Parametric normalization for full-energy peak count rates obtained at different geometries

The Effective Interaction Depth (EID) law has been systematically studied and applied to parametric normalization for peak count rates obtained at different source-detector distances (S-D). The errors caused by EID normalization are less than 4% over the full range of S-D (from to several mm) for true coincidence-free -rays. Parametric corrections for the true coincidence (summing) effect are also established, based on simplified decay schemes and P/T ratio determinations. The total response of Ge detector for single-energy -rays (T) is clearly defined with scattering contributions from surroundings included. Errors from summing effect corrections are also less than 4%. The combined EID normalization and summing effect corrections give an error no greater than 5.7% for the worst situations (several mm S-D and cascade-crossover decay scheme), acceptable for most practical K₀ NAA.     

用超临界气体抽提方法研究抚顺烟煤的组成和结构——Ⅰ.抽出物的分离及GC、GC/MS分析

将抚顺烟煤用甲苯作溶剂,在半连续抽提装置上,于350℃、20MPa条件下,进行超临界气体抽提。抽出物先分离成油、沥青烯及前沥青烯三个族组份,再用离子交换树脂、硅胶柱色谱作进一步分离。GC和GC/MS的分析结果表明,油段分中存在正构烷烃(C_(13)—C_(31))、类异戊二烯化合物及长链烷基苯系列,这些化合物可提供抚顺烟煤的地球化学信息。     

Intermolecular contact interactions and their temperature dependence

A model, based on inverse gas chromatography experiments, has been developed for intermolecular interaction and its temperature dependence. The model ascribes to each substance a four-component solubility parameter; the four components reflect the van der Waals, polar, electron donor, and electron acceptor interactive properties. Their values depend on temperature in the same manner as does the cohesive energy. The latter was found to depend only on the critical temperature, the acentric factor, and the reduced temperature. The model was used for evaluation of the solubility parameters from polymer-solvent interaction coefficients and their temperature dependence with high accuracy. For binary solventsolvent mixtures, the free energy of mixing and its temperature dependence, as well as enthalpy of mixing can be derived from this model with a good accuracy.     

Re(CO)5Br-catalyzed addition of carboxylic acids to terminal alkynes: a high anti-Markovnikov and recoverable homogeneous catalyst

The addition of carboxylic acids to terminal alkynes is efficiently catalyzed by the early transition-metal complex Re(CO)5Br in toluene or n-heptane at 110 degrees C in an air atmosphere, affording the anti-Markovnikov adducts in good yields with high selectivity. In most cases, the reactions afford unusual Z-adduct predominantly. When n-heptane was used as solvent, Re(CO)5Br can be partly recovered from the reaction mixture.     

Dialane anion: three-center two-electron or two-center one-electron bonded

Dialane anions can be formed via a single three-center two-electron (3c-2e) or two-center one-electron (2c-1e) bond. The 2c-1e bonded anion Al(2)H(6)(-)(D(3)(d)) and the 3c-2e bonded anion Al(2)H(6)(-)(C(s)) have significant thermodynamic stabilities with respect to the neutral Al(2)H(6)(D(2)(h)) and correspond to 0.22 and 0.32 eV of the adiabatic electron affinities, respectively. In particular, the 2c-1e bond plays an essential role in stabilizing the Al(2)H(6)(-)(D(3)(d)) anion.     

偶极积分与Boys法分子轨道定域化

定域分子轨道在分子体系的化学图象和物理图象之间充当重要的桥梁作用,它的产生依赖于定域化准则,其中最普遍使用的是Foster-Boys和Edmiston-Ruedenberg(E—R)提出的两种定域化准则。这两种定域化准则是等价的,因而结果也是一致的。但对于E—R定域化来说,由于涉及到大量的多中心积分的计算,计算极为费时,因而远不如Foster-Boys定     

Total synthesis of methyl protodioscin: a potent agent with antitumor activity

Methyl protodioscin (1), otherwise known as 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-d-glucopyranosyl]-26-O-[beta-D-glucopyranosyl]-22-methoxy-25(R)-furost-5-ene-3 beta,26-diol, has been synthesized for the first time from diosgenin through nine steps in an overall yield of 7.8%.     

Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide

The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods…