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961.
962.
采用高温淬火方法制备了Tc在27.4K至92.4K之间的一组不同氧含量的PMP(粉末熔融工艺)法YBCO超导体。通过对这些超导体样品的磁滞回线及不可逆线的研究发现,随着氧空位的增加,超导体的磁通钉扎力减小 相似文献
963.
本文介绍了一种新的焊接方法——真空磁压缩等离子弧焊接。真空磁压缩等离子弧是将低真空中的自由电弧用与电极同轴向的磁场压缩后获得的。实验表明,随着气压的降低,自由电弧会越来越扩展,弧根区的电流密度越来越低,直至产生“旁弧”,不能稳定燃烧而熄灭。而且这种低真空自由电弧难以用和普通等离子弧相似的机械方法压缩。采用轴向磁场可以有效地压缩真空电弧。磁压缩的效果随气压的降低趋于明显,气压低于1.33×10~2Pa 时,几十分之一特斯拉(T)的磁场就可获得略粗于电极、上下直径近似相等的弧柱,我们称之为真空磁压缩等离子弧。使用真空磁压缩等离子弧作为热源,可以焊接一般金属和活泼金属,其熔透工件的能力可超过大气氩弧,并可用调节磁场强度的方法,调节电弧的能量分布。与常规氩弧焊、等离子孤焊、电子束焊相比,真空磁压缩等离子弧焊接有其独到的优点,可望在不久的将来获得广泛的应用。 相似文献
964.
以钨酸铵溶液为原料,采用超声喷雾干燥法制备了超微钨粉。研究了该方法中钨酸铵浓度对超微钨粉形貌的影响。结果表明,当溶液中钨酸铵的浓度为10%时,得到了球形度很好的非完全结晶的前驱体。当钨酸铵浓度达25%时,得到了层片状的晶态前驱体。钨酸铵溶液浓度对干燥时晶体生长速度具有重要的影响。分别采用这2种前驱体在630℃,保温30min和氢气流莆4L/min条仲下能够完全还原,得到超微α—W粉。所制得的钨粉形貌完全遗传了其前驱体的形貌,分别得到球状和层状钨粉。球状钨粉由纳米颗粒聚集而成。片层状钨粉的厚度在1mm以下。 相似文献
965.
采用在铸型中放置石墨片,然后浇注低碳合金钢的方法,制造表面耐磨材料。分析了铸造过程中渗碳的效果及机理,讨论了影响组织和渗层深度的因素。 相似文献
966.
Z.Y. Wu J. Zhang K. Ibrahim M.I. Abbas G. Li Y. Tao T.D. Hu F.Q. Liu H.J. Qian Y.N. Xie Q.H. Zhang L. Gao Z.Z. Chen 《金属学报(英文版)》2002,15(1):53-57
As a potential application of titanium-oxide nanoparticles, it is extremely important to investigate a detailed picture of the surface and interior structural properties of nanocrystalline materials, such as rutile and anatase with diameters 7.0 and 4.5nm, respectively. X-ray absorption spectroscopy has been used to identify the local Ti environment and related electronic structure. We combine the experimental results at the Ti edge in both bulk and nano-crystals to determine the lattice distortion in terms of differently characteristic preedge features and the variation in the multiple-scattering region of X-ray absorption near-edge structure (XANES) spectra. The relationship between the transition peaks and the surface-to volume ratio is also discussed. 相似文献
967.
968.
本文主要从质量体系的产生和发展、质量体系分析的资料、质量体系的环境分析及结构型式分析几个方面探讨分析了大型铸锻件的质量体系 ,可供大型铸锻件生产厂按 ISO90 0 0系列标准分析、设计、建立和完善大型铸锻件质量体系时参考。 相似文献
969.
The application of remote sensing monitoring techniques plays a crucial role in evaluating and governing the vast amount of ecological construction projects in China. However, extracting information of ecological engineering target through high-resolution satellite image is arduous due to the unique topography and complicated spatial pattern on the Loess Plateau of China. As a result, enhancing classification accuracy is a huge challenge to high-resolution image processing techniques. Image processing techniques have a definitive effect on image properties and the selection of different parameters may change the final classification accuracy during post-classification processing. The common method of eliminating noise and smoothing image is majority filtering. However, the filter function may modify the original classified image and the final accuracy. The aim of this study is to develop an efficient and accurate post-processing technique for acquiring information of soil and water conservation engineering, on the Loess Plateau of China, using SPOT image with 2.5 m resolution. We argue that it is vital to optimize satellite image filtering parameters for special areas and purposes, which focus on monitoring ecological construction projects. We want to know how image filtering influences final classified results and which filtering kernel is optimum. The study design used a series of window sizes to filter the original classified image, and then assess the accuracy of each output map and image quality. We measured the relationship between filtering window size and classification accuracy, and optimized the post-processing techniques of SPOT5 satellite images. We conclude that (1) smoothing with the majority filter is sensitive to the information accuracy of soil and water conservation engineering, and (2) for SPOT5 2.5 m image, the 5×5 pixel majority filter is most suitable kernel for extracting information of ecological construction sites in the Loess Plateau of China. 相似文献
970.
Huang Yao Tang Yong Yuan Wei Fang GuoYun Yang Yang Zhang XiaoQing Wu YaoPeng Yuan YuHang Wang Chun Li JinGuang 《中国科学:技术科学(英文版)》2021,64(5):919-956
Electric vehicles(EVs) are globally undergoing rapid developments, and have great potentials to replace the traditional vehicles based on fossil fuels. Power-type lithium-ion batteries(LIBs) have been widely used for EVs, owing to high power densities,good charge/discharge stability, and long cycle life. The driving ranges and acceleration performances are gaining increasing concerns from customers, which depend highly on the power level of LIBs. With the increase in power outputs, rising heat generation significantly affects the battery performances, and in particular operation safety. Meanwhile, the cold-start performance is still an intractable problem under extreme conditions. These challenges put forward higher requirements for a dedicated battery thermal management system(BTMS). Compared to traditional BTMSs in EVs, the heat pipe-based BTMS has great application prospects owing to its compact structure, flexibility, low cost, and especially high thermal conductivity. Encompassing this topic, this review first introduces heat generation phenomena and temperature characteristics of LIBs. Multiple abuse conditions and thermal runaway issues are described afterward. Typical cooling and preheating methods for designing a BTMS are also discussed. More emphasis on this review is put on the use of various heat pipes for BTMSs to enhance the thermal performances of LIBs. For lack of wide application in actual EVs, more efforts should be made to extend the use of heat pipes for constructing an energy-efficient, cost-effective, and reliable BTMS to improve the performances and safety of EVs. 相似文献