须条与长丝间距对Sirofil成纱结构性能的影响

分析了Sirofil纺纱过程中“V”形区的动态变化及粗纱须条与长丝间距大小对“V”形区形状和单纱受力的影响,认为间距增大会使“V”形区夹角增大、单纱段长度变长,并以此为依据,保持其他工艺参数不变,改变粗纱与长丝间距大小,试纺Sirofil纱,通过理论分析和实验比较讨论间距大小对Sirofil成纱结构性能的影响。结果表明：随着间距增大,成纱直径系数趋小、毛羽减少、强伸性与条干均呈非单调性变化;综合考虑成纱结构和性能,在其他参数相同时,Sirofil最佳成纱间距为12～16mm。     

Enzymes and receptors in the leukotriene cascade

Leukotrienes are a family of paracrine hormones derived from the oxidative metabolism of arachidonic acid. These lipid mediators are recognized as important signal molecules in a variety of inflammatory and allergic conditions affecting the skin, joints, gastrointestinal and respiratory systems, in particular asthma. Such conditions are typified by local pain, tissue edema, hyperemia and functional losses. In the tissues, immunocompetent cells accumulate at the site of injury which contribute to tissue damage and perpetuation of the disease process. Leukotrienes can elicit most, if not all, of these signs and symptoms. Thus, leukotriene B₄ is one of the most powerful chemotactic agents known to date and participates in the recruitment of leukocytes. The cysteinyl leukotrienes, on the other hand, contract smooth muscles, particularly in the peripheral airways and microcirculation. Recently, drugs which block the formation and action of leukotrienes have been introduced as novel antiasthmatic medications. This chapter reviews the biochemistry, molecular biology and cell biology of the key enzymes and cognate receptors in the leukotriene cascade.     

立体车库钢结构系统失效树分析及软件研制

基于有限元理论 ,结合优化准则法 ,提出了立体停车库钢结构系统失效树理论分析方法 ,开发了计算软件FTA ,算例结果表明 :根据结构规模和具体特征选择合理的控制参数 ,不仅可以提高计算效率 ,而且可以保证计算的准确性 ;失效树中第一个失效元件是导致其余元件失效的根源 ,加强第一个失效元件 ,是保证结构系统不失效的最合理、最经济的方法 ;本文提出的分析计算方法及其软件FTA是有效的。     

CD1d and natural T cells: how their properties jump-start the immune system

Cellular and humoral immune mechanisms recruited to defend the host from infectious agents depend upon the early immune events triggered by antigen. The cytokine milieu within which the immune response matures is the most important of many factors that govern the nature of the immune response. Natural T cells, whose function is controlled by CD1d molecules, are an early source of cytokines that can bestow type 1 or type 2 differentiative potential upon helper T lymphocytes. This review attempts to illuminate the glycolipid antigen presentation properties of CD1d, how CD1d controls the function of natural T cells and how CD1d and natural T cells interact to jump start the immune system. CD1d is postulated to function as a sensor, sensing alterations in cellular lipid content by virtue of its affinity for such ligands. The presentation of a neo-self glycolipid, presumably by infectious assault of antigen-presenting cells, activates natural T cells, which promptly release pro-inflammatory and anti-inflammatory cytokines and jumpstart the immune system. Received 10 July 2000; received after revision 16 October 2000, accepted 16 November 2000     

多复变中Dp和H∝及βp空间的一些关系

在 Cⁿ中的单位球上, 讨论了Dirichlet 型空间D_p和广义Bloch空间β^q的相互包含关系以及D_p 和Hardy空间H^∝之间的点乘子,根据 p 的一些不同情形对M(H^∝, D_p ) 和 M( D_p , H^∝) 进行了刻划.     

计算机在地理空间概念教学中的应用

空间性是地理学科的重要特征 依据地理空间概念的特点 ,结合地理教学的实际 ,指出了常用软件Mapinfo、powerpoint在地理空间概念教学中的重要作用     

Role of Cys221 and Asn116 in the zinc-binding sites of the Aeromonas hydrophila metallo-β-lactamase

The CphA metallo--lactamase produced by Aeromonas hydrophila exhibits two zinc-binding sites. Maximum activity is obtained upon binding of one zinc ion, whereas binding of the second zinc ion results in a drastic decrease in the hydrolytic activity. In this study, we analyzed the role of Asn116 and Cys221, two residues of the active site. These residues were replaced by site-directed mutagenesis and the different mutants were characterized. The C221S and C221A mutants were seriously impaired in their ability to bind the first, catalytic zinc ion and were nearly completely inactive, indicating a major role for Cys221 in the binding of the catalytic metal ion. By contrast, the binding of the second zinc ion was only slightly affected, at least for the C221S mutant. Mutation of Asn116 did not lead to a drastic decrease in the hydrolytic activity, indicating that this residue does not play a key role in the catalytic mechanism. However, the substitution of Asn116 by a Cys or His residue resulted in an approximately fivefold increase in the affinity for the second, inhibitory zinc ion. Together, these data suggested that the first zinc ion is located in the binding site involving the Cys221 and that the second zinc ion binds in the binding site involving Asn116 and, presumably, His118 and His196.Received 3 March 2003; received after revision 4 August 2003; accepted 25 August 2003     

Structure and morphogenesis of bacteriophage T4

Bacteriophage T4 is one of the most complex viruses. More than 40 different proteins form the mature virion, which consists of a protein shell encapsidating a 172-kbp double-stranded genomic DNA, a tail, and fibers, attached to the distal end of the tail. The fibers and the tail carry the host cell recognition sensors and are required for attachment of the phage to the cell surface. The tail also serves as a channel for delivery of the phage DNA from the head into the host cell cytoplasm. The tail is attached to the unique portal vertex of the head through which the phage DNA is packaged during head assembly. Similar to other phages, and also herpes viruses, the unique vertex is occupied by a dodecameric portal protein, which is involved in DNA packaging.Received 18 February 2003; received after revision 16 April 2003; accepted 9 May 2003     

cDNA cloning and functional analysis of 4-coumarate --CoA: ligase (4CL) gene in Chinese white aspen

cDNA encoding 4-coumarate: CoA ligase (4CL) was isolated from the secondary developing xylem of Chinese white aspen (Populus tomentosa) by RT-PCR for the first time, which was 1619 bp in length. The coding sequence and putative amino acid sequence showed 97.53% and 97.00% identity to that of Pt4CL1 in quaking aspen (P. tremuloids), respectively. Molecular analysis indicated that 4CL was encoded by multiple genes in P.tomentosa, its mRNA was highly accumulated in xylem and the expression of 4CL revealed a biphasic pattern in one growing season, almost in phase with the expression of other related enzymes in lignin biosynthesis. Transgenic research showed that expression of antisense 4CL cDNA led to the decreasing of lignin content in transgenic tobaccos, among which the average reduction was 10.3% and the highest could be up to 18.9%. These data suggested that 4CL gene was a potential gene used in altering lignin biosynthesis by biotechnology for producing new materials of papermaking.