A direct position determination method with combined TDOA and FDOA based on particle filter

The localization of a stationary transmitter using moving receivers is considered. The original Direct Position Determination (DPD) methods, with combined Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA), do not perform well under low Signal-to-Noise Ratio (SNR), and worse still, the computation cost is difficult to accept when the computational capabilities are limited. To get better positioning performance, we present a new DPD algorithm that proves to be more computationally efficient and more precise for weak signals than the conventional approach. The algorithm partitions the signal received with the same receiver into multiple non-overlapping short-time signal segments, and then uses the TDOA, the FDOA and the coherency among the short-time signals to locate the target. The fast maximum likelihood estimation, one iterative method based on particle filter, is designed to solve the problem of high computation load. A secondary but important result is a derivation of closed-form expressions of the Cramer-Rao Lower Bound (CRLB). The simulation results show that the algorithm proposed in this paper outperforms the traditional DPD algorithms with more accurate results and higher computational efficiency, and especially at low SNR, it is more close to the CRLB.     

频率标准用超导铌腔内表面处理工艺研究

频率标准用超导铌腔内表面的处理是影响超导腔Q值的最大因素。本文首先通过理论分析确定了超导腔Q与表面剩余电阻的关系,其次通过一系列的表面处理工艺来保证超导腔内表面的剩余电阻尽量小,最后通过实验得到了超导腔的Q值为1.9E9,与理论计算结果相近,证明了表面处理的有效性。     

Is the North Atlantic Oscillation modulated by solar and lunar cycles? Some evidences from Hurst autocorrelation analysis

Several studies have suggested that the Sun and Moon cycles affect the Earth climatic dynamics. Nevertheless, there is a long-standing controversy whether solar variability and tides can significantly generate climate change, and how this may occur. Spectral analysis of climatic indices has provided only indirect evidences of the effects of solar–tidal periodicities in the Earth climate. This work addresses the issue by considering the dynamics of the daily North Atlantic Oscillation index over the period from 1950 to 2009. In contrast to previous studies, this work proposes that external cycles can be detected in the autocorrelation dynamics rather than in the raw North Atlantic Oscillation index series. Here, the R/S-scaling analysis is used to quantify, via the so-called Hurst exponent, the presence of autocorrelations along the studied years. Fourier analysis scan of the autocorrelation series thus show two prominent spectral components near (±3%) the lunar tidal 4.425 and the solar 11 years cycles. Intermediate spectral components near 6.4, 7.75 and 8.9 years are proposed to be, at least partially, a result of energy capture from internal mechanisms into cycles resulting from the nonlinear resonance of the fundamental solar–tidal cycles. The dominant effect of the solar variability is clarified by showing that in about 70% of the studied period the sunspot number and the Hurst exponent phases are synchronized, indicating that a higher solar activity enhances the North Atlantic Oscillation index predictability.     

Radial and latitudinal gradients of galactic cosmic rays in the heliosphere at solar maximum

Our understanding of galactic cosmic ray (GCR) modulation has advanced greatly in the last three decades. However, we still need an appropriate knowledge of the GCR intensity gradient. Numerical simulations of the transport particle equation allow interpretation of cosmic ray intensities in the heliosphere. We use the numerical solution of the GCR transport equation during solar maximum epoch to compute the radial and latitudinal gradients. Our analysis indicates that adiabatic energy loss plays an important role in the radial distribution of GCR in the inner heliosphere, while in the outer region the diffusion and convection are the relevant processes. The latitudinal gradient is small.     

一种基于SPWM方法的三相变频逆变电源

给出了一种新的SPWM控制算法。采用该方法可以很方便的实现SPWM变频逆变的控制,并以增强型高速51单片机W77E58为主处理器构成系统,实现了三相变频逆变电源。该电源具有频率、电压的调节、指示及过流保护等功能。     

New field of application of the IRI modeling – Determination of ionosphere transfer characteristic for radio astronomical signals

We suggest a new field of application of IRI modeling – determination of ionosphere transfer characteristic (ITC) for radio astronomical signals (RAS). VHF and HF RAS are widely used for observations of the Sun and pulsars. It is necessary to take into account possible distortions of RAS in the Earth ionosphere. However, in contrast to modern navigation systems (GPS, GLONASS, GALILEO), where very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ITC has not been appropriately worked out yet. It collides with increasing requirements to accuracy of the analysis of RAS amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation. We have developed a method and software for calculation of the ionosphere measure of rotation (RM) and the measure of dispersion (DM). We used the ionosphere model IRI-2001, magnetic-field model IGRF-10 and values of ionosphere total electron content as deduced from GPS measurements. The obtained values of the ionosphere DM and RM were recalculated into characteristics of phase delay, Faraday amplitude modulation and polarization changes. We made calculations for different levels of geomagnetic activity and for different angular position of radio sources as well.     

频率计数器在航天器信号频率测量中的适用性分析

从频率计数器的工作原理出发,分析了航天器测控通信中常用的调相信号、调频信号和相移键控信号的频率测量误差,给出了调相信号和调频信号的测量误差表达式。使用频率计数器对上述3种航天器信号进行了频率测量试验。理论分析和试验结果表明,频率计数器适用于航天器调相信号和调频信号的频率测量,不适用于相移键控信号的频率测量。在实际使用中,为保证测量精度,应根据被测信号的调制方式选择适当的测量方法。     

Control system design of the Korean lunar lander demonstrator

In preparation for the lunar exploration program scheduled to be launched during the early 2020s in Korea, a lunar lander demonstrator, which will be used for developing and demonstrating lunar landing technologies, is being developed. The control configuration of the lunar lander demonstrator is determined with the consideration of available technologies and flight requirements. It is suggested that altitude control be achieved by clustering five 200 N monopropellant thrusters and attitude control with eight 3 N thrusters. A control algorithm designed to follow a predefined trajectory is developed using quaternion feedback. Control system configuration and control logic are verified by using computer simulations. Simulation results show that a soft landing with a touchdown velocity of less than 3 m/s is achieved. Attitude control performance is also verified using computer simulations. The developed control configuration will be further tested by hardware in the loop simulations and ground based firing tests during the next phase of the study.     

Time variations of cosmic-ray helium isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5 days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5 GV and results are compared to previously reported proton data and neutron monitor data.     

本地标准时间频率的产生与保持

近年来，地方协调时UTC(BIRM)守时能力稳步提升，截至目前，UTC(BIRM)与UTC的相对频率偏差优于3E-14，时间偏差优于20ns。本文概括介绍了守时系统的组成，本地频率驾驭与主备同步技术，以及TA(BIRM)算法研究等。