国内外致泻大肠埃希氏菌O157:H7的检测标准比较及建议

致泻大肠埃希氏菌O157:H7（STEC O157:H7）是大肠埃希氏菌中致病性最严重的一种食源性致病菌,主要存在于牛肉、牛奶、水果及其制品中,对身体健康造成很大危害,甚至引发死亡。食品中STEC O157:H7检测尤为重要。本文对国内外STEC O157:H7的检测标准进行比较,提出我国标准在样品前处理、快速筛选方法的应用等方面需要加强,以便为该菌快速准确检测提供帮助,实现与国际标准化体系建设接轨,满足实验室检测需要。     

猪源ST9型耐甲氧西林金黄色葡萄球菌中前噬菌体的流行状况与转导分析

本研究旨在分析猪源ST9型耐甲氧西林金黄色葡萄球菌(Staphylococcus aureus,MRSA)中前噬菌体的流行情况、结构特点和转导能力,探究前噬菌体在猪源MRSA流行克隆形成中的作用。基于全基因组信息,分析了近年来从我国多省分离的131株ST9型MRSA中前噬菌体的流行率、分型、亲缘关系和结构特征;选取含不同分型前噬菌体的菌株进行诱导,对诱导获得的噬菌体颗粒进行转导,测定转导子的耐药表型及体外适应性。研究结果显示：猪源ST9型MRSA的前噬菌体携带率为78.6%(103/131株),其中,63株携带完整前噬菌体序列,所有前噬菌体序列均不含耐药基因,仅2.9%(3/103株)的前噬菌体序列含毒力基因;前噬菌体谱型丰富,其整合酶分型主要为Sa2int和Sa4int;各型别前噬菌体结构同源性较高,完整前噬菌体可被诱导为长尾噬菌体;噬菌体颗粒可包装供体菌的aadD、tet(L)耐药基因并转导至受体菌中;转导子可获得卡那霉素、四环素耐药表型,体外生长能力与受体菌株无明显差异(P>0.05)。研究结果表明：猪源ST9型MRSA的前噬菌体携带率较高,谱型丰富,不携带耐药基因,部分噬菌体可包装供体菌的耐药基因转导至受体菌,产生的适应性代价小。     

Influence of Steam Turbine System on Low Frequency Oscillation

Low frequency oscillation of electric power system is a problem which electric workers always care about. The influences of prime mover characteristics were ignored in the past research. The paper introduces the models of steam turbine system and each part of electric power system, and calculates the corresponding eigenvalues, then analyzes the influences of steam turbine system on low frequency oscillation.     

Analysis of thermal stress in a water pipe of blast furnace copper stave

To solve the general problem that copper staves experience water pipe failure in blast furnace,the effects of constraints on the thermal stress distribution of copper stave water pipe are investigated by thermal-structural coupling analysis.In this study,a mathematical model of thermal stress of copper stave is established to analyze the thermal deformation and stress distribution of water pipe under subject to different types of constraints.The results show that the thermal stress on the root of water pipe is larger than others as the terminal of water pipe is free or being fixed.But the equivalent stress on the root of water pipe is just 45 MPa as the terminal of water pipe is free,which is lower than the yield strength of pure copper.The equivalent stress on the root of water pipe is about 272 MPa as the terminal of water pipe is being fixed,and exceeds the yield strength of pure copper.The water pipes should be flexible.The maximum equivalent stress is about 600 MPa as the water pipe is subjected to the constraint of shell,which is far beyond the yield strength of pure copper.The maximum displacement is located at the end of water pipe and is about 1.73 mm.Then the diameter of the hole should be 120 mm with taking installation error into consideration.     

Dynamics of Actin Polymerization

The process of actin polymerization and depolymerization have some relation with its function,the activation of such process is compatible to its functions. The polymerization progress is divided into four steps: The first step is the activation of the monomer actin. The nucleation of actin nucleus forms in the second step which limits the polymerization speed. The elongation of the F-actin filaments happens in the following step. In the last step, a steady-state is attained, the length of the filament does not change because the polymerizing rate in the barbed end is the same with the depolymerizing rate in the pointed end. Some factors which affect the polymerizing process, such as nucleotide, actin related proteins are discussed. The aim is to know more about how to assemble the complicated system with biomacromolecule and what to function.     

Adaptive Intrusion Detection System Based on Agent and Data Mining

Intrusion detection system is an essential component of network security protection mechanisms. Most intrusion detection system can not adapt the variation of network environment. Aiming at this problem, an adaptive strategy that composed of condition space and strategy space is proposed. The condition space describes the network environment and the strategy space describes the strategy. There is an exclusive strategy corresponds to a certain environment state in condition space. On the base of the adaptive strategy, an adaptive intrusion detection system based on agent and data mining is designed. The simulation experiments indicate that the adaptive strategy is effective.     

Water model study on flow optimization of five streams L-type tundish

In this paper, the water model method is used to optimize the flow behavior of asymmetrical five streams L-type tundish in a steelmaking plant. The results show that the optimization plan is set up with turbulence suppressor T+ vice guide wall D2+ main guide wall with three holes (D1a) which consists of top two holes with 25° inclination and one hole with 30° inclination below. With this plan, the time which the colorants reach to the outlets increases, the difference of response time in all outlets decreases, the peak concentration of the RTD reduces, the existence time of high concentration liquid steel extends, and the ratio of dead zone in each streams reduces.     

Behavior and Design of High-strength Bolt in Tensile Connection

The tensile strength of high strength bolt is affected by many factors, including prying force. The prying force can result in the increment of bolt force, for which the connection failed ahead of time. Several methods are presented for calculating the prying force. In the China's "Code for Design of Steel Structure" (GB50017), there is no formula for calculation of prying force and a factor of 0.8 is considered in formula for tensile strength of bolt for taking the prying force into account. It is proposed that the design value of tensile resistance for high strength bolt should be increased.