The archaebacteria and eukaryotic origins

Critical analysis of the phylogeny of prokaryotes is in its infancy. Woese and others have made the startling proposal that methane-producing bacteria and a few others form a phyletically unified group, the Archaebacteria, as old and as diverse (although not now as numerous) as all other bacteria. The only critique of this proposal is inadequate. Here we present an alternative view, that the Archaebacteria were derived from other bacteria and contain the ancestor of a cell which engulfed others, eventually to become the first eukaryote.     

CP破坏的物理根源

本文介绍了几个重要的CP破坏模型,讨论了它们的成功之处和所存在的问题,结合CP破坏研究的现状,提出几点展望。     

The origins and the future of microfluidics

The manipulation of fluids in channels with dimensions of tens of micrometres--microfluidics--has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.     

新疆油画特色及其形成原因

新疆油画的发展是从建国后开始的,20世纪70年代末期开始进入快速发展时期。由于地理位置的原因,新疆油画同苏派油画有着密切的联系。加之伊斯兰文化、新疆歌舞、新疆石窟壁画、中亚细密画等诸多原因的影响,使得新疆油画形成了一种独特的风格,为中国油画百花园增添了一支奇葩。     

基于路径的图像变形算法

针对计算机辅助图案设计系统中基于路径的图像变形问题，提出了通过构造笛卡尔坐标系来建立变形映射关系的算法。探讨了两种变形方式：柱状变形和带状变形，并利用带状变形模拟了一种双面带的变形效果。对路径剧烈转折时柱状变形效果差的弱点，采用了一种限制映射区域的变形方法，改善了图像剧烈弯折时的变形效果。另还讨论了图像的反混淆问题，并结合变形算法，提出了一种基于平滑直线的图像反混淆算法。     

昆虫成虫滞育的研究进展

本文综述了近年来有关昆虫成虫滞育的研究概况,阐述了昆虫成虫滞育的特点,滞育的生理生化变化,以及滞育与环境因素的关系。其中滞育的生理生化研究方面主要介绍了能量代谢和代谢物质的变化。     

抗虫基因Bt的研究进展

植物抗虫基因为防治农业害虫提供了一条崭新途径。而Bt基因的应用最普遍，对Bt基因的作用机理、分类、应用及可行性改造等方面作了详尽的阐述，着重分析和探讨了目前抗虫基因Bt植物转基因育种中存在的一些问题。并就这些问题及如何合理持续利用Bt基因进行了探讨。     

Multiple evolutionary origins of prochlorophytes within the cyanobacterial radiation.

The taxonomic group Prochlorales (Lewin 1977) Burger-Wiersma, Stal and Mur 1989 was established to accommodate a set of prokaryotic oxygenic phototrophs which, like plant, green algal and euglenoid chloroplasts, contain chlorophyll b instead of phycobiliproteins. Prochlorophytes were originally proposed (with concomitant scepticism) to be a monophyletic group sharing a common ancestry with these 'green' chloroplasts. Results from molecular sequence phylogenies, however, have suggested that Prochlorothrix hollandica is not on a lineage that leads to plastids. Our results from 16S ribosomal RNA sequence comparisons, which include new sequences from the marine picoplankter Prochlorococcus marinus and the Lissoclinum patella symbiont Prochloron sp., indicate that prochlorophytes are polyphyletic within the cyanobacterial radiation, and suggest that none of the known species is specifically related to chloroplasts. This implies that the three prochlorophytes and the green chloroplast ancestor acquired chlorophyll b and its associated structural proteins in convergent evolutionary events. We report further that the 16S rRNA gene sequence from Prochlorococcus is very similar to those of open ocean Synechococcus strains (marine cluster A), and to a family of 16S rRNA genes shotgun-cloned from plankton in the north Atlantic and Pacific Oceans.     

The concepts of 'sameness' and 'difference' in an insect

Insects process and learn information flexibly to adapt to their environment. The honeybee Apis mellifera constitutes a traditional model for studying learning and memory at behavioural, cellular and molecular levels. Earlier studies focused on elementary associative and non-associative forms of learning determined by either olfactory conditioning of the proboscis extension reflex or the learning of visual stimuli in an operant context. However, research has indicated that bees are capable of cognitive performances that were thought to occur only in some vertebrate species. For example, honeybees can interpolate visual information, exhibit associative recall, categorize visual information and learn contextual information. Here we show that honeybees can form 'sameness' and 'difference' concepts. They learn to solve 'delayed matching-to-sample' tasks, in which they are required to respond to a matching stimulus, and 'delayed non-matching-to-sample' tasks, in which they are required to respond to a different stimulus; they can also transfer the learned rules to new stimuli of the same or a different sensory modality. Thus, not only can bees learn specific objects and their physical parameters, but they can also master abstract inter-relationships, such as sameness and difference.     

Multiple evolutionary origins of prochlorophytes, the chlorophyll b-containing prokaryotes.

Prochlorophytes are prokaryotes that carry out oxygenic photosynthesis using chlorophylls a and b, but lack phycobiliproteins as light-harvesting pigments. These characteristics distinguish them from cyanobacteria, which contain phycobiliproteins, but no chlorophyll b. Three prochlorophyte genera have been described: Prochloron, Prochlorothrix and Prochlorococcus. The prochlorophytes share their pigment characteristics with green plant and euglenoid chloroplasts, which has led to a debate on whether these chloroplasts may have arisen from an endosymbiotic prochlorophyte rather than a cyanobacterium. Molecular sequence data, including those presented here based on a fragment of the rpoC1 gene encoding a subunit of DNA-dependent RNA polymerase, indicate that the known prochlorophyte lineages do not include the direct ancestor of chloroplasts. We also show that the prochlorophytes are a highly diverged polyphyletic group. Thus the use of chlorophyll b as a light-harvesting pigment has developed independently several times in evolution. Similar conclusions have been reached in parallel studies using 16S ribosomal RNA sequences.