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701.
702.
文章结合在工程中遇到的动不平衡实际问题,根据平衡机的基本工作原理,提出了双平面分别配重、合成计算的解决思路,并在理论上对自旋稳定卫星的双平面配重的动不平衡配重的计算方法进行了分析和研究,验证了配平计算方法的正确性和可行性。最后,根据配重计算方法提出了配重调整的工艺步骤。 相似文献
703.
704.
康巍巍 《华北航天工业学院学报》2014,(1):43-45
本文着眼于高校外语专业的发展,以通识性教育为切入点,并以北华航天工业学院外语系为研究对象,通过课堂形式,课堂内容,师资建设三方面开展实践研究和探索,分析其成功经验和不足,并对高校外语专业通识化教育发展提出合理化建议,尝试性构建专业教育+通识教育发展的新模式,进一步推动高校外语专业教学改革的步伐。 相似文献
705.
Giannina Poletto 《Space Science Reviews》1994,70(1-2):241-252
Streamers have been observed since far back in time, but our knowledge of their morphology and of their physical characteristics is still very limited. As a consequence, the present streamer picture is largely incomplete: because individual features are poorly known, their role in more general phenomena (like the evolution of the global corona or the solar wind mass and flow pattern) is also poorly known. In this presentation, the more relevant open problems in the understanding of streamers will be illustrated and it will be shown how new data acquired by SOHO may help us to reach a better understanding of these structures. 相似文献
706.
Satoru Katsuda Hiroshi Tsunemi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):383-389
We have observed the Cygnus Loop from the northeast (NE) to the southwest (SW) with XMM-Newton. We extracted spectra from 3′-spaced annular regions across the Loop and fitted them either with a one-kTe-component non-equilibrium ionization (NEI) model or with two-kTe-component NEI model. We found that the two-kTe-component model yields significantly better fits in almost all the spectra than the one-kTe-component model. Judging from the abundances, the high-kTe-component in the two-temperature model must be fossil ejecta while the low-kTe-component comes from the swept-up interstellar medium (ISM). The distributions of Ne, Mg, Si, and S for fossil ejecta appear to retain the onion-skin structure at the time of a supernova explosion, suggesting that significant overturning of the ejecta has not occurred yet. Comparing the relative abundances of fossil ejecta estimated for the entire Cygnus Loop with those from theoretical calculations for Type-II SN, the mass of the progenitor star is likely to be ∼13 M⊙. The trends of the radial profiles of kTe and emission integral for the swept-up ISM are adequately described by the Sedov model, suggesting that the swept-up ISM is concentrated in a shell-like structure. Comparing our data with the Sedov model, we found the ambient medium density to be ∼0.7 cm−3. Then, we estimated the total mass of the swept-up ISM and the age of the remnant to be ∼130 M⊙ and 13,000 years, respectively. Note that if the explosion occurred within a stellar wind cavity, then the density in the cavity, the total swept-up mass in the cavity, and the age of the remnant are estimated to be ∼0.14 cm−3, ∼25 M⊙, and ∼10,000 years, respectively. 相似文献
707.
刘洋 《沈阳航空工业学院学报》2008,25(6)
受多种因素的影响,现阶段高校学风总体状态呈现下滑趋势。这无疑是给高校学生管理工作者提出了一个"如何扭转学风下滑现状,不断提高学生管理工作水平"的新任务。以普通工科院校为对象,在对学风建设和学生管理工作现状进行比较全面的调查分析基础上,提出了五种改善和加强普通工科院校学风建设和学生管理工作的有效途径。 相似文献
708.
应用试验模态参数修正理论模型的最佳矩阵逼近法 总被引:3,自引:0,他引:3
张宪民 《北京航空航天大学学报》1994,20(2):142-149
本文从特征方程和模态正交性条件出发,给出了一种应用模态参数识别结果修正理论模型的最佳矩阵逼近方法。该方法通过对识别出的模态矩阵进行奇异值分解并结合特征方程和模态正交条件导出了修正理论模型的通解表达式,在此基础上,给出了最佳逼近解的定义,研究了最佳逼近解的唯一性,给出了最佳修正质量矩阵和刚度矩阵的具体表达式,数值计算表明,本文方法具有很高的修正精度,对于大误差模型也有较好的修正能力,具有一定的应有和 相似文献
709.
G. Meynet 《Space Science Reviews》1993,66(1-4):417-420
Let us suppose that it is possible observationally to determine the number ratio of WR to O stars in a starburst galaxy (cf. e. g. Vacca &; Conti 1992) and that one can also have some information on the way the different WR subtypes are distributed (number ratios as WN/WR, WNL/WR etc ...), the question is, what can we deduce from these values on the burst of star formation which gave birth to these WR stars? Is it possible for instance to constrain the age of the burst (i.e. the time elapsed since the beginning of the burst of star formation), its intensity (i.e. the ratio of the star formation rate during the burst to that before the burst) or the metallicity of the cloud from which the stars formed? We present here models of starbursts based on the most recent models for single stars computed by the Geneva group and show that the study of the WR population in a starburst provides very useful insights on the age of the burst and on the metallicity of the star forming zone. 相似文献
710.
In a paper submitted to A&A we present the first line blanketed hydrodynamic models of spherically expanding atmospheres of hot stars. This paper is complementary to the submitted paper. Here, we emphasize the advantages and the weak points of our approach and we present additional technical aspects.The models are characterised by a simultaneous solution of the equation of motion, the non-LTE populations of H and He, and radiation transfer in a line blanketed atmosphere. The entire domain from the optically thick photosphere out to the terminal velocity of the wind is treated. The radiative forces are evaluated consistently with the depth-dependent radiation field, taking into account multiple scattering by metal lines and line overlap. 相似文献