Noise in wireless systems from solar radio bursts

Solar radio bursts were first discovered as result of their interference in early defensive radar systems during the Second World War (1942). Such bursts can still affect radar systems, as well as new wireless technologies. We have investigated a forty-year record of solar radio burst data (1960–1999) as well as several individual radio events in the 23rd solar cycle. This paper reviews the results of a portion of this research. Statistically, for frequencies f  1 GHz (near current wireless bands), there can be a burst with amplitudes >10³ solar flux units (SFU; 1 SFU = 10⁻²² W/m²) every few days during solar maximum conditions, and such burst levels can produce problems in contemporary wireless systems.     

A survey of radio jets with Chandra and HST

Relativistic jets are a common property of radio-loud Active Galactic Nuclei (AGN). Understanding jet physical properties is an essential precursor to understanding the mechanisms of energy transport, and ultimately, how energy is extracted from the central black hole. In this paper, I highlight recent developments from Chandra and HST observations of kpc-scale jets in AGN, with particular emphasis on our survey of 17 radio jets in a sample of FRII radio galaxies. These observations show that (1) X-ray and optical emission is common from kpc-scale jets, (2) a large fraction of the bolometric luminosity is emitted at X-rays, and (3) in most sources, a candidate emission process for the X-rays is inverse Compton scattering of the Cosmic Microwave Background off the relativistic electrons in the jet. If the latter scenario holds, the implication is that jets are still relativistic on kpc scales.     

Hexapod多自由度微激励系统的振动时域波形控制

摘要： Hexapod多自由度微激励系统常用于航天器有效载荷在轨微振动环境的模拟，但采用现有控制方法无法精确稳定跟踪低频正弦加速度，这是由于系统耦合度高、非线性在低频段较强，被控对象相位滞后过大造成的.针对此问题，基于传统离线迭代控制方法，提出一种复合超前校正、多倍频陷波滤波器的改进离线迭代控制方法.其中，离线迭代进行补偿控制，超前校正进一步补偿系统相位，多倍频陷波滤波器去除非线性干扰.跟踪低频定频正弦加速度的实验结果表明，对比传统离线迭代控制方法，改进方法收敛快、控制精度高；对比现有自适应正弦振动控制方法，改进方法将符合精度要求的加速度控制频带下限由14.5 Hz扩宽至8 Hz.实验结果验证了所提方法的有效性.     

一次民机飞行中甚高频通信不稳定的排故

针对某型号民用飞机甚高频通信系统在飞行中出现断续故障的情况，对系统的架构进行描述，分析了故障产生的机理，提出了排故思路，记述了排故过程，并总结了甚高频通信系统的设计要点和工艺要点。     

Abnormal changes of dynamic derivatives at low reduced frequencies

A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.     

基于TC783A的三相电动机缺相保护电路的设计与实现

介绍用于三相电动机缺相保护装置的设计方法,采用集成芯片TC783A为核心元件实现,有效地解决三相电动机其他保护元件的局限性。具有快速切断控制回路电源的功能及缺相指示和相序指示,试验证明系统工作性能良好。     

Ionospheric F2-Layer critical frequency retrieved from COSMIC radio occultation: A statistical comparison with measurements from a meridional ionosonde chain over Southeast Asia

In this paper, we compared the F2-Layer critical frequency (foF2) derived from FORMOSAT-3/COSMIC radio occultation (RO) and ionosondes at Chiang Mai, Chumphon and Kototabang during the years 2008–2015 to evaluate the performance of COSMIC RO over Southeast Asia region. The results show that the time development of foF2 values derived from COSMIC RO generally agrees well with those from ionosonde measurements. However, the differences between the foF2 derived from COSMIC RO and that derived from ionosonde observations display latitudinal dependence. COSMIC RO tends to underestimate foF2 at Chiang Mai and Kototabang, which is near to the north EIA crest and the south one, respectively, while a little overestimate foF2 at Chumphon, which is close to the geomagnetic equator. COSMIC RO agrees best with ionosonde at Chumphon and worst at Chiang Mai. At each ionosonde station, the quality of COSMIC RO data degrades with the increase of solar activity. In addition, at the station Chiang Mai and Kototabang, COSMIC RO performs better in summer than in equinox and winter. Furthermore, the differences in foF2 derived from COSMIC RO and that from ionosonde measurements vary with local time, i.e., the differences in foF2 are generally smaller at night and larger in noontime when equatorial ionization anomaly (EIA) is well developed.     

采用霍尔传感器的旋翼频率采集设计

为达到对旋翼飞机的控制,需要对旋翼转速进行采集.霍尔转速传感器以其高可靠性等优点常被用来测量转速.介绍了一种使用霍尔传感器进行旋翼转速采集系统,包括硬件构架,逻辑采集单元和软件设计,并给出了优化策略;通过试验数据分析,采集精度达到了预期.     

RFID技术在航空领域的应用研究

射频识别(RFID)技术现已广泛用于物流、金融、零售等各个行业.航空领域的RFID应用起步较晚,通过对RFID技术在飞机制造商、原始设备生产厂家(OEM)、航空公司的一些典型的应用案例的分析,提出RFID技术应用于航空领域所面临的挑战及必要性,为其未来航空业自动识别技术的发展指明了方向.     

基于飞行试验数据的双转子航空发动机 加减速瞬态模型辨识

为辨识航空发动机飞行过程中加减速瞬态模型,通过对某型航空发动机慢车至中间以及中间至慢车过程的飞行试验数据进行分析整理,将发动机上述加、减速过程简化为静态参数预测过程,利用3层前向人工神经网络,建立了某型发动机加、减速瞬态过程中的发动机关键参数预测模型,对发动机参数预测模型预测结果与飞行试验记录数据进行了对比分析,同时利用额外的飞行试验数据验证了辨识模型的泛化能力.结果表明:辨识得到的发动机模型在油门杆稳定时参数预测相对误差不超过3％,在油门杆动作期间参数预测相对误差不超过5％;验证点上辨识模型参数预测误差不超过3％.证明该型发动机参数预测模型可以很好地预测发动机瞬态过程中的参数变化情况.该方法为建立发动机其他状态的加、减速过程参数变化模型奠定了基础,也能为建立全包线范围内发动机瞬态参数预测模型提供参考.