Permanent magnet system of alpha magnetic spectrometer

Alpha magnetic spectrometer (AMS) is the first large magndtic spectrometer in space. Its precursor flioht was completed successfully in June 1998. The key part of AMS is the permanent magnet system, which was built by the lnstitute of Electric Engineering, the institute of High Energy Physics and the Chinese Academy of Launch Vehicle Technology. This system includes a permanent magnet made of high grade NdFeB and a support structure. The unique design of the permanent magnet based on the magic ring fulfills the severe requirements on the magnetic field leakage and the dipole moment for space experiments. The permanent magnet weighs about 2 tons, and provides a geometric acceptance of 0.6 m² · sr and an analyzing powerBL ² of 0.135 T · m². It works up to 40°C without demagnetization. The main structure is a thin double shell, which undergoes the strong magnetic force and torque of the permanent magnet, as well as the large load during launching and landing. The permanent magnet system fulfills the requirements from AMS, and satisfies the strict safety standards of NASA.     

层状地基中的单桩沉降分析

本文利用薄层法得出层状地基在内、外部荷载作用下的位移格林函数,并由此结果求得层状地基的柔度矩阵。在此基础上,文中利用子结构法分析单桩的沉降问题,并与工程实测进行了比较,二者较为一致,说明了本文方法的有效性。     

轴对称横观各向同性层状弹性半空间问题受力分析

本文从柱坐标系弹性力学基本方程出发,将位移场和应力场在径向进行Ｈａｎｋｅｌ变换,利用常微分主程求解原理,直接得出在轴对称荷载作用下横观各向同性半无限弹性空间的位移场,利用此结果推导出单层元的刚度矩阵。     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

气固反应的终止判断与酸性气体干式净化能限分析

借助成核—晶体生长模型，对气固反应过程中固体产物层的形成进行能耗分析，提出最小稳定晶核尺寸与成长后的晶粒相等的终止判据，与原来普遍使用的阅值孔隙率终止判据相补充，全面考虑气固反应的终止原因．在数值模拟中利用这些终止判据，预测垃圾焚烧炉排烟中HCI气体与钙吸收剂之间的干式反应程度，分析烟气干式净化的使用条件．     

Two component LDV system with dual-differential acousto-optical frequency shift and its applications

This paper describes the main properties of the two component LDV system developed with the dual-differential frequency shift technique. It has the advantages of multiple functions, better SNR and high utilization of information. So it offers as a complete technique and method for measuring 2-D complex flows. By applying this system, 2-D turbulent separated flow measurements have been made in a duct with an asymmetrical sudden expansion and in a wind tunnel flow over a 2-D rib. The Reynolds numbers were at 5900 and 4500 respectively.     

On the Static Solutions of Massive Yang-Mills Equations

关于Yang-Mills方程的静态解，Desert，S^[5]。证明了：当n\ne 5时，无质量的紧致群Yang-Mills方程不存在满足条件(i)无奇性(ii)能量有限(iii)当r\arrow \infty时，场强f_\lambda\mu\arrow 0足够快的静态解。又已知当n=5时，正则静态解确实存在^[6]。 对于具实质量的紧致群Yang-Mills方程，作者^[8]证明了：当n\ne 4时，不存在满足条件(i)无奇性(ii）能量有限(iii)当r\arrow \infty时规范势b_\lambda与场强f_\lambda\mu\arrow 0足够快的静态解。从而发现在n=5，当质量m\arrow 0时，对Yang-Mills方程的可解性问题而言，在性质上有一种“不连续性”。物理学家认为这是存在着经典的不连续性的第一个明确的例子，并对包括Higgs场的情况作了推广的研究^[9]。 本文进一步证明了上述两个结果中不仅条件(iii)可以取消，而且条件(ii)也可减弱。即能量为无限，但当以r为半径的球体的总能量趋于无限相当慢时定理仍成立。这时经典的“不连续性”也仍成立。由于能量有限与能量无限在物理上有根本的不同，所揭示的现象是值得注意的。 文中又证明，如果取消总能量趋于无限相当慢这个条件，定理的结论就不成立。 这里的证明方法，可用更一般的情况。例如包括Higgs场的情况。从而[9]中的结果也得到改进。     

Nonexistence theorems for Yang-Mills fields and harmonic maps in the Schwarzschild spacetime (II)

We continue the study of the nonexistence of static pure Yang-Mills fields and harmonic maps defined on the Schwarzschild spacetime outside the black hole. Both the conditions on the regions and on the energy density are improved. For the case of harmonic maps, the region is precisely the best one, i.e., r2M, as was conjectured in Lett. Math. Phys. 14, 253 (1987).Research supported by the Science Fund of the Chinese Academy of Sciences, Forschungsschwerpunkt Geometrie and SFB 123 of Heidelberg University.     

超高效液相色谱-串联质谱法同时测定食品级聚苯乙烯和聚乙烯色母粒中33种初级芳香胺

建立了超高效液相色谱-三重四极杆质谱(UPLC-MS/MS)同时测定食品级聚苯乙烯(PS)和聚乙烯(PE)色母粒中33种初级芳香胺(PAAs)的检测方法。PS色母粒用二氯甲烷溶解,超声提取后加入甲醇沉淀,并将提取液过石墨化碳固相萃取柱净化;PE色母粒用二氯甲烷超声溶胀提取;将PS色母粒过柱液和PE色母粒提取液浓缩,浓缩液用甲醇-水(1:9, v/v)定容至2 mL, 0.22 μm膜过滤后上机检测。采用BEH Phenyl色谱柱(100 mm×2.1 mm, 1.7 μm),以0.07%(v/v)甲酸甲醇溶液-水(1:9, v/v)为流动相,梯度洗脱分离,UPLC-MS/MS多反应监测(MRM)模式检测,同位素内标法定量。优化了色谱分离条件、质谱碎裂电压、碰撞能量等,并考察了提取时间、提取溶剂、浓缩方式等对回收率的影响。33种PAAs的方法检出限为6~10 μg/kg,定量限为20~30 μg/kg, 2种不同基质样品在20、100、200 μg/kg等3个添加水平的平均回收率为61.3%~119.8%,相对标准偏差(RSD)为1.4%~14.8%。本方法操作简便、快速、准确、灵敏度高,能满足相关测定要求。