登月下降级液氧甲烷发动机方案研究

月球软着陆下降级发动机在载人登月任务中起着至关重要的作用,必须具备高性能、长期贮存、多次点火起动、大范围推力调节等能力。针对此技术需求,论述了液氧甲烷推进剂具有空间可贮存、不易积碳和结焦、能够实现膨胀循环等技术优点,且相关技术已得到国内外试验验证,技术可行性高,是登月下降级发动机理想选择。经过论证,确定了发动机采用泵压膨胀循环、双涡轮泵串联的系统方案。最后,介绍了国内液氧甲烷下降级发动机火炬式电点火器、大范围变工况喷注器等关键技术的研究进展。

推力调节阀流场分析

为研究推力调节阀结构对内流场分布及流量特性的影响,利用计算流体力学方法对窗口式气体调节阀的流场进行了仿真计算,该调节阀在作为软着陆下降级的液氧/甲烷发动机中起到推力调节作用。仿真得到了调节阀流场的压力分布、速度分布。速度场分布给出了流场中各处流速分布及漩涡出现位置,证明了出口锥角对流场导流作用,能显著影响出口流场中的漩涡数量;压力场结果准确表明流场中节流只发生在窗口位置,不存在二次节流,验证窗口设置及结构的合理性;计算得到了不同调节工况下调节阀的流量系数,变化趋势为随着推力工况增高而降低。

月面着陆器结构及可持续利用研究综述与展望

概述了月面着陆器主要功能和系统组成及其可持续利用的国内外研究现状,指出了月面着陆器结构在未来探月任务中存在巨大的可持续利用潜力,之后重点介绍了月面着陆器主要组成部分——着陆器下降级,分析和归纳了下降级的结构形式及特点,并分述了下降级的设计要求、基体结构及其着陆缓冲机构.随后归纳了月面着陆器结构的可持续利用方案,包括着陆器结构的可移动性、可组合性、可扩展性和可回收性等,并分别介绍了不同方案的思路、利用方式及特点,最后总结展望了月面着陆器的发展方向,为未来月面着陆器的结构和性能设计提供借鉴和参考.

Patterns and mechanisms of belowground carbon responses to changes in precipitation

It is well known that aboveground productivity usually increases with precipitation.However,how belowground carbon(C)processes respond to changes in precipitation remains elusive,although belowground net primary productivity(BNPP)represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere.This paper reviews the patterns of belowground C processes(BNPP and soil C)in response to changes in precipitation from transect studies,manipulative experiments,modeling and data integration and synthesis.The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation,which is largely different from linear response for aboveground productivity.C allocation,root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes.In addition,microbial community structure and long-term ecosystem processes(e.g.mineral assemblage,soil texture,aggregate stability)may also affect patterns of belowground C processes in response to changes in precipitation.At last,we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation.

Decline of selectivity of V1 neurons to visual stimulus spatial frequencies in old cats

Objective To examine whether the selectivity of visual cortical neurons to stimulus spatial frequencies would be affected by aging in cats.Methods In vivo extracellular single-unit recording techniques were employed to record the tuning responses of V1 neurons to different stimulus spatial frequencies in old and young adult cats.Results Statistical analysis showed that the mean optimal spatial frequency of grating stimuli that evoked the maximal response of V1 neurons in old cats was significantly lower than that in young adult cats.Furthermore,the mean high cut-off spatial frequency of grating stimuli that evoked the half amplitude of the maximal response of V1 neurons in old cats was also significantly lower than that in young adult cats.Conclusion These results are consistent with those reported in the V1 of old monkeys,suggesting that the age-related decline in the selectivity of visual cortical cells to spatial frequency could be generalized to all mammalian species and might contribute to visual acuity reduction in senescent individuals.

Untangling the interactions among the Sustainable Development Goals in China

Understanding the interactions(synergies and trade-offs)among the Sustainable Development Goals(SDGs)is crucial for enhancing policy coherence between different sectors.However,spatial differences in the SDG interactions and their temporal variations at the sub-national scale are still critical gaps that need to be urgently filled.Here,we assess the spatial and temporal variation of the SDG interactions in China based on the systematic classification framework of SDGs.The framework groups the seventeen SDGs into three categories,namely“Essential Needs”“Objectives”,and“Governance”.Spatially,we found that the SDGs in“Essential Needs”&“Objectives”and“Essential Needs”&“Governance”generally show trade-offs in the eastern provinces of China.Synergies among all three SDG categories are observed in some central and western China provinces,which implies that these regions conform to sustainable development patterns.In addition,temporally,the synergies of the three SDG categories have shown a weakening trend in the last decade,mainly due to the regional differences in the progress of SDG7(Affordable and Clean Energy).Overall,our results identify the necessity for provinces to enhance the synergies between SDG12(Responsible Production and Consumption)and other SDGs to tackle the trade-offs between the“Essential Needs”and“Objectives”.Meanwhile,promoting the progress of SDG7 will also contribute to balanced development across provinces.