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131.
机载激光武器每次工作时会产生几百千瓦的废热,国外研究机构普遍采用相变储热换热器,对其进行短时存储、长时排散。基于此,针对国际先进相变储热换热器技术进行探索性研究,提出一种三通道板翅式相变储热换热器构型,通过数值模拟的方式,定量分析了换热器主要结构参数对工作性能的影响。结果表明,热流体出口温度随相变材料通道翅片高度的增加而下降,且随流体通道翅片高度和翅片节距的增加而上升。此外,换热器内部区域存在低效储热区、高效储热区和控温缓冲区3个部分,需要通过设置多流程的方式,以确保蓄热期间内热流体出口温度始终满足设计要求。 相似文献
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134.
采用有限元仿真(FEM)与地面热平衡试验验证相结合的方法,计算并模拟了30 cm离子推力器处于在轨环境时,有、无主动热控对三栅极相对位移变化造成的影响,并对目前离子推力器设置的工作启动流程可能造成的打火风险进行了预估。结果显示:三栅极组件的热形变方向均为法向方向,且栅极中心区域的间距最小;在 -269 ℃ 在轨极限环境温度下,推力器在5 kW工作模式下温度平衡后的屏栅与加速栅最大热态间距为0.14 mm,加速栅和减速栅则已发生贴合;在受太阳辐照以及卫星帆板恒温边界的影响下,栅面最低初始温度为-102 ℃;当推力器主动热控保证温控点为20 ℃时,栅面最低启动温度为-25 ℃,且推力器工作8000 s后,屏栅与加速栅、加速栅与减速栅的最小间距分别稳定在0.25 mm和0.20 mm;当推力器主动热控保证温控点为50 ℃时,推力器工作9000 s后,屏栅与加速栅、加速栅和减速栅最小间距分别稳定在0.31 mm和0.30 mm,能够满足0.25 mm的栅极安全打火间距要求。 相似文献
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从经济学视角出发,发现企业变革中存在阻力问题的原因主要表现在以下三个方面:一是路径依赖使企业变革受到惯性阻力;二是信息不对称使得员工恐惧产生变革阻力;三是变革的风险成本大于收益,困扰企业变革前进的脚步。基于此,要消除企业变革的阻力问题可以从加强对员工的培训力度、让员工参与变革、塑造共同愿景、建立强有力的领导团队以及提高员工对变革的适应性等几个方面着手。 相似文献
137.
A.H. Maghrabi H.M. Al Dajani 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Water vapor is the most important greenhouse gas. It plays a major role in the dynamics of atmospheric circulation, radiation exchange within the atmosphere, and climate variability. Knowledge of the distribution of water vapor is important for understanding climate change and global warming. 相似文献
138.
《Space Policy》2014,30(4):190-192
The external and internal environments of NASA have been shifting, necessitating new approaches to problem solving and innovation. Based on a strategic alignment analysis, and an understanding of NASA's internal and external contexts, we have two modest proposals: First, give NASA flexibility to manage its human resources and infrastructure based on market-based, competitive, performance-oriented principles. Second, it is time for NASA to become a real network organization. One that is properly integrated both internally (across NASA centers) as well as externally with whatever organizations have superior space-related knowledge and technology, wherever they are. 相似文献
139.
L. Bengtsson 《Space Science Reviews》2006,125(1-4):187-197
The climate response to changes in radiative forcing depends crucially on climate feedback processes, with the consequence
that solar and greenhouse gas forcing have both similar response patterns in the troposphere. This circumstance complicates
significantly the attribution of the causes of climate change. Additionally, the climate system displays a high level of unforced
intrinsic variability, and significant variations in the climate of many parts of the world are due to internal processes.
Such internal modes contribute significantly to the variability of climate system on various time scales, and thus compete
with external forcing in explaining the origin of past climate extremes. This highlights the need for independent observations
of solar forcing including long-term consistent observational records of the total and spectrally resolved solar irradiance.
The stratospheric response to solar forcing is different from its response to greenhouse gas forcing, thus suggesting that
stratospheric observations could offer the best target for the identification of the specific influence of solar forcing on
climate. 相似文献
140.
C.J. Merchant D. Llewellyn-Jones R.W. Saunders N.A. Rayner E.C. Kent C.P. Old D. Berry A.R. Birks T. Blackmore G.K. Corlett O. Embury V.L. Jay J. Kennedy C.T. Mutlow T.J. Nightingale A.G. O’Carroll M.J. Pritchard J.J. Remedios S. Tett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):1-11
We describe the approach to be adopted for a major new initiative to derive a homogeneous record of sea surface temperature for 1991–2007 from the observations of the series of three along-track scanning radiometers (ATSRs). This initiative is called (A)RC: (Advanced) ATSR Re-analysis for Climate. The main objectives are to reduce regional biases in retrieved sea surface temperature (SST) to less than 0.1 K for all global oceans, while creating a very homogenous record that is stable in time to within 0.05 K decade−1, with maximum independence of the record from existing analyses of SST used in climate change research. If these stringent targets are achieved, this record will enable significantly improved estimates of surface temperature trends and variability of sufficient quality to advance questions of climate change attribution, climate sensitivity and historical reconstruction of surface temperature changes. The approach includes development of new, consistent estimators for SST for each of the ATSRs, and detailed analysis of overlap periods. Novel aspects of the approach include generation of multiple versions of the record using alternative channel sets and cloud detection techniques, to assess for the first time the effect of such choices. There will be extensive effort in quality control, validation and analysis of the impact on climate SST data sets. Evidence for the plausibility of the 0.1 K target for systematic error is reviewed, as is the need for alternative cloud screening methods in this context. 相似文献