Determining the keyhole geometry based on double-elliptic distribution of plasma arc pressure

The plasma arc pressure plays an important role in determining the keyhole formation and size. So it is of great significance to choose adaptive distribution mode of the plasma arc pressure for determining keyhole shape and size. In this study, through employing a double-elliptic distribution mode of plasma arc pressure, three-dimensional keyhole was numerically simulated. The unsymmetric feature of the keyhole inside the weld pool was described. The development of keyhole was demonstrated under different levels of welding current. The critical current required to form an open keyhole was obtained for the study cases.     

In vivo lipolysis induced by heparin injection or fasting: a proton MR spectroscopy analysis of human plasma

The impact of induced lipolysis on the composition of plasma lipids is analyzed by proton magnetic resonance spectroscopy (MRS) in humans. The variations of the methylene and methyl resonances from lipids in lipoproteins are studied under two sets of lipolytic conditions: acute endovascular lipolysis induced by an intravenous injection of heparin and subacute lipolysis induced by short fasting. During acute lipolysis, the degradation of the very low density lipoproteins structures is well correlated to the modifications observed in the areas of CH₂ and CH₃ MRS signals. The comparison of regular spectra, spectra with water signal suppression, and spectra recorded with a spin-echo sequence provides information on the behavior of the different parts of the lipoproteins, that is, the neutral core, little affected by heparine-induced lipoprotein lipase (LPL) activation, and the surface layer supplying substrates to LPL. During 48 h of fasting, only limited modifications occur on the MR spectra, and lipolysis cannot be documented in details.Address for correspondence: CRMBM-CNRS, Faculté de Médecine, 27, bd Jean Moulin, 13005 Marseille, France.     

可变色霓虹灯机理探讨

本文主要探讨了装饰霓虹灯通过变化放电正柱区的电子温度来控制灯管色彩变化的原理。同时剖析和实验证实了：对一支充有Ｈｇ和１０ＴｏｒｒＮｅ的气体放电灯管、通过改变供电的脉冲电压（４００Ｖ～１０００Ｖ），重复频率（５０Ｈｚ～１０００Ｈｚ）和持续时间（５μＳ～１５０μＳ），可以使灯管辐射从红色（０．５４５，０．２６２）变化为兰色（０．７０５，０．２９５），亮度从１４ｄｃｄ／ｍ￣２增加到１６４０ｃｄ／ｍ￣２的物理现象。文中最后提出了将变色放电技术应用于生产新颖霓虹灯产品的展望。     

氮化铝超微细粉制备规律的研究

利用直流电弧等离子体具有的高温、高反应活性和高的急冷速度等特点，通过氮等离子体与金属铝反应的方法，制备了平均粒径为５０ｕｍ的高纯氮化铝（ＡＩＮ）超微细粉，并对氮化反应原理及ＡｌＮ的成核机理进行了探讨。结果表明，等离子条件下的化学反应是极其复杂的，等离子态有利于氮化反应。ＡｌＮ的成核速率与反应物的浓度和反应温度有关。实验中，通过控制反应气体的分压、反应的温度及冷却速度等工艺参数，制备出了粗径可控的ＡｌＮ超微细粉。     

适于等离子喷涂的PSZ粉末的性能研究

研究了用共沉淀法制备的，适于等离子喷涂的８ｗｔ％Ｙ２Ｏ３－ＺｒＯ２部分稳定氧化锆粉末的性能。用日本Ｄ／ＭＡＸ－１ＡＸＸ－射线衍射仪（ＸＲＤ）研究了粉末的相组成；用日本ＳＸ－４０扫描电镜（ＳＥＭ）观察了颗粒形貌和团聚状况；用日本Ｈ－６００分析电镜（ＳＴＥＭ）确定晶粒大小和化学组成；用英国激光粒度分布测定仪测定了粉末的粒度分布；用日本粉体综合测定仪测定了粉末的流动性。并探讨了所制粉末性能与制备工艺的关系。     

高温气相合成超细氮化钛反应速率的研究

本文研究了等离子法合成超细氮化钛反应动力学,建立了 TiCl_4—NH_3—H_2—N_2系统在高频等离子反应器中气相合成超细 TiN 粉末的反应动力学模型,对影响反应速度的主要因素进行了分析,为控制 TiN 产品的质量及对等离子反应器的优化设计提供了理论依据。     

TiN膜的电子显微分析

本文是用JEM-2000EX型电镜,对射频等离子体沉积的TiN薄膜进行具体分析,从而得到TiN的形貌及晶体结构。     

Numerical Simulation of the Thomson Scattering Experiment Performed with 0.351 μm Laser-Produced Aluminum Plasmas

The evolutions of the electron temperatures of Muminum plasmas produced with 0.351 μm laser are simulated by means of one-dimensional hydrodynamic code. The simulations show that the plasma geometry has strong influence on the electron temperature＇s evolution while the effect of the flux limiter is not so significant. The simulations are in good agreement with the experiments only at some spatial points. A full comparison between the simulations and experiments indicates that the one-dimensional code is not accurate enough to characterize the laser-produced plasmas. A post-processor code based on the hydro code is developed to generate the streak image of the Thomson scattering spectra, which can be directly compared with the experimental data.     

Preliminary Studies of Practicability of Laminar Plasma Surface Treatment Process

The basic remelting and cladding tests with laminar plasma technology on metals have been conducted in order to demonstrate the possibility of the technology applied in material surface modification. The experimental results show that the properties of the modified layers of the cast iron surface can be improved notably by the remelting treatment and those of the stainless steel by the cladding treatment. The related results are also verified by microscopic studies such as scanning electron microscopic （SEM） observations, energy dispersive spectra （EDS） analysis and the Vickers hardness measurements of the surface modified layers.     

Numerical Analysis of Plasma Initiated Polymerization

Plasma initiated polymerization is a kind of well-known radical polymerization mechanism, but it has the ＇living＇ polymerization feature and produces ultra-high molecular weight polymer. In order to explain such phenomena, we calculate the basic data of plasma initiated polymerization of methylmethacrylate （MMA） according to the principle of polymer physics and chemistry. It results in that the radical concentration ranges from 10^-12mol/L to 10^-16mol/L corresponding to the radical life in 10^4s to 10^8s, which means the radicals have a long lifetime. Moreover because of the long lifetime radicals it causes a unique feature rather than the common radical polymerization, and also shows no ＂living polymerization＂. It is noticed in experiments that there are two key factors playing important roles. One is the effective radical amount produced during the plasma discharging while the another is the diffusion factor.