Probing Solar Subsurface Magnetic Fields

Helioseismology uses solar p-mode oscillations to probe the structure of the solar interior. The modifications of p-mode properties due to the presence of solar magnetic fields provide information on the magnetic fields in the solar interior. Here we review some of results in helioseismology on the magnetic fields in the solar convection zone. We will also discuss a recent result on the magnetic fields at the base of the convection zone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ionic Charge States of Solar Energetic Particles: A Clue to the Source

The ionic charge of solar energetic particles (SEP) as observed in interplanetary space is an important parameter for the diagnostic of the plasma conditions at the source region and provides fundamental information about the acceleration and propagation processes at the Sun and in interplanetary space. In this paper we review the new measurements of ionic charge states with advanced instrumentation onboard the SAMPEX, SOHO, and ACE spacecraft that provide for the first time ionic charge measurements over the wide energy range of ∼0.01 to 70 MeV/nuc (for Fe), and for many individual SEP events. These new measurements show a strong energy dependence of the mean ionic charge of heavy ions, most pronounced for iron, indicating that the previous interpretation of the mean ionic charge being solely related to the ambient plasma temperature was too simplistic. This energy dependence, in combination with models on acceleration, charge stripping, and solar and interplanetary propagation, provides constraints for the temperature, density, and acceleration time scales in the acceleration region. The comparison of the measurements with model calculations shows that for impulsive events with a large increase of Q _Fe(E) at energies ≤1 MeV/nuc the acceleration occurs low in the corona, typically at altitudes ≤0.2 R _S .     

FSK调制与解调在C54 DSP上的实现

数据通信的发展，对相应的传输设备提出了更高要求，尤其是速度方面。DSP的运算速度快的优点正好能满足FSK调制解调器在速度方面的要求。本文通过对FSK调制与解凋原理的分析，提出了用DSF实现FSK调制与解调的方法，重点讨论该方法的软件设计。通过实验证明，本方法设计的FSK调制解调器具有调制相位连续、解调无相位抖动、传输速率快等特性。     

Short Quasi-Periodic MHD Waves in Coronal Structures

The possibility of remote diagnostics of coronal structures with impulsively-generated short-period fast magnetoacoustic wave trains is demonstrated. An initially broad-band, aperiodic fast magnetoacoustic perturbation guided by a 1D plasma inhomogeneity develops into a quasi-periodic wave train with a well-pronounced frequency and amplitude modulation. The quasi-periodicity results from the geometrical dispersion of the modes, determined by the transverse profile of the loop, and hence contains information about the profile. Wavelet images of the wave train demonstrate that their typical spectral signature is of a “crazy tadpole’’ shape: a narrow spectrum tail precedes a broad-band head. The instantaneous period of the oscillations in the wave train decreases gradually with time, with a mean value of several seconds for typical coronal values. The period and the spectral amplitude evolution are determined by the steepness of the transverse density profile and the density contrast ratio in the loop, which offers a tool for estimation of the sub-resolution structuring of the corona.     

The Role of Dynamics in Solar Forcing

This paper reviews the solar influence on climate through stratospheric dynamical processes. There are two possible processes, both being a consequence of the wave-mean flow interaction in the upper stratosphere. One involves changes in the vertical propagation of planetary waves and the resultant tropospheric circulation change in the extratropics of the winter hemisphere. The other involves change in the global meridional circulation in the stratosphere and associated convective activity change in the tropics. These processes have been discussed on an 11-year solar cycle, but they are also applicable for centennial-scale solar influence on climate.     

Characteristics of reattached boundary layer in shock wave and turbulent boundary layer interaction

The reattached boundary layer in the interaction of an oblique shock wave with a flatplate turbulent boundary layer at Mach number 2.25 is studied by means of Direct Numerical Simulation(DNS). The numerical results are carefully compared with available experimental and DNS data in terms of turbulence statistics, wall pressure and skin friction. The coherent vortex structures are significantly enhanced due to the shock interaction, and the reattached boundary layer is characterized by large-scale...     

下一代数据中继卫星系统发展思考

通过系统阐述中继卫星系统的发展过程,给出了主要国家和组织的中继卫星系统技术体制和现状.再结合卫星、载人航天器和深空探索的未来发展趋势,分析了下一代中继卫星系统的发展需求.在此基础上,从体系结构、卫星平台、链路调制体制、网络协议等方面,探讨并给出了下一代中继卫星系统的发展趋势和技术途径.为满足未来近地、深空航天任务,以及临近、低空快速移动用户的不同要求,节约系统成本,下一代中继卫星系统将向专业化和与其他系统融合的方向发展:星间链路将增加激光链路,数据速率可达到10 Gbit/s以上;多址业务成为主用,同时支持用户数能力将极大提高;对于链路调制体制,在采用CR(Cognitive Radio,认知无线电)和SDR(Software Defined Radio,软件定义无线电)技术的基础上,可实现实时自适应调整和根据需求加载配置;数据传输将采用网络化方式,天地间构成一体化DTN(Delay Tolerant Network,容延迟网络).     

一种改进型光纤陀螺惯导系统单轴旋转调制方案

在常规单轴两位置旋转调制方案基础上,提出了一种改进型光纤陀螺惯导系统单轴旋转调制方案,该方案深入研究了载体航向角变化时,通过优选惯性测量组合(IMU)的旋转停止位置,实现了比常规调制方案更好的导航误差自补偿效果.通过理论推导和仿真验证,证明了本方案的有效性、可行性.     

系统非线性对主字母安控性能影响分析

针对新型的主字母安控体制特点,为了分析非线性对主字母安控体制的影响,对主字母安控体制工作原理和非线性产生原理进行了理论推导.通过对“11选3”主字母安控体制的实例分析、解调性能计算与性能仿真,验证了系统非线性对解调性能与安控可靠性的影响.仿真结果表明:调制指数的大小直接影响解调性能,调制指数太小会使主字母信号能量变低,调制指数太大则会导致非线性,所以需要选择合理的调制指数应用在体制设计中;信道非线性在放大器饱和放大时出现,会导致字母能量分散、信噪比恶化.     

A substitute for BOC modulation based on SS-CPM

CPM (continuous phase modulation) has been widely used in the field of satellite communication, which has high spectrum efficiency and constant envelope. This paper explores the applicability of CPM to satellite navigation. A SS-CPM (Spread-Spectrum CPM) modulation is investigated. The SS-CPM with tuned parameters can resemble the spectrum of Binary Offset Carrier (BOC) modulation and yields comparable performance in terms of tracking accuracy, multipath mitigation, anti-jamming, and compatibility. The BOC-like SS-CPM signal maintains the constant envelope at transmission and less out-band emission in radio determination satellite service (RDSS) band, which provides a reference modulation for COMPASS satellite navigation signal.