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101.
曹知红  李文浩  李彦良  张喦  田宁 《宇航学报》2020,41(8):1076-1083
针对锈层对过冷沸腾换热冷却效果的影响,本文进行了理论分析、实验研究和仿真校验。首先结合经典的过冷沸腾换热理论,分析了锈层对冷却效果影响最大的几个因素。然后进行了一组夹套内壁生锈和未生锈两种情况下冷却效果的对比实验。实验发现,内壁生锈造成入口段温度大幅升高,且温升沿流道方向递次减小。接着分析了造成该现象的几大因素,推断锈层影响了流态进而抑制了沸腾换热机制是最主要的因素,并对不同入口流态下管内沸腾换热进行数值仿真,校验了上述分析结果。最后,根据研究结论,对过冷沸腾换热中易生锈或类似的粗糙内壁槽道的设计方法提出了建议。  相似文献   
102.
本文通过对廊坊市工业企业技术创新现状调查研究,剖析了区域技术创新系统存在的问题和原因,提出了加快廊坊市工业企业技术创新的思路和对策。  相似文献   
103.
Parametric study of turbine NGV blade lean and vortex design   总被引:1,自引:1,他引:0  
《中国航空学报》2016,(1):104-116
The effects of blade lean and vortex design on the aerodynamics of a turbine entry nozzle guide vane (NGV) are considered using computational fluid dynamics. The aim of the work is to address some of the uncertainties which have arisen from previous studies where conflicting results have been reported for the effect on the NGV. The configuration was initially based on the energy efficient engine turbine which also served as the validation case for the computational method. A total of 17 NGV configurations were evaluated to study the effects of lean and vortex design on row efficiency and secondary kinetic energy. The distribution of mass flow ratio is introduced as an additional factor in the assessment of blade lean effects. The results show that in the turbine entry NGV, the secondary flow strength is not a dominant factor that determines NGV losses and therefore the changes of loading distribution due to blade lean and the associated loss mecha-nisms should be regarded as a key factor. Radial mass flow redistribution under different NGV lean and twist is demonstrated as an addition key factor influencing row efficiency.  相似文献   
104.
层次分析法在空间推进系统综合评价中的应用   总被引:3,自引:0,他引:3  
林庆国 《上海航天》2000,17(1):19-23
在建立航天器推进系统综合评定体系的基础上,动用层次分析法对已经应用飞行的推进系统和有未来应用潜力的推进系统进行了评估。评估结果表明,从能量特性,使用性能、系统可靠性、经济性、系统特性五个准则上看,过氧化氢/煤油无毒推进系统是未来航天器在轨推进的最优选择。  相似文献   
105.
文章首先简要总结了国内外英汉对比微观研究的现状,指出了理论研究主要在语言结构的普遍性方面,而目前最迫切的是要进行大量实用方面的研究,其重点在于两种语言的相异之处,包括同中有异和一方有一方无,同时又提出了对比中宏观研究的问题及宏观研究的两种重要方法-结合语言的社会功能和语言心理进行对比研究的方法,这就扩大了对比研究的领域,把英汉对比研究推进了一步。  相似文献   
106.
借鉴"读者接受"理论中以"读者为中心"的观点,研究《高级英语》课程教学的自主学习模式。本文认为,学生是审美活动的主体,在该教学模式中研究学生的元认知特点、教材、教学任务的设计和有效控制等因素,注重教学过程的研究,在实践中有效实现以学生为中心、培养学生综合素质的教学理念。  相似文献   
107.
With the installation of a new module and the relocation of three other modules, including multiple hand-offs from the station arm (SSRMS) to the shuttle arm (SRMS), International Space Station (ISS) assembly mission 10A/STS-120 was anticipated to be one of the most complicated ISS assembly missions ever attempted. The assembly operations became even more complex when a solar array wing (SAW) on the relocated Port-6 (P6) truss segment ripped while being extended. Repairing the torn SAW became the single most important objective for the remainder of STS-120, with future ISS assembly missions threatened by reduced power generation capacity if the SAW could not be repaired. Precise coordination between the space shuttle and ISS robotics teams led to an operational concept that combined the capabilities of the SRMS and SSRMS robotic systems in ways far beyond their original design capacities. Benefits of consistent standards for ISS robotic interfaces have been previously identified, but the advantages of having two such versatile and compatible robotic systems have never been quite so spectacular. This paper describes the role of robotics in the emergency SAW repair and highlights how versatility within space robotics systems can allow operations far beyond the intended design scenarios.  相似文献   
108.
高等教育结构存在的主要问题与创新——以河南省为例   总被引:1,自引:0,他引:1  
河南省高等教育结构目前尚存在学科专业结构不舍理、产学研相结合未形成良性互动机制、高层次研发人才培养能力不足和高等职业教育人才培养模式还需优化等问题。要切实落实河南省高等教育基础性、先导性、全局性的战略地位,在确立适度超前发展的理念下,坚持可持续发展、本土化、开放协作和生态和谐的原则,以培育高等教育园区发展极作为河南高等教育结构创新的战略目标,以和谐的生态结构作为结构创新的基本形态,以学科专业调整与发展作为结构创新的核心工作,以产学研有效结合作为结构创新的突破口,全力推进河南省高等教育结构的创新。  相似文献   
109.
The success of long-duration space missions depends on the ability of crewmembers and mission support specialists to be alert and maintain high levels of cognitive function while operating complex, technical equipment. We examined sleep, nocturnal melatonin levels and cognitive function of crewmembers and the sleep and cognitive function of mission controllers who participated in a high-fidelity 105-day simulated spaceflight mission at the Institute of Biomedical Problems (Moscow). Crewmembers were required to perform daily mission duties and work one 24-h extended duration work shift every sixth day. Mission controllers nominally worked 24-h extended duration shifts. Supplemental lighting was provided to crewmembers and mission controllers. Participants' sleep was estimated by wrist-actigraphy recordings. Overall, results show that crewmembers and mission controllers obtained inadequate sleep and exhibited impaired cognitive function, despite countermeasure use, while working extended duration shifts. Crewmembers averaged 7.04±0.92 h (mean±SD) and 6.94±1.08 h (mean±SD) in the two workdays prior to the extended duration shifts, 1.88±0.40 h (mean±SD) during the 24-h work shift, and then slept 10.18±0.96 h (mean±SD) the day after the night shift. Although supplemental light was provided, crewmembers’ average nocturnal melatonin levels remained elevated during extended 24-h work shifts. Naps and caffeine use were reported by crewmembers during ∼86% and 45% of extended night work shifts, respectively. Even with reported use of wake-promoting countermeasures, significant impairments in cognitive function were observed. Mission controllers slept 5.63±0.95 h (mean±SD) the night prior to their extended duration work shift. On an average, 89% of night shifts included naps with mission controllers sleeping an average of 3.4±1.0 h (mean±SD) during the 24-h extended duration work shift. Mission controllers also showed impaired cognitive function during extended duration work shifts.These findings indicate that extended duration work shifts present a significant challenge to crewmembers and mission support specialists during long-duration space mission operations. Future research is needed to evaluate the efficacy of alternative work schedules and the development and implementation of more effective countermeasures will be required to maintain high levels of performance.  相似文献   
110.
With the rapid increase of GPS/GNSS receivers being deployed and operated in China, real-time GPS data from nearly a thousand sites are available at the National Center for Space Weather, China Meteorology Administration. However, it is challenging to generate a high-quality regional total electron content (TEC) map with the traditional two-dimensional (2-D) retrieval scheme because a large horizontal gradient has been reported over east–south Asia due to the northern equatorial ionization anomaly. We developed an Ionosphere Data Assimilation Analysis System (IDAAS), which is described in this study, using an International Reference Ionosphere (IRI) model as the background and applying a Kalman filter for updated observations. The IDAAS can reconstruct a three-dimensional ionosphere with the GPS slant TEC. The inverse slant TEC correlates well with observations both for GPS sites involved in the reconstruction and sites that are not involved. Based on the IDAAS, simulations were performed to investigate the deviation relative to the slant-to-vertical conversion (STV). The results indicate that the relative deviation induced by slant-to-vertical conversion may be significant in certain instances, and the deviation varies from 0% to 40% when the elevation decreases from 90° to 15°, while the relative IDAAS deviation is much smaller and varies from −5% to 15% without an elevation dependence. Compared with ‘true TEC’ map derived from the model, there is large difference in STV TEC map but no obvious discrepancy in IDAAS map. Generally, the IDAAS TEC map is much closer to the “true TEC” than is STV TEC map is.  相似文献   
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