Synthesis of Chiral Sulfoxides and Application in Enantioselective Allylation of Aldehydes with Allyltrichlorosilane

1 Results The enantioselective addition of allylic organometallic reagents to aldehydes is a fundamental tool in organic synthesis.The high degree of both diastereo-and enantioselectivity gives the possibility to obtain a wide series of homoallylic alcohols,versatile intermediates in a great number of synthesis[1]. One of the most successful approaches is related to the discovery that organocatalytic activation of the nucleophilic allyltrichlorosilanes by means of neutral Lewis bases,such as formamides,...     

Myeloid leukaemia inhibitory factor maintains the developmental potential of embryonic stem cells

Embryonic stem (ES) cells, the totipotent outgrowths of blastocysts, can be cultured and manipulated in vitro and then returned to the embryonic environment where they develop normally and can contribute to all cell lineages. Maintenance of the stem-cell phenotype in vitro requires the presence of a feeder layer of fibroblasts or of a soluble factor, differentiation inhibitory activity (DIA) produced by a number of sources; in the absence of DIA the ES cells differentiate into a wide variety of cell types. We recently noted several similarities between partially purified DIA and a haemopoietic regulator, myeloid leukaemia inhibitory factor (LIF), a molecule which induces differentiation in M1 myeloid leukaemic cells and which we have recently purified, cloned and characterized. We demonstrate here that purified, recombinant LIF can substitute for DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.     

优化设计中的拟网格原理（I）

在研究目标函数和约束条件的性质与允许误差的条件下,研究了断定全局优化方案就存在于变量网格结点中的若干个结点之间的问题.提出了拟三维空间和超球体概念;导出了确定可计算的网格结点公式,证明了持定点的覆盖定理。     

Stem cells, cancer, and cancer stem cells.

Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' - rare cells with indefinite potential for self-renewal that drive tumorigenesis.     

磁流变液阻尼器用于转子振动控制的实验研究

实验研究了一种剪切式磁流变流阻尼器在转子振控制中的应用,实验发现,磁流变液阻尼器的刚度和阻尼随施工磁场强度的增加而增大;支承在磁流变液阻尼器上的转子系统的振幅在亚临界区及临界转速处随施加的磁场强度的增加而减小,而在超临界区则随磁场强度的增加而增大;系统的临界转速随磁场强度的增加而升高,通过简单的开关控制,可使转子的振动在全转速区的内达到最小。     

Modified binary particle swarm optimization

This paper presents a modified binary particle swarm optimization （BPSO） which adopts concepts of the genotype-phenotype representation and the mutation operator of genetic algorithms. Its main feature is that the BPSO can be treated as a continuous PSO. The proposed BPSO algorithm is tested on various benchmark functions, and its performance is compared with that of the original BPSO. Experimental results show that the modified BPSO outperforms the original BPSO algorithm.     

大豆蛋白质的泡沫分离研究 I.操作工艺条件

在一连续操作的泡沫精馏塔中，考察了各种操作条件对大豆蛋白质溶液泡沫分离过程的影响，包括：进料浓度、进气流量、ｐＨ值、回流比等，确定了较佳的操作条件。用流动法测定了大豆蛋白质在气液界面上的表面过剩浓度并回归了线性吸附方程。结果表明：在溶液浓度较稀时，表面过剩浓度与溶液浓度呈线性关系。     

土壤微生物群落及其活性与植被的关系

植被通过影响土壤环境,从而影响到土壤微生物群落的结构和多样性．受植被影响的土壤环境中土壤微生物群落的多样性比不受植被影响或者没有植被的土壤环境中的微生物群落的多样性要高很多,不受植被影响的表面以下土壤环境中的微生物群落具有显著的优势ＯＴＵ种群,而表层土壤环境中没有显著的优势ＯＴＵ种群．植被对微生物的影响同时也表现在对生命物质ＤＮＡ的影响,即有植被的土壤环境中的微生物ＤＮＡ具有更高的活性,其基因在克隆过程中更容易被转移,获得更多的克隆细胞和种群．     

弹塑性回映算法及其在板成形模拟中的应用

结合退化壳单元模型的平面应力条件,给出了弹塑性本构方程应力求解的弹性预测－径向回映算法,用于板料成形的动力显式有限元模拟,利用自行开发的板料成形模拟动力显式有元分析程序VIFORM,对Numisheet′96标准考题S型轨的成形过程进行了模拟,计算结果表明该地算精度高、速度快。