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。     

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。     

ALE有限元法解二维自由面流体大晃动问题

从Navier-Stokes方程和连续性方程出发，在ALE描述下，用四边形单元对所求区域加以划分；并借助于Galerkin加权余量法导出相应的有限元方程组，在有限元计算中速度和压力均采用四节点线性插值函数；通过二维自由面流体大晃动问题实例的计算，给出相应的计算结果，阐明了该方法的优越性和局限性。     

弹性地基连续板的三弯矩方程

借助单跨弹性地基板弯曲方程的标准解答组，方便地导出了两对边简支弹性地基连续板的三弯矩方程．推导过程中，根据两对边简支的边界条件，同时还利用板中间支座处的变形连续条件，将板的挠度沿ｙ方向展成正弦级数．因导得的连续板三弯矩方程给计算带来了很大方便，故在工程设计中有重要应用．另外，提出的推导方法不仅概念清晰，而且容易推广到解决正交异性连续板的三弯矩方程     

界面处理和冷却条件对玻璃纤维与聚丙烯界面结合的影响 I.不同界面处理对界面剪切强度的影响

通过测定,得出马来酸酐改性聚丙烯（ＭＰＰ）是提高玻璃纤维与聚丙烯树脂界面剪切强度的关键因素,而偶联剂的变化对体系界面剪切强度的影响较少,用仪器分析证实了酸酐基团与玻璃纤维表面发生化学反应的实质,以及当界面存在改性聚丙烯时,应选择Ａ－１７４ＴＭ硅烷偶联剂处理增强聚丙烯的玻璃纤维,而不是传统的Ａ－１１００ＴＭ硅烷偶联剂。     

水泥土环境中粉煤灰水化与活性激发研究

水泥—粉煤灰与土充分拌合条件下,经过初级和次级2个过程形成水泥土固结体。粉煤灰的活性效应较之形态效应和微集料效应对水泥土强度的贡献是显著和持久的。活性激发剂———粉状硅酸钠溶出的OH-对粉煤灰网络聚合度比较高的“硬壳层”有腐蚀作用,同时硅酸钠水解产生的SiO32-在水化环境中可阻止水化硅酸钙生成过多而沉积在粉煤灰表面。通过构建粉煤灰在水泥土环境中的水化模型及SEM、力学性质等测试手段,分析了粉煤灰的水化与固结特性。     

A separate two-stage pulse tube cooler working at liquid helium temperature

A novel 4 K separate two-stage pulse tube cooler (PTC) was designed and tested. The cooler consists of two separate pulse tube coolers, in which the cold end of the first stage regenerator is thermally connected with the middle part of the second regenerator. Compared to the traditional coupled multi-stage pulse tube cooler, the mutual interference between stages can be significantly eliminated. The lowest refrigeration temperature obtained at the first stage pulse tube was 13.8 K. This is a new record for singlestage PTC. With two compressors and two rotary valves driving mode, the separate two-stage PTC obtained a refrigeration temperature of 2.5K at the second stage. Cooling capacities of 508mW at 4.2K and 15W at 37.5K were achieved simultaneously. A one-compressor and one-rotary valve driving mode has been proposed to further simplify the structure of separate type PTC.     

供应链中电子市场与合约市场的协调研究

供应链的供求关系可以建立在两个不同的交易方式上,一种是通过电子市场,另一种是通过合约市场．这两种交易方式各有其优缺点,电子市场具有灵活性,但缺乏稳定性,合约市场则相反．为了使供应商与制造商能够充分利用电子市场与合约市场的优点,设计了一种以期权合约为基础的协调机制,并且利用期权的思想,求出了在这种协调机制下供应商与制造商的最优策略．