On uncertainties in carbon flux modelling and remotely sensed data assimilation: The Brasschaat pixel case

Uncertainty on carbon fluxes is determined by the uncertainties of ecosystem model structure, data and model parameter uncertainties and the temporal and spatial inaccuracy of the input data retrieval. The objective of this paper is to understand the error propagation and uncertainty of evaporative fraction (EF), soil moisture content (SMC) and water limited net ecosystem productivity (NEP). In this respect, C-Fix and spaceborne remote sensing are used for the ‘Brasschaat’ pixel. A simple model based on error theory and a Monte-Carlo approach are used. Different error scenarios are implemented to assess input uncertainty on EF, SMC and NEP as estimated with C-Fix.     

开放式二氧化碳制冷性能

二氧化碳属于对环境友好的自然制冷工质,使用时直接排放对环境影响很小。本文提出一种开放式二氧化碳制冷系统,研究了高压二氧化碳在25,30和35°C三种典型储存环境下的制冷特性,同时考察了影响开放式二氧化碳制冷性能的各种因素。研究结果表明:二氧化碳储存状态对其制冷性能影响较大,在超临界条件下制冷量损失较大,同时,纯气体节流时储罐中的制冷量损失要远大于气液两相节流,为二氧化碳开放式制冷的应用提供了实验依据。     

C／C复合材料石墨化度的测定和评价

用Ｘ射线衍射方法对不同热处理温度下Ｃ／Ｃ复合材料石墨化度进行了测定，并对衍射峰进行了分峰处理。得出该材料由三种不同组元构成，即树脂炭，碳纤维和热解炭，求出各组元的石墨化度值及所占比例，进而得到试样的加权平均石墨化度。     

Lightweight Design of Spaceborne CFRP Rigid Antenna Reflector

In order to overcome the shortcoming of space-borne rigid antenna reflector made of carbon fiber reinforced plastic (CFRP) skins with aluminum honeycomb sandwich (SAHS) structure, a new type of full CFRP skin plus rib (SPR) structure ring-focused parabolic surface antenna reflector with the size of 2.5 m 1.9 m is designed. Under the condition that the original caliber, surface type, and interface remain unchanged, the main influence factors are designed and controlled. First, from the perspective of high stiffness, lightweight, and easy to form, a finite element simulation software is used to analyze and optimize the layout of the rib, the cross-sectional shape of the rib, the size of the rib, and the matching of the size and the coefficients of thermal expansion (CTEs) of the rib and the skin. Second, two structures are prepared by the autoclave molding process. Third, the weight and the surface precision root mean square (RMS) value are measured. The results show that the fundamental frequency of the SPR structure is 142.2 Hz, which is 3.5 Hz higher;the number of the new structural parts is reduced by 40%, and the forming process is greatly simplified. The total weight of the new structure is 11.9 kg, lighter 42.5%, indicating that the weight loss is obvious. The RMS value is 0.15 mm, which is slightly lower 0.01 mm but satisfies the accuracy requirement not greater than 0.3 mm. It is proved that the SPR structure reflector is a superior structure of the lightweight spaceborne antenna reflector.     

Impact of COVID-19 lockdown on the fine particulate matter concentration levels: Results from Bengaluru megacity,India

Leveraging the COVID-19 India-wide lockdown situation, the present study attempts to quantify the reduction in the ambient fine particulate matter concentrations during the lockdown (compared with that of the pre-lockdown period), owing to the highly reduced specific anthropogenic activities and thereby pollutant emissions. The study was conducted over Bengaluru (India), using PM_2.5 (mass concentration of particulate matter having size less than or equal to 2.5 µm) and Black Carbon mass concentration (BC) data. Open-access datasets from pollution control board (PCB) were also utilised to understand the spatial variability and region-specific reduction in PM_2.5 across the city. The highest percentage reduction was observed in BC_ff (black carbon attributable to fossil fuel combustion), followed by total BC and PM_2.5. No decrease in BC_bb (black carbon attributable to wood/biomass burning) was observed, suggesting unaltered wood-based cooking activities and biomass-burning (local/regional) throughout the study period. Results support the general understanding of multi-source (natural and anthropogenic) nature of PM_2.5 in contrast to limited-source (combustion based) nature of BC. The diurnal amplitudes in BC and BC_ff were reduced, while they remained almost the same for PM_2.5 and BC_bb. Analysis of PCB data reveal the highest reduction in PM_2.5 in an industrial cluster area. The current lockdown situation acted as a natural model to understand the role of a few major anthropogenic activities (viz., traffic, construction, industries related to non-essential goods, etc.) in enhancing the background fine particulate matter levels. Contemporary studies reporting reduction in surface fine particulate matter and satellite retrieved columnar Aerosol Optical Depth (AOD) during COVID-19 lockdown period are discussed.     

Exploration life support technology challenges for the Crew Exploration Vehicle and future human missions

As NASA implements the U.S. Space Exploration Policy, life support systems must be provided for an expanding sequence of exploration missions. NASA has implemented effective life support for Apollo, the Space Shuttle, and the International Space Station (ISS) and continues to develop advanced systems. This paper provides an overview of life support requirements, previously implemented systems, and new technologies being developed by the Exploration Life Support Project for the Orion Crew Exploration Vehicle (CEV) and Lunar Outpost and future Mars missions. The two contrasting practical approaches to providing space life support are (1) open loop direct supply of atmosphere, water, and food, and (2) physicochemical regeneration of air and water with direct supply of food. Open loop direct supply of air and water is cost effective for short missions, but recycling oxygen and water saves costly launch mass on longer missions. Because of the short CEV mission durations, the CEV life support system will be open loop as in Apollo and Space Shuttle. New life support technologies for CEV that address identified shortcomings of existing systems are discussed. Because both ISS and Lunar Outpost have a planned 10-year operational life, the Lunar Outpost life support system should be regenerative like that for ISS and it could utilize technologies similar to ISS. The Lunar Outpost life support system, however, should be extensively redesigned to reduce mass, power, and volume, to improve reliability and incorporate lessons learned, and to take advantage of technology advances over the last 20 years. The Lunar Outpost design could also take advantage of partial gravity and lunar resources.     

带有SiC涂层的C/C复合材料的氧化行为

采用包埋法在C/C复合材料表面制备了SiC高温防氧化涂层。利用SEM和XRD等方法对涂层的微观形貌和晶相组成进行了观察与分析,并对带涂层试样在室温~1 500℃范围内的氧化行为进行了研究。结果表明,涂层主要由β-SiC和少量的游离Si组成,涂层表面有裂纹存在,涂层与C/C复合材料基体结合良好,呈现犬牙状结合。在室温~1 500℃之间,带SiC涂层C/C复合材料的氧化行为可分为4个阶段,涂层在高温区具有较好的防氧化性能。     

Compressive properties of homemade carbon fiber composite laminates with delamination defect

Large numbers of aircraft composite structures were researched, and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated. An experiment was conducted to probe into the effect of delamination sizes and through thickness positions on the compressive strengths of laminates with single embedded circular delamination with the most dangerous delamination sizes and positions defined from the distribution. A shell model was established for compressive strength prediction, and the virtual crack closure technique (VCCT) was employed for the strain energy release rate calculation. The finite element (FE) prediction was in good agreement with the experimental measurements, for the predicted compressive strengths stood within 10% error of experimental results. It was observed that the compressive strength was highly effected by the delamination size, while the though thickness position of delamination did not have significant effect on the compressive strength.      

Effects of different carbon dioxide and LED lighting levels on the anti-oxidative capabilities of Gynura bicolor DC

Gynura bicolor DC is not only an edible plant but also a kind of traditional Chinese herbal medicine. G. bicolor DC grown in controlled environmental chambers under 3 CO₂ concentrations [450 (ambient), 1500 (elevated), 8000 (super-elevated) μmol mol⁻¹] and 3 LED lighting conditions [white (WL), 85% red + 15% blue (RB15), 70% red + 30% blue (RB30) ] were investigated to reveal plausible antioxidant anabolic responses to CO₂ enrichment and LED light quality. Under ambient and elevated CO₂ levels, blue light increasing from 15% to 30% was conducive to the accumulation of anthocyanins and total flavonoids, and the antioxidant activity of extract was also increased, but plant biomass was decreased. These results demonstrated that the reinforcement of blue light could induce more antioxidant of secondary metabolites, but depress the effective growth of G. bicolor DC under ambient and elevated CO₂ levels. In addition, compared with the ambient and elevated CO₂ levels, the increased anthocyanins, total flavonoids contents and antioxidant enzyme activities of G. bicolor DC under super-elevated CO₂ level could serve as important components of antioxidative defense mechanism against CO₂ stress. Hence, G. bicolor DC might have higher tolerance to CO₂ stress.     

碳纤维复合材料湿热老化加速关系

受环境因素作用,碳纤维增强聚合物基复合材料(Carbon fiber reinforced polymer composities,CFRP)湿热环境下发生性能退化是一个重要的工程问题,而如何通过实验室加速试验再现自然环境对复合材料的老化作用成为解决此问题的关键。基于时间-温度-湿度等效原理,将湿热环境下CFRP粘弹性能的改变作为材料的老化损伤度量,建立不同湿热环境之间当量折算关系,提出加速老化当量折算系数的确定方法。以典型军机结构用CFRP为例,实例计算了材料不同温度、湿度环境下的当量折算系数,根据地面停放环境谱当量折算得到加速试验谱,加速效果令人满意。最后,对比分析了温度与湿度对当量折算系数的影响,结果表明,温度变化对当量折算系数的影响要比湿度变化的影响显著。