基于小波变换的彩色图像压缩技术的研究

结合人眼视觉特性和零树理论,在SPIHT编码算法的改进和扩展的基础上提出了一套彩色图像压缩方案.经测试,该方案具有良好的效果,并且易于实现.     

Target mimicry provides a new mechanism for regulation of microRNA activity

MicroRNAs (miRNA) regulate key aspects of development and physiology in animals and plants. These regulatory RNAs act as guides of effector complexes to recognize specific mRNA sequences based on sequence complementarity, resulting in translational repression or site-specific cleavage. In plants, most miRNA targets are cleaved and show almost perfect complementarity with the miRNAs around the cleavage site. Here, we examined the non-protein coding gene IPS1 (INDUCED BY PHOSPHATE STARVATION 1) from Arabidopsis thaliana. IPS1 contains a motif with sequence complementarity to the phosphate (Pi) starvation-induced miRNA miR-399, but the pairing is interrupted by a mismatched loop at the expected miRNA cleavage site. We show that IPS1 RNA is not cleaved but instead sequesters miR-399. Thus, IPS1 overexpression results in increased accumulation of the miR-399 target PHO2 mRNA and, concomitantly, in reduced shoot Pi content. Engineering of IPS1 to be cleavable abolishes its inhibitory activity on miR-399. We coin the term 'target mimicry' to define this mechanism of inhibition of miRNA activity. Target mimicry can be generalized beyond the control of Pi homeostasis, as demonstrated using artificial target mimics.     

Anisotropy and Corotation of Galactic Cosmic Rays

Based on some 40 billion cosmic ray events collected from 1997 to 2005 by the Tibet Air Shower Array experiment (a major scientific collaboration between China and Japan) operating at the YangBaJing Cosmic Ray Observatory (90.522 E, 30. 102 N; 4300 m above sea level) near Lhasa in Tibet, a two-dimensiondl cosmic-ray intensity map in the sky was obtained with very high directional granularity and unprecedented precision in intensity at a level of 10-4.     

The earliest dromaeosaurid theropod from South America

The evolutionary history of Maniraptora, the clade of carnivorous dinosaurs that includes birds and the sickle-clawed Dromaeosauridae, has hitherto been largely restricted to Late Jurassic and Cretaceous deposits on northern continents. The stunning Early Cretaceous diversity of maniraptorans from Liaoning, China, coupled with a longevity implied by derived Late Jurassic forms such as Archaeopteryx, pushes the origins of maniraptoran lineages back to Pangaean times and engenders the possibility that such lineages existed in Gondwana. A few intriguing, but incomplete, maniraptoran specimens have been reported from South America, Africa and Madagascar. Their affinities remain contested, however, and they have been interpreted as biogeographic anomalies relative to other faunal components of these land-masses. Here we describe a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.     

Genomic sequence of the pathogenic and allergenic filamentous fungus Aspergillus fumigatus

Aspergillus fumigatus is exceptional among microorganisms in being both a primary and opportunistic pathogen as well as a major allergen. Its conidia production is prolific, and so human respiratory tract exposure is almost constant. A. fumigatus is isolated from human habitats and vegetable compost heaps. In immunocompromised individuals, the incidence of invasive infection can be as high as 50% and the mortality rate is often about 50% (ref. 2). The interaction of A. fumigatus and other airborne fungi with the immune system is increasingly linked to severe asthma and sinusitis. Although the burden of invasive disease caused by A. fumigatus is substantial, the basic biology of the organism is mostly obscure. Here we show the complete 29.4-megabase genome sequence of the clinical isolate Af293, which consists of eight chromosomes containing 9,926 predicted genes. Microarray analysis revealed temperature-dependent expression of distinct sets of genes, as well as 700 A. fumigatus genes not present or significantly diverged in the closely related sexual species Neosartorya fischeri, many of which may have roles in the pathogenicity phenotype. The Af293 genome sequence provides an unparalleled resource for the future understanding of this remarkable fungus.     

Unexpected diversity of small eukaryotes in deep-sea Antarctic plankton

Phylogenetic information from ribosomal RNA genes directly amplified from the environment changed our view of the biosphere, revealing an extraordinary diversity of previously undetected prokaryotic lineages. Using ribosomal RNA genes from marine picoplankton, several new groups of bacteria and archaea have been identified, some of which are abundant. Little is known, however, about the diversity of the smallest planktonic eukaryotes, and available information in general concerns the phytoplankton of the euphotic region. Here we recover eukaryotes in the size fraction 0.2-5 microm from the aphotic zone (250-3,000 m deep) in the Antarctic polar front. The most diverse and relatively abundant were two new groups of alveolate sequences, related to dinoflagellates that are found at all studied depths. These may be important components of the microbial community in the deep ocean. Their phylogenetic position suggests a radiation early in the evolution of alveolates.     

Mesoscale vertical motion and the size structure of phytoplankton in the ocean

Phytoplankton size structure is acknowledged as a fundamental property determining energy flow through 'microbial' or 'herbivore' pathways. The balance between these two pathways determines the ability of the ecosystem to recycle carbon within the upper layer or to export it to the ocean interior. Small cells are usually characteristic of oligotrophic, stratified ocean waters, in which regenerated ammonium is the only available form of inorganic nitrogen and recycling dominates. Large cells seem to characterize phytoplankton in which inputs of nitrate enter the euphotic layer and exported production is higher. But the size structure of phytoplankton may depend more directly on hydrodynamical forces than on the source of available nitrogen. Here we present an empirical model that relates the magnitude of mesoscale vertical motion to the slope of the size-abundance spectrum of phytoplankton in a frontal ecosystem. Our model indicates that the relative proportion of large cells increases with the magnitude of the upward velocity. This suggests that mesoscale vertical motion-a ubiquitous feature of eddies and unstable fronts-controls directly the size structure of phytoplankton in the ocean.     

馏分油脱酸剂技术的应用研究

针对直馏柴油、减压馏分油碱洗电精制脱酸工艺存在的不足,开发了一种新的馏分油脱酸剂技术,完成了实验室研究、工业试验和工业应用。该技术使用现有的馏分油碱洗电精制工艺设备,只需增加水洗和脱酸剂回收系统,技术改造费用少。与传统的碱洗脱酸工艺比较,具有适应原料范围宽,烧碱用量下降67% ~75%,完全消除乳化,混合强度不影响脱酸效果,馏分油损失下降50% ~60%;脱酸剂再生循环使用,无废碱液排放,环境污染大为降低等优点。在最优操作条件下精制油酸值为零,已达到最苛刻的变压器油酸值指标(酸值<0. 017mgKOH/g),回收石油酸达到石油酸一级品65号酸的质量标准(SH/T0530-92)。     

GA-ANN综合优化地震属性的应用研究

讨论了应用遗传算法对地震属性进行优化组合的合理性和可行性,并依据遗传算法的框架提出了算法的实现步骤。在设计个体适应度评价函数环节讨论了以对非线性映射具广泛适应性的人工神经网络模型替代优化目标函数的思想的合理性及实现方法。最后以应用实例的数据对算法进行了检验并得到较满意的结果。