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Search Results: 1 - 10 of 32301 matches for " Fei Zheng "
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On oxygen isotope fractionation in carbonate and sulfate minerals
Zheng Yong-Fei
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891661
A Multivariate Empirical Orthogonal Function-Based Scheme for the Balanced Initial Ensemble Generation of an Ensemble Kalman Filter
ZHENG Fei,ZHU Jiang,
,ZHU Jiang

大气和海洋科学快报 , 2010,
Abstract: The initial ensemble perturbations for an ensemble data assimilation system are expected to reasonably sample model uncertainty at the time of analysis to further reduce analysis uncertainty. Therefore, the careful choice of an initial ensemble perturbation method that dynamically cycles ensemble perturbations is required for the optimal performance of the system. Based on the multivariate empirical orthogonal function (MEOF) method, a new ensemble initialization scheme is developed to generate balanced initial perturbations for the ensemble Kalman filter (EnKF) data assimilation, with a reasonable consideration of the physical relationships between different model variables. The scheme is applied in assimilation experiments with a global spectral atmospheric model and with real observations. The proposed perturbation method is compared to the commonly used method of spatially-correlated random perturbations. The comparisons show that the model uncertainties prior to the first analysis time, which are forecasted from the balanced ensemble initial fields, maintain a much more reasonable spread and a more accurate forecast error covariance than those from the randomly perturbed initial fields. The analysis results are further improved by the balanced ensemble initialization scheme due to more accurate background information. Also, a 20-day continuous assimilation experiment shows that the ensemble spreads for each model variable are still retained in reasonable ranges without considering additional perturbations or inflations during the assimilation cycles, while the ensemble spreads from the randomly perturbed initialization scheme decrease and collapse rapidly.
The Study of Search Engine on the Internet--AltaVista

Zheng Fei,

现代图书情报技术 , 1998,
Abstract: 介绍了一个 Internet信息资源的搜索引擎 Alta Vista的产生背景和技术特点 ,并研究了它的查询方法与技巧。
A Statistical-Dynamical Scheme for the Extraseasonal Prediction of Summer Rainfall for 160 Observation Stations across China

LANG Xianmei,ZHENG Fei,

大气科学进展 , 2011,
Abstract: The purpose of this study was to design and test a statistical--dynamical scheme for the extraseasonal (one season in advance) prediction of summer rainfall at 160 observation stations across China. The scheme combined both valuable information from the preceding observations and dynamical information from synchronous numerical predictions of atmospheric circulation factors produced by an atmospheric general circulation model. First, the key preceding climatic signals and synchronous atmospheric circulation factors that were not only closely related to summer rainfall but also numerically predictable were identified as the potential predictors. Second, the extraseasonal prediction models of summer rainfall were constructed using a multivariate linear regression analysis for 15 subregions and then 160 stations across China. Cross-validation analyses performed for the period 1983--2008 revealed that the performance of the prediction models was not only high in terms of interannual variation, trend, and sign but also was stable during the whole period. Furthermore, the performance of the scheme was confirmed by the accuracy of the real-time prediction of summer rainfall during 2009 and 2010.
A Novel Multi-Aperture Based Sun Sensor Based on a Fast Multi-Point MEANSHIFT (FMMS) Algorithm
Zheng You,Jian Sun,Fei Xing,Gao-Fei Zhang
Sensors , 2011, DOI: 10.3390/s110302857
Abstract: With the current increased widespread interest in the development and applications of micro/nanosatellites, it was found that we needed to design a small high accuracy satellite attitude determination system, because the star trackers widely used in large satellites are large and heavy, and therefore not suitable for installation on micro/nanosatellites. A Sun sensor + magnetometer is proven to be a better alternative, but the conventional sun sensor has low accuracy, and cannot meet the requirements of the attitude determination systems of micro/nanosatellites, so the development of a small high accuracy sun sensor with high reliability is very significant. This paper presents a multi-aperture based sun sensor, which is composed of a micro-electro-mechanical system (MEMS) mask with 36 apertures and an active pixels sensor (APS) CMOS placed below the mask at a certain distance. A novel fast multi-point MEANSHIFT (FMMS) algorithm is proposed to improve the accuracy and reliability, the two key performance features, of an APS sun sensor. When the sunlight illuminates the sensor, a sun spot array image is formed on the APS detector. Then the sun angles can be derived by analyzing the aperture image location on the detector via the FMMS algorithm. With this system, the centroid accuracy of the sun image can reach 0.01 pixels, without increasing the weight and power consumption, even when some missing apertures and bad pixels appear on the detector due to aging of the devices and operation in a harsh space environment, while the pointing accuracy of the single-aperture sun sensor using the conventional correlation algorithm is only 0.05 pixels.
Performance Analysis of Sub-Rating for Handoff Calls in HCN  [PDF]
Xiaolong WU, Min HE, Fei WANG, Jun ZHENG, Emma REGENTOVA, Guoshun HAO
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.21003
Abstract: Hierarchical Cellular Networks (HCN) offer more efficient channel utilization and better quality of service (QoS) under the high tele-traffic condition compared to the single-tier system. One of the important measures of QoS in HCN as in any single-tier system is the handoff dropping rate. Although the existing approaches such as guard channel and queuing can reduce forced termination probability, they also result in higher new call blocking probability. The channel sub-rating strategy has found to be an effective technique to reduce the handoff force termination probability while preserving the new call blocking probability in a single-tier system. In this paper, we propose a new call admission control scheme for HCN based on the channel sub-rating. Analytic models based on 1-D Markov process in microcell and 2-D Markov process in macrocell are developed. Experimental results show that our scheme achieves lower blocking and forced termination probabilities compared to the traditional guard channel scheme. The effect of channel sub-rating on the voice quality degradation is also studied. Results demonstrate that we can establish a good balance between the forced termination probability and the voice quality degradation by varying the number of sub-ratable full-rate channels.
Effect of the Random Error on the Radiation Characteristic of the Reflector Antenna Based on Two-Dimensional Fractal
Na Li,Baoyan Duan,Fei Zheng
International Journal of Antennas and Propagation , 2012, DOI: 10.1155/2012/543462
Abstract: Influence of the random error due to the distortion of the antenna reflector was discussed by using the two-dimensional fractal model. Firstly, a mathematical model of the random error was presented to investigate its impact on the radiation characteristic of the antenna, which was filtered from the two-dimensional fractal by using the wavelet analysis method. Based on the error model, a density formulation of the far field of the antenna with random error was deduced. Finally, a 3.7 m and a 3 m antennas were used to validate the proposed models, and a novel simulation method was put forward to remedy the deficiencies of existing software tools for the antenna with error. Results of the proposed methods showed a good agreement with the experimental data, and the existence of error broadened the beam width and raised the sidelobe level of the antenna, while it had little influence to the antenna gain. By comparison on results of the different scales error, the main influencing parameter of error was found out, which can provide the theoretical foundation for the control of the antenna surface working.
The oxygen and hydrogen isotope compositions of different gneisses associated with eclogites at Shuanghe in the Dabie Mountains
Fu Bin,Zheng Yong-Fei
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891429
Experimental studies of oxygen and hydrogen isotope fractionations between brucite and water at low temperatures
Baolong Xu,Yong-Fei Zheng
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891637
ENSO ensemble prediction: Initial error perturbations vs. model error perturbations
Fei Zheng,Hui Wang,Jiang Zhu
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0179-2
Abstract: Based on our developed ENSO (El Ni o-Southern Oscillation) ensemble prediction system (EPS), the impacts of stochastic initial-error and model-error perturbations on ENSO ensemble predictions are examined and discussed by performing four sets of 14-a retrospective forecast experiments in both a deterministic and probabilistic sense. These forecast schemes are differentiated by whether they considered the initial or model stochastic perturbations. The comparison results suggest that the stochastic model-error perturbations, which are added into the modeled physical fields to mainly represent the uncertainties of the physical model, have significant, positive impacts on improving the ensemble prediction skills during the entire 12-month forecast process. However, the stochastic initial-error perturbations have relatively small impacts on the ensemble prediction system, and its impacts are mainly focusing on the first 3-month predictions.
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