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571.
A Controlled Ecological Life Support System (CELSS) is a sealed system used in spaceflight in order to provide astronauts with food and O2 by plants. It is of great significance to increase the energy-using efficiency because energy is extremely deficient in the space. Therefore, the objective of this research was to increase the energy-using efficiency of wheat by regulating the photoperiod. Sixteen treatments were set in total: four photoperiods before flowering (PBF) combined with four photoperiods after flowering (PAF) of 12 h, 16 h, 20 h and 24 h. The light source was red–blue LED (90% red+10% blue). As a result, the growth period of wheat was largely extended by shorter PBF, particularly the number of days from tillering to jointing and from jointing to heading. The period from flowering to maturity was extended by shorter PAF. Shorter PBF and longer PAF could increase not only the yield but also the energy-using efficiency of wheat. As for the nutritional quality, longer photoperiod (both PBF and PAF) increased starch concentration as well as decreased protein concentration of seeds. The effects of PBF and PAF were interactional. The lighting strategy with PBF of 12 h and PAF of 24 h was proved to be the optimum photoperiod for wheat cultivation in CELSS. The mechanisms of photoperiod effect contain two aspects. Firstly, photoperiod is a signal for many processes in plant growth, particularly the process of ear differentiation. Shorter PBF promoted the ear differentiation of wheat, increasing the spikelet number, floret number and seed number and thus enhancing the yield. Secondly, longer photoperiod leads to more light energy input and longer time of photosynthesis, so that longer PAF provided more photosynthate and increased seed yield. 相似文献
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573.
在分析反辐射导弹末制导段特点的基础上,针对其跟踪模型不满足可观测性要求的问题,提出了一种基于方位/俯仰角的跟踪方案。理论分析和仿真验证了该方案具有较高的跟踪精度和实时性,并具有较好的通用性,为解决不可观测情况下的高精度稳定跟踪问题提供了一种新的思路。 相似文献
575.
在航空航天领域,作用在结构上动载荷的确定对结构健康监测是非常必要和重要的。为此,本文以类似机翼结构的变截面悬臂梁结构为研究对象,提出了一种基于光纤光栅传感器与卡尔曼滤波器的动载荷识别方法。首先,根据变截面梁单元形式,推导出变截面梁的质量矩阵与刚度矩阵,建立动力学运动方程。然后,以光纤光栅传感器测得的应变信息作为观测信号,通过卡尔曼滤波器生成的增益矩阵、新息序列矩阵以及协方差矩阵,得到灵敏度矩阵和估计力的增益矩阵。在此基础上,利用广义回归模型及其最小二乘算法,估算出动载荷大小、判断出动载荷激励位置。借助数值仿真与实验手段,分别验证了该方法对于单点正弦激励、方波激励、锯齿波激励以及多点同时激励等工况下的动载荷识别效果。结果表明,本文所提算法具有较好的动载荷识别效果和噪声抑制能力,能够为未来风洞试验和真实飞行试验环境中诸如大展弦比机翼表面气动压力等载荷实时辨识、气动外形自适应控制以及结构健康监测提供技术支撑。 相似文献
576.
介绍了教练机制造工艺设计过程的基本特征,描述了协同工艺设计的方法和要求,揭示了协同工艺设计工作在教练机零件制造和部件装配中的作用及意义。 相似文献
577.
J. Olwendo P.J. Cilliers O. Ming 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3187-3201
Ionospheric irregularities are well-known phenomena associated with ionospheric scintillation. These irregularities comprise steep electron density gradients in the equatorial F region some 1 to 2 h after sunset in regions close to the geomagnetic equator. Using the IGS network of GNSS receivers spread across the low-latitude region over the African sector, we present the monthly trends in ionospheric irregularity activity levels based on Rate of TEC Index (ROTI) during the declining phase of solar 24. The monthly trends are statistically represented by counts of the night time ROTI values exceeding a threshold of 0.4 TECU/min. A clear trend emerges on the irregularity occurrence across the African sector: during the first four months of the year, the irregularity occurrence is highly pronounced on the western side of the region. The irregularity occurrence then shifts to the eastern side during the months of May, June, July, and August. During the last four months of the year, the irregularity occurrence is again more intense on the western side of Africa than on the eastern side. The occurrence of irregularity structures on only one side of the region during a given night is an unusual feature reported here for the first time. 相似文献
578.
Wenjie Lou Ming Zhu Xiao Guo Haoquan Liang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1111-1121
This paper presents two sliding mode controllers to address the trajectory tracking problem of unmanned airships in the presence of unknown wind disturbance. The sliding mode controller proposed first is designed by a fast power rate reaching law(FPRRL). The disturbance is compensated by a radial basis function neural network (RBFNN). To avoid the aggressive adaptation, the controller is augmented by a command filter. The controller provides good robustness and tracking performance with no chattering under the hypothesis of ideal wind field. However, serious chattering occurs when simulation is performed under discontinuous wind field. To simulate the wind in practice, the wind field employed in the simulation is generated by the combination of a constant field and white noise. The controller is improved subsequently with an extended model to suppress the chattering induced by the white noise. The enhanced controller manipulates the derivation of system input, thus attenuating the chattering. Stability analysis shows that both controllers drive the tracking error into a controllable small region near zero. Simulations are provided to validate the performance of the proposed controllers under different wind hypothesis. 相似文献
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580.