本地标准时间频率的产生与保持

近年来,地方协调时UTC(BIRM)守时能力稳步提升,截至目前,UTC(BIRM)与UTC的相对频率偏差优于3E-14,时间偏差优于20ns。本文概括介绍了守时系统的组成,本地频率驾驭与主备同步技术,以及TA(BIRM)算法研究等。     

基于代理模型的高超声速飞行器外形参数优化

针对高超声速飞行器分析复杂且难度较大,提出了一种代理模型的构建方法,使用代理模型近似替代性能分析与优化过程中含有复杂学科耦合的机理模型。根据巡航任务需求,确定了优化目标为静动态性能最优与模型差异最小。使用灵敏度分析的方法,建立了代理模型。将代理模型进行静动态性能分析,并与机理模型配平结果进行了对比验证,发现两个模型的配平特性趋势是完全一致的,迎角的数值差不足3%,升降舵偏转角的数值差仅在前体下倾角较大时偏大,约为20%。基于构建的代理模型与优化的性能指标,对模型的外形参数进行了配平性能优化与间隙度量优化,并与机理模型的优化结果与优化效率进行对比,发现两者结果相差不足2%,但使用代理模型的优化效率提高了456%,证明了基于代理模型的优化可以在确保精度的基础上提高优化效率。      

国外高等教育投融资体制对我国高等教育投融资体系的启示

面对我国当前高等教育因扩招而导致资金紧缺的现状,通过分析国外高校投资体制中的成熟经验,为我国推进和改善高等教育投融资体制提供更多借鉴。     

基于无旋转原点的参考系转换方法及其计算

基于引入无旋转原点可以克服春分点的固有缺陷的特性,在分析GCRS (Geocentric Celestial Reference System,地心天球参考系)与ITRS(International Terrestrial Reference System,国际地球参考系)之间基于无旋转原点的转换过程基础上,计算了IERS(International Earth Rotation and reference systems Service,国际地球自转与参考系服务)1996、2003、2010等规范所推荐的3组转换参数的具体数值及其差异,并以太阳系10个天体为例进行了参考系转换计算.结果表明:IERS 2003、2010规范中推荐的2组转换参数间的差异较小,对坐标转换的影响在0.5 mas以内;IERS 1996规范中推荐的转换参数与另外2组转换参数间的差异较大,对坐标转换的影响在2.5 mas以内.基于无旋转原点转换和基于春分点的岁差章动转换2种方法间的差异对坐标转换的影响,在IERS 2003、2010规范中不超过5 μas,而在IERS 1996规范中由于未考虑框架偏差的影响导致差异较大.     

Effect of Stagnation Temperature on the Supersonic Two Dimensional Plug Nozzle Conception. Application for Air

When the stagnation temperature of a perfect gas increases, the specific heats and their ratio do not remain constant any more and start to vary with this temperature. The gas remains perfect, its state equation remains always valid, except it will name in more calori-cally imperfect gas or gas at High Temperature. The goal of this research is to trace the profiles of the supersonic plug nozzle when this stagnation temperature is taken into account, lower than the threshold of dissociation of the molecules, by using the new formula of the Prandtl Meyer function, and to have for each exit Mach number, several nozzles shapes by changing the value of this temperature. A study on the error given by the PG (perfect gas) model compared to our model at high temperature is presented. The comparison is made with the case of a calorically perfect gas aiming to give a limit of application of this model. The application is for the air.     

政府对培育国际竞争优势的作用分析

随着中国加入世界贸易组织 ,土生土长的国内企业该如何走向世界 ,这是摆在我们面前的一个课题 ,但这里的“走向世界”并不是地理意义上的世界 ,国内企业要在本土市场上参与国际竞争 ,政府的作用是必不可少的     

A new approach to the telescope operation method for satellite tracking using a time synchronization technique

For the development of a telescope that is capable of precisely tracking satellites and high-speed operation such as satellite laser ranging, a special method of telescope operation is required. This study aims to propose a new telescope operation method and system configuration for the independent development of a mount and an operation system which includes the host computer. Considering that the tracking of a satellite is performed in real time, communication and synchronization between the two independent subsystems are important. Therefore, this study applied the concept of time synchronization, which is used in various fields of industry, to the communication between the command computer and the mount. In this case, communication delays do not need to be considered in general, and it is possible to cope with data loss. Above all, when the mount is replaced in the future, only the general communication interface needs to be modified, and thus, it is not limited by replacement in terms of the overall system management. The performance of the telescope operation method developed in this study was verified by applying the method to the first mobile SLR system in Korea. This study is significant in that it proposed a new operation method and system configuration, to which the concept of time synchronization was applied, for the observation system that requires an optical telescope.     

Statistical validation of HZETRN as a function of vertical cutoff rigidity using ISS measurements

Measurements taken in Low Earth Orbit (LEO) onboard the International Space Station (ISS) and transit vehicles have been extensively used to validate radiation transport models. Primarily, such comparisons were done by integrating measured data over mission or trajectory segments so that individual comparisons to model results could be made. This approach has yielded considerable information but is limited in its ability to rigorously quantify and differentiate specific model errors or uncertainties. Further, as exploration moves beyond LEO and measured data become sparse, the uncertainty estimates derived from these validation cases will no longer be applicable. Recent improvements in the underlying numerical methods used in HZETRN have resulted in significant decreases in code run time. Therefore, the large number of comparisons required to express error as a function of a physical quantity, like cutoff rigidity, are now possible. Validation can be looked at in detail over any portion of a flight trajectory (e.g. minute by minute) such that a statistically significant number of comparisons can be made. This more rigorous approach to code validation will allow the errors caused by uncertainties in the geometry models, environmental models, and nuclear physics models to be differentiated and quantified. It will also give much better guidance for future model development. More importantly, it will allow a quantitative means of extrapolating uncertainties in LEO to free space. In this work, measured data taken onboard the ISS during solar maximum are compared to results obtained with the particle transport code HZETRN. Comparisons are made at a large number (∼77,000) of discrete time intervals, allowing error estimates to be given as a function of cutoff rigidity. It is shown that HZETRN systematically underestimates exposure quantities at high cutoff rigidity. The errors are likely associated with increased angular variation in the geomagnetic field near the equator, the lack of pion production in HZETRN, and errors in high energy nuclear physics models, and will be the focus of future work.     

Statistical ionospheric E layer properties measured with the Cyprus Digisonde and comparisons with IRI predictions

This paper reports the diurnal, seasonal, and long term variability of the E layer critical frequency (foE) and peak height (hmE) derived from Digisonde measurements from 2009 to 2016 at the low-middle latitude European station of Nicosia, Cyprus (geographical coordinates: 35°N, 33°E, geomagnetic lat. 29.38°N, I = 51.7°). Manually scaled monthly median values of foE and hmE are compared with IRI-2012 predictions with a view to assess the predictability of IRI. Results show that in general, IRI slightly overestimates foE values both at low and high solar activity. At low solar activity, overestimations are mostly limited to 0.25?MHz (equivalent electron density, 0.775?×?10³?el/m^?3) but can go as high as 0.5?MHz (equivalent electron density, 3.1?×?10³?el/m^?3, during noon) around equinox. In some months, underestimations, though sporadic in nature, up to 0.25?MHz are noted (mostly during sunrise and sunset). At high solar activity, a similar pattern of over-/underestimation is evident. During the entire period of study, over-/under estimations are mostly limited to 0.25?MHz. In very few cases, these exceed 0.25?MHz but are limited to 0.5?MHz. Analysis of hmE reveals that: (1) hmE remains almost constant during ±2 to ±4?h around local noon, (2) hmE values are higher in winter than in spring, summer and autumn, (3) there are two maxima near sunrise and sunset with a noontime minimum in between. During the entire period of study, significant differences between observed hmE and the IRI predictions have been noted. IRI fails to predict hmE and outputs a constant value of 110?km, which is higher than most of the observed values. Over- and under estimations range from 3 to 13?km and from 0 to 3?km respectively.     

Heterogeneous solid/gas chemistry of organic compounds related to comets,meteorites, Titan,and Mars: Laboratory and in lower Earth orbit experiments

To understand the evolution of organic molecules involved in extraterrestrial environments and with exobiological implications, many experimental programs in the laboratory are devoted to photochemical studies in the gaseous phase as well as in the solid state. The validity of such studies and their applications to extraterrestrial environments can be questioned as long as experiments conducted in space conditions, with the full solar spectrum, especially in the short wavelength domain, have not been implemented. The experiments that are described here will be carried out on a FOTON capsule, using the BIOPAN facility, and on the International Space Station, using the EXPOSE facility. Vented and sealed exposition cells will be used, which will allow us to study the chemical evolution in the gaseous phase as well as heterogeneous processes, such as the degradation of solid compounds and the release of gaseous fragments.