Impact of GPS antenna phase center variations on precise orbits of the GOCE satellite

The first European Space Agency Earth explorer core mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) has been launched on March 17, 2009. The 12-channel dual-frequency Global Positioning System receiver delivers 1 Hz data and provides the basis for precise orbit determination (POD) on the few cm-level for such a very low orbiting satellite (254.9 km). As a member of the European GOCE Gravity Consortium, which is responsible for the GOCE High-level Processing Facility (HPF), the Astronomical Institute of the University of Bern (AIUB) provides the Precise Science Orbit (PSO) product for the GOCE satellite. The mission requirement for 1-dimensional POD accuracy is 2 cm. The use of in-flight determined antenna phase center variations (PCVs) is necessary to meet this requirement. The PCVs are determined from 154 days of data and the magnitude is up to 3-4 cm. The impact of the PCVs on the orbit determination is significant. The cross-track direction benefits most of the PCVs. The improvement is clearly seen in the orbit overlap analysis and in the validation with independent Satellite Laser Ranging (SLR) measurements. It is the first time that SLR could validate the cross-track component of a LEO orbit.     

小型二冲程航空发动机燃烧循环变动研究

利用峰值压力、最大压力上升率、燃烧百分率以及它们各自所对应的曲轴转角和相空间重构投影法评价小型二冲程航空发动机的燃烧循环变动.通过比较,认为燃烧百分率所对应的曲轴转角能更好地表征发动机的燃烧循环变动.针对发动机在中速和不同负荷条件下的燃烧循环变动分析,结果表明随负荷的加大,缸内燃烧的循环变动会变小,认为是负荷加大,气体...     

高抗干扰性的多普勒频率测量系统

提供一种在噪声背景下可靠测量多普勒频谱信号中心频率值的方法，将锁相理论应用于干扰情况下的多普勒频率测量系统，利用跟踪搜索转换电路，实现了在窄频带内跟踪，宽频带内搜索，使系统具有抗干扰能力强，灵敏度高等优点。实验表明，当系统跟踪多普勒频率信号后，对较强的邻频干扰信号，不产生错误跟踪。     

液相过渡扩散焊

重点介绍液相过渡扩散焊的特点及国外近年的研究和应用情况。     

H6飞机最大起飞质量数学模型的研究

正确确定最大起飞质量，对于轰炸机和大型运输机的起飞安全有着非常重要的意义。确定最大起飞质量，以往多采用作图的方法，由于影响最大起飞质量的因素比较复杂，所以比较准确的数学模型未曾建立。近几年来对这个问题进行了多方面的探讨，得出一个计算Ｈ６最大起飞质量比较准确的数学模型。此数学模型的建立为其它轰炸机、运输机最大起飞质量的计算开辟了一条新路，对工程应用具有一定的参考价值。     

Design and implementation of five-axis transformation function in CNC system

To implement five-axis functions in CNC system, based on domestic system Lan Tian series, an improved design method for the system software structure is proposed in this paper. The numerical control kernel of CNC system is divided into the task layer and the motion layer. A five-axis transformation unit is integrated into the motion layer. After classifying five-axis machines into different types and analyzing their geometry information, the five-axis kinematic library is designed according to the abstract factory pattern. Furthermore, by taking CA spindle- tilting machine as an example, the forward and the inverse kinematic transformations are deduced. Based on the new software architecture and the five-axis kinematic library, algorithms of RTCP （rotation tool center point control） and 3D radius compensation for end-milling are designed and realized. The milling results show that, with five-axis functions based on such software struc- ture, the instructions with respect to the cutter＇s position and orientation can be directly carried out in the CNC system.     

提高导航精度的载波相位平滑伪距方法研究

本文推导了基于载波相位平滑伪距技术的SINS/BD组合导航公式并进行误差分析.结合北斗卫星伪距的无模糊度和载波相位的高精度的特点,在组合导航系统中采用北斗载波相位平滑伪距的方法提高导航的精度,最终对处理效果进行实验验证.验证了此方法提高组合导航精度的有效性.     

星载可移动多馈源单口径多波束天线研究

针对我国通信业务容量提升以及热点区域动态变化的保障能力需求,设计了Ka频段多馈源单口径可移动多波束天线,研究了波束馈源簇形成方式、相邻波束馈源交叠方案、天线转动方式、波束形成网络,以实现覆盖区域的高增益通信和波束灵活调整。通过高增益低旁瓣多波束天线的频率复用设计和波束形成网络技术研究,提升卫星通信系统的容量及天线覆盖的灵活性。重点改善波束扫描后的形状畸变和性能恶化问题,仿真表明,对波束幅相权值的优化可以保证天线转动前后波束增益和C/I性能稳定。     

Vibration coupling effects and machining behavior of ultrasonic vibration plate device for creep-feed grinding of Inconel 718 nickel-based superalloy

Ultrasonic vibration-assisted grinding(UVAG) is an effective and promising method for machining of hard-to-cut materials. This article proposed an ultrasonic vibration plate device enabling the longitudinal full-wave and transverse half-wave(L2T1) vibration mode for UVAG.The characteristics of two-dimensional coupled vibration in different directions were analyzed on the basis of apparent elastic method and finite element method. Furthermore, a correction factor was applied to correct the freque...     

Exploiting the Sentinel-3 tandem phase dataset and azimuth oversampling to better characterize the sensitivity of SAR altimeter sea surface height to long ocean waves

Being the very first SAR mode altimeter tandem phase, the Sentinel-3 A/B tandem phase has provided an unprecedented opportunity to better characterize the sensitivity of SAR altimetry retrievals to high-frequency processes, such as long ocean waves. In this paper, we show that for some sea-state conditions, that are still to be precisely characterized, long ocean waves are responsible for high-frequency (spatial and temporal) coherent Sea Level Anomaly (SLA) signals. It is found that the peak wavelength corresponds to the dominant swell wavelength. Furthermore, the short time lag between S3-A and S3-B acquisitions allows performing cross-spectral analyses that reveal phase shifts consistent with waves travelling according to the wave dispersion relation. It is also demonstrated that the classical 20 Hz sampling frequency is insufficient to properly sample most swell-induced SLA signals and that aliasing can generate errors over the entire frequency spectrum, including at long wavelengths. These results advocate for the use of azimuth oversampling (40 Hz or 80 Hz). Low-pass filtering should be applied prior to any down-sampling to 20 Hz, in order to prevent long-wavelength errors induced by spectral leakage.