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601.
在分析离散数据插值与逼近方法的基础上,讨论了B-样条拟合算法;并针对超精密非球曲面的测量数据,分析了B-样条拟合算法的拟合误差与阶次的关系,同时与多项式最小二乘拟合做了比较.对比结果表明,B-样条拟合能达到更高的精度,并建议在非球曲面拟合中采用4阶次B-样条、51个控制节点,能达到较好的拟合效果. 相似文献
602.
为了提高铝阳极材料的耐析氢腐蚀和活化性能,用失重腐蚀、电化学等方法研究了在4 mol/LKOH溶液中,丙炔醇对铝阳极(99.999%)电化学性能的影响,结果表明:添加0.5%丙炔醇,不仅使铝的析氢腐蚀速率降低(缓蚀率达85.35%),又能最大程度保持铝阳极的活性(超过铝在4 mol/L KOH溶液中的活性),开路电位Eocp负移达-2.033 V.此外,在"饱和Ca(OH)2+4 mol/L KOH"溶液中,添加0.5%丙炔醇时,铝的缓蚀率高达93.21%,其表面腐蚀均匀,活化性能进一步提高,Eocp负移达-2.011 V.为铝阳极材料的应用提供了有实用价值的添加剂配方. 相似文献
603.
N. Prantzos 《Space Science Reviews》2007,130(1-4):27-42
After a short historical (and highly subjective) introduction to the field, I discuss our current understanding of the origin
and evolution of the light nuclides D, 3He, 4He, 6Li, 7Li, 9Be, 10B and 11B. Despite considerable observational and theoretical progress, important uncertainties still persist for each and every one
of those nuclides. The present-day abundance of D in the local interstellar medium is currently uncertain, making it difficult
to infer the recent chemical evolution of the solar neighborhood. To account for the observed quasi-constancy of 3He abundance from the Big Bang to our days, the stellar production of that nuclide must be negligible; however, the scarce observations of its abundance in planetary nebulae seem to contradict this idea. The observed
Be and B evolution as primaries suggests that the source composition of cosmic rays has remained ∼constant since the early
days of the Galaxy, a suggestion with far reaching implications for the origin of cosmic rays; however, the main idea proposed
to account for that constancy, namely that superbubbles are at the source of cosmic rays, encounters some serious difficulties.
The best explanation for the mismatch between primordial Li and the observed “Spite-plateau” in halo stars appears to be depletion
of Li in stellar envelopes, by some yet poorly understood mechanism. But this explanation impacts on the level of the recently
discovered early “6Li plateau”, which (if confirmed), seriously challenges current ideas of cosmic ray nucleosynthesis. 相似文献
604.
如何在以建模量为协调依据的老飞机上实施数字化技术,并在原则上不报废原有工装的情况下,建立一套与现行生产所用外形数据协调一致的设计和生产可用的飞机外形数学模型是一个急需解决的问题,本文给出了建立符合原有工装的飞机外形数学模型的一种方法。 相似文献
605.
The European Large Area ISO Survey (ELAIS) was the largest Open Time survey on the Infrared Space Observatory (ISO). It was
designed to explore obscured galaxies and hence quantify the recent star-formation history of the Universe. The final reanalysis
of the data has been completed and a band-merged catalogue with associations across many wavelengths compiled and released
the data to the global astronomical community (http://astro.imperial.ac.uk/Elais/). This paper summarises some of the key
results.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
606.
三月的苏州花红柳绿、春意融融 ,但我们无暇领略小桥、流水、人家的水乡风情 ,直奔苏州高新技术园区。坐落在园区中心地段的苏州沙迪克三光机电有限公司就是我们此次苏州之行的访问对象 ,宽敞明亮的厂房、整齐有序的装配线、统一着装的员工和好客的主人预示着我们将会有一次愉快和轻松的采访。颇有学者风范、侃侃而谈的包志书董事长向我们说起电加工行业的龙头老大———沙迪克三光的昨天、今天和明天。 相似文献
607.
608.
The continuous growth of air traffic has led to acute airspace congestion and severe delays, which threatens operation safety and cause enormous economic loss. Flight assignment is an economical and effective strategic plan to reduce the flight delay and airspace congestion by reasonably regulating the air traffic flow of China. However, it is a large-scale combinatorial optimization problem which is difficult to solve. In order to improve the quality of solutions, an effective multi-objective parallel evolution algorithm(MPEA) framework with dynamic migration interval strategy is presented in this work. Firstly, multiple evolution populations are constructed to solve the problem simultaneously to enhance the optimization capability. Then a new strategy is proposed to dynamically change the migration interval among different evolution populations to improve the efficiency of the cooperation of populations. Finally, the cooperative co-evolution(CC) algorithm combined with non-dominated sorting genetic algorithm II(NSGA-II) is introduced for each population. Empirical studies using the real air traffic data of the Chinese air route network and daily flight plans show that our method outperforms the existing approaches, multiobjective genetic algorithm(MOGA), multi-objective evolutionary algorithm based on decomposition(MOEA/D), CC-based multi-objective algorithm(CCMA) as well as other two MPEAs with different migration interval strategies. 相似文献
609.
610.
高效加工已经成为现代航空制造业发展的重要趋势,而高效装夹也成为影响高效加工的重要决定因素之一。针对立卧转换机床自身特点,通过自主设计的工艺夹具,对不同类型的航空结构件,采用适合的装夹策略,构建出基于立卧转换机床的数控加工高效装夹系统。实践证明,该系统能显著提高设备利用率。 相似文献