空蚀坑周围彩虹区的形成机理

经过1 min的超声振动空蚀试验后,在不锈钢试样表面形成的空蚀坑周围出现环形彩虹区.表面检测结果表明,该区域经历了高于300℃的高温加热过程.数值计算结果表明在空泡溃灭形成的微射流的高速冲击下,试样表面材料在短时间内发生的塑性变形所释放出的能量是造成材料局部升温的主要原因.在塑性变形相同的情况下,材料的导热系数是影响彩虹环区域大小的关键因素.     

Temperature Effects on Attenuation Due to Rain for Millimeter and Centimeter Waves

Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aR^b Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%.     

Use of calibration gases in the U.S. acid rain program

The United States Acid Rain Program continuous emission monitors (CEMs) have been successful in producing quality-assured data 95% of the time, and in meeting a relative accuracy standard of less than or equal to 10.0% at over 99% of the CEMs in the program. One key reason for this high accuracy is the required use of high quality calibration gases in certification and quality assurance/quality control (QA/QC) tests. An annual QA audit helps ensure high quality calibration gases. A third party purchases gases from gas vendors. An Environmental Protection Agency (EPA) laboratory analyzes the gases and compares the results with the tag value on the cylinder. The results are posted on an EPA website. This allows purchasers of calibration gases to buy gases from vendors producing the most accurate gases. Over time, we believe it also results in better accuracy from all gas vendors. Because of a change in SO₂ quantification methodology, SO₂ emissions were underreported by approximately 2% between 1989 and 1996. EPA, the National Institute for Standards and Technology and calibration gas vendors collaborated to produce a correction policy and a standard correction form to be used by affected electric utility plants. Calibration gas cylinder tag values were required to be corrected by 1 January, 1997. In the future, it is possible that cleaner, more varied sources will be regulated for greenhouse effect, ozone and toxic emissions control. This will probably require more accurate CEMs, lower calibration gas concentrations, and a broader menu of gas mixtures. Received: 23 December 1999 Accepted: 12 December 2000     

镧对38CrMoAl钢氮化层组织和抗冲蚀磨损性能的影响

考察了在气体氮化渗剂中加入微量镧元素对３８ＣｒＭｏＡｌ钢氮化层组织,韧性及抗冲蚀磨损性能的影响。试验结果表明,含镧的氮化层的韧性和抗冲蚀磨损性能明显优于普通氮化层。这是由于镧在氮化时渗入到钢表层并发生微合金化,从而改善渗层的组织所致,采用扫描电子显微镜对冲蚀磨损试样表面形貌进行观察发现,普通氮化层的磨损机理为塑性变形及犁沟剥落,并伴随着横向裂纹的萌生和大块磨屑的剥落,而含镧的氮化层和磨损机理为塑性     

环境保护中辐射技术的应用研究

介绍了近年来利用稳定同位素C和N以及放射性元素^7Be和^137Cs作为示踪元素应用在土壤侵蚀、水土流失研究中所取得的重要进展,讨论了电子束辐照和γ射线辐照在工业废水和废气处理的机理及其应用,说明了辐射技术在环境保护中具有重要的作用。The important progresses of studies on water loss and soil erosion using stable carbon, nitrogen isotopes and ^7Be, ^137Cs as tracers is introduced. The mechanisms and applications of the electron beam and y rays irradiation in industrial effluent disposal and tail gas treatment are discussed, which indicates the importances of the irradiation technology in environment protection.     

镍铝介金属镀膜之抗坑蚀行为

采用3种原子百分比Ni52Al48,Ni60Al40及Ni70Al30成分的靶材以阴极电弧放电离子被覆技术制备不同组成的Ni＿Al薄膜于AISI1045中碳钢基材表面上,并观察镀膜微结构与成分随靶材成分的变化,评估应用Ni＿Al于抗坑蚀功能方面的可行性.研究结果显示:使用上述3种靶材所获致的镀膜组成依次为Ni62Al38,Ni63Al37及Ni69Al31,镀膜镍含量随靶材镍含量增加而增加.3种镀膜的相组成均以Ni3Al为主,从富镍Ni70Al30靶材所得的镀膜尚含有部分镍相.镀膜具有极强的附着性并反映在镀膜的抗坑蚀性上.在纯水中,所有的Ni＿Al镀膜试片均能提高中碳钢基材的抗坑蚀性,约达10倍.在3.5wt%盐水与3.5wt%盐酸中亦分别有两倍以上的效果.而在这3种测试环境中,3种镀膜试片的坑蚀损失差别均不明显,无法判断镀膜组成对抗坑蚀性的影响.从动电位极化曲线可以看出,镀膜试片均能大幅提高基材在盐酸与盐水溶液中的抗蚀性,然而因坑蚀破坏而形成的孔洞会由于孔蚀而导致腐蚀加剧,造成镀膜试片在腐蚀溶液中之抗坑蚀效果低于电化学量测时所预期的保护效果.     

低密度等离子体融断开关的粒子模拟研究

 采用2.5维柱坐标粒子模拟程序研究了低密度等离子体融断开关（PEOS）工作过程中的物理现象,介绍了计算模型的建立和复杂边界的算法处理。模拟结果表明,在PEOS导通电流的过程中,电流通道最初在等离子体的发生器端形成,并且随着导通时间的增大而向负载端漂移。离子的空间分布并没有明显的变化,当PEOS发生断路时,等离子体离子的密度会迅速降低,并最终导致PEOS阴极附近的等离子体的密度已接近为零,此时,阴极电子完全受磁场箍缩作用而不能到达阳极,PEOS完全断开。     

Arc root dynamics in high power plasma torches — Evidence of chaotic behavior

Although plasma torches have been commercially available for about 50 years, areas such as plasma gun design, process efficiency, reproducibility, plasma stability, torch lives etc. have remained mostly unattended. Recent torch developments have been focusing on the basic understanding of the plasma column and its dynamics inside the plasma torch, the interaction of plasma jet and the powders, the interaction of the plasma jet with surroundings and the impingement of the jet on the substrate. Two of the major causes of erratic and poor performance of a variety of thermal plasma processes are currently identified as the fluctuations arising out of the arc root movement on the electrodes inside the plasma torch and the fluid dynamic instabilities arising out of entrainment of the air into the plasma jet. This paper reviews the current state of understanding of these fluctuations as well as the dynamics of arc root movement in plasma torches. The work done at the author’s laboratory on studying the fluctuations in arc voltage, arc current, acoustic emissions and optical emissions are also presented. These fluctuations are observed to be chaotic and interrelated. Real time monitoring and controlling the arc instabilities through chaos characterization parameters can greatly contribute to the understanding of electrode erosion as well as improvement of plasma torch lifetime.     

Formation of compression erosion plasma fluxes of a given composition in dense gases

This article presents the results of experimental investigations of compression erosion plasma fluxes of a given composition determined by the material of the internal electrode; the fluxes have been obtained for the first time in air at atmospheric pressure. It is shown that a compression erosion plasma flux possesses marked absorption in the visible spectral region. The basic thermodynamic parameters of these fluxes were determined with the use of a two-channel system of recording plasma radiation. Reported at the International Conference on Plasma Physics and Plasma Technologies, Minsk, September 15–19, 1997. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 229–233, March–April, 2000.     

原子吸收光谱和原子发射光谱法测定酸雨中钾、钠、钙、镁方法比较

采用原子吸收光谱法和原子发射光谱法分别测定了酸雨中的钾、钠、钙、镁4种元素的含量,并对两种方法的样品前处理技术、标准曲线、方法检出限、准确度、精密度、干扰及消除等进行了比较研究。结果表明,两种方法无显著性差异,均可用于酸雨中钾、钠、钙、镁4种元素的测定。