激光诱导击穿光谱法对钢中夹杂物类型的表征

激光诱导击穿光谱( LIBS)不仅可以对材料整体成分进行分析,还可进行微区及成分分布分析。本实验采用激光诱导击穿光谱对两牌号钢铁样品进行扫描分析,尝试对34CrNiMo6钢中的MnS夹杂物和重轨钢中的Si-Al-Ca-Mg复合夹杂物进行表征。结果表明,34CrNiMo6钢中元素信号的二维强度分布及元素通道合成后,个别位置Mn及S两元素的信号强度同时异常高,可确定试样中存在较多MnS夹杂物;重轨钢中元素的二维强度分布及元素通道合成后,个别位置Si、Ca、Mg及Al元素的信号同时异常高,可确定试样中存在Si-Al-Ca-Mg复合夹杂物。采用扫描电子显微镜/能谱法( SEM/EDS)对上述样品中夹杂物的对比分析结果表明,两种方法对夹杂物类型的判定结果一致。     

The Synthesis and Application of the Mesoporous Molecular Sieves MCM-41 — A Review

We report a “delayed neutralization” process for the preparation of highly-ordered aluminosilicate MCM-41 molecular sieves with high thermal and hydrothermal stability, and sharp pore size distribution. However, the structural order and pore size are dependent on the carbon chain length. In the mixture surfactant systems, the pore size of the MCM-41 materials could be fine-tuned. The pore size can be extended from 2.5 to 4.5 nm by adding a suitable amount of hydrocarbons. The tubular morphology of the MCM-41 material of 0.3 to 10 micrometers diameter, where the wall consists of coaxial cylindrical pores of nanometers MCM-41, can be obtained by careful control of the surfactant-water content and the rate of condensation of silica. An optimum condition for automatic synthesis of the hierarchical TWT structure has been accomplished. The addition of 1-alkanols as cosurfactant would not only improve the order of the MCM-41 hexagonal structure but also promote the formation of micrometer-sized hierarchical materials, for example: tubules-within-tubule and uniform-sized hollow spheres of diameter 5.0 ± 1.0 μm. However, the inside of the micron spheres has intricate structures possessing various topological genus ranks. The MCM-41 is a good supporter for Molybdenum oxide catalysts. The rate of deactivation in the catalytic reaction of ethyl-benzene dehydrogenation to styrene increases in the order: M_T < M_P < SiO₂. The physically mixed samples have higher catalytic activity than impregnated ones.     

不同光谱预处理对激光诱导击穿光谱检测猪肉中铅含量的影响

为了研究适合激光诱导击穿光谱(LIBS)检测猪肉中重金属铅(Pb)元素含量的光谱预处理方法,将配制的84个猪肉腿肌样品分为校正集和预测集,以相关系数(R)、内部交叉验证均方差(RMSECV)和预测均方根误差(RMSEP)作为评价指标,比较了5种光谱预处理方法对偏最小二乘法(PLS)建模预测效果的影响.结果表明,多元散射校正(MSC)预处理效果最好,定标模型预测值与实验室分析元素检测值的相关系数(R)达到0.9908,RMSECV为0.302,RMSEP为0.282,主成分数为16,18个预测集样品的验证结果的平均相对预测误差(ARPE)为7.8％.说明MSC是LIBS检测猪肉Pb含量的有效光谱预处理方法,该研究为进一步实现食品中重金属快速定量分析提供了方法和数据参考.     

一种用于冶金炉前快速分析的新仪器——激光诱导击穿光谱仪

冶金炼钢要求快速分析冶金炉前样品来及时掌握冶炼过程。文章介绍了自主研制的一种新型的光谱仪——激光诱导击穿光谱仪,该仪器采用ns级脉宽的Nd∶YAG激光器作为样品离子化光源,激光聚焦样品表面激发产生的等离子体光谱依次经帕邢-龙格光学系统进行分光、光电倍增管探测、门控积分器积分、模拟数字转换器转换后获得的最终结果输入计算机进行数据处理。和目前冶金炉前样品分析常用的光谱仪相比,该仪器无需样品预处理,分析速度快(1 min或更少),准确灵敏度高,非常适用于冶金炉前样品的快速分析。近年来随着光纤技术的迅速发展,使用该仪器进行钢液实时在线分析和动态控制冶金工艺必将成为现实。     

An intracloud discharge caused by extensive atmospheric shower

The observational evidence of RB-EAS discharge in a thunderstorm atmosphere is presented. After RB-EAS discharge we name a discharge of a special type developing due to the runaway breakdown (RB) mechanism while an extensive atmosphere shower (EAS) passes through a thundercloud electric field. The observations were fulfilled at the Tien-Shan Mountain Cosmic Ray Station. The widely spread system of oscillation detectors, the special EAS trigger array and the HF radio interferometer were used for measurements.     

Barrier degradation of tunneling magnetoresistance device with MgO barrier and low resistance-area product

MgO barrier degradation is studied in a tunneling magnetoresistance head with low resistance-area product. As the stress current is increased, the resistance is significantly reduced before the barrier breakdown, while the magnetoresistance ratio remains almost unvaried. At the same time, the bias dependence of the resistance becomes less affected by the bias polarity, suggesting that slight degradation occurs at the interface between MgO and the ferromagnetic electrode. Just before the breakdown, the bias dependence shows an increasing tendency, indicating the defect accumulation inside the MgO barrier. The results are helpful for understanding the mechanisms of barrier degradation, which is critical for developing future magnetic tunneling junction devices.     

Scale-Invariant Branch Distribution from a Soluble Stochastic Model

We consider a general model of branch competition that automatically leads to a critical branching configuration. This model is inspired by the 4– expansion of the dielectric breakdown model, but the mechanism of arriving at the critical point may be of relevance to other branching systems as well, such as fractures. The exact solution of this model clarifies the direct renormalization procedure used for the dielectric breakdown model, and demonstrates nonperturbatively the existence of additional irrelevant operators with complex scaling dimensions leading to discrete scale invariance. The anomalous exponents are shown to depend upon the details of branch interaction; we contrast with the branched growth model in which these exponents are universal to lowest order in 1–, and show that the branched growth model includes an inherent branch interaction different from that found in the dielectric breakdown model. We consider stationary and non-stationary regimes, corresponding to different growth geometries in the dielectric-breakdown model.     

Correlation between formation conditions and breakdown voltage of anodic oxide films on aluminum

Two series of samples were investigated: a) aluminum films with a sublayer of tantalum; b) industrial aluminum alloys AMg-2m; D16; AMc; AD-1n. The optimum composition of re-anodizing electrolyte was chosen on the basis of a solution of citric acid and ethylene glycol. The results of investigations of the sparking voltage at re-anodizing for various aluminum alloys and thicknesses of primary porous oxide are presented. The analytical dependence of breakdown voltage value on forming voltage value for alloy AD-1n was obtained. The original design of re-anodizing cell allowing increase of the sparking voltage was developed.     

Delayed breakdown diode and its optimal design for solid state picosecond closing switch

We study a Si-based diode with a p⁺nn⁺ structure for picosecond semiconductor closing switch and discuss the physical process, which underlies the operation principle of high-power closing switch based on a delayed breakdown diode (DBD). From the results of numerical simulations and theoretical analysis, single device has demonstrated reliable operation at 2.3 kV, 89 ps risetime, and high output dV/dt(30 kV/ns). As a contribution to the optimal design, some conclusions about trade-off are drawn by changing structure parameters and physical parameters.     

A note on Nasr's and Wong's papers

In the case of oscillatory potentials, we give sufficient conditions for the oscillation of the forced nonlinear second order differential equations with delayed argument in the form