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化学农药在土壤中残留造成的环境污染和给人类健康带来的危害日益严重,土壤微生物在土壤残留农药降解中起着关键作用,利用微生物来降解农药可以保障土壤的健康发展.本文从土壤残留农药的种类、降解农药的微生物类群、微生物降解农药的机理、微生物降解的影响因素等方面进行了综述,并且对土壤农药微生物降解的研究趋势提出了自己的观点. 相似文献
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考虑了带随机回报的一类离散马氏风险模型.在此模型中,赔付的发生概率,赔付额的分布函数都是由一个离散时间的马氏链调控.当保险公司采用门槛分红策略时,通过计算得到了破产前的期望折现分红总量满足的一组线性方程.最后,给出了期望折现分红总量的显式解析式. 相似文献
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existing multi-period portfolio diversification performance evaluation models
are mainly divided into two categories. The first category is to build a
performance evaluation model based on the return rate of portfolio at each period.
The other category is to evaluate portfolio performance by using efficient
frontier. However, the former ignores the dynamic relationship among the time
periods, while the latter has limitations when there exists friction in
financial market. To address this problem, the actual investment of the input-output
process was clarified and defined, and the definition of multi-period portfolio
efficiency were given based on the distance between portfolio under evaluation and its projection point on the efficient frontier.
Under the multi-period mean-variance theoretical framework, the middle
connection condition in the multi-period portfolio evaluation problem was
derived by using the wealth dynamic process, so as to build a two-period
portfolio efficiency estimation model under different orientation. Since the
above-mentioned middle connection condition is random, it not workable in actual
evaluation. Therefore, in this paper, the first moment and second moment of the
above random conditions were used to replace the original one, and another kind
of two-period portfolio efficiency estimation model was built. The numerical
analyses show that this proposed model is effective. 相似文献
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本文基于初步划分-综合评价-精准划分的多层次递进模块划分架构, 为模块化无人机设计中模块划分提供可信、有效的方法。以提升模块划分结果的可信度为目标, 在模块划分指标评价中引入基于专家信度的评分机制, 形成了基于模糊聚类和专家评分机制的多层次模块划分方法。以一次性、可重复使用无人机为例, 采用本文提出的模块划分方法, 进行零部件聚类并形成模块划分方案。由模块划分结果可知, 本文模块划分方法可对不同模式的无人机获得符合其使用特点、可信的模块划分方案, 进而验证了方法的合理性和有效性。 相似文献
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