Evaluation and improvement of coastal GNSS reflectometry sea level variations from existing GNSS stations in Taiwan

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1?m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10?cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7?cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.     

有限长度的过渡领域微槽道流动(-分析预测和试验的比较)

在连续介质和滑流区有限长度槽道内的稳定气流,通过整体质量守恒规律得到了沿槽道轴向的压力分布和质量流率的分析表达式.在过渡领域区,也提供了槽道流动压力分布的严格的动理学理论解.在Poiseuille流动的质量流率动理学理论解给定的情况下,压力分布的控制方程被证实是被前一作者从轴承润滑问题移植到解微槽道问题的退化Reynolds方程.同时得到了质量流率分析表达式,它们和现有试验数据的比较相符很好.     

稳态等离子体推进器羽流的粒子模拟

利用结合了particle-in-cell方法的直接模拟Monte Carlo方法模拟了稳态等离子体推进器的羽流场。为了更真实地再现实验设备中的流动,模拟中包含了背压气体,并在计算中直接模拟,改变了以往的中性粒子平衡态的处理方式。为了匹配试验结果,修正了推进器出口处气流偏转角分布,并建议最大偏转半角取为20°。计算结果与现有的实验结果符合较好。     

对LVDSMC方法的改进(英文)

最近,Homolle和Hadjiconstantinu提出了新的粒子模拟方法———LVDSMC方法[1],该方法采用了减少方差的思想从而提高了低速流动问题中的计算效率。本文针对LVDSMC方法提出两点改进:第一,除了方法中原来已采用的偏差粒子,在计算近自由分子流问题时建议额外地采用一些辅助粒子,从而可以约束计算过程中原始算法在生成偏差粒子时计算误差的累积效应;第二,提出一个可选的用于计算潜在Maxwell Boltzmann分布函数中的速度参数的增量,从而使得表面的应力及热流的计算变得简单。     

A new power collection architecture for future spacecraft

The generalized tree-like transmission line network system having n layers in total with m-to-1 branch connection at each joint (T-TLNS-n-m) is proposed to replace the traditional series-parallel combined dc networks to automatically accumulate identically distributed power cells into the large amount of useful power for the spacecrafts. The proposed system has the attractive features of simple structure, easy construction and maintenance, and low cost, because two kinds of parts, ac current sources and m-to-1 transmission line (TL) branch connection parts, are used in the whole system. A method of implementing ac current cells having high output impedance is proposed to improve the power collection efficiency of the whole network system. Simulated results show that that low-pass nominal /spl pi/- or T-circuit with high characteristic impedance, which is used for the voltage source to current source converter in the current cell, improves the efficiency of the voltage inverter, filters out the harmonics, and increases the output impedance of the whole current cell.     

Comparison of various periodograms for sinusoid detection andfrequency estimation

With the advent of the fast Fourier transform (FFT) algorithm, the periodogram and its variants such as the Bartlett's procedure and Welch method, have become very popular for spectral analysis. However, there has not been a thorough comparison of the detection and estimation performances of these methods. Different forms of the periodogram are studied here for single real tone detection and frequency estimation in the presence of white Gaussian noise. The threshold effect in frequency estimation, that is, when the estimation errors become several orders of magnitude greater than the Cramer-Rao lower bound (CRLB), is also investigated. It is shown that the standard periodogram gives the optimum detection performance for a pure tone while the Welch method is the best detector when there is phase instability in the sinusoid. As expected, since the conventional periodogram is a maximum likelihood estimator of frequency, it generally provides the minimum mean square frequency estimation errors     

井下数据的数字传输

数字传输技术是信息工程和钻井测试技术中的一项关键技术。本文介绍了适用于石油地质领域的数字传输技术,设计了以微处理器为中心的发送、接收等硬件装置,给出了数据接收软件框图,并从理论和实践上对传输线的匹配问题作了较详细的讨论。