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MO Yi-Rong WU Wei ZHANG Qian-ErDepartment of Chemistry Xiamen University Xiamen Fujian China 《中国化学》1995,13(1):27-32
The π electronic delocalization in trans-C4H6 and cis-C4H6 has been investigated in the frame of ab initio valence bond theory with 6-31G basis set. The result shows that the Csp2-Csp2 single bond length (1.506 A) is only about 0.024 A shorter than the Csp3-Csp3 bond, thus the central bond length shortening would be mainly due to π conjugation. The theoretical resonance energies of the trans-C4H6 and cis-C4H6 are 8.48 and 7.44 kcal/mol, respectively. 相似文献
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The possible existence of a compensation effect, i.e. concurrent changes in activation energy and prefactor, is investigated for the hydrogenation and dehydrogenation kinetics of metal hydrides, by analyzing a series of reported kinetic studies on Mg and LaNi(5) based hydrides. For these systems, we find a clear linear relation between apparent prefactors and apparent activation energies, as obtained from an Arrhenius analysis, indicating the existence of a compensation effect. Large changes in apparent activation energies in the case of Mg based hydrides are rationalized in terms of a dependency of observed apparent activation energy on the degree of surface oxidation, i.e., a physical effect. On the other hand, we find the large concurrent changes in apparent prefactors to be a direct result of the Arrhenius analysis. Thus, we find the observed compensation effect to be an artifact of the data analysis rather than a physical phenomenon. In the case of LaNi(5) based hydrides, observed scatter in reported apparent activation energies is less pronounced supporting the general experience that LaNi(5) is less sensitive toward surface contamination. 相似文献
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交替三线性分解算法与反相高效液相-二极管阵列检测方法相结合同时测定苯二酚的位置异构体 总被引:3,自引:0,他引:3
利用交替三线性分解算法与反相高效液相 二极管阵列检测 (RP HPLC DAD)相结合 ,在洗脱时间为1 0 86min~ 1 399min(间隔 1 / 1 50min)、紫外吸收波长为 2 68nm~ 2 98nm(间隔 1nm)时对苯二酚位置异构体的重叠及光谱体系进行了分辨研究。分辨结果与实际结果一致。同时测定了水溶液中共存的邻苯二酚、间苯二酚和对苯二酚的含量 ,回收率分别为 (1 0 0 1± 1 0 ) % ,(99 4± 1 4) % ,(1 0 0 5± 1 7) %。研究结果表明 :该方法定量快速准确 ,实验操作步骤简单 ,解决了在干扰物存在条件下三者很难同时分辨的问题。 相似文献
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We consider affine systems inR n constructed from a given integral invertible and expansive matrixR, and a finite setB of translates,σ bx:=R–1x+b; the corresponding measure μ onR n is a probability measure fixed by the self-similarity $\mu = \left| B \right|^{ - 1} \sum\nolimits_{b \in B} {\mu o\sigma _b^{ - 1} } $ . There are twoa priori candidates for an associated orthogonal harmonic analysis: (i) the existence of some subset Λ inR n such that the exponentials {eiλ·x}Λ form anorthogonal basis forL 2(μ); and (ii) the existence of a certaindual pair of representations of theC *-algebraO N wheren is the cardinality of the setB. (For eachN, theC *-algebraO N is known to be simple; it is also called the Cuntz algebra.) We show that, in the “typical” fractal case, the naive version (i) must be rejected; typically the orthogonal exponentials inL 2(μ) fail to span a dense subspace. Instead we show that theC *-algebraic version of an orthogonal harmonic analysis, namely (ii), is a natural substitute. It turns out that this version is still based on exponentialse iλ·x, but in a more indirect way. (See details in Section 5 below.) Our main result concerns the intrinsic geometric features of affine systems, based onR andB, such that μ has theC *-algebra property (ii). Specifically, we show that μ has an orthogonal harmonic analysis (in the sense (ii)) if the system (R, B) satisfies some specific symmetry conditions (which are geometric in nature). Our conditions for (ii) are stated in terms of two pieces of data: (a) aunitary generalized Hadamard matrix, and (b) a certainsystem of lattices which must exist and, at the same time, be compatible with the Hadamard matrix. A partial converse to this result is also given. Several examples are calculated, and a new maximality condition for exponentials is identified. 相似文献
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广山药中16种元素的分析比较 总被引:21,自引:1,他引:21
用原子吸收法和分光光度法测定了5个产地的广山药及怀山药中16种元素的含量,并进行了比较。发现广山药及怀山药中均含有Mn,Fe,Zn,Ca,Cu,Mg,P,Se等元素,5个产地的广山药中的Cu/Zn值均低于正常人血清的Cu/Zn,这些元素可能是怀山药,广山药具有补脾养胃,生津益肺,补肾涩精,治疗糖尿病等功效的物质基础之一;广山药长期作为山药的一个品种同等入药,食用是有科学根据的;广山药,怀山药中含有一定量的As,Hg。 相似文献
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