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891.
Ziegler用三乙基铝为催化剂使乙烯聚合的工作是衆所周知的,这样,乙烯就可以不用压力而进行聚合。还在Ziegler工作以前,人们认为乙烯是属于不容易聚合的不饱和化合物之类,因此新的催化剂既然可以使乙烯进行聚合,那么似乎也可以用来引发其他易於聚合的单体。但是像丙烯腈和甲基丙烯酸甲酯这类单体在有三乙基铝存在时并不聚合,在苯乙烯的情况下虽有聚 相似文献
892.
The forward current-voltage (I-V) characteristics of polycrystalline CoSi2/n-Si(100) Schottky contacts have been measured in a wide temperature range. At low temperatures (≤200K), a plateau-like section is observed in the I-V characteristics around 10-4A·cm-2. The current in the small bias region significantly exceeds that expected by the model based on thermionic emission (TE) and a Gaussian distribution of Schottky barrier height (SBH). Such a double threshold behaviour can be explained by the barrier height inhomogeneity, i.e. at low temperatures the current through some patches with low SBH dominates at small bias region. With increasing bias voltage, the Ohmic effect becomes important and the current through the whole junction area exceeds the patch current, thus resulting in a plateau-like section in the I-V curves at moderate bias. For the polycrystalline CoSi2/Si contacts studied in this paper, the apparent ideality factor of the patch current is much larger than that calculated from the TE model taking the pinch-off effect into account. This suggests that the current flowing through these patches is of the tunnelling type, rather than the thermionic emission type. The experimental I-V characteristics can be fitted reasonably well in the whole temperature region using the model based on tunnelling and pinch-off. 相似文献
893.
894.
制备、表征了混合铝/铬金属氧化物柱撑α-磷酸锆(Al/Cr-ZrP),并对胶体化使用有机胺的种类、柱化液金属离子浓度以及金属离子用量等因素进行了研究。研究表明以乙醇胺为胶体化有机胺比使用正丙胺为胶体化有机胺所得到的产物的层间距更大;采用较低金属离子浓度、较高金属离子用量有利于Al/Cr-ZrP的合成。在Al/Cr比为1、以正丙胺为胶体化有机胺、金属离子浓度为0.067mol·L-1、金属离子用量为6.67CEC的条件下,制备出了混合金属氧化物柱撑α-磷酸锆,其层间距可达3.60nm, 相似文献
895.
P‐doped TiO2 (PTIO) thin‐films with different P contents were prepared using a sol‐gel method. The thin‐film samples were characterized using various techniques. The photocatalytic activity was evaluated by decomposing butyl benzyl phthalate under visible‐light irradiation. The results showed that the transformation of anatase to the rutile phase was inhibited and grain growth of TiO2 was prevented by P doping. The results confirm that the doped P atoms existed in two chemical forms, and those incorporated in the TiO2 lattice may play a positive role in photocatalysis. The high photocatalytic activities of the PTIO thin‐films may be the result of extrinsic absorption through the creation of oxygen vacancies, rather than excitation of the intrinsic absorption band of bulk TiO2 . The PTIO can be recycled with little depression of the photocatalytic activity. After six cycles, the photocatalytic activity of the PTIO film was still higher than 98%. 相似文献
896.
被激发到电离阈值以上的分子体系的演化依赖于激发态的特征和与连续态的耦合等多种参数. 这些特性主要是与分子体系的复杂性,更准确地说与分子的大小,态密度,内自由度中的耦合强度有关.本文通过Na2的里德堡态的自电离,富勒烯C60的延迟电离,阴离子小团簇的延迟解离研究了在小分子中起主导作用的自电离和在大分子以及团簇中出现的延迟电离之间的转变过程. 由于这些体系中相对较慢的内能转移过程,这些研究是在纳秒激光的激发下进行. 相似文献
897.
The structural and spectroscopic properties of Na2O-Al2O3-SiO2-xP2O5 glasses(x = 0 to 7 mol%) are investigated.Both Raman and IR spectra reveal that discrete phosphate species([PO4]-3,[PO3O1/2]-2) with low polymerization degree can be formed in the silicate glass.These phosphate structures scavenge non-bridging oxygen ions and cations from the silicate network,resulting in an increase of the glass transition temperature.According to the Judd-Ofelt intensity parameters(Ω2,Ω4,Ω6) of Er3+.the asymmetry of local environment around Er3+ becomes higher,and the bond covalency between Er3+ and O2-decreases after P2O5 is introduced.In the emission spectra,photo-luminescence intensity increases with increasing P2O5 concentration and the spectra are inhornogeneously broadened,revealing that the ligand electric field around Er3+ is dramatically changed,and the glass matrix becomes disordered. 相似文献
898.
LU Zaiping WANG Changqun & XU MingyaoLMAM School of Mathematical Sciences Peking University Beijing China Department of Mathematics Zhengzhou University Zhengzhou ChinaPresent address: Department of Mathematics Qufu Normal University Qufu China. 《中国科学A辑(英文版)》2004,47(1):1-17
A graph r is said to be G-semisymmetric if it is regular and there exists a subgroup G of A := Aut(Г) acting transitively on its edge set but not on its vertex set. In the case of G. = A, we call r a semisymmetric graph. The aim of this paper is to investigate (G-)semisymmetric graphs of prime degree. We give a group-theoretical construction of such graphs, and give a classification of semisymmetric cubic graphs of order 6p2 for an odd prime p. 相似文献
899.
A chromatographic method and a dynamic Wicke-Kallenbach method (DMWK) were used to determine the diffusion characteristics of two industrial copper containing catalysts. The first catalyst was used in nitrobenzene hydrogenation to aniline and the second was used in a low temperature water-gas shift reaction. Experimental results show that application of these two methods leads to similar results. Experimental data obtained allow for monitoring changes in the texture of the catalyst grains and intraparticle diffusivity of gaseous reagents at different states of the catalyst activity and use, which can be used as criteria for designing optimal industrial catalyst pellets. 相似文献
900.
XU Kai JI Hong YUE Guang-xin Telecommunication Engineering School Beijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2004,11(Z1)
1 Introduction MobileIPv6requirestheMobileNode (MN)toregisterwiththeHomeAgent (HA)andtheCorre spondentNode (CN)whenitchangesitspointofattachmentintheInternet[1~ 3] .Therefore ,thiscauseMobileIPv6toincurlongdelayintheregis tration process,andaddsignalingtraffictothebackbonenetworkespeciallywhentheHAandCNarefarawayfromtheMN .Inordertominimizethisdelay ,andthesignalingoverhead presentinMobileIPv6,literatures[4~7] proposeHierarchicalMobileIPv6(HMIPv6)architectureandafasthan dover… 相似文献