一类重入型网络在优先服务原则下的扩散近似

本文研究了一类重入型网络在优先服务原则下的扩散近似,运用随机分析方法,证明了标准化队长过程的C-紧性．在优先服务原则下,给出了这类网络的标准化队长过程扩散近似存在的充分条件．     

Rapid identification of chemical compositions of three species of Schisandra chinensis by ultra-high-performance liquid chromatography quadrupole-orbitrap-mass spectrometry

Schisandra chinensis is a traditional Chinese medicine, which has played an important role in the field of medicine and food. In this study, ultra-high-performance liquid chromatography quadrupole-orbitrap-mass spectrometry was used to rapidly classify and identify the chemical compositions. Note that 32, 28, and 30 kinds of compounds were successfully identified from northern Schisandra chinensis, vinegar-processed Schisandra chinensis, and wine-processed Schisandra chinensis, respectively. The cleavage patterns of various components including lignans, organic acids, flavonoids, and terpenoids were summarized, and the effects of different processing methods on Schisandra chinensis were analyzed through chemical composition. This method realized the rapid classification and identification of raw Schisandra chinensis and two different processed products, and provided references for improving the traditional processing methods, strengthening quality control, and ensuring safe clinical application.     

Synthesis and characterization of novel thermosetting polyphosphazene‐urethanes

Polyphosphazenes are ready to move from the level of a mere scientific curiosity to the rank of industrially and commercially important macromolecules because they have experienced an explosive development during the last 10 years. In this paper, novel linear poly [bis‐(phenoxy) _1.8 (4‐hydroxybutaneoxy) _0.2 phosphazene] (PPHBP) was synthesized and characterized by FTIR, NMR, and GPC. Then, a series of new thermosetting polyphosphazene‐urethanes (PPU)s were prepared by using PPHBP polyol via a two‐step method. The FTIR spectra have showed the PPUs were successfully prepared. Compared to conventional polyurethane, the results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) have indicated that the PPUs exhibited better thermal stability and flame resistance. The study on water contact angle showed that PPUs were more hydrophobic than conventional polyurethane. This may widen the opportunities for producing a new class of polyurethanes with broad range of uses. Copyright © 2009 John Wiley & Sons, Ltd.     

Total synthesis of neopeltolide and analogs

Neopeltolide, a potent cytotoxin from a Carribean sponge, was synthesized through a brief sequence that highlights the use of ethers as oxocarbenium ion precursors. Other key steps include an acid-mediated etherification and sequence that features a Sonogashira reaction, an intramolecular alkyne hydrosilylation reaction, and a Tamao oxidation. The alkene that is required for the oxidative cyclization can be hydrogenated to provide access to the natural product or an epimer, or can be epoxidized or dihydroxylated to form polar analogs.     

A Closed Concept of Extractive Whole Cell Microbial Transformation of Benzaldehyde into l-Phenylacetylcarbinol by Saccharomyces cerevisiae in Novel Polyethylene-Glycol-Induced Cloud-Point System

Extractive microbial transformation of benzaldehyde into l-phenylacetylcarbinol (l-PAC) by Saccharomyces cerevisiae (Baker’s yeast) has been carried out in a novel polyethylene-glycol-induced cloud-point system (PEG-CPS). The extractive microbial transformation in the PEG-CPS and a downstream process for stripping of the product from the microbial transformation broth with microemulsion extraction are demonstrated. The results indicate that the PEG-CPS maintains the advantage of CPS for in situ extraction of polar product in the microbial transformation. At the same time, the utilization of hydrophilic nonionic surfactant in the PEG-CPS is favorable for stripping of product from the nonionic surfactant in the microbial transformation broth by Winsor I microemulsion extraction. Thus, a closed concept of in situ extraction of polar product in microbial transformation and its downstream process of product recovery are fulfilled at the same time.     

一类一维在线单位聚类问题的随机近似算法

在给定的度量空间中, 单位聚类问题就是寻找最少的单位球来覆盖给定的所有点。这是一个众所周知的组合优化问题, 其在线版本为: 给定一个度量空间, 其中的n个点会一个接一个的到达任何可能的位置, 在点到达的时候必须给该点分配一个单位聚类, 而此时未来点的相关信息都是未知的, 问题的目标是最后使用的单位聚类数目最少。本文考虑的是带如下假设的一类一维在线单位聚类问题: 在相应离线问题的最优解中任意两个相邻聚类之间的距离都大于0.5。本文首先给出了两个在线算法和一些引理, 接着通过0.5的概率分别运行两个在线算法得到一个组合随机算法, 最后证明了这个组合随机算法的期望竞争比不超过1.5。     

Tracking antiangiogenic components from Glycyrrhiza uralensis Fisch. based on zebrafish assays using high-speed countercurrent chromatography

Natural products are some of the most important sources of lead compounds for drug discovery. The advanced isolation technique of lead compounds of natural origin using therapeutically relevant bioassays is capable of enhancing work efficiency from complex multiconstituent extracts. In the present study, a bioassay-guided isolation strategy combined with bioactivity screening was used to identify novel angiogenesis inhibitors from licorice (Glycyrrhiza uralensis Fisch.) based on the zebrafish model and rapid preparative separation by high-speed countercurrent chromatography. Zebrafish embryos at 24 h postfertilization were chosen as the angiogenesis inhibition model for bioactivity screening. A solvent system (n-hexane-ethyl acetate-methanol-water) with different ratios was optimized and applied in the high-speed countercurrent chromatography separation of two fractions, Fr5 and Fr6, from the ethyl acetate extract of licorice. Blood circulation and vascular outgrowth in intersegmental vessels were found to be simultaneously inhibited by isoliquiritigenin and isolicoflavonol in a dose-dependent manner. Thus, these two compounds were identified and considered as active inhibitors against angiogenesis. These experimental results indicate that zebrafish bioassays combined with high-speed countercurrent chromatography may provide an alternative pathway for the rapid isolation of bioactive natural products.     

次Hermite矩阵的对角化及次Hermite矩阵的应用

循环矩阵在理论及实际问题上都得到了广泛的应用,而循环矩阵是一类典型的次对称矩阵,此外Hadamare 矩阵中也涉及到了次对称矩阵,本文将对次对称矩阵进一步的推广,定义了次Hermite 矩阵及次正定的次Hermite 矩阵.并且讨论它们的对角化方法,得出了类以于Hermite 矩阵的一些结论,最后作为应用,讨论了次Hermite 矩阵的算子范数及F—范数的理论值。关键词次Hermite 矩阵次特征值及次特征向量次正定的次Hermite 矩阵.     

铅在人体中的允许量及其与锌的相关性

236名健康人按年龄分6组统计，发铅值（x±S）为8．98×10－6±4．95×10－6~25.66×10－6±14．16×10-6；高锌及低锌儿童共69例的发铅、发锌相关系数r＝-0．2849，呈负相关，P＜0．01。