甲烷部分氧化（POM）制合成气反应性能。结果表明,Y₂O₃的引入减小了金属Ni的粒径,有效提高了Ni在载体表面的分散性,增强了金属Ni与载体SiO₂间的相互作用,从而使催化剂的抗烧结、抗积碳能力,以及催化剂的POM反应性能得以改善。     

Melting phenomenon in magneto hydro-dynamics steady flow and heat transfer over a moving surfacein the presence of thermal radiation

The Lie group method is applied to present an analysis of the magneto hydro-dynamics(MHD) steady laminar flow and the heat transfer from a warm laminar liquid flow to a melting moving surface in the presence of thermal radiation.By using the Lie group method,we have presented the transformation groups for the problem apart from the scaling group.The application of this method reduces the partial differential equations(PDEs) with their boundary conditions governing the flow and heat transfer to a system of nonlinear ordinary differential equations(ODEs) with appropriate boundary conditions.The resulting nonlinear system of ODEs is solved numerically using the implicit finite difference method(FDM).The local skin-friction coefficients and the local Nusselt numbers for different physical parameters are presented in a table.     

La2O3对Ni-Cu/MgSiO催化剂的甲烷部分氧化制氢反应性能的影响

 用等体积浸渍法制备了MgO-SiO2(MgSiO)复合氧化物负载的Ni-Cu双金属催化剂,采用程序升温还原(TPR),X光电子能谱(XPS),红外光谱(IR),程序升温脱附(TPD)及微反技术考察了稀土La2O3的加入对CH4和H2O在Ni-Cu/MgSiO催化剂表面上的吸附及甲烷部分氧化制氢反应性能的影响. 结果表明,加入La2O3使催化剂表面Ni和Cu原子的电子云密度增加,CH4和H2O在催化剂表面上的吸附增强. CH4与O2和H2O在Ni-Cu/MgSiO催化剂上反应的主要产物为H2和CO2. La2O3的加入有利于提高CH4转化率及H2的选择性,并可提高催化剂稳定性及抗积炭能力. 讨论了La2O3的助催化作用机理.     

用于多阶光盘游长检测的PRML系统

对用于多阶光盘游长检测的部分响应最大似然（PRML）检测器的设计和实现进行了详细研究。分析了多阶光盘的编码形式,并将编码进行简化以减小维特比检测器的路径数和运算复杂度。为了提高PR均衡器和维特比检测器的性能,分析了目标PR多项式系数和记忆长度的选择。阐述了多阶光盘游长识别的维特比算法,对算法进行仿真,分析了维特比算法的识别效果,并与与传统识别算法的效果进行了比较。     

New cytotoxic cerebroside from Gynura divaricata

A new cerebroside,gynuraoside(1),was isolated from the aerial parts of Gynura divaricata DC.It was determined to be 1-O-β- D-glucopyranosyl-(2S,3S,4R,10E)-2-[(2′R)-2′-hydroxyldocosanoyl-amino]-10-octadecene-1,3,4-triol on the basis of chemical and spectroscopic evidence.This compound showed strong cytotoxicity against L1210 leukemia cell line in vitro.     

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article)

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al₂O₃ in the temperature range of 600 to 850 °C. XRD, H₂-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al₂O₃ and that strongly interacted with the support, were identified by H₂-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH₄ combustion and the highly endothermic CH₄ reforming (with H₂O and CO₂) reactions (or the less exothermic direct partial oxidation of methane to CO and H₂), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.     

部分信息的完全耦合正倒向系统的随机最大值原理

本文研究了系统为Brown运动驱动的完全耦合的非线性正倒向随机微分方程的随机最优控制问题．系统要求可允许控制过程适应于标的Brown运动生成的盯域流的一个子盯域流．对于这种部分信息的随机最优控制问题,在控制区域为凸集和控制变量可以进入控制系统正向扩散系数的情形下,证明了最优性的一个充分条件（验证定理）和一个必要条件．     

半群CSPO_n中星理想的秩和相关秩

设自然数n≥4,CSPO_n是有限链[n]上的严格部分保序且压缩奇异变换半群.对任意的r(0≤r≤n-1),记N_P~*(n,r)={α∈CSPO_n:|Im(α)|≤r}为半群CSPO_n的双边星理想.通过对秩为r的元素和星格林关系的分析,分别获得了半群N_P~*(n,r)的极小生成集和秩.进一步确定了当0≤l≤r时,半群N_P~*(n,r)关于其星理想N_P~*(n,l)的相关秩.     

两部分因子分析模型的贝叶斯推断

半连续数据在经济和社会科学调查中普遍存在.在分析该类数据时,经典两部分回归模型经常被用来刻画协变量对响应变量可变性的影响.然而,包含协变量并不能完全解释响应变量的可变性.忽略未被观测的数据异质性将导致方差的剧烈波动.在本文中,我们将两部分回归模型推广到两部分因子分析模型.多变量半连续数据未观测的异质性由潜在因子部分来解释.此外,通过引入潜在性因子,多重变量间的相依性也以线性组合方式通过共享因子变量得到刻画.在贝叶斯框架内,我们运用马尔可夫链蒙特卡洛(MCMC)方法来进行后验分析.GIBBS采样器被用于从后验分布中抽取样本.基于模拟的随机样本,未知参数估计和模型评价等统计推断问题获得解决.随机模拟和可卡因使用数据分析等实证结果显示了该方法的有效性和实用性.     

几何级数撷趣

我们知道几何级数为∑n=1∞aq^n-1=a aq aq^2 … aq^n-1…其中首项a≠0,公比为q。当|q|≥1时发散。