Detection of CD2 expression in chicken hematogenic embryo yolk sac lymphoid cells prior to thymus genesis

Lymphoid mononuclear cells from chick embryos at stage 16 were collected prior to fetal liver and thymus genesis to study the differentiation and function of the hematogenic yolk sac and to detect whether CD2 occurs on the surface of lymphoid mononuclear cells. The phenotype and functional activity of the cell surface protein E receptor and the ultrastructure of embryonic E＋ cells were compared with those of mature T cells. Our results indicate 99.36% homology between the E receptors of embryonic lymphocytes and mature T cells. Other similarities, including molecular distribution, motivation, the ability to form an erythrocyte rosette, the structure of the receptor-ligand complex, and the conformation of the signal channel, were detected between embryonic lymphocytes and mature CD2-expressing T cells. These results indicate that CD2 is already expressed prior to fetal liver and thymus genesis and that its expression is not dependent on the thymic microenvironment.     

Effects on the early development of the pearl sac by cytochrome c, yolk lecithin and polyvinyplyrro

Mantle pieces ofHyriopisis cumingii was treated by three kinds of solution, These mantle pieces were inserted together with paraffin nucleuses into the connective tissue of three groups ofHyriopisis cumingii. These operated animals were cultured in a pool for a month. Several pearl sacs were put out and immersed by Bouin's solution after every five days. Sections of each animals were made by histological method. Those without treatment were in a control group. Observations of these sections showed that cytochrome c and yolk lecithin have an accelerated roles on pearl sac development and pearl layer secretion. No effects on pearl sac development by polyvinyplyrrolidone (PVP). Zheng Junying:born in May, 1966, Lecturer     

牛顿对色散研究的贡献

文章综述了历史上我国与欧洲一些国家的科学家对色散的研究，总结了牛顿对色散研究的突出贡献。     

Human contribution to the European heatwave of 2003

The summer of 2003 was probably the hottest in Europe since at latest ad 1500, and unusually large numbers of heat-related deaths were reported in France, Germany and Italy. It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate--for example, increasing concentrations of greenhouse gases in the atmosphere--because almost any such weather event might have occurred by chance in an unmodified climate. However, it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave. Here we use this conceptual framework to estimate the contribution of human-induced increases in atmospheric concentrations of greenhouse gases and other pollutants to the risk of the occurrence of unusually high mean summer temperatures throughout a large region of continental Europe. Using a threshold for mean summer temperature that was exceeded in 2003, but in no other year since the start of the instrumental record in 1851, we estimate it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude.     

欧拉对函数概念的发展

目的 探讨欧拉(Leonard Euler,1707-1783)对函数概念的贡献.方法 文献考证与历史分析.结果 欧拉定义的作为解析式的函数概念,使函数概念由几何形态转向代数形态;对超越函数幂级数展式的研究把微积分的研究对象由代数函数扩展为解析函数;对连续性的研究引出了对解析函数的探讨;由物理推理及几何直观催生的非连续函数为微积分的发展提出了新的问题.它的出现预示着微积分研究对象面临着新一轮的扩展;1775年提出的一个更为广泛的函数概念对19世纪的函数概念产生了深刻的影响.结论 欧拉对函数概念的发展不仅推动了微积分的发展,而且为现代函数概念的产生做了准备.     

Ribosomal RNA sequence shows Pneumocystis carinii to be a member of the fungi

Pneumocystis carinii pneumonia is the most common opportunistic infection in AIDS, and accounts for significant morbidity and mortality in these and other immunocompromised patients. P. carinii is a eukaryotic microorganism of uncertain taxonomy that can infect numerous mammalian hosts. Developing from a small, unicellular 'trophozoite' into a 'cyst' containing eight 'sporozoites', its life cycle superficially resembles those seen both in the Protozoa and Fungi. Morphological and ultrastructural observations have lead some investigators to conclude that the organism is a protozoan, while others have felt that it more closely resembles a fungus. Phylogenetic relationships can be inferred from comparisons of macromolecular sequences. Small subunit ribosomal RNAs (16S-like rRNAs) are well-suited for this purpose because they have the same function in all organisms and contain sufficient information to estimate both close and distant evolutionary relationships. Phylogenetic frameworks based upon such comparisons reveal that the plant, animal and fungal lineages are distinct from the diverse spectrum of protozoan lineages. In this letter, phylogenetic analysis of Pneumocystis 16S-like rRNA demonstrates it to be a member of the Fungi.     

毛泽东对统一战线理论的伟大贡献

统一战线在我国革命和建设中有着特殊的地位,毛泽东同志对统一战线理论的形成和发展起着极其重要的伟大作用.本文从新民主主义革命时期、社会主义建设时期和改革开放不同的历史阶段,较详尽地阐述了毛泽东对统一战理论的贡献,以及统一战线作为"法宝"主要内容和重大意义.     

Measurement of thermal contribution to photoreceptor sensitivity

Activation of a visual pigment molecule to initiate phototransduction requires a minimum energy, Ea, that need not be wholly derived from a photon, but may be supplemented by heat. Theory predicts that absorbance at very long wavelengths declines with the fraction of molecules that have a sufficient complement of thermal energy, and that Ea is inversely related to the wavelength of maximum absorbance (lambda(max)) of the pigment. Consistent with the first of these predictions, warming increases relative visual sensitivity to long wavelengths. Here we measure this effect in amphibian photoreceptors with different pigments to estimate Ea (refs 2, 5-7) and test experimentally the predictions of an inverse relation between Ea and lambda(max). For rods and 'red' cones in the adult frog retina, we find no significant difference in Ea between the two pigments involved, although their lambda(max) values are very different. We also determined Ea for the rhodopsin in toad retinal rods--spectrally similar to frog rhodopsin but differing in amino-acid sequence--and found that it was significantly higher. In addition, we estimated Ea for two pigments whose lambda(max) difference was due only to a chromophore difference (A1 and A2 pigment, in adult and larval frog cones). Here Ea for A2 was lower than for A1. Our results refute the idea of a necessary relation between lambda(max) and Ea, but show that the A1 --> A2 chromophore substitution decreases Ea.     

The contribution of bone to whole-organism physiology

The mouse genetic revolution has shown repeatedly that most organs have more functions than expected. This has led to the realization that, in addition to a molecular and cellular approach, there is a need for a whole-organism study of physiology. The skeleton is an example of how a whole-organism approach to physiology can broaden the functions of a given organ, reveal connections of this organ with others such as the brain, pancreas and gut, and shed new light on the pathogenesis of degenerative diseases affecting multiple organs.     

基于POV-ray逆向光线追踪模型模拟地表反射率图像

基于DEM数字高程模型、高空间分辨率地表反射率图像,采用POV-ray逆向光线追踪模型考虑地形影响,进行不同观测几何下的低空间分辨率地表反射率图像模拟;并以垂直观测为例,基于POV-ray逆向光线追踪模型生成地表反射率;并通过与真实反射率图像做比较,得到整幅图像的相对误差在-0.01～0.结果表明,基于POV-ray模拟地表反射率可行.     

运动目标的快速检测与跟踪算法研究

传统的模板匹配算法精度虽高,但运算量大、效率较低。本文结合了帧差法以及多分辨率图像匹配的优点对模板匹配算法进行改进,并通过引入“预测”机制改变初始搜索点,减少了匹配区域,提高了运算速度,满足了实时处理要求。同时,采用了一种根据灰度特征进行模式匹配的跟踪算法,提高了模板匹配法对于目标运动姿态变化的自适应能力。仿真结果表明:上述算法在目标方向、平移、旋转以及图像背景、对比度、亮度发生改变时,均能较好的检测到目标。     

从《艺术人生》看明星类谈话节目的特点

以《艺术人生》为例,从五个方面论述了明星类谈话节目的特点:即以情感人;以诚动人;以"悬念"吸引人;以自然感召人,以"即时性"满足人。     

《韩非子》在古代文体流变史上的贡献

从文章学的角度看,《韩非子》是古代文体的集大成者,它不仅是诸多文体之流,而且是某些文体之源,体裁多样,在中国古代文体流变史上具有特殊的贡献。     

论邓小平同志对统一战线的历史性贡献

邓小平同志在新的历史条件下,坚持、继承和发展了毛泽东的统一战线理论.他关于统一战线的本质、地位和作用的论述,关于统一战线性质、对象和范围的论述,关于多党合作的论述,关于统一战线为经济建设服务的论述,关于"一国两制",和平统一祖国的论述,关于知识分子是工人阶级一部分的论述,关于民族问题的论述都从理论和实践的结合上充实和丰富了我们党的统一战线理论,为科学社会主义的理论宝库增添了新内容.