Recent advances in the study of Mesozoic-Cenozoic petrified wood from Thailand

Mesozoic to Cenozoic petrified woods are very rich and well preserved in the Khorat Plateau, Northeast Thailand, serving as remarkable material for investigations of tropical vegetation history, paleoclimatic evolution, and paleoenvironmental changes. Our recent field survey and investigations have defined about 50 species of fossil wood assigned to 19 genera and 11 families from Mesozoic to Cenozoic deposits in this region. These woods are ascribed to two groups, gymnosperms and angiosperms. Among them, about 20 species assigned to 7 genera and 5 families are the first reports of the taxa in Thailand. The fossil wood floras indicate that during the late Mesozoic period, the tropical conifer vegetation in Northeast Thailand was dominated by the family Araucariaceae. From the Miocene to Pleistocene, a tropical climate prevailed in this region with perhaps both deciduous and evergreen broadleaf forests comprising the vegetation.     

直流磁控溅射Ti-Si-N 超硬纳米复合膜的结构与力学性能

采用Ti-Si复合靶在321不锈钢基体上用直流磁控反应溅射方法制得超硬纳米复合Ti-Si-N膜层,并借助能谱仪(EDX)、X射线衍射(XRD)、X光电子谱(XPS)、原子力显微镜(AFM)、纳米压入仪和划痕仪对膜层的成分、结构和力学性能进行了分析.结果表明:随着膜层中Si含量的增加,Ti-Si-N膜的硬度逐渐升高,当a(Si)=11.2%时达到峰值42 GPa;随着Si含量的进一步增长,膜层硬度开始下降.XRD和XPS结果显示,最硬的Ti-Si-N膜层包含大小约为8 nm的TiN纳米晶以及包围在其周围的非晶态Si3N4.XRD结果显示,随着Si的引入,膜层中TiN晶粒的择优取向由纯TiN膜层中的(111)变为Ti-Si-N膜层中的(200).划痕实验也显示了Si的添加对膜层结合力的影响.最后对该纳米复合膜的强化机制进行了探讨.     

Receptors for B-cell stimulatory factor-1 expressed on cells of haematopoietic lineage

B-cell stimulatory factor-1 (BSF-1) is a T-cell product of relative molecular mass 20,000 (Mr, 20K) initially described as a cofactor required for DNA synthesis by resting mouse B cells stimulated with low concentrations of anti-IgM antibodies. It acts on resting B cells to enhance the expression of class II major histocompatibility complex (MHC) molecules, to prepare these cells to respond more promptly to subsequent stimuli, such as anti-IgM antibodies, and causes the secretion of IgG1 and IgE by B cells stimulated with lipopolysaccharide (LPS). BSF-1 has been shown to stimulate T cell lines, resting T cells and some mast cell lines. Recently, the designation interleukin-4 (IL-4) has been suggested for BSF-1. We report here the existence of high-affinity cell-surface receptors specific for BSF-1 on both B and T lymphocytes, and on cells of several other haematopoietic lineages, including mast cell, macrophage and undifferentiated haematopoietic cell lines. Resting B and T lymphocytes express receptors, which increase in number upon activation of B cells with LPS or anti-IgM, and of T cells with concanavalin A. Cross-linking of 125I-labelled-BSF-1 to its receptors creates a complex of Mr approximately 80,000.