Distribution of Listeria monocytogenes molecular subtypes among human and food isolates from New York State shows persistence of human disease--associated Listeria monocytogenes strains in retail environments

While there is considerable information available regarding Listeria monocytogenes contamination patterns in food processing plants, our understanding of L. monocytogenes contamination and transmission in retail operations is limited. We characterized 125 food, 40 environmental, and 342 human clinical L. monocytogenes isolates collected in New York State from 1997 to 2002 using automated ribotyping and hly allelic variation. All environmental isolates were obtained from retail establishments and the majority of food isolates (98 isolates) were obtained from foods that were prepared or handled at retail. Overall, food and/or environmental isolates from 50 different retail establishments were characterized. The 125 food and 40 environmental isolates were differentiated into 29 and 10 ribotypes, respectively. For 16 retail establishments, we found evidence for persistence of one or more specific L. monocytogenes strains as indicated by isolation of the same EcoRI ribotype from food or environmental samples collected in a given establishment on different days. The human isolates were differentiated into 48 ribotypes. Statistical analyses showed that two ribotypes were significantly (P < 0.0001) more common among food isolates as compared with human isolates. However, a total of 17 ribotypes found among the human clinical isolates were also found among the food and environmental isolates. We conclude that L. monocytogenes, including subtypes that have been linked to human disease, can persist in retail environments. Implementation of Listeria control procedures in retail operations, which process and handle products that permit the growth of L. monocytogenes, are thus a critical component of a farm-to-table L. monocytogenes control program.     

Self-oscillations in field emission nanowire mechanical resonators: a nanometric dc-ac conversion

We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study, we have already achieved approximately 50% dc/ac (direct to alternating current) conversion. Electrical self-oscillations in NEMS open up a new path for the development of high-speed, autonomous nanoresonators and signal generators and show that field emission (FE) is a powerful tool for building new nanocomponents.     

RAYLEIGH-TAYLOR INSTABILITIES BY OVERTURNING EXPERIMENTS IN TANK

A laboratory study of the turbulence front initiated by the Rayleigh-Taylor instabilities was conducted by overturning a two-layer stratified flow in a tank. Dye was introduced to the upper layer and the concentration of the dye was determined using a video imaging method. The mass center of the heavier upper layer moved continuously to a lower elevation because of the intrusion of the heavier fluid into the lower layer and the lighter fluid into the upper layer. The downward movement of the mass center was accurately determined from the dye concentration profile. It is concluded that the initial advancement of the mass center follows a quadratic relation with time and the final advancement obeys a linear relation with time.     

船舶操纵性约束模测量系统设计与分析

为解决实验室船舶操纵性约束模实验中的测量及数据分析处理技术问题,开发组建实验测量系统,推导数据分析处理方法,以期实现约束模实验的测量与数据在线分析处理。根据前期研究经验,设计了较为完善的测量硬件系统方案;其中为实现约束模中精确的零相位整周期测量要求,采用光电开关利用数据采集卡的硬件触发启动功能来实现,并给出了整数周期测量的方案;利用最小二乘拟合及傅里叶分析等方法推导给出各船舶水动力导数数据处理方法。在此基础上,作为重点编写了完整的在线测量与数据在线分析程序,主要功能内部独立实现;该系统手工介入频度低,基本实现了测量的自动化,效率得到大幅提高。最后展开实际测量验证,数据的拟合结果与测量结果符合良好,验证了本文系统的可靠性;同时处理结果显示船舶附加质量导数Yv同船舶惯性质量很接近,而导数Yr'',Nv''数值很小近于零。     

面心立方结构钛的研究进展

面心立方结构钛是一种亚稳相，最早发现于超薄钛膜。除此之外，钛及钛合金在经历大塑性变形之后，也常常会发生hcp→fcc钛及钛合金的相变。近年来，大量研究报道了钛及钛合金经冷轧、压缩、拉伸和球磨等加工后观察到面心立方结构钛。为此，对近几十年来面心立方结构钛的制备方法、相变机理及其变形行为的研究进展进行了详细介绍。现有研究已证实，面心立方结构钛不仅能够协调材料的变形，而且有利于材料强度的提高。     

单层金刚石工具螺旋钻削复合材料的性能比较（英文）

使用不同形状、不同磨粒尺寸的单层金刚石工具以螺旋钻孔方式加工多向碳纤维-环氧树脂层压板，比较各工具的加工性能。在复合材料上钻孔时，和传统钻削相比，螺旋钻孔是更先进和完善的方法。选择7种不同工具开展性能试验，研究金刚石磨粒尺寸、刀具槽口类型和末端几何形状对钻进力、温度、钻进缺陷和表面完整性的影响。结果发现高速旋转钻削可以显著降低钻削力。使用磨粒尺寸更小的工具进行加工，可以改善钻孔表面粗糙度，但是其钻削力更大、钻削温度更高。带有槽口的工具可以减轻工具表面堵塞。和平直末端或无槽口的工具相比，球形末端的工具性能更好。