Shiga toxin producing Escherichia coli(STEC)outbreak is a public health concern as it can potentially cause a variety of clinical manifestations including diarrhea,hemorrhagic colitis and hemolytic uremic syndrome(HUS...Shiga toxin producing Escherichia coli(STEC)outbreak is a public health concern as it can potentially cause a variety of clinical manifestations including diarrhea,hemorrhagic colitis and hemolytic uremic syndrome(HUS).However E.coli are generally innocuous commensal organisms,and there is a need to discriminate pathogenic from non-pathogenic isolates rapidly and accurately.In this study,we have used standard culture based methods and advanced molecular approaches to characterize E.coli in food in a local outbreak investigation.We show that the application of DNA based detection methods including real-time PCR and DNA microarray along with a traditional culture method can identify the organism implicated in an outbreak at the strain level for pathogenic potential.展开更多
联合双频GPS数据,利用相位平滑伪距算法,可得到包含斜向电离层总电子含量(slant total electron content,sTEC)、测站和卫星差分码偏差(differential code bias,DCB)的电离层观测值(称之为"平滑伪距电离层观测值"),常应用于...联合双频GPS数据,利用相位平滑伪距算法,可得到包含斜向电离层总电子含量(slant total electron content,sTEC)、测站和卫星差分码偏差(differential code bias,DCB)的电离层观测值(称之为"平滑伪距电离层观测值"),常应用于与电离层有关的研究。然而,平滑伪距电离层观测值易受平滑弧段长度和与测站有关的误差影响。提出一种新算法:利用非组合精密单点定位技术(precise point positioning,PPP)计算电离层观测值(称之为"PPP电离层观测值"),进而估计sTEC和站星DCB。基于短基线试验,先用一台接收机按上述两种方法估计sTEC,用于改正另一接收机观测值的电离层延迟以实施单频PPP,结果表明,利用PPP电离层观测值得到的sTEC精度较高,定位结果的可靠性较强。随后,选取全球分布的8个IGS(internationalGNSS service)连续跟踪站2009年1月内某四天的观测数据,利用上述两种电离层观测值计算所有卫星的DCB,并将计算结果与CODE发布的月平均值进行比较,其中,平滑伪距电离层观测值的卫星DCB估值与CODE(Centre for Orbit Deter mination in Europe)发布值的差别较大,部分卫星甚至可达0.2～0.3 ns,而PPP电离层观测值而言,绝大多数卫星对应的差异均在0.1 ns以内。展开更多
文摘Shiga toxin producing Escherichia coli(STEC)outbreak is a public health concern as it can potentially cause a variety of clinical manifestations including diarrhea,hemorrhagic colitis and hemolytic uremic syndrome(HUS).However E.coli are generally innocuous commensal organisms,and there is a need to discriminate pathogenic from non-pathogenic isolates rapidly and accurately.In this study,we have used standard culture based methods and advanced molecular approaches to characterize E.coli in food in a local outbreak investigation.We show that the application of DNA based detection methods including real-time PCR and DNA microarray along with a traditional culture method can identify the organism implicated in an outbreak at the strain level for pathogenic potential.
文摘利用全球导航卫星系统(Global Navigation Satellite System,GNSS)双频差分信号进行电离层电子含量反演是一种常用的电离层探测手段,但GNSS信号在强电磁干扰环境下,被淹没于电磁噪声中而无法被提取,影响电离层总电子含量(total electron content,TEC)反演系统的可靠性。采用传统调零抗干扰阵列天线方案能解决干扰源剥离的问题,但调零信号的天线相位中心不稳定导致高精度的相位平滑伪距和精密单点定位(precise point positioning,PPP)算法无法收敛。针对强干扰环境下的电离层监测需求,本文提出一种抗干扰TEC数据反演手段,通过对阵列天线通道幅相一致性进行校正,保证相位中心的稳定性,从而推算出准确的电离层TEC信息,提高了系统的可靠性和抗干扰能力。
文摘联合双频GPS数据,利用相位平滑伪距算法,可得到包含斜向电离层总电子含量(slant total electron content,sTEC)、测站和卫星差分码偏差(differential code bias,DCB)的电离层观测值(称之为"平滑伪距电离层观测值"),常应用于与电离层有关的研究。然而,平滑伪距电离层观测值易受平滑弧段长度和与测站有关的误差影响。提出一种新算法:利用非组合精密单点定位技术(precise point positioning,PPP)计算电离层观测值(称之为"PPP电离层观测值"),进而估计sTEC和站星DCB。基于短基线试验,先用一台接收机按上述两种方法估计sTEC,用于改正另一接收机观测值的电离层延迟以实施单频PPP,结果表明,利用PPP电离层观测值得到的sTEC精度较高,定位结果的可靠性较强。随后,选取全球分布的8个IGS(internationalGNSS service)连续跟踪站2009年1月内某四天的观测数据,利用上述两种电离层观测值计算所有卫星的DCB,并将计算结果与CODE发布的月平均值进行比较,其中,平滑伪距电离层观测值的卫星DCB估值与CODE(Centre for Orbit Deter mination in Europe)发布值的差别较大,部分卫星甚至可达0.2～0.3 ns,而PPP电离层观测值而言,绝大多数卫星对应的差异均在0.1 ns以内。
