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151.
P. De Bièvre 《Accreditation and quality assurance》2000,5(6):224-230
Traceability is a property of the result of a measurement. Since values carried by (reference) materials must also have been
obtained, of necessity, by measurement, the definition of traceability also applies to reference materials. It is extremely
helpful to give the traceability (of the origin) of a reference material a separate name, i.e. 'trackability'. An analysis
of the function of values carried by reference materials, shows that they can fulfill different functions, depending on the
intended use. One of the functions located outside the traceability chain – and hence not very relevant for establishing traceability
– is evaluating the approximate size of the uncertainty of the measurement of an unknown sample by performing a similar measurement
on a reference material, used as a 'simulated sample'. Another function is located inside the traceability chain, where the
reference material is used as an added 'internal standard'. Then, the value carried by the reference material is essential
for establishing the traceability of the measured value of an unknown sample. In the latter application, the reference material
acts as an 'amount standard' (the certified value for amount is used).
Received: 11 November 1999 / Accepted: 24 February 2000 相似文献
152.
连接基团链长度对季铵盐二聚表面活性剂C12-s-C12·2Br在水溶液中胶团化行为的影响 总被引:12,自引:1,他引:12
用电导法、稳态荧光法和粘度法研究了二聚表面活性剂C12-s-C12*2Br分子中的连接基团链长度(s=2, 3, 4, 6)对其在水溶液中聚集行为的影响. 实验发现, C12-s-C12*2Br的胶团生成能力远比其单体C12TABr强得多, 前者cmc值较后者降低一个数量级. 胶团聚集数N随表面活性剂浓度c的增大而增大, 其中当s=2时的N值在c=7.7 mmol/L后开始急剧增大. 计算结果表明, 此时胶团形状发生了明显变化, 形成了椭球形的胶团. 粘度测定结果也证实了这一点. 相似文献
153.
双金属氰化物配合物的制备、表征及催化性能 总被引:7,自引:0,他引:7
制备了基于钴氰化锌的双金属氰化物配合物(DMC)催化剂,并\r\n用元素分析、X射线衍射和红外光谱等手段进行了表征,考察了催化剂\r\n的结构与组成对其催化活性的影响以及该催化体系催化环氧烷烃开环聚\r\n合的特点.结果表明,含ZnCl2和叔丁醇的非晶态DMC催化剂具有最高的\r\n催化活性.该催化体系使聚合物的分子量可控,不饱和度很低(<14μ\r\neq/g),逐步聚合所得到的聚合物的分子量分布较窄(Mn/Mw<1.4\r\n8).13CNMR分析结果表明,甲基氧丙环均聚物的链结构具有无规立构\r\n的特点,且链节分布几乎都为头-尾方式.IR分析结果表明,甲基氧丙\r\n环-环氧乙烷共聚物的链结构是无规分布的. 相似文献
154.
155.
Mixed-metal sulfido cluster [(PdCl2)(Cp*Ir)2(μ3-S)2] (Cp*=η5-C5Me5) dissolved in CH2Cl2 reacted with two equivalent of L (L=nicotinamide, isonicotinamide, or N-methylnicotinamide) in the presence of AgBF4 to give the cationic clusters [(PdL2)(Cp*Ir)2(μ3-S)2][BF4]2. The single-crystal X-ray diffraction studies of these products have disclosed that in the solid state the PdIr2S2 cores are self-assembled to form one-dimensional chains through the intermolecular hydrogen-bonding between the amide groups for L=nicotinamide or two-dimensional sheets via the hydrogen-bonding between the amide groups and the BF4 anions for L=isonicotinamide, whereas no organization of the cluster cores is observed for L=N-methylnicotinamide. 相似文献
156.
157.
Margarita Acevedo Alain Fradet 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):817-830
2,2′-Bis(4,4-dimethyl-5(4H)-oxazolone) ( B3 ) and 2,2′-(1,2-ethylene)-bis(4,4-dimethyl-5(4H)oxazolone) ( B4 ) have been reacted in the bulk with α, ω-diamino polyamide-12 ( PA12 ) of M?n = 1000. The reactions have been studied by SEC, and 1H- and 13C-NMR and resulting polymers characterized by DSC and TGA. The chain coupling reaction is fast and gives high molar mass polymers within 10 min at 200°C with B4 while some side reactions occur with B3 leading to polymers of lower molar mass. The crystallinity of resulting polymers is lower than that of starting oligomer. However, the thermal stability is higher. Model reactions using B3 or B4 and hexamethylene diamine or 1-dodecanamine have been carried out and studied. An intramolecular cyclodehydration giving 2-imidazolin-5-ones takes place during the reactions. Higher cyclization extent is found in the presence of amino group excess. 2-Imidazolin-5-one heterocyclic structures are also observed in the chains of the polymers obtained from PA12 and B3 or B4 . © 1993 John Wiley & Sons, Inc. 相似文献
158.
直链醇链长对层状液晶结构与稳定性的影响 总被引:8,自引:4,他引:8
作为助表面活性剂,直链醇在层状溶致液晶的制备中是非常重要的。本文以层状液晶的相行为和小角度X射线衍射测量,研究了直链醇链长对层状液晶结构与稳定的影响。 相似文献
159.
Virgil Percec Anatoliy V. Popov Ernesto Ramirez‐Castillo 《Journal of polymer science. Part A, Polymer chemistry》2005,43(2):287-295
The single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride (VC) in H2O/tetrahydrofuran at 25 °C catalyzed by thiourea dioxide [(NH2)2C?SO2] is reported. This polymerization occurs only in the presence of a basic sodium bicarbonate (NaHCO3) buffer and the electron‐transfer cocatalyst octyl viologen. The resulting poly(vinyl chloride) (PVC) has a number‐average molecular weight of 1500–7000 and a weight‐average molecular weight/number‐average molecular weight ratio of 1.5. This PVC does not contain detectable amounts of structural defects and has both active chloroiodomethyl and inactive chloromethyl chain ends. Because of possible side reactions caused by the primary sulfoxylate anion (SO), the catalytic activity of (NH2)2C?SO2 in the SET–DTLRP of VC is lower than that of the single‐electron‐transfer agent sodium dithionite. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 287–295, 2005 相似文献
160.
Karel Strnský Tom Jursík Antonín Vítek Jií Skoepa 《Journal of separation science》1992,15(11):730-740
A method has been developed for calculating more accurate and reproducible equivalent chain length (ECL) values of 33 straight-chain fatty acids (FA), with various positions and numbers of cis double bonds, chromatographed on DB-Wax and DB-1 columns. The dependence of ECL values on the position and the number of double bonds is described, as is a method of utilizing these relationships for the characterization of FA by gas chromatography. 相似文献