A new parameter to define interplanetary coronal mass ejections

The interplanetary manifestations of coronal mass ejections, ICMEs, have many signatures in the solar wind but none of these signatures in the velocity, density, temperature, magnetic field, plasma composition or energetic particles uniquely and unambiguously identifies the occurrence of an ICME. Different investigators identify different events when confronted with the same data. Herein, we present a single physical parameter that combines information from multiple plasma components and that holds the promise of defining a beginning and an end of the region of influence ICME and an indication of the location of the encounter with the ICME relative to its central meridian. This parameter is the total plasma pressure perpendicular to the magnetic field, consisting of the sum of the magnetic pressure and plasma kinetic or thermal pressure. It provides a vehicle for classifying the nature of the ICME encounter and, in many cases, provides an unambiguous start and stop time of the event. However, it does not provide a start and stop time for any embedded flux rope. This identification depends on examination of the magnetic field.     

Orbital phase spectroscopy of X-ray pulsars to study the stellar wind of the companion

High Mass X-ray Binary Pulsars (HMXBP), in which the companion star is a source of supersonic stellar wind, provide a laboratory to probe the velocity and density profile of such winds. Here, we have measured the variation of the absorption column density along with other spectral parameters over the binary orbit for two HMXBP in elliptical orbits, as observed with the Rossi X-ray Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric wind profile was used as a model to compare the observed column density variations. In 4U 1538-52, we find the model corroborating the observations; whereas in GX 301-2, the stellar wind appears to be very clumpy and a smooth symmetric wind model seems to be inadequate in explaining the variation in column density.     

Prediction of geosynchronous electron fluxes using an artificial neural network driven by solar wind parameters

There are hundreds of satellites operating at the geosynchronous (GEO) orbit where relativistic electrons can cause severe damage. Thus, predicting relativistic electron fluxes is significant for spacecraft safety. In this study, using GOES satellite data during 2011–2020, we propose two neural network models with two hidden layers to predict geosynchronous relativistic electron fluxes at two energy channels (>0.8 MeV and > 2 MeV). The number of input neurons of the two channels (>0.8 MeV and > 2 MeV) are determined to be 36 and 44, respectively. The > 0.8 MeV model has 22 and 9 neurons in the hidden layers, while the > 2 MeV model has 25 and 15 neurons in the hidden layers. The input parameters include the north–south component of the interplanetary magnetic field, solar wind speed, solar wind dynamic pressure and solar wind proton density. Through the analysis of different time delays, we determine that the optimal time delays of two energy channels (>0.8 MeV and > 2 MeV) are 8 days and 10 days, respectively. The training set and validation set (Jan 2011-Dec 2018) are divided by the 10-fold cross-validation method, and the remaining data (Jan 2019-Feb 2020) is used to analyze the model performance as a test set. The prediction results of both energy channels show good agreement with satellite observations indicated by low RMSE (～0.3 cm^-2sr^-1s^?1), high PE (～0.8) and CC (～0.9). These results suggest that only using solar wind parameters is capable of obtaining reasonable predictions of geosynchronous relativistic electron fluxes.     

Absolute and Convective Instabilities of Circularly Polarized Alfvén Waves

We discuss the recent progress in studying the absolute and convective instabilities of circularly polarized Alfvén waves (pump waves) propagating along an ambient magnetic field in the approximation of ideal magnetohydrodynamics (MHD). We present analytical results obtained for pump waves with small dimensionless amplitude a, and compare them with numerical results valid for arbitrary a. The type of instability, absolute or convective, depends on the velocity U of the reference frame where the pump wave is observed with respect to the rest plasma. One of the main results of our analysis is that the instability is absolute when U _l < U < U _r and convective otherwise. We study the dependences of U _l and U _r on a and the ratio of the sound speed to the Alfvén speed b. We also present the results of calculation of the increment of the absolute instability on U for different values of a and b. When the instability is convective (U < U _l or U > U _r) we consider the signalling problem, and show that spatially amplifying waves exist only when the signalling frequency is in two symmetric frequency bands. Then, we write down the analytical expressions determining the boundaries of these frequency bands and discuss how they agree with numerically calculated values. We also present the dependences of the maximum spatial amplification rate on U calculated both analytically and numerically. The implication of the obtained results on the interpretation of observational data from space missions is discussed. In particular, it is shown that circularly polarized Alfvén waves propagating in the solar wind are convectively unstable in a reference frame of any realistic spacecraft.     

砾漠大风地区铁路路堤风载荷模拟实验研究

利用大气边界层风洞对砾漠大风地区铁路路堤进行风载荷模拟实验研究。实验中较好地满足了相似准则，重现了风区现场实测所获得的大气边界层风特性。通过对模型表面平衡和脉动压力的测量以及对模型附近流场的测量，分析研究了路堤风蚀机理，为采取防风蚀的工程措施提供了科学依据，事实证明模拟实验结果是十分有效的。     

大型水陆两栖飞机吹气襟翼设计与分析验证

针对大型水陆两栖飞机的使用特点和指标要求,以原型机翼为基础,重点开展机翼附面层控制增升装置设计技术研究,设计了附面层控制的吹气襟翼方案.采用计算流体动力学方法作为初步设计的评估手段,全面分析评估了设计方案的气动力特性和流场结构,最后通过风洞试验验证了该方案的增升效果.结果显示该设计方案在较宽的吹气动量系数范围内,最大升力系数均有不同程度的增幅,在吹气动量系数约为0.2左右时,获得最大的升力系数增量约为1.0,按照原型机的滑流影响规律推算,当采用吹气襟翼的主动流动控制方案后,起降速度能下降约30%,达到了设计指标.      

非对称安装布局下大型高超声速风洞引射增强型二次喉道数值优化

增强二次喉道扩压能力,降低接力引射器的引射流量是提高大型高超声速风洞运行经济性的重要技术措施。引射增压型二次喉道通过在二次喉道侧壁引射低总压介质增强其扩压能力,是一种非常有潜力的实用方案。本文通过数值模拟研究了其在长模型大攻角等非对称安装布局条件下的运行流场,并进一步优化了压力、介质类型等引射条件。结果表明,优化方案在高超声速风洞复杂运行条件下仍能保持较高的二次喉道扩压能力,较大幅度降低接力引射器的引射流量,具有可行性和实用性。     

脉冲风洞油流和液晶热图流动显示技术

介绍适合脉冲风洞进行表面流动显示的油流和液晶热图技术。前者用油滴流动迹线显示表面流线方向和形状，后者用液晶层反射光的波长（即颜色）分布显示表面温度分布。用这两种方法在定常流时间７ｍｓ至５００ｍｓ的脉冲风洞中成功地获得了尖前缘翼、钝翼和方向的三维干扰流油流和液晶热图清晰照片，清楚地显示出三维干扰流动特征。结果表明，用油流、液晶热图和薄膜电阻温度计热流分布测量得到的干扰流特征位置完全吻合，证实了显示方     

在常规小风洞中实现大风洞中的气动力实验

就风洞尺寸要多大才比较合理以及小风洞的改造和挖潜等问题进行了讨论。认为风洞尺寸不是越大越好,而是在不同速度范围存在着一组相对适中的带某种唯一性的风洞尺寸。这种风洞尺寸,既能满足航天器研制的需要,又具有合理的经费开支。文中推荐了不同速度下一组较合适的且能满足需要的风洞尺寸,供人们参考。同时本文还认为,在一定的风洞条件下,实验数据的精准度与风洞尺寸的大小无关,只要相似模拟的条件正确,就能给出同样精准度的实验数据。就这一观点,列举了在北京空气动力研究所的FD 02小风洞中做出的几种实验。     

柔性飘带气动特性初探

气动中心首次进行了柔性飘带弹的气动特性试验，对柔性飘带提供安定作用的机理进行了分析。常规刚性尾翼（舵）是基于自身升力产生安定力矩，而柔性飘带的安定性是由它产生的总阻力提供的。文中还对影响飘带气动特性诸因素进行了探讨。