Solar wind low-energy energetic ion enhancements: A tool to forecast large geomagnetic storms

Predicting the occurrence of large geomagnetic storms more than an hour in advance is an important, yet difficult task. Energetic ion data show enhancements in flux that herald the approach of interplanetary shocks, usually for many hours before the shock arrival. We present a technique for predicting large geomagnetic storms (Kp  7) following the arrival of interplanetary shocks at 1 AU, using low-energy energetic ions (47–65 keV) and solar wind data measured at the L1 libration point. It is based on a study of the relationship between energetic ion enhancements (EIEs) and large geomagnetic storms by Smith et al. [Smith, Z., Murtagh, W., Smithtro, C. Relationship between solar wind low-energy energetic ion enhancements and large geomagnetic storms. J. Geophys. Res. 109, A01110, 2004. doi:10.1029/ 2003JA010044] using data in the rise and maximum of solar cycle 23 (February 1998–December 2000). An excellent correlation was found between storms with Kp  7 and the peak flux of large energetic ion enhancements that almost always (93% of time in our time period) accompany the arrival of interplanetary shocks at L1. However, as there are many more large EIEs than large geomagnetic storms, other characteristics were investigated to help determine which EIEs are likely to be followed by large storms. An additional parameter, the magnitude of the post-shock total magnetic field at the L1 Lagrangian point, is introduced here. This improves the identification of the EIEs that are likely to be followed by large storms. A forecasting technique is developed and tested on the time period of the original study (the training data set). The lead times, defined as the times from the arrival of the shock to the start of the 3-h interval of maximum Kp, are also presented. They range from minutes to more than a day; the average for large storms is 7 h. These times do not include the extra warning time given when the EI flux cross the high thresholds ahead of the shock. Because the data-stream used in the original study is no longer available, we extended the original study (1998–2000) to 2001, in order to: (a) investigate EIEs in 2001; (b) present a validation of the technique on an independent data set; (c) compare the results based on the original (P1) energy channel to those of the replacement (P1′) and (d), determine new EIE thresholds for forecasting geomagnetic storms using P1′ data. The verification of this P1′ training data set is also presented, together with lead times.     

轮式起降无人机安全起飞纵向控制

为了提高无人机在风干扰下的起飞安全性,对无人机常规起飞纵向控制方案加以改进,提出了基于直接升力控制的安全起飞纵向控制方案.采用由低通滤波器和超前补偿通道组成的组合滤波方案,用以解决所提出控制方案中无人机升降速度信号的精确获取问题,通过所研制的专用升降测试台和基于频谱分析的设计方法,对组合滤波方案进行了参数选取和仿真验证.基于Matlab/Simulink仿真环境建立某型无人机的全量非线性数学模型,通过仿真设计相应的襟翼偏转控制律.仿真结果表明,应用组合滤波方案获取的升降速度信号精度较高,满足起飞控制的使用要求.安全起飞纵向控制方案可显著增强无人机的抗干扰能力,从而提高起飞过程的安全性.     

SiC颗粒增强铝基复合材料的热变形本构方程及其优化

通过热压缩试验研究了SiC颗粒增强铝基复合材料在应变速率为0.001～1s-1,变形温度为713～773K时的热成形性能,并在试验数据分析的基础上,引入Zener-Hollomon参数建立了用于描述复合材料高温变形行为的本构关系模型,通过分析比较和对本构方程的进一步优化,提高了颗粒增强型铝基复合材料本构方程的拟合精度,使得计算值更接近于试验值.     

一种基于感知的大规模场景粒子系统绘制方法

在分析已有的大规模场景下使用粒子系统对自然现象等模拟方法的基础上,提出了一种绘制大规模粒子系统的方法.在大规模粒子系统的绘制过程中引入基于视截体模型的感知算法对粒子进行细化并引入双重缓冲技术以及粒子动态纹理.将粒子按所属不同区域进行分层次绘制,提高了真实性和灵活性,最终解决了传统绘制方法不适用大规模粒子系统的问题.实验表明,系统的模拟效果真实,满足系统对实时性的要求,适合大规模粒子系统的绘制.     

Plant mineral nutrition,gas exchange and photosynthesis in space: A review

Successful growth and development of higher plants in space rely on adequate availability and uptake of water and nutrients, and efficient energy distribution through photosynthesis and gas exchange. In the present review, literature has been reviewed to assemble the relevant knowledge within space plant research for future planetary missions. Focus has been on fractional gravity, space radiation, magnetic fields and ultimately a combined effect of these factors on gas exchange, photosynthesis and transport of water and solutes.     

Solar particle precipitation into the polar atmosphere and their dependence on hemisphere and local time

The precipitation of solar energetic particles, protons as well as electrons, at high latitudes is commonly assumed to be homogeneous across both polar caps. Using Low-Earth Orbit POES (Polar Orbiting Environmental Satellites) we determine particle penetration ratios into the polar atmosphere for protons ranging from about 0.1 MeV to 500 MeV and for electrons spanning about one order of magnitude in energy with a maximum of 0.3 MeV. Based on power law fits for the POES spectrum we show, that for energies interesting for middle and lower atmosphere chemistry, particle flux over the poles is comparable in magnitude to flux at the geostationary orbit or at L1 in interplanetary space. The time period under study are the solar energetic particle (SEP) event series of October/November 2003 and January 2005.     

同轴送粉喷嘴保护气体流场研究

为解决飞机结构损伤激光在线修复过程中同轴送粉喷嘴气体保护效果不佳的问题,利用粒子图像测速(Particle image velocimetry,PIV)和Fluent软件对喷嘴保护气体流场进行了研究。将喷嘴气流的同轴射流和同轴冲击射流的数值计算结果和实验测量结果进行了比较,分析了喷嘴气流速度变化对流场稳定性的影响。结果表明:喷嘴中心、内环和外环气流流速由内向外递减时可获得稳定的流场;喷嘴中心、内环、外环喷出的气流速度接近一致时,流场比较稳定;喷嘴中心气流速度小于内环和外环的气流速度时,工件表面出现漩涡,破坏了流场的稳定性。     

碳纳米管/HTPB复合粒子的制备及其催化性能研究

用HTPB对碳纳米管（CNTs）进行改性,改善其对AP热分解的催化性能,并使用TEM和FTIR对其进行表征。热重分析表明,CNTs／HTPB复合粒子中HTPB的含量为28．57％。采用差示热分析（DTA）研究了CNTs／HTPB复合粒子对AP热分解的催化性能。结果表明,CNTs／HTPB复合粒子对AP的热分解具有一定的催化性能,与纯AP相比,高温分解峰温提前了111．9℃,表观分解热由309．92J／g提高到987．18J／g,优于CNTs与AP的简单混合样,表明经过HTPB改性后CNTs对AP具有较好催化性能,同时AP与CNTs／HTPB复合可使其高温分解峰温进一步降低9．8℃。     

二维凹面腔内暂冲式激波聚焦机理的实验

针对两级脉冲爆震发动机中第二级凹面腔内激波聚焦起爆能量和周期的研究,设计了二维凹面腔内暂冲式激波聚焦实验系统。通过分析粒子图像测速系统捕捉的照片和动态压力数据,获得了凹面腔内激波聚焦高压区压力特性和多循环流场演化特征。并且开展了A和B两种型面凹面腔的对比实验,进一步分析了多循环激波聚焦的形成机理。结果表明:入射激波第一次在凹面腔底部聚焦后形成的聚焦反射激波在喷口射流边界上发生反射,产生的反射激波再次在凹面腔底部聚焦,形成了第二次激波聚焦,如此往复便形成了周期性的激波聚焦,聚焦频率高达7~10kHz;并且,速度场和射流强度随入射激波碰撞而减弱,在排气过程中又增强,呈现周期性变化。      

GPS/BDS/INS tightly coupled integration accuracy improvement using an improved adaptive interacting multiple model with classified measurement update

An Extended Kalman Filter (EKF) is commonly used to fuse raw Global Navigation Satellite System (GNSS) measurements and Inertial Navigation System (INS) derived measurements. However, the Conventional EKF (CEKF) suffers the problem for which the uncertainty of the statistical properties to dynamic and measurement models will degrade the performance. In this research, an Adaptive Interacting Multiple Model (AIMM) filter is developed to enhance performance. The soft-switching property of Interacting Multiple Model (IMM) algorithm allows the adaptation between two levels of process noise, namely lower and upper bounds of the process noise. In particular, the Sage adaptive filtering is applied to adapt the measurement covariance on line. In addition, a classified measurement update strategy is utilized, which updates the pseudorange and Doppler observations sequentially. A field experiment was conducted to validate the proposed algorithm, the pseudorange and Doppler observations from Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) were post-processed in differential mode. The results indicate that decimeter-level positioning accuracy is achievable with AIMM for GPS/INS and GPS/BDS/INS configurations, and the position accuracy is improved by 35.8%, 34.3% and 33.9% for north, east and height components, respectively, compared to the CEKF counterpart for GPS/BDS/INS. Degraded performance for BDS/INS is obtained due to the lower precision of BDS pseudorange observations.