Liquid phase microextraction applications in food analysis

Over the last years, liquid-phase microextraction (LPME) in its different application modes (single drop microextraction, dispersive liquid-liquid microextraction and hollow fiber-LPME) has been increasingly applied for the extraction of both inorganic and organic analytes from different matrices. Its advantages over conventional extraction procedures (simplicity, effectiveness, rapidity and low consumption of organic solvents) has also attracted its application in the complex food analysis field, in which it has clearly provided good and challenging results. A comprehensive review dealing with those articles published since its introduction till the end of March 2011 is presented, offering also a critical vision of the analytical potential of LPME for the analysis of foods.     

基于 OpenStack 的中小企业服务云平台架构研究

根据中小企业信息服务平台建设需求, 解决传统中小企业信息系统竖井式部署带来的管理分散、 资源利用率低等问题, 提出中小企业服务平台的整体框架, 并基于 OpenStack 开源云框架对中小企业云平台进行实验部署, 最后对中小企业服务云平台的高可用性技术进行初探。 结果表明, 基于基础资源层、 数据中台层、 业务中台层和应用层等 4 层的平台框架, 解决了传统信息系统竖井方式部署产生的信息孤岛问题, 基于 OpenStack框架搭建的原型系统验证了OpenStack 较适合于建设中小企业私有云平台。     

改进的Whipple防护结构与相关数值模拟方法研究进展

基于弹丸在超高速撞击薄板时破碎形成碎片云的机理,Whipple防护结构能够对航天器所面临的空间碎片及微流星体等威胁形成有效防护。通过回顾Whipple防护结构的研究和发展历程,对多层板结构、填充式防护结构、夹芯板结构等进行对比,分析其力学效应和防护性能;总结可应用于含泡沫、蜂窝、梯度和编织等材料的防护结构超高速撞击的数值模拟方法及其改进方法;结合相关材料的超高速撞击试验及数值模拟结果,为防护结构未来的研究方向提出建议。     

基于云模型和熵权法的配电网项目融资租赁风险评估

为合理评估配电网项目融资租赁的风险,构建了全面的配电网项目融资租赁风险评估指标体系,提出了一种基于云模型和熵权法的综合评估模型,用于对配电网项目融资租赁风险进行评估。云模型能够实现定性概念与定量数据之间的自由转换;并能够同时表征风险的随机性和模糊性。熵权法则可以客观地确定各指标的权重。选取某个省公司配电网融资租赁项目,运用云模型和熵权法对其风险进行了评估,评估结果直观且符合实际。     

星载微光立体成像技术及实现

为了监测夜间和晨昏时段的低云大雾,实现云的三维立体成像,对微光立体成像的关键技术进行了研究。首先,介绍了微光立体成像原理,分析了成像需要解决的宽视场覆盖和多镜头布局。然后,介绍了实现微光探测需要解决的低照度成像技术及其实现方法。最后,针对观测目标照度变化较大的问题,提出了动态范围拓展技术,介绍了后期数据处理中的云雾监测技术。仿真计算结果表明：采用电子倍增CCD（EMCCD）探测器和推扫扫描成像模式、集成探测器组件以及多台相机拼接方案可有效实现微光立体成像,相机扫描幅宽超过2800km;高程分辨率〈817．7m。提出的成像技术可在低照度条件下监测低云大雾,获取高分辨率的三维立体云图,满足气象海洋探测的需求。     

整幅卫星云图数据的高效无失真压缩

整幅卫星云图数据的高效无失真压缩吴乐南（东南大学无线电工程系，南京２１００１８）范天锡，王大昌，张其松，戎志国（中国气象局国家卫星气象中心北京１０００８１）气象业务需要无损失地长期保存全尺寸的原始地球气象卫星数字遥感云图，但是，整幅云图的数据量极其庞...     

The terminal phase of an unconfined hemispherical deflagration

The aerial pressure wave generated by the deflagration of a truly unconfined vapour cloud is known to be composed of a positive (overpressure) part as the flame expands, followed by a negative (underpressure) part, when the deflagration vanishes. Basically, this second part is ignored in safety predictions. The present study proposes an empirical method estimating the amplitude and the duration of the negative part of the wave, provided the mixture, the size of the cloud and the maximum flame velocity be known a priori, or estimated. This method is deduced from spherical piston flow model properties and results of small scale experiments carried out for flame spatial velocities in the range 5 to 200 m/s. Received 4 August 1995 / Accepted 12 December 1995     

大质量恒星的形成:理论与观测

文章简要叙述了有关大质量恒星形成的理论以及相关观测证据。目前大质量恒星形成的理论主要有两种，即吸积说和并合说．吸积说认为，大质量星可能与小质量星形成于相似的过程；并合说主张大质量星可能是由小质量年轻星碰撞合并而成．解决这两种理论争论的关键在于在大质量星附近能否观测到吸积盘的存在，最新的观测表明大质量星更有可能是通过吸积增加自身的质量，但最终解决这一问题可能还需要更多的观测证据。文章还提出了一些本领域尚未解决的问题，为感兴趣的研究者提供参考。     

Determination of copper in water samples by atomic absorption spectrometry after cloud point extraction

Cloud point extraction employing the new reagent 6-[2′-(6′-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic acid as complexing agent and Triton X-114 as the surfactant is proposed for copper determination. A sample volume of 10 mL was used. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the copper contents were measured by flame atomic absorption spectrometry. Variables affecting the system were optimized using factorial design and Doehlert matrix. Signals were measured as peak height using an instrument software. Using the experimental conditions defined in the optimization, the method allowed copper determination with a detection limit of 1.5 μg L⁻¹. The calculated enrichment factor is 14. The effects of foreign ions are reported. The accuracy of the procedure was tested by analyzing certified reference material. The method was successfully applied to copper determination in natural and drinking water samples.     

Interaction of water with poly(vinyl methyl ether) in aqueous solution

Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43°C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35°C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. © 1994 John Wiley & Sons, Inc.