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851.
Daily UK Met Office stratospheric assimilated data for the Northern and Southern Hemispheres, accumulated for the period from 2004 to 2012 and pressure range of 1000–0.1 hPa, are used in this paper. The paper presents and thoroughly discusses spatial–temporal distributions of stationary planetary wave (SPW) amplitudes and phases, calculated on the basis of geopotential height, temperature, zonal and meridional wind data for zonal wave numbers 1 and 2 (SPW1 and SPW2). The climatological planetary wave amplitudes and phases are calculated by extracting waves from three types of data: daily, monthly mean and climatological monthly mean. It has been established that magnitude of amplitudes and height-latitude distribution of amplitudes of SPW1 and SPW2 depend on data processing method for all parameters. It has also been established that height-latitude distribution amplitudes and phases significantly differ for geopotential height, temperature, zonal and meridional wind and depend on wave number and hemisphere. However, height-latitude distributions of phases are little different from each other for the used methods of data processing.  相似文献   
852.
Planetary protection has been recognized as one of the most important issues in sample return missions that may host certain living forms and biotic signatures in a returned sample. This paper proposes an initiative of sample capsule retrieval and onboard biosafety protocol in international waters for future biological and organic constituent missions to bring samples from possible habitable bodies in the solar system. We suggest the advantages of international waters being outside of national jurisdiction and active regions of human and traffic affairs on the condition that we accept the Outer Space Treaty. The scheme of onboard biological quarantine definitely reduces the potential risk of back-contamination of extraterrestrial materials to the Earth.  相似文献   
853.
This article focuses on the genetic identification of observed small cosmic bodies with alleged parental bodies; namely, comets, asteroids and meteoroid swarms. There is a problem of the upper D-value limit as a measure of proximity between the orbits of the bodies in the five-dimensional phase space (Southworth and Hawkins, 1963). In the study of genetic relationships of the comet and meteor complexes, the D value is usually taken as equal to 0.2 for all meteor showers. However, the upper D limit should be investigated for each meteoroid complex. For example, such investigation was performed for the Taurid meteor complex (Porub?an et al., 2006). In this paper, the upper D-criterion limit value was investigated for the Perseid meteor shower. The 1862 III Swift–Tuttle comet is its parental comet.  相似文献   
854.
To optimize cutting control parameters and provide scientific evidence for controlling cutting forces,cutting force modeling and cutting control parameter optimization are researched with one tool adopted to orbital drill holes in aluminum alloy 6061.Firstly,four cutting control parameters(tool rotation speed,tool revolution speed,axial feeding pitch and tool revolution radius)and affecting cutting forces are identified after orbital drilling kinematics analysis.Secondly,hybrid level orthogonal experiment method is utilized in modeling experiment.By nonlinear regression analysis,two quadratic prediction models for axial and radial forces are established,where the above four control parameters are used as input variables.Then,model accuracy and cutting control parameters are analyzed.Upon axial and radial forces models,two optimal combinations of cutting control parameters are obtained for processing a13mm hole,corresponding to the minimum axial force and the radial force respectively.Finally,each optimal combination is applied in verification experiment.The verification experiment results of cutting force are in good agreement with prediction model,which confirms accracy of the research method in practical production.  相似文献   
855.
运用广义随机Petri网的方法,得到了测试性参数指标与保障性参数可用度Ao之间的关系,另外还推导出了测试性参数指标与维修性MTTR之间的关系。以A0和MTTR为目标,进行测试性参数指标的寻优求解,从而得到测试性参数指标的选取方法,并举例验证了该选取方法的正确性、可行性。  相似文献   
856.
根据经济周期谷底的特性以及中美两国经济紧密关联和经济周期越来越契合的规律,可以印证2009年就是新一轮经济周期的谷底,由此可以断定当前处于复苏阶段.然而近三年来我国经济增速持续下滑至谷底以下,这一反常现象是由于经济短周期冲高回落与经济增长阶段转换相互叠加造成的.河南省与全国经济周期高度一致,时滞半年左右.在高速经济增长阶段河南省潜在经济增长率比全国高出2个百分点,中高速阶段高出1.5个百分点.河南省近几年经济增速深度下滑,其关键原因是投资增速下滑,其根本原因是结构升级缓慢.未来河南经济要摆脱持续下行趋势,保持经济中高速增长,应坚持调结构、扩投资、促改革的政策思路,“调结构”是根本,“扩投资”是基础,“促改革”是保障.  相似文献   
857.
实质意义上的权力制约肇始于权力分化之后,历经以道德制约权力、以权力制约权力、以社会制约权力等经典范式,体现了权力制约活动从关注权力执掌者、权力本体到关注权力归属者不断演变的内在逻辑。植根于我国国情的权力制约实践在伦理学、社会学途径方面与西方存有共性,但于政治学途径却存有个性。实现我国权力制约的语境化既需要体现权力制约的普遍性规律,更需要把握马克思主义政治观视域下权力制约的特殊性。  相似文献   
858.
对合肥市会计服务业及其发展进行了研究,研究2009-2013年安徽省(合肥市)会计师事务所数量和注册会计师数量,发现合肥市会计服务业发展形势较为严峻,具体表现为:会计师事务所规模较小,内部治理机制不够完善、业务种类不够全面,管理机制不够健全,人才结构不够合理,高端人才较少,国际化程度不高,并提出合肥市应当加强会计服务行业地方法规政策的完善与制定、提高会计服务业的社会透明度、加强会计服务业的多元化发展、加强业务创新,开创自身特色、加强复合型人才培养,提升会计服务业人员整体素质、推行联合重组,避免内部竞争,以促进会计服务业的进一步发展。  相似文献   
859.
王俨剀  王彤  廖明夫  王鑫 《推进技术》2021,42(9):2105-2118
盘腔积液现象在舰用燃气轮机工作过程中时有发生,汽化的滑油和水蒸气凝结形成积液。转子带动腔内的积液旋转,引发振动失稳,严重时会对发动机结构造成致命性破坏。为此,本文开展燃气轮机压气机盘腔积液的模拟实验研究,以双盘双支承的卧式柔性转子系统作为研究对象,重点关注小积液量的特点,对积液转子的动力学稳定性进行了研究。观测到转子的失稳现象,开展了不同积液体积、不同积液类型(水、植物油和滑油)等因素的影响规律研究,揭示了小积液的卧式转子动力学特征。研究结果表明:①对于积液失稳振动,存在失稳边界积液量,当积液量大于该边界值时,失稳将会发生。②失稳边界转速及恢复转速均高于临界转速。当转速高于失稳边界转速时,失稳将会发生。转速进一步增加,高于恢复转速时,失稳现象可能消失。③失稳时的振动特征为:出现幅值突增,次谐波成分也随之增加;基频和次谐波发生调制,表现出拍振特征。④随着积液体积的增加,失稳边界转速先减小后增加。⑤随着积液粘度系数增大,失稳边界转速和边界积液量均增大。  相似文献   
860.
The interaction between electromagnetic waves and matter is the working principle of a photon-propelled spacecraft, which extracts momentum from the solar radiation to obtain a propulsive acceleration. An example is offered by solar sails, which use a thin membrane to reflect the impinging photons. The solar radiation momentum may actually be transferred to matter by means of various optical phenomena, such as absorption, emission, or refraction. This paper deals with the novel concept of a refractive sail, through which the Sun’s light is refracted by crossing a film made of polymeric micro-prisms. The main feature of a refractive sail is to give a large transverse component of thrust even when the sail nominal plane is orthogonal to the Sun-spacecraft line. Starting from the recent literature results, this paper proposes a semi-analytical thrust model that estimates the characteristics of the propulsive acceleration vector as a function of the sail attitude angles. Such a mathematical model is then used to analyze a simplified Earth-Mars and Earth-Venus interplanetary transfer within an optimal framework.  相似文献   
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