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61.
This is the second part of a paper which deals with the advantages and disadvantages of relative instrumental neutron activation
analysis concerning traceability and uncertainty, and the current scope and possible future extensions of neutron activation
analysis as a primary ratio method. The first part of this paper has been published in this Journal [1].
Received: 19 March 2001 Accepted: 2 October 2001 相似文献
62.
63.
Summary To match the need of high efficiency capillary column (plate number N2, Plate height H2 and carrier gas linear velocity U2), a new high efficiency packed column (N1, H1 and U1) at high carrier gas velocity with small capacity factor has been developed in the light of theoretical discussion of factors
effecting the column efficiency utilization ratio. 相似文献
64.
在乙烯-四氟乙烯溶液共聚合体系研究中,我们曾编制了一个简易的计算机程序,用于测定二种单体的共聚竞聚率,这一方法计算方便,而且可以避免原先作图法中的误差,结果较为可靠。前文我们报道了四氟乙烯与两个新的全氟烷基乙烯基醚的共聚合反应,并对其中一个新单体——7,7-二氯-3-氧杂-全氟庚烯-1——与四氟乙烯的共聚进行了单体竞聚率的测定。结果表明,这一新的含氟烯醚单体的聚合活性较其它已有报道的同类单体大。为了验证这一 相似文献
65.
We have investigated the effect of the Ca/P molar ratio on the structural and morphological properties of hydroxyapatite (HA) gels and nanocrystals. The sol-gel process was carried out in aqueous, and alternatively in alcoholic medium (50% water-50% ethanol), at 37°C. Gel samples were obtained by drying the sols at 37°C or at 80°C, whereas powder samples were obtained by filtering the sols. Heat treatment at temperatures as low as 300°C is enough to obtain pure HA from the gels with a Ca/P molar ratio of 1.00 and 1.67. At variance, heat treatment of the gels with a Ca/P of 2.55 always produces secondary phases. The degree of crystallinity of HA increases with the Ca/P molar ratio of the sols, and it is slightly affected by the presence of ethanol in the precipitation medium. Filtering of the sols provides powders constituted of nanocrystalline HA that exhibit degree of crystallinity, crystal morphology and thermal stability closely related to the sols composition. 相似文献
66.
TONG Yi-Ping 《结构化学》2007,26(1)
The zinc(Ⅱ) complex with Hpbx (Hpbx = 2-(benzoxazol-2-yl)phenol) and Hpbm (Hpbm=2-(benzimidazol-2-yl)phenol),namely[Zn(pbm)2]1.633[Zn(bpx)2]2.367·DMF·2H2O1,has been synthesized and characterized by X-ray crystallography,FTIR and elemental analysis.The coordination structures are statistically disordered and can be regarded as a co-crystal of [Zn(pbm)2]and [Zn(pbx)2] with the ratio of ca.0.408/0.592.Solvate water and DMF molecules are also present in the lattice.Crystal data for 1:monoclinic,space group P21/c,Mr= 2049.02,Z = 2,α = 9,7571(6),b = 25.6415(16),c = 19.8675(10)(A),β = 111.342(2)°,V = 4629.7(5) (A)3,Dc = 1.470 g/cm3,μ =1.100 mm-1,F(000) = 2104,R = 0.0575 and wR = 0.1282 for 5528 observed reflections (I> 2σ(I)).The photoluminescent spectra for this compound have also been studied. 相似文献
67.
Aldehyde-2,4-dinitrophenylhydrazones exist as (E)- and (Z)-geometrical isomers, and adventitious isomerization during sample preparation can cause analytical errors. Purified alkenal-2,4-dinitrophenylhydrazone derivatives comprise only the (E)-isomer. However, partial isomerization to the (Z)-isomer occurs upon addition of acid to attain an equilibrium isomer ratio. The UV-visible spectral properties of the isomers differ; the (Z)-isomer exhibiting a 6-10 nm lower absorption maximum compared to the (E)-isomer. Alkenal-2,4-dinitrophenylhydrazones having a CC double bond at the 2- or 3-position of the alkenal exhibited similar absorption maxima with an equilibrium isomer ratio (0.035) that was much lower than those of other alkenals. The CC double bond at the 3-position migrates to a position of conjugation with the CN double bond during hydrazone synthesis to form a stabilized molecular structure. Alkenal-2,4-dinitrophenylhydrazones having a double bond at the 4-position or greater exhibited a similar absorption maxima equilibrium isomer ratio (0.14) to alkanal-2,4-dinitrophenylhydrazones. The quantitative analysis of carbonyl compounds in air or water using DNPH is usually conducted in the presence of an acid catalyst. Consequently, the solution of the direct extract prepared for HPLC or GC analysis contains both (E)- and (Z)-isomers. 相似文献
68.
依据柱相比的热力学定义和反相液相色谱中溶质的计量置换保留理论(the stoichiometric dispheement heory of solute for retention,SDT-R),对反相液相色谱中固定相和流动相性质、温度对柱相比的影响进行了研究。结果表明:固定相的种类和配基的疏水性对柱相比影响较大,而流动相中有机溶剂的种类,特别是脂肪酸作为置换剂时,对柱相比的影响更大,而柱相比受温度的影响较小。此外,通过用27种小分子溶质对柱相比的测定,其logI和Z良好的线性关系,进一步证明柱相比是一个与溶质性质无关的常数。 相似文献
69.
对130℃下1,3 二烯基 1,1,3,3 四甲基二硅氧烷(DVDS)/苯乙烯(St)的溶液环化共聚合动力学进行了研究.根据低转化率(<10%)的共聚物组成及环状结构比例,通过参数估计方法,求得环化率与竞聚率,分别为r1=0102、r2=348、rc=00210、Kc=381mol/L、K′c=0389mol/L,同时得到它们95%置信概率的联合置信区间及其交互影响的联合置信区间.表明DVDS的反应活性较St低,其非环状结构自由基具有较强的分子内环化反应能力;环的位阻效应使环状结构DVDS自由基的活性低于其非环状结构自由基. 相似文献
70.
Study on Bifunctionality of Mo/HZSM-5 Catalysts for Methane Dehydro-Aromatization under Non-oxidative Condition 下载免费PDF全文
Lingling Su Yide Xu Xinhe BaoState Key Laboratory of Catalysis Dalian Institute of Chemical Physics Chinese Academy of Sciences Zhongshan Road P. O. Box Dalian ChinaManuscript received June revised July 《天然气化学杂志》2002,(Z1)
The optimum Mo/[H~+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by 1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst. On the other hand, it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell. 相似文献