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1.
Junhyeok Jeon Young-Joo Kwon Yong-Sam Lee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(8):2116-2123
Observing Venus during the daytime is challenging. However, observational data of Venus during the daytime can be found in history books from East Asian countries such as Korea, China and Japan. In this study, we are focused on data from Korean history book, and using records left in the Joseon wangjo sillok, one of the Korean history books from the Joseon dynasty (CE 1392–1910), tries to prove whether the reported observations were actual observation data. We collected these 4663 records from the Joseon wangjo sillok to determine whether they were actual observations, and to confirm the scientific validity of the records. When we looked at the distribution of observations on a yearly basis, we noticed that there were more observations in the fall and winter, while there were only limited numbers of observations in the spring. This difference in distribution suggests that observations were strongly affected by atmospheric conditions due to the weather. From the 4663 data collected, we found a cycle of about 1.6?years. The cycle of about 1.6?years is assumed to be related to the conjunction cycle of Venus. And, we found a cycle of about 1.0?years. The cycle of about 1.0?years is assumed to reflect the indirect effects of the Asian dust phenomenon. Our research result verified the record as actual observational data. In addition, this result verified that meteorological factors were involved in the recorded astronomical observation data. We think that our data can be helpful to climate studies on the natural sources of key climate-affecting aerosols. 相似文献
2.
3.
A Bayesian network (BN) is a compact representation for probabilistic models and inference. They have been used successfully for many military and civilian applications. It is well known that, in general, the inference algorithms to compute the exact a posterior probability of a target node given observed evidence are either computationally infeasible for dense networks or impossible for general hybrid networks. In those cases, one either computes the approximate results using stochastic simulation methods or approximates the model using discretization or a Gaussian mixture model before applying an exact inference algorithm. This paper combines the concept of simulation and model approximation to propose an efficient algorithm for those cases. The main contribution here is a unified treatment of arbitrary (nonlinear non-Gaussian) hybrid (discrete and continuous) BN inference having both computation and accuracy scalability. The key idea is to precompile the high-dimensional hybrid distribution using a hypercube representation and apply it for both static and dynamic BN inference. Since the inference process essentially becomes a combination of table look-up and some simple operations, the method is shown to be extremely efficient. It can also he scaled to achieve any desirable accuracy given sufficient preprocessing time and memory for the cases where exact inference is not possible 相似文献
4.
Performance evaluation for MAP state estimate fusion 总被引:1,自引:0,他引:1
Chang K.C. Zhi Tian Mori S. 《IEEE transactions on aerospace and electronic systems》2004,40(2):706-714
This paper presents a quantitative performance evaluation method for the maximum a posteriori (MAP) state estimate fusion algorithm. Under ideal conditions where data association is assumed to be perfect, it has been shown that the MAP or best linear unbiased estimate (BLUE) fusion formula provides the best linear minimum mean squared estimate (LMMSE) given local estimates under the linear Gaussian assumption for a static system. However, for a dynamic system where fusion is recursively performed by the fusion center on local estimates generated from local measurements, it is not obvious how the MAP algorithm will perform. In the past, several performance evaluation methods have been proposed for various fusion algorithms, including simple convex combination, cross-covariance combination, information matrix, and MAP fusion. However, not much has been done to quantify the steady state behavior of these fusion methods for a dynamic system. The goal of this work is to present analytical fusion performance results for MAP state estimate fusion without extensive Monte Carlo simulations, using an approach developed for steady state performance evaluation for track fusion. Two different communication strategies are considered: fusion with and without feedback to the sensors. Analytic curves for the steady state performance of the fusion algorithm for various communication patterns are presented under different operating conditions. 相似文献
5.
Dong-Wook Lee McClellan J.H. 《IEEE transactions on aerospace and electronic systems》1997,33(3):795-801
The problem of extracting multiple frequencies from phase-only data is addressed. Multiple frequency estimation is accomplished by reconstructing the Fourier transform of the complex-valued time signal and then finding peaks in the frequency domain. We present a set of conditions under which a discrete-time complex sequence can be completely specified by its phase-only information. Two candidate multiple frequency estimation schemes are introduced, one based on a closed-form least-squares inverse, the other an iterative reconstruction algorithm. The uniqueness of the closed-form solution and the convergence of the iterative scheme have been proven under certain conditions. Several examples are given, including the case where the phase is quantized as would happen in an analog-to-digital (A/D) converter. Extensions to the multidimensional case, and to the case of real-part only reconstruction are straightforward. 相似文献
6.
Bor-Ren Lin Yung-Chuan Lee Tsung-Yu Yang 《IEEE transactions on aerospace and electronic systems》2004,40(1):180-189
A three-phase four-wire power factor corrector based on neutral-point-clamped (NPC) topology is adopted to reduce the current harmonics and increase the input power factor. Using the NPC topology, the voltage stress of power switches can be reduced to the half of the dc-link voltage. With the dc-link voltage controller and the phase locked loop circuit, the balanced and sinusoidal line currents can be drawn from the ac supply system under the balance and unbalance mains voltages. The hysteresis current comparators are adopted in the current control loop to track the line current commands. Three voltage levels are generated on the ac terminal to the neutral point. Simulations and experiments are provided to verify the validity and the effectiveness of the proposed control scheme. 相似文献
7.
Martin A. Lee 《Space Science Reviews》2007,130(1-4):221-229
Gradual solar energetic particle (SEP) events are evidently accelerated by coronal/interplanetary shocks driven by coronal
mass ejections. This talk addresses the different factors which determine the composition of the accelerated ions. The first
factor is the set of available seed populations including the solar wind core and suprathermal tail, remnant impulsive events
from preceding solar flares, and remnant gradual events. The second factor is the fractionation of the seed ions by the injection
process, that is, what fraction of the ions are extracted by the shock to participate in diffusive shock acceleration. Injection
is a controversial topic since it depends on the detailed electromagnetic structure of the shock transition and the transport
of ions in these structured fields, both of which are not well understood or determined theoretically. The third factor is
fractionation during the acceleration process, due to the dependence of ion transport in the turbulent electromagnetic fields
adjacent to the shock on the mass/charge ratio. Of crucial importance in the last two factors is the magnetic obliquity of
the shock. The form of the proton-excited hydromagnetic wave spectrum is also important. Finally, more subtle effects on ion
composition arise from the superposition of ion contributions over the time history of the shock along the observer’s magnetic
flux tube, and the sequence of flux tubes sampled by the observer. 相似文献
8.
Tsai-Fu Wu Chh-Lung Shen Chien-Hsuan Chang Jeiyang Chiu 《IEEE transactions on aerospace and electronic systems》2003,39(2):635-646
This paper presents a single-phase three-wire (1/spl phi/ 3W) grid-connection photovoltaic (PV) power inverter with a of partial active power filter (PAPF) feature, which can not only deal with PV power but filter current harmonics and improve power factor. Once the processed power exceeds the switch ratings, the inverter can reduce its output reactive power and harmonic power, while still supplying the maximum real power generated by the PV arrays. In the derivation of control laws, a limit circle is defined to confine the output power of the inverter. To determine the power that the inverter can process, the instantaneous reactive power of a 1/spl phi/ 3W system is defined and used to calculate reactive power, which can avoid complex detections of phase angle and magnitude of the fundamental component of a nonlinear load current. Simulation results and experimental measurements have verified the proposed algorithm and the feasibility of the inverter. 相似文献
9.
掠海飞行导弹击水概率的仿真研究 总被引:9,自引:0,他引:9
本文对掠海导弹的击水概率问题进行了研究,提出了用均匀设计、Monte—Carlo法和逐步回归法建立击水概率预报公式的仿真方法,并结合某型号的反舰导弹进行计算,得到了满意的结果。本文还利用表观频率和表观频谱的概念,建立起飞航导弹的背景干扰——海浪和阵风的数学模型,并用波叠加法进行了数字仿真。 相似文献
10.