Equatorial anomaly according to the Interkosmos-19 data and IRI model: A comparison

The comparison of the IRI model with the foF2 distribution in the equatorial anomaly region obtained by topside sounding onboard the Interkosmos-19 satellite has been carried out. The global distribution of foF2 in terms of LT-maps was constructed by averaging Intercosmos-19 data for summer, winter, and equinox. These maps, in fact, represent an empirical model of the equatorial anomaly for high solar activity F10.7 ~ 200. The comparison is carried out for the latitudinal foF2 profiles in the characteristic longitudinal sectors of 30, 90, 210, 270, and 330°, as well as for the longitudinal variations in foF2 over the equator. The largest difference between the models (up to 60%) for any season was found in the Pacific longitudinal sector of 210°, where there are a few ground-based sounding stations. Considerable discrepancies, however, are sometimes observed in the longitudinal sectors, where there are many ground-based stations, for example, in the European or Indian sector. The discrepancies reach their maximum at 00 LT, since a decay of the equatorial anomaly begins before midnight in the IRI model and after midnight according to the Interkosmos-19 data. The discrepancies are also large in the morning at 06 LT, since in the IRI model, the foF2 growth begins long before sunrise. In the longitudinal variations in foF2 over the equator at noon, according to the satellite data, four harmonics are distinguished in the June solstice and at the equinox, and three harmonics in the December solstice, while in the IRI model only two and one harmonics respectively are revealed. In diurnal variations in foF2 and, accordingly, in the equatorial anomaly intensity, the IRI model does not adequately reproduce even the main, evening extremum.     

Spacecraft formation flying control around L2 sun-earth libration point using on–off SDRE approach

In this paper, on–off SDRE control approach is presented for spacecraft formation flying control around sun-earth L2 libration point. Orbits around libration points are significant targets for many space missions mainly because of efficient fuel consumption. Furthermore, less propellant usage can be achieved by considering optimal control approaches in spacecraft formation flying control design. Among various nonlinear and optimal control methods, SDRE has shown to be a popular controller in various missions due to the privileges including efficiency, accuracy and robustness. The spacecraft are assumed to have on–off thrusters as actuators. It requires them to be fed with a sequence of on–off pulses which is regarded as a challenge for spacecraft designers. Hence, the main contribution of this paper is designing an on–off SDRE approach for the formation flight around sun-earth L2 point with uncertainty with energy and accuracy considerations. Including on–off input as a constraint is not feasible for SDRE implementation because it makes the system non-affine. An alternative is utilizing an integral action technique and an auxiliary control to make the system affine which leads to on–off SDRE approach. It has also been shown that the proposed method is robust against parametric uncertainties of the states. Present study aims to design an energy-beneficial, simple and attractive controller for a complex nonlinear system with on–off inputs and uncertainty in CRTBP. Simulation results show that the on–off SDRE control could provide the formation flight around L2 point with high accuracy using less energy consumption.     

A comparative study of ionospheric IRIEup and ISP assimilative models during some intense and severe geomagnetic storms

Three-dimensional (3-D) electron density matrices, computed in the Mediterranean area by the IRI climatological model and IRIEup and ISP nowcasting models, during some intense and severe geomagnetic-ionospheric storms, were ingested by the ray tracing software tool IONORT, to synthesize quasi-vertical ionograms. IRIEup model was run in different operational modes: (1) assimilating validated autoscaled electron density profiles only from a limited area which, in our case, is the Mediterranean sector (IRIEup_re(V) mode); (2) assimilating electron density profiles from a larger region including several stations spread across Europe: (a) without taking care of validating the autoscaled data in the assimilation process (IRIEup(NV)); (b) validating carefully the autoscaled electron density profiles before their assimilation (IRIEup(V)).The comparative analysis was carried out comparing IRI, IRIEup_re(V), ISP, IRIEup(NV), and IRIEup(V) foF2 synthesized values, with corresponding foF2 measurements autoscaled by ARTIST, and then validated, at the truth sites of Roquetes (40.80°N, 0.50°E, Spain), San Vito (40.60°N, 17.80°E, Italy), Athens (38.00°N, 23.50°E, Greece), and Nicosia, (35.03°N, 33.16°E, Cyprus). The outcomes demonstrate that: (1) IRIEup_re(V), performs better than ISP in the western Mediterranean (around Roquetes); (2) ISP performs slightly better than IRIEup_re(V) in the central part of Mediterranean (around Athens and San Vito); (3) ISP performance is better than the IRIEup_re(V) one in the eastern Mediterranean (around Nicosia); (4) IRIEup(NV) performance is worse than the IRIEup(V) one; (5) in the central Mediterranean area, IRIEup(V) performance is better than the IRIEup_re(V) one, and it is practically the same for the western and eastern sectors.Concerning the overall performance, nowcasting models proved to be considerably more reliable than the climatological IRI model to represent the ionosphere behaviour during geomagnetic-ionospheric storm conditions; ISP and IRIEup(V) provided the best performance, but neither of them has clearly prevailed over the other one.     

哨兵2卫星综合水质指标的河流水质遥感监测方法

上海市河流水污染监测是当前研究的热点问题。针对上海市河流水质监测的需求,提出了一种基于因子分析的河流综合水质遥感反演的方法。以欧洲航空局发射的哨兵-2A(Sentinel-2A)卫星搭载的多光谱成像仪获取的遥感影像,以及准同步获取的河流断面实测水质参数数据为例,研究对象为上海市青浦区和松江区部分河道。选取高锰酸盐指数、氨氮等5项主要水质参数为监测指标,在因子分析的基础上建立水质遥感反演的模型,得到综合水质指标用于确定水质类别。实验结果表明:综合水质指标值越小,内陆河流水质状况越良好,水体更清洁。该方法能够应用于内陆河流水质遥感监测,为水环境管理部门提供参考信息。     

深化失效学的哲学理念探索,强化材料失效交叉技术研究

力图从哲学的高度,对失效学的认识论、矛盾论、系统论和方法论进行简要的阐释,从中提出一些要点,并对失效学哲学理念在失效事故分析诊断预防技术中的应用提出建议,为深化失效学的哲学理念探讨奠定初步基础。从失效学的理论基础、应用基础和工程技术等3个方面总结提出了失效学的理论和技术体系,为失效学的体系建设提供了技术框架;还从材料服役前、使用中和失效后等3个阶段归纳了材料失效交叉技术领域中的科学问题或关键技术,为加强其交叉技术的研究提炼出了若干重点方向。     

基于流管试验的管道声传播预测

通过平板声衬流管试验，测试了管道内无流动和有流动下不同入射声波频率的管道壁面复声压，并基于试验模型与数据分别开展了二维和三维管道声传播预测，将试验测量结果与预测结果进行了对比。结果表明:二维和三维的预测结果非常吻合，尤其是在无流动条件下；在不同流动条件和不同频率下，声传播预测给出了与试验数据较为吻合的结果，壁面声压级的趋势与试验结果一致，基本验证了管道声传播预测模型的准确性；对比不同流动条件和频率点，有流动下预测的壁面声压级的误差比无流动更大，低频下预测的壁面声压级的误差比高频更大。      

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS.     

Effects of in-track maneuver on Sun illumination conditions of near-circular low Earth orbits

By developing approximate analytical models considering the J₂ perturbation, the effects of an in-track maneuver on the orbital Sun illumination conditions of near-circular low Earth orbits are analyzed. First, two approximate models for the variations in orbital sunshine angles are developed, one for variations at a given time and the other for variations at a given argument of latitude. Next, two approximate models for variations in orbital arc in Earth shadow are developed, one considers the small eccentricity and the other uses the zero eccentricity. Finally, the developed approximate models are applied to analyzing the Sun illumination conditions of a typical in-track maneuver mission on a near-circular low Earth orbit. From the results obtained, three major conclusions can be drawn. First, the variations in orbital sunshine angles at a given time may reach tens of degrees when the drifting time reaches hundreds of orbital periods, and the approximate model for that situation cannot effectively approach the numerical results. Second, the variations in orbital sunshine angles for any given argument of latitude are only a couple of degrees even when the drifting time reaches 500 orbital periods, and the approximation model developed can effectively approach the numerical results. Third, for variations in orbital arc in Earth shadow, the approximate model considering the small eccentricity has simple expressions and can effectively approach the numerical results; in contrast, the approximate model using the zero eccentricity has relatively worse precision.     

单/双轴预拉载荷对碳纤维复合材料高速冲击性能的影响研究

针对发动机工作时受预载荷的叶片受到外物冲击的情况,设计一种面内单轴及双轴预加载装置,开展单轴与双轴不同大小预拉载荷下碳纤维/环氧树脂复合材料（T700/TDE-86）的高速冲击试验,探究预拉载荷对复合材料抗冲击性能的影响,并结合超声C扫描分析预拉载荷对损伤面积的影响。结果表明：面内初始载荷对复合材料层合板抗冲击性能和分层损伤面积有显著影响;预拉载荷会提高靶板的抗弯刚度,减少靶板吸收的能量,减小弹道极限,且在双轴预拉情况下更明显;弹体击穿靶板后分层损伤面积几乎不变,而预拉载荷会减小分层损伤面积,且在双轴预拉情况下更明显。     

PS-PVD用CeO2掺杂8YSZ团聚粉末及其涂层

在纳米ZrO₂-8%Y₂O₃(摩尔分数)(8YSZ)粉末中掺杂20%(质量分数)微米级CeO₂粉末,并通过喷雾干燥合成CeO₂-8YSZ(CYSZ)复合团聚粉体。借助激光粒度仪和扫描电镜(SEM)及附带能谱仪(EDS)考察羧甲基纤维素黏结剂(carboxymethyl cellulose,CMC)质量分数对复合团聚粉体性能影响。采用PS-PVD制备具有柱状结构的CYSZ热障涂层,对涂层截面和表面进行EDS分析。采用X射线衍射(XRD)和X射线光电子能谱(XPS)分析涂层物相。结果表明:黏结剂质量分数达到2%时可获得球形度高、粒度分布均匀的团聚粉体;制备的涂层中Ce元素呈均匀分布;涂层物相基本为t-相结构,其中Ce⁴⁺取代Zr⁴⁺进入ZrO₂晶格形成类质同象的固溶体结构,显示出CeO₂掺杂对t-相向m-相转变的抑制作用;所制备CYSZ涂层在1100℃,水冷循环100次后仍保持完整,展现出较高的抗热冲击性能。