General method for plasmid construction using homologous recombination

We describe a general method for plasmid assembly that uses yeast and extends beyond yeast-specific research applications. This technology exploits the homologous recombination, double-stranded break repair pathway in Saccharomyces cerevisiae to join DNA fragments. Synthetic, double-stranded "recombination linkers" were used to "subclone" a DNA fragment into a plasmid with > 80% efficiency. Quantitative data on the influence of DNA concentration and overlap length on the efficiency of recombination are presented. Using a simple procedure, plasmids were shuttled from yeast into E. coli for subsequent screening and large-scale plasmid preps. This simple method for plasmid construction has several advantages. (i) It bypasses the need for extensive PCR amplification and for purification, modification and/or ligation techniques routinely used for plasmid constructions. (ii) The method does not rely on available restriction sites, thus fragment and vector DNA can be joined within any DNA sequence. This enables the use of multifunctional cloning vectors for protein expression in mammalian cells, other yeast species, E. coli and other expression systems as discussed. (iii) Finally, the technology exploits yeast strains, plasmids and microbial techniques that are inexpensive and readily available.     

基于改进信号注入配电网单相接地故障定位研究

针对配电网单相接地故障定位难的问题,阐述了传统信号注入法的基本原理,提出了改进信号注入法,建立了matlab/simulink仿真模型。通过Matlab仿真实例验证,该方法有效可行,实现了在线故障定位,有效地缩短了停电时间和减少停电次数,提高了配电网供电质量稳定性。     

全桥拓朴隔离式开关电源主变压器磁设计

全桥拓朴结构的隔离式开关电源能在较小的尺寸下实现较高的功率变换,是高功率密度电源的重要电路结构,其高频主变压器磁心一般选择低损耗功率锰锌软磁铁氧体材料,其设计对电源的尺寸、性能有显著影响.磁设计的目的是用尽可能小的磁心传输尽可能高的功率,但受到两个限制性条件的制约,即磁心的发热和磁饱和.在散热充分的情况下,限制性条件就...     

混凝土坝裂缝变形的不确定性分析模型

混凝土坝裂缝的发生和发展受到不确定因素影响。将大坝系统及其安全监控看作一个受诸多因素影响的不确定性系统,结合裂缝实测资料,应用近似推理模型和信息分配法,建立了裂缝变形的不确定性分析模型。     

鄂尔多斯盆地高自然伽马异常特征

为了加深对盆地深部和浅部高自然伽马异常特征综合分析研究,揭示高自然伽马异常地质成因,从而 促进盆地多种能源矿产协同开发研究,针对收集大量的地球物理测井资料、地质资料及其他相关成果,绘制并分 析了相关成果图。研究中遵循从单孔测井曲线特征分析到典型剖面研究,并按层对高自然伽马的平面分布特征 进行分析研究。化验测试结果和自然伽马能谱测井成果研究表明,在本区,自然伽马异常增大主要是由于铀的 活化和聚集,导致铀元素增加而引起。相关研究表明,盆地深部和浅部的铀异常具有一定的关系,盆地历经的沉 积环境变迁是铀元素富集的主导因素。     

Microstructural Changes in Wood Plastic Composites Due to Wetting and Re-drying Evaluated by X-ray Microtomography

An extruded wood polypropylene composite subjected to soaking-drying cycles in distilled water was investigated nondestructively using an X-ray microtomography. The representative elementary volumes of the material were examined and discussed using means/median of image intensity values and void contents in 3D XMT images. A 2 mm cube was determined as the representative elementary volume for this material. There were some differences for means in the dry, wet, and re-dried states. The specimen cutting position, i.e., surface or core, affects the results because there was a “resin rich/glazed” surface layer formed during extrusion and the WPPC material had a larger scale heterogeneity, which relates to the difference in flow rate between the core and face of a die. The void contents of re-dried specimens were higher than those of dry specimens.     

天然气加热炉的腐蚀原因及防护对策

天然气加热炉的腐蚀是一个普遍现象.本文从引起腐蚀的因素人手,详细剖析腐蚀发生的原因,提出监测和治理相结合的方法,系统地介绍了几种常用的防腐技术,包括添加缓蚀剂、使用耐腐蚀材料、界面涂层、电化学防腐及其它相关防腐技术.     

PDF417二维条码肖像图片压缩编码的优化算法研究

针对PDF417二维条码存储空间有限的问题，提出了一种基于小波变换的有损图像压缩算法，通过这个算法，可以将静态图片信息加入PDF417条码中，并能够满足在指定字节数情况下保证高质量地压缩图像，该文在分析小波变换等算法理论的基础上，详细介绍了PDF417二维条码肖像图片压缩编码的优化算法及该算法的实验结果与美国Symbol公司的PC2VQ算法结果对比。     

Fact-oriented modelling for data analysis

Abstract. Although entity-relationship modelling is the most popular means of specifying the conceptual schema for the data perspective of an information system, an alternative design approach known as fact-oriented modelling appears to offer advantages. This paper provides an overview of fact-oriented modelling, including some recent revisions and an evaluation of how the method has coped with large-scale practical applications. One distinguishing feature of the approach is its emphasis on natural verbalization of information examples in terms of elementary facts. This notion of elementarity is clarified to cater for a problematic case involving compositely identified object types. Finally, the algorithm for mapping a conceptual to a relational schema is revised to cater for lazy object types.     

An automatic braking system that stabilizes leukocyte rolling by an increase in selectin bond number with shear

Wall shear stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall shear stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall shear stress increases the rate of dissociation of individual selectin-ligand tether bonds exponentially (, ) thereby destabilizing rolling. We find that this is compensated by a shear-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low shear stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall shear stress and ligand density, in contrast to rolling on antibodies (). Furthermore, our data successfully predict the threshold wall shear stress below which rolling does not occur. This is a special case of the more general regulation by shear of the number of bonds, in which the number of bonds falls below one.