Determination of trace elements in ambient aerosol samples

A microwave-assisted digestion procedure using HNO₃, HF, and H₂O₂ has been developed for analysis of elements in ambient particulate matter (PM). The samples are collected on cellulose filters and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS is calibrated with external standards, and recovery of analytes is tested with NIST SRM 1648 Urban Dust. This method has been used to quantify the airborne concentrations of a large number of elements, including Ag, As, Ba, Be, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Se, Sb, Sr, Ti, Tl, V, and Zn. For the majority of these elements, recovery of the NIST SRM is within 15% of the certified values.     

Experimental Study of Liquid Hydrocarbons Pyrolysis to Acetylene in H2/Ar Plasma

Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H₂/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8?ms in Ar/H₂ plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7?×?10⁴?kJ/kg, the n-hexane conversion is over 90?% and the yield of acetylene reaches 70?%. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (R _C/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed.     

Precipitate Contribution to the Acoustic Nonlinearity in Nickel-Based Superalloy

The influence of γ′ precipitate on the acoustic nonlinearity is investigated for a nickel-based superalloy, which is subjected to creep deformation. During creep deformation, the cuboidal γ′ precipitate is preferentially coarsened in a direction perpendicular to the applied stress axis. The length and shape factor of the γ′ precipitate increase with creep time. The increase of relative acoustic nonlinearity with increasing fraction of creep life is discussed in relation to the rafting of γ′ precipitate, which is closely related to the scattering and distortion of the acoustic wave     

Z,Z-dienes via acetylene carbocupration: synthesis of navel orangeworm pheromone

A range of conjugated $\text{Z}$,$\text{Z}$-dienes have been prepared in a stereo-specific manner $\text{via}$ acetylene carbocupration: the value of this procedure has been illustrated by an extremely short synthesis of hexadeca-11$\text{Z}$, 13$\text{Z}$-dienal a principle component of Navel Orangeworm Pheromone.     

海生物附著对钢板管椿腐蚀之影响

为了解海生物对钢板管椿腐蚀之影响 ,将SS4 1金属试片浸渍于高雄港 #1 4码头水深 3m处及实验室人造海水中 .试验期间 ,以DC直流动电位极化曲线扫描与AC交流电阻抗分析现场量测各试片的瞬间腐蚀速率 .结果发现 :宏观地看 ,海生物在金属 (或锈层 )表面的附著可以减缓金属腐蚀 ,但从微观 (micro)的观点推论 ,海生物在金属表面的附著亦可以造成氧差或浓度差异电池 ,促成局部腐蚀 .此外 ,等效电路的模拟 ,有助于了解海生物附著对金属腐蚀的影响 ,即随浸渍时间的延长 ,金属表面因锈层增厚且趋于致密 ,以致锈层电阻增加 ;又因海生物种类不同 ,含水量不同 ,海生物电阻可能会有极大的差异     

Optimal rigid body motions,part 2: Minimum time solutions

The time-optimal control of rigid-body angular rates is investigated in the absence of direct control over one of the angular velocity components. The existence of singular subarcs in the time-optimal trajectories is explored. A numerical survey of the optimality conditions reveals that, over a large range of boundary conditions, there are in general several distinct extremal solutions. A classification of extremal solutions is presented, and domains of existence of the extremal subfamilies are established in a reduced parameter space. A locus of Darboux points is obtained, and global optimality of the extremal solutions is observed in relation to the Darboux points. The continuous dependence of the optimal trajectories with respect to variations in control constraints is noted, and a procedure to obtain the time-optimal bang-bang solutions is presented.This work was supported in part by DARPA under Contract No. ACMP-F49620-87-C-0016, by SDIO/IST under Contract No. F49620-87-C0088, and by Air Force Grant AFOSR-89-0001.