In this paper the heat withstanding mechanism of heat-resisting aluminum alloy conductor is discussed, the types and performance of the conductor and its application on transmission lines are analyzed and introduced, ...In this paper the heat withstanding mechanism of heat-resisting aluminum alloy conductor is discussed, the types and performance of the conductor and its application on transmission lines are analyzed and introduced, and suggestions on accelerating exploitation and application of the conductor are put forward.展开更多
In reliability theory and survival analysis, the problem of point estimation based on the censored sample has been discussed in many literatures. However, most of them are focused on MLE, BLUE etc; little work has bee...In reliability theory and survival analysis, the problem of point estimation based on the censored sample has been discussed in many literatures. However, most of them are focused on MLE, BLUE etc; little work has been done on the moment-method estimation in censoring case. To make the method of moment estimation systematic and unifiable, in this paper, the moment-method estimators(abbr. MEs) and modified momentmethod estimators(abbr. MMEs) of the parameters based on type Ⅰ and type Ⅱ censored samples are put forward involving mean residual lifetime. The strong consistency and other properties are proved. To be worth mentioning, in the exponential distribution,the proposed moment-method estimators are exactly MLEs. By a simulation study, in the view point of bias and mean square of error, we show that the MEs and MMEs are better than MLEs and the “pseudo complete sample” technique introduced in Whitten et al.(1988). And the superiority of the MEs is especially conspicuous, when the sample is heavily censored.展开更多
The threat of space debris on spacecraft has increased our attention to the survivability enhancement design of spacecraft. This paper studies the survivability assessment method, which has mainly two parts, namely su...The threat of space debris on spacecraft has increased our attention to the survivability enhancement design of spacecraft. This paper studies the survivability assessment method, which has mainly two parts, namely susceptibility assessment and vulnerability assessment. Our emphasis focuses on how to assess the vulnerability of spacecraft to space debris. The basic vulnerability assessment process includes： （1） the analyses of the threat environment of space debris; （2） the process of identification of critical components of spacecraft, in which a DMECA （damage mode, effects, and criticality analysis） is introduced and an expert system is proposed to get the damage ratio of each component; （3） the spacecraft geometrical description method, in which ＂ shot line scanning method＂ is described to calculate the projected/overlapping area of components and determine the masking/shielding relationship among components; （4） the calculation of spacecraft kill probability and vulnerable area. At last, the authors conclude that the proposed assessment method is systemic and feasible, and it can give a quantitative assessment result of survivability/vulnerability in the spacecraft conceptual design. The theory contained in this paper is useful to develop computerized tool for spacecraft survivability analysis.展开更多
文摘In this paper the heat withstanding mechanism of heat-resisting aluminum alloy conductor is discussed, the types and performance of the conductor and its application on transmission lines are analyzed and introduced, and suggestions on accelerating exploitation and application of the conductor are put forward.
基金This research is partially supported by National Science Foundation of China (No. 69971016).
文摘In reliability theory and survival analysis, the problem of point estimation based on the censored sample has been discussed in many literatures. However, most of them are focused on MLE, BLUE etc; little work has been done on the moment-method estimation in censoring case. To make the method of moment estimation systematic and unifiable, in this paper, the moment-method estimators(abbr. MEs) and modified momentmethod estimators(abbr. MMEs) of the parameters based on type Ⅰ and type Ⅱ censored samples are put forward involving mean residual lifetime. The strong consistency and other properties are proved. To be worth mentioning, in the exponential distribution,the proposed moment-method estimators are exactly MLEs. By a simulation study, in the view point of bias and mean square of error, we show that the MEs and MMEs are better than MLEs and the “pseudo complete sample” technique introduced in Whitten et al.(1988). And the superiority of the MEs is especially conspicuous, when the sample is heavily censored.
基金This project is supported by National Natural Science Foundation of China （10372082） the Aerospace Science Foundation （02B53008） and the Doctorate Foundation of Northwestern Polytechnical University （CX200301）
文摘The threat of space debris on spacecraft has increased our attention to the survivability enhancement design of spacecraft. This paper studies the survivability assessment method, which has mainly two parts, namely susceptibility assessment and vulnerability assessment. Our emphasis focuses on how to assess the vulnerability of spacecraft to space debris. The basic vulnerability assessment process includes： （1） the analyses of the threat environment of space debris; （2） the process of identification of critical components of spacecraft, in which a DMECA （damage mode, effects, and criticality analysis） is introduced and an expert system is proposed to get the damage ratio of each component; （3） the spacecraft geometrical description method, in which ＂ shot line scanning method＂ is described to calculate the projected/overlapping area of components and determine the masking/shielding relationship among components; （4） the calculation of spacecraft kill probability and vulnerable area. At last, the authors conclude that the proposed assessment method is systemic and feasible, and it can give a quantitative assessment result of survivability/vulnerability in the spacecraft conceptual design. The theory contained in this paper is useful to develop computerized tool for spacecraft survivability analysis.
