Haze aerosols in the atmosphere of early Earth: manna from heaven

An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under early Earth conditions when both CO(2) and CH(4) may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH(4)/CO(2) ratios. Here, we show that haze aerosols are able to form at CH(4) mixing ratios of 1,000 ppmv, a level likely to be present on early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After life arose, the haze may thus have provided food for biota.     

The NASA Performance Assessment Workstation: cognitive performance during head-down bed rest

The NASA Performance Assessment Workstation was used to assess cognitive performance changes in eight males subjected to seventeen days of 6 degrees head-down bed rest. PAWS uses six performance tasks to assess directed and divided attention, spatial, mathematical, and memory skills, and tracking ability. Subjective scales assess overall fatigue and mood state. Subjects completed training trials, practice trials, bed rest trials, and recovery trials. The last eight practice trials and all bed rest trials were performed with subjects lying face-down on a gurney. In general, there was no apparent cumulative effect of bed rest. Following a short period of performance stabilization, a slight but steady trend of performance improvement was observed across all trials. For most tasks, this trend of performance improvement was enhanced during recovery. No statistically significant differences in performance were observed when comparing bed rest with the control period. Additionally, fatigue scores showed little change across all periods.     

联锁式砼铺块机场道面

该文结合拉斯市沃思堡国际机场介绍了联锁式砼铺块机场道面的特点及其设计、施工的要求。     

超声自动检测系统的应用

介绍了基于无损探伤技术的C扫描自动检测系统的工作原理和软硬件设计思路,并提供了测试方法.     

经纬仪测点工艺技术研究

经纬仪定标测点是通过两台经纬仪进行互瞄,并对一根标尺标定组成测量系统,再由该系统进行点坐标测量.该技术是目前卫星部件制造和总装中的一项关键工序.文章阐述了经纬仪定标测点的原理,对测量过程中的定标和测点两个环节进行了精度分析,对标尺的不同摆放方案进行了比较,给出了最佳布局方法和被测点在不同位置时的误差分布曲线.     

异构数据库集成的研究与实现

对异构数据库集成做了详细的研究并提出了具体的实现方法。通过分析比较了目前已有的集成方案,本文提出集成异构数据库可以有四个步骤,分别是用控制表变化法提取有效数据、用XML定义传输数据格式、用JMS传输数据、用全局数据模式集成数据来实现。     

位移约束下火箭橇结构拓扑优化方法研究

兼顾安全性与经济性的高性能结构优化设计是结构设计领域的重要需求,面向火箭橇结构的拓扑优化设计对火箭橇试验具有重要意义.本文在火箭橇结构动力学仿真分析的基础上,基于变密度法建立了火箭橇结构的拓扑优化模型,利用伴随矢量求解了目标函数与约束函数关于设计变量的灵敏度,通过移动渐近线算法驱动了设计变量的更新迭代,最后对拓扑优化设...     

基于模糊层次分析法的黔西南岩溶石漠化演化趋势预测及评价

以岩溶石漠化及水土流失现象较为严重的黔西南地区为研究对象,应用模糊层次分析法,结合研究区地层岩性、地形地貌、土地利用模式、覆盖层条件、人类活动、气候条件等概况,对黔西南地区岩溶石漠化的演化趋势进行分析.首先确定石漠化演化的影响因子及各因子的权重值,据此划分石漠化强度等级,然后根据各权重建立数学模型进行演化趋势的预测.结...     

火花型合成射流控制运输机后体流动分离的数值研究

利用火花型合成射流对运输机后体流动分离进行了主动控制的数值研究。研究结果表明:火花型合成射流一方面直接向边界层分离区域输入高能动量,另一方面与外流相互作用后形成的旋涡强化了高速外流和低速边界层流的混合,从而推迟了运输机后体的流动分离,减小了分离区的大小;在相同的合成射流激励参数下,在边界层分离点处以及分离点后施加主动控制后的作用效果更好,平均阻力系数最大减小3.26%;与当量的定常射流、脉冲射流相比较,脉冲射流减阻效果优于定常射流,火花型合成射流优于脉冲射流。      

适合空间应用的高速图像压缩核设计

针对空间遥感图像压缩的具体应用,给出了基于CCSDS ［1］ 算法的 高速图像压缩核的设计和实现。对CCSDS算法的实现方法进行了优化,算法的VLSI架构 设计充分利用了流水和并行技术,使处理速度相比串行方式平均提高了40倍。压缩验证系统 实验结果表明压缩核在编码效率、处理速度和容错能力上均具有较高的性能,50MHz频 率下压缩核的数据处理速度可达12.5Mpixels／s。