Control of Jupiter's radio emission and aurorae by the solar wind

Radio emissions from Jupiter provided the first evidence that this giant planet has a strong magnetic field and a large magnetosphere. Jupiter also has polar aurorae, which are similar in many respects to Earth's aurorae. The radio emissions are believed to be generated along the high-latitude magnetic field lines by the same electrons that produce the aurorae, and both the radio emission in the hectometric frequency range and the aurorae vary considerably. The origin of the variability, however, has been poorly understood. Here we report simultaneous observations using the Cassini and Galileo spacecraft of hectometric radio emissions and extreme ultraviolet auroral emissions from Jupiter. Our results show that both of these emissions are triggered by interplanetary shocks propagating outward from the Sun. When such a shock arrives at Jupiter, it seems to cause a major compression and reconfiguration of the magnetosphere, which produces strong electric fields and therefore electron acceleration along the auroral field lines, similar to the processes that occur during geomagnetic storms at the Earth.     

An Earth-like correspondence between Saturn's auroral features and radio emission

Saturn is a source of intense kilometre-wavelength radio emissions that are believed to be associated with its polar aurorae, and which provide an important remote diagnostic of its magnetospheric activity. Previous observations implied that the radio emission originated in the polar regions, and indicated a strong correlation with solar wind dynamic pressure. The radio source also appeared to be fixed near local noon and at the latitude of the ultraviolet aurora. There have, however, been no observations relating the radio emissions to detailed auroral structures. Here we report measurements of the radio emissions, which, along with high-resolution images of Saturn's ultraviolet auroral emissions, suggest that although there are differences in the global morphology of the aurorae, Saturn's radio emissions exhibit an Earth-like correspondence between bright auroral features and the radio emissions. This demonstrates the universality of the mechanism that results in emissions near the electron cyclotron frequency narrowly beamed at large angles to the magnetic field.     

高速时钟电路设计

在当今的电子设计中，系统越来越复杂，工作频率越来越高，时钟子系统是关于整个系统成败的关键．因此，如何设计出一个高效、高稳定性的时钟子系统成为摆在工程师面前一个头等重要的问题．文章通过分析3种时钟信号的抖动现象(Cycle—Cycle．Jitter、Period Jitter、Long—term Jitter)，针对其产生的原因，提出高速时钟电路设计的解决方案，并结合实际情况给出布线模型．     

基于LIBSVM的风速预测方法研究

由于风速随机性大且影响风速大小的因素较多,为了提高风速预测的准确性,研究了将支持向量机(support vector machine, SVM)应用于风速预测的方法,通过交叉验证选取LIBSVM回归机的最优参数组合并建立模型。实验结果表明,该方法在风速的实际预测中具有可行性。     

Drifting bands of solar radio spikes

The solar flare （1N/C5.3） occurred in NOAA 8742 on October 27, 1999, end the accompanied complex radio burst was observed by the spectrometer with both high temporal （5 ms） end frequency （10 MHz） resolutions at Purple Mountain Observatory （PMO）. It started at 04：27：42 UT, peaked at 04：28：42 UT end ended at 04：29：18 UT. The most significant feature of the event might be the sequential spikes in both time and frequency to form three slow drift bands over the frequency range of -5 to ≥7.5 GHz with almost the same drift rate about 2.7 GHz/s. The relative bandwidth for the individual spikes varied from 1.6% to 4.9%, typically 3.3%. Based on electron cyclotron maser action driven by loss-cone enisotropy, the rare phenomena of slow drift band consisting of spikes were interpreted by spike source moving back and forth along the magnetic loop. Also, the estimations of the narrow bandwidths of spike given by electron cyclotron maser theory coincided well with the observations.     

以电波钟为基准的时间控制器

采用无线控制授时技术（RCT），解决了大部分时间控制器的时间控制不精确，误差累积严重的问题，且成本低，电路简单。     

OFDM软件无线电接收机的采样时钟同步

针对正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)采样时钟同步问题,提出了一种适合于软件无线电(Software-.Defined Radio,SDR)接收机的全数字实现方案.该方案的整体结构基于经典的Gardner环路,借助联合迭代估计算法来进行误差的动态跟踪,并通过对接收信号进行异步重采样来实现采样时钟误差的实时校正.误差检测环节不仅能消除载波频率误差的影响,还可以在维持环路的响应速度的同时提高误差检测的精度.误差校正环节利用一种简单的动态延迟技术来对信号重采样进行直接控制,尽管增加了一些处理延迟,但能使重采样过程平稳进行.理论分析和仿真结果表明,新的采样时钟同步方案在多径信道环境中能有效工作,算法的性能优于其他同类算法.     

Mediation of the solar wind termination shock by non-thermal ions

Broad regions on both sides of the solar wind termination shock are populated by high intensities of non-thermal ions and electrons. The pre-shock particles in the solar wind have been measured by the spacecraft Voyager 1 (refs 1-5) and Voyager 2 (refs 3, 6). The post-shock particles in the heliosheath have also been measured by Voyager 1 (refs 3-5). It was not clear, however, what effect these particles might have on the physics of the shock transition until Voyager 2 crossed the shock on 31 August-1 September 2007 (refs 7-9). Unlike Voyager 1, Voyager 2 is making plasma measurements. Data from the plasma and magnetic field instruments on Voyager 2 indicate that non-thermal ion distributions probably have key roles in mediating dynamical processes at the termination shock and in the heliosheath. Here we report that intensities of low-energy ions measured by Voyager 2 produce non-thermal partial ion pressures in the heliosheath that are comparable to (or exceed) both the thermal plasma pressures and the scalar magnetic field pressures. We conclude that these ions are the >0.028 MeV portion of the non-thermal ion distribution that determines the termination shock structure and the acceleration of which extracts a large fraction of bulk-flow kinetic energy from the incident solar wind.     

微机型超声瞬时风速风谱测量系统

介绍一种微机型超声瞬时风速风谱测量系统。该系统发挥无惯性检测的优势,结合计算机技术,完成瞬时风速和阵风风速谱的测量,从更高层次上揭示自然风的特性。经过风洞鉴定及强台风野外实测考验证明,该系统具有精度高、频响快、工作可靠等特点,有广阔的应用前景     

基于风速估计和风剪切的风力发电机组变桨距控制

为提高大型风力发电机组捕获风能的能力,改善其主要零部件受荷载情况,提出基于有效风速估计和风剪切的风力发电机组独立变桨距控制策略.以某5 MW变速变桨风力发电机组为验证对象,基于Bladed软件平台对传统统一变桨控制策略和独立变桨控制策略进行仿真比较.结果表明:相对于统一变桨距控制策略,独立变桨距控制策略不但能满足维持风力发电机组输出功率额定值稳定的要求,而且使发电机组主要零部件的受荷载情况得到明显改善.     

Multi-scale pressure-balanced structures in the solar wind observed by WIND

This work detects multi-scale, from hour to seconds, pressure-balanced structures (PBSs) in the solar wind based on the anti- correlation between the plasma thermal pressure and the magnetic pressure measured by WIND at 1 AU on April 5th, 2001. In our former research based on Cluster measurements, we showed the anti-correlation between the electron density and the magnetic field strength in multi-scales, and we supposed these structures may be pressure-balanced structures. Thus, in this work we aim to prove our speculation by the direct evidence on pressure measurements. Different from our previous work, we apply the WIND measurements this time, for they have both the magnetic pressure and the plasma pressure which Cluster could not offer. We use the wavelet cross-coherence method to analyze the correlation between the plasma pressure (P th ) and the magnetic pressure (P B ), and also the electron density (N e ) and the magnetic field strength (B) on various scales. We observe the anti-correlation between P th and P B distributed at different temporal scales ranging from 1000 s down to 10 s. This result directly indicates the existence of pressure- balanced structures (PBSs) with different sizes in the solar wind. Further, We compare the wavelet cross correlation spectrum of P th -P B and N e -B. We notice that the two spectra are similar in general. Thus this result confirms that the relation between P th -P B and N e -B are consistent with each other in the PBSs we study. Moreover, we compare the power spectrum density (PSD) of relative N e fluctuation with our previous work based on Cluster measurements. The two spectra show similar trend with Komolgorov’s -5/3 as their slopes. This may imply the similarity of the structures observed by both WIND and Cluster spacecrafts. Finally, we discuss the possible formation mechanisms for these multi-scale pressure-balanced structures. Our result is important to support the existence of multi-scale PBSs from one-hour scale down to one-minute, and is helpful to understand the role of compressive fluctuation in the solar wind turbulence dominated by Alfvénic cascading.     

Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae

The interaction of the solar wind with Earth's magnetosphere gives rise to the bright polar aurorae and to geomagnetic storms, but the relation between the solar wind and the dynamics of the outer planets' magnetospheres is poorly understood. Jupiter's magnetospheric dynamics and aurorae are dominated by processes internal to the jovian system, whereas Saturn's magnetosphere has generally been considered to have both internal and solar-wind-driven processes. This hypothesis, however, is tentative because of limited simultaneous solar wind and magnetospheric measurements. Here we report solar wind measurements, immediately upstream of Saturn, over a one-month period. When combined with simultaneous ultraviolet imaging we find that, unlike Jupiter, Saturn's aurorae respond strongly to solar wind conditions. But in contrast to Earth, the main controlling factor appears to be solar wind dynamic pressure and electric field, with the orientation of the interplanetary magnetic field playing a much more limited role. Saturn's magnetosphere is, therefore, strongly driven by the solar wind, but the solar wind conditions that drive it differ from those that drive the Earth's magnetosphere.     

环境条件对直流风洞风速测量结果的影响

为了研究风速仪器检定对环境测量仪器性能参数的要求,确定检定过程中环境条件的限制范围,通过动态测量和数据比对的方法,获得不同环境条件下风速测量结果的实验数据,定量分析了风速检定实验室的房间阻挡物、温度、湿度和气压等要素对测量结果的影响。结果表明,实验室内有阻挡物时的风速稳定性系数和测量误差均比无阻挡物时大1倍以上;实验室的温度、气压和湿度3个要素中,温度变量对风速测量结果影响最大,相对湿度的影响最小;在检定过程中,当实验室温度变化超过1℃、气压变化超过25hPa、相对湿度变化超过38%RH时,会对测量结果造成可估量影响。     

On theories of solar type III radio bursts

In solar radiophysics,many theories for type Ⅲ bursts have been proposed during the past 60 years.Almost all these theories are based on the plasma hypothesis,which assumes that(i)the radiation is mainly generated by Langmuir waves via nonlinear processes and(ii)the radiation has frequencies close to the local plasma frequency and/or its second harmonic in the source region. We feel strongly that it is time to advocate an alternative approach without recourse to the plasma hypothesis.This brief discussion explains why.     

An asymmetric solar wind termination shock

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, approximately 10 au closer to the Sun than found by Voyager 1 in the north. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field, from transient-induced shock motion, or from the solar wind dynamic pressure. Here we report that the intensity of 4-5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma, magnetic field, plasma-wave and lower energy particle observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock or in the heliosheath. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath or the local interstellar Galactic cosmic ray intensity is lower than expected.     

偏低风速风力发电系统的研制应用

给出了吉林低风速风力发电系统的研制现状。     

Three-dimensional MHD simulation for the solar wind structure observed by Ulysses

Ulysses has been the first spacecraft to explore the high latitudinal regions of the heliosphere till now. During its first rapid pole-to-pole transit from September 1994 to June 1995, Ulysses observed a fast speed flow with magnitude reaching 700—800 km/s at high latitudinal region except 20°area near the ecliptic plane where the velocity is 300—400 km/s. The observations also showed a sudden jump of the velocity across the two regions. In this note, based on the characteristic and representative observations of the solar magnetic field and K-coronal polarized brightness, the large-scale solar wind structure mentioned above is reproduced by using a three-dimensional MHD model. The numerical results are basically consistent with those of Ulysses observations. Our results also show that the distributions of magnetic field and plasma number density on the solar source surface play an important role in governing this structure. Furthermore, the three-dimensional MHD model used here has a robust ability to simulate this kind of large-scale wind structure.     

高层建筑风场的脉动风速时程模拟

采用经过FFT算法改进的谐波叠加法(WAWS)及自回归(AR)模型的线性滤波法对实际工程进行脉动风速时程模拟.对2种算法所模拟的风速时程进行分析,结果显示了风速功率谱及相关函数的特性,分析结果说明AR模型中模型阶次及时间步长对风速时程产生较大影响.根据结构的有限元动力分析,采用能量相等的原则,即使结构固有频率段内的目标谱和模拟谱能量相等,对风速时程进行修正,使模拟风速时程更趋合理.     

基于AVR单片机的风速模拟器的设计

根据风速风向传感器的原理，结合带编码器的无刷电机，以AVR单片机为核心控制器，设计了可以模拟测试多种风速风向传感器风速数据准确性的风速模拟器。实验结果证明，基于AVR单片机的风速模拟器达到设计要求，体积小、功耗低且可靠性高，可以准确地模拟测试风速数据。