SBA-15 supported vanadium oxide catalyst for selective oxidation of methane

The VOx/SBA-15 has been found to be a better catalyst for the selective oxidation of methane to formaldehyde than SBA-15-supported Mo and W oxides. The influences of catalyst support and vanadium source on catalytic performances have been studied. The results show that SBA-15 is a better support than MCM-41 and Cab-O-Sil, and the catalyst with NH4VO3 as the precursor exhibits higher performances. The addition of phosphorus has been found to enhance slightly the selectivity to HCHO. Characterizations by XRD, N-2 physical adsorption, Raman spectroscopy and H-2-TPR suggest that the supported VOx species with loading amounts lower than 3 wt% be highly dispersed (probably as monomer) and contribute to the selective oxidation of methane to formaldehyde

超大截面矩形顶管监理质量控制要点

随着中国基本建设的迅猛发展，超大截面矩形顶管在中国大中城市市政建设中应用将越来越广泛，特别是在解决穿越公路、铁路、河流、地面建（构）物的地下交通工程中，更显其优越性。同时，超大截面矩形顶管工程按照中国住建部发布的《危险性较大的分部分项工程安全管理规定》又为超过一定规模的危大工程。因此，其质量控制对参建各方尤其重要，论文讲述监理方在此类工程中质量控制的要点。　</jats:p

基于PMT的紫外光语音接收系统优化设计

针对以LED（发光二极管）为光源的紫外光通信系统中接收端紫外光信号较弱的问题,对基于PMT（光电倍增管）的紫外光语音接收系统提出了一套完整的优化设计方案,系统包括电流/电压变换、放大、滤波以及整形电路等,利用模块化设计思想完成了各部分电路的设计与实现,并进行了仿真和实验测试。结果表明,当光源采用1.6mW的紫外LED发射速率为4.8kbit/s的语音信号时,系统在10m半径范围内准视距条件下可以正确恢复出语音信号,话音清晰完整

超大矩形顶管下穿污水箱涵监测实录

顶管下穿污水箱涵施工时，对合流污水箱涵会产生扰动，导致污水箱涵下沉或变形缝变化异常。采用3DM监测系统对污水箱涵全程进行监测，确保污水箱涵沉降可控，施工现场和周围环境安全，这种监测形式合理、安全、可靠。</jats:p

超大类矩形顶管下穿压力污水箱涵施工的风险分析以及预防控制措施

中国上海市淞沪路-三门路下立交超大类矩形顶管工程工点多、路线长、顶管管径超大，且下穿年久压力污水箱涵，施工难度大、风险高。论文结合该工程施工实践情况，通过对污水箱涵的预加固和下穿污水箱涵顶进工况风险的提前分析，顺利地解决了顶进中土体不均匀沉降、污水箱涵渗漏等问题。过程中污水箱涵变形小于 ± 2mm，远小于产权单位不大于 ± 10mm 的要求。总体效果非常显著，可为类似工程的质量控制提供很好的参考。</jats:p

弯折光子晶体波导性能的研究

提出了带有光子晶体环形谐振器（PCRR）的二维光子晶体弯折波导结构,采用有限差分时域法分别研究了带有3×3结构和带有4×4结构PCRR的光子晶体波导中电磁波的传输性能,分析了其结构整体介质柱相对介电常数取3组不同值时的传输性能,结果表明:使用带有PCRR的波导能实现电磁波的低损耗传输。此外,该结构还具有宽频带和结构紧凑等特点,在光通信器件制作、光子晶体集成制作等方面具有潜在的应用价值

Effect of Counter Anions of Potassium Salts on Propylene Epoxidation Catalyzed by K~+-FeO_x/SBA-15

考察了在以N2O为氧化剂的丙烯气相环氧化反应中,FeOx/SBA-15催化剂上添加具有不同阴离子的钾盐修饰时,共存阴离子对K+-FeOx/SBA-15催化剂的丙烯环氧化反应性能的影响.研究表明,共存阴离子的电子亲和势是影响催化剂活性中心反应性能的重要因素.阴离子的电子亲和势越大,其所修饰的活性氧物种的亲电氧化性高,催化剂的丙烯环氧化性能高.与其它阴离子相比,KCl修饰的FeOx/SBA-15催化剂具有最佳的丙烯环氧化催化性能.The present paper studied the effect of counter anions of potassium salts added in a FeO_x/SBA-15 catalyst on the catalytic performances for the epoxidation of propylene with N_2O as an oxidant.Although the modification of the FeO_x/SBA-15 catalyst with all of the potassium salts investigated in this work could shift the main reaction route from the allylic oxidation to the epoxidation,the nature of the counter anion of potassium exerted a big influence on the catalytic performances.It was found that the electron affinity of the counter anion was a crucial factor in determining the catalytic properties in the epoxidation of propylene with N_2O.Catalysts modified by potassium salts with counter anions possessing higher electron affinities exhibited both higher propylene conversion and higher propylene oxide selectivity.The higher catalytic performances probably resulted from the generation of more highly electrophilic oxygen species in the presence of a counter anion possessing higher electron affinity.As compared with other potassium salts such as KF,KBr,KI,KAc and KNO_3,the modification of FeO_x/SBA-15 with KCl showed the best catalytic performance for the epoxidation of propylene with N_2O.国家自然科学基金(20273054)资

河北省城乡收入差距与统筹城乡发展

目前,我国城乡居民收入差距仍在扩大,城乡社会发展差距悬殊,其深刻根源在于城乡二元体制。没有城乡经济的统筹发展,就没有经济协调、可持续的发展。就河北近5年的城乡差距及城市化与城乡差距的相关关系做了实证分析,对河北省促进城乡发展提出了相应对策

时隙速率对APD直接检测接收机差错性能的影响

在光通信中,采用高调制阶数可获得高功率利用率,但同时也会导致时隙速率增大。针对于此,文章研究了时隙速率对雪崩光电二极管（APD）直接检测接收机差错性能的影响。在给出接收机模型的基础上,以脉冲位置调制（PPM）为例,推导了差错概率解析式,并分析了产生影响的根本原因。数值结果表明,时隙速率的增大减弱了系统的抗噪声性能,当误码率为10-6时,调制阶数每增加1,需要增加约1 dBm的信号接收功率