Bubble boiling in droplets of water and lithium bromide water solution

The dynamics of growth and interaction of vapor bubbles in droplets of pure water and LiBr water solution on a horizontal wall were investigated in a wide superheating range. The growth rates of bubbles were determined both in a distillate droplet and in a salt solution droplet. The bubble growth rate in a pure water droplet at the final stage is somewhat lower than in pool boiling. The bubble growth rate in a salt solution is substantially lower than for pure water. Due to the bubble density maldistribution, the vapor flow density is appreciably higher at the droplet edges than on the droplet axis. Collective behavior of the bubbles possesses both stochastic character and elements of self-organization. The thermal measurements were carried out by means of high-speed video and blowup thermal imager.     

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通过测量大气压介质阻挡放电等离子体辐射信号,建立偶极子辐射模型,利用快速傅立叶变换,计算了大气压介质阻挡放电等离子体中离子速度分布。计算结果表明,速度分布偏离麦克斯韦分布,并且随着放电过程的进行,离子速度及相对离子数进行有规律的变化。     

Effect of inhomogeneity on magnetic, magnetocaloric, and magnetotransport properties of La0.6Pr0.1Ca0.3MnO3 single crystal

The effect of magnetic inhomogeneity on magnetic, magnetocaloric, and transport properties of the colossal magnetoresistance manganites with first order ferromagnetic-to-paramagnetic phase transition is studied. The experiments were performed on the single-crystalline samples of La_0.6Pr_0.1Ca_0.3MnO₃. The inhomogeneity is described by the Curie temperature distribution function, which is found from the magnetization data. The temperature dependence of the magnetic field induced change in the entropy is shown to be determined by the distribution function and the shift of the transition temperature in a magnetic field. Similarly, magnetoresistance in the transition region is determined by the resistivity at H=0 and the shift of the transition temperature. The maximum entropy change as well as maximum magnetoresistance can be achieved in the magnetic field of order δT_C/B_M where δT_C is the transition width and B_M is the rate of change of the Curie temperature with magnetic field.Our approach to analysis of the effects of inhomogeneity is general and therefore can be used for all compounds with the first order magnetic phase transition.     

Edge searching weighted graphs

In traditional edge searching one tries to clean all of the edges in a graph employing the least number of searchers. It is assumed that each edge of the graph initially has a weight equal to one. In this paper we modify the problem and introduce the Weighted Edge Searching Problem by considering graphs with arbitrary positive integer weights assigned to its edges. We give bounds on the weighted search number in terms of related graph parameters including pathwidth. We characterize the graphs for which two searchers are sufficient to clear all edges. We show that for every weighted graph the minimum number of searchers needed for a not-necessarily-monotonic weighted edge search strategy is enough for a monotonic weighted edge search strategy, where each edge is cleaned only once. This result proves the NP-completeness of the problem.     

On the asymptotic efficiency of normality tests based on the Shepp property

New invariant tests of normality based on Shepp property are constructed and studied. Test statistics are functions of a U-empirical process. The limiting distributions and large deviations of test statistics under the null-hypothesis are described. Local Bahadur efficiency of new tests is calculated under simplest parametric alternatives (shift, skew, and contamination alternatives).     

电感耦合等离子体-质谱法测定工业硅中的痕量硼和磷

建立电感耦合等离子体-质谱法(ICP-MS)测定工业硅中痕量B和P的分析方法.采用HF-HNO3混合酸处理样品,对仪器工作参数进行优化,以Rh为校正内标,有效克服了基体效应及多元素分子离子干扰.分析结果表明,方法的检出限为:B为2.0μg·L-1、P为8.5μg · L-1,B和P的加标回收率分别为:97.2％-103.6％、95.2 ％-102.8％,精密度分别为2.6％、3.5％.方法可准确、快速测定工业硅中痕量元素B和P.     

光电侦察与跟瞄装备测试技术

在现代信息化战争中,光电侦察与跟瞄装备的研制试验和使用维护都离不开其测试技术的保障。从4方面简述了国内外光电侦察与跟瞄装备测试技术的发展现状,目前,可见光及微光成像性能参数已实现数字化的综合测量,其中,像面均匀性和畸变检校的测量不确定度分别达到1%和0.2%,最小可分辨温差(MRTD)等红外热成像系统性能参数已出现客观的评测方法,最大测程等激光测距系统性能参数的测量允许误差极限达到1%以内,多光轴一致性的检校测量不确定度达到2。未来,我国在该领域的研究热点将集中在发展各种现场快速精准的检校手段,以及继续提升红外、紫外、微光和白光成像测试技术等方面,并建立和完善其相应的测试标准和保障系统。     

基于模块计算机的千兆网磁共振谱仪控制接口

提出了一个基于模块计算机的磁共振谱仪的控制接口,它建立了核磁共振成像谱仪与上位计算机之间的通信,实现了控制谱仪、上传和下载、数据处理等功能,具备较高的传输速度,以及较好的实时性. 该接口以硬件模块的方式集成到谱仪上,通过千兆和百兆以太网连接上位机,接收下传至谱仪的序列;用中断机制和直接内存存取(DMA)方式实现与谱仪的数据传输,并将处理采集到的回波数据并上传到上位机. 控制接口的设计采用模块计算机Computer-On-Module(COM)的设计思路,以高性能的处理器为嵌入式平台,在Linux操作系统下开发驱动程序和应用程序. 实验证明,该模块具有数据处理速度快、传输速率高,成本低,体积紧凑,扩展性强等特点,是实现磁共振谱仪高性能的控制接口的理想方案.     

基于平行平板的折射率高精度非接触测量

常用的测量折射率的方法如偏向角法、自准直法、临界角法、 V棱镜法等,这些方法通常需特制三棱镜与待测件。待测样品不一致且过程复杂,测试定标周期长,难于自动化。为了保证待测材料的完整及实现自动化测量,进行了基于平行平板的折射率非接触测量的尝试。运用该方法进行折射率的测量,不需特制三棱镜并且待测件与待测样品一致。分析表明,通过选择合适的测量角度,该方法旋转角度精度为a=0.003（即10）,导轨精度为L=0.000 8 mm,平行平板厚度测量精度为d=0.001 mm。     

Organometallic titanocene complex as highly efficient bifunctional catalyst for intramolecular Mannich reaction

Bifunctional catalysts bearing two catalytic sites, Lewis acidic organometallic titanocene and Brønsted acidic COOH, have been assembled in situ from Cp₂TiCl₂ with carboxylic acid ligands, showing high catalytic activity over an intramolecular Mannich reaction towards synthesis of 2‐aryl‐2,3‐dihydroquinolin‐4(1H)‐ones. The determination of the bifunctional catalyst Cp₂Ti(C₈H₄NO₆)₂ was elucidated by single X‐ray HR‐MS and investigation of catalytic behavior. In particular, masking the Brønsted acidic COOH catalytic site with dormant COOMe lowered the reaction yield greatly, indicating that two catalytic sites work together to maintain high catalytic efficiency.