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731.
以硅酸钠为硅源、硫酸铝为铝源、CTAB为模板剂,采用水热法合成了负载型固体酸Al-MCM-41中孔分子筛催化剂,并通过X射线衍射(XRD)、热重差热分析(TG-DTA)、扫描电镜(SEM)和红外(IR)方法对其进行了表征,同时研究了该催化剂在二芳基乙烷合成反应中的催化性能。考察了各种反应因素的影响,确定其最佳合成条件为:原料苯乙烯与二甲苯质量之比为1∶7.5,催化剂用量为1 %(总投料质量百分比),反应时间为3 h,反应温度为140 ℃,产率可达87.1 %,比传统催化剂浓硫酸提高了17 %。研究结果表明,该催化剂是替代液体酸合成二芳基乙烷的理想固体酸催化剂。 相似文献
732.
SHENG Li-Na SONG Ming-Tao ZHANG Xiao-Qi YANG Xiao-Tian GAO Da-Qing HE Yuan ZHANG Bin LIU Jie SUN You-Mei DANG Bing-Rong LI Wen-Jian SU Hong MAN Kai-Di GUO Yi-Zhen WANG Zhi-Guang ZHAN Wen-Long 《中国物理C(英文版)》2009,33(4):315-320
A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to pre-selected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simulta-neously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C6+ ion beam to 1 μm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced. 相似文献
733.
When dynamic force is applied to a saturated porous soil,drainage is common.In this paper,the saturated porous soil with a two-phase saturated medium is simulated,and Lamb's integral formulas with drainage and stress formulas for a two-phase saturated medium are given based on Biot's equation and Betti's theorem(the reciprocal theorem).According to the basic solution to Biot's equation,Green's function Gij and three terms of Green's function G4i,Gi4,and G44 of a two-phase saturated medium subject to a concentrated force on a spherical coordinate are presented.The displacement field with drainage,the magnitude of drainage,and the pore pressure of the center explosion source are obtained in computation.The results of the classical Sharpe's solutions and the solutions of the two-phase saturated medium that decays to a single-phase medium are compared.Good agreement is observed. 相似文献
734.
Taking into account both the intrinsic curvature and
Zeeman effects, persistent currents in a multi-walled carbon nanotorus
are explored by using a supercell method, within the tight-binding
formalism. It is shown that in the absence of the Zeeman effect, the
intrinsic curvature induces some dramatic changes in energy spectra
and thus changes in the shape of the flux-dependent current. A
paramagnetism--diamagnetism transition is observed. With consideration of
the Zeeman splitting energy, the period of persistent current is
destroyed, and a diamagnetism--paramagnetism transition is obtained
at high magnetic field. In addition, we further explore the effect
of external electric field energy (Eef) on persistent
current, indicating that it changes unmonotonously with Eef. 相似文献
735.
737.
一类含联二萘结构的新型聚芳醚酮类刚性大环及其二聚体的合成与表征 总被引:4,自引:0,他引:4
通过一定的分子设计,利用一种全新的双酚单体(4-氯代苯基对苯二酚)和含有联二萘结构的双氟三聚体(BNDIF)经一步法合成环状齐聚物,制得了一类含有氯代苯基侧基和联二萘结构的新型聚芳醚酮类刚性大环;并通过氯苯基的催化偶联反应得到了该类刚性大环的二聚体(一类含有2个联二萘结构的新型结构双环齐聚物).利用MALDI-TOFMS和1HNMR及H-HCOSY分析,证明了目标产物的结构. 相似文献
738.
综述了DNA辐射损伤导致的细胞阻遏于G1期以及在该时期对DNA的修复活动, 提出了较大剂量辐射诱导的三磷酸腺苷不足导致细胞凋亡的假说, 并分析了细胞走向凋亡与修复的辨正关系。 DNA damage induced by irradiation,which makes the cell arrested at G1 stage and DNA repair being activated in this stage,are summarized. It is proposed that the deficiency of adenosine triphosphate which is induced by the larger irradiation dose, induces cell apoptosis. And the relationship of cell selecting repair and apoptosis is also analyzed. 相似文献
739.
740.