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971.
针对GPS接收机在跟踪过程中由频率误差引起的位同步概率下降问题,提出了一种基于频率补偿的GPS位同步方法.分析了环路中频率误差引起相干积分累加值衰减的机理,利用不同频率的复信号分别对相干积分结果进行补偿,计算出20个候选位置的值,最大值对应的位置即为数据边界位置.该方法有效减少了由频率误差导致的相干累加损耗,提高了位同步的概率.在弱信号情况下,使用非相干积分方法可进一步提高信号增益和位同步概率.与其他位同步方法相比,所提方法可容忍更大的频率误差,即使跟踪环路处于失锁状态也能准确实现位同步,且在频率误差小于25 Hz的情况下表现出更优的位同步性能. 相似文献
972.
973.
Critical Systems Thinking on the Inefficiency in Post-Earthquake Relief: A Practice in Longmen Shan Fault Area 总被引:1,自引:1,他引:0
Jiuping Xu Jiuzhou Dai Renqiao Rao Huaidong Xie Yi Lu 《Systemic Practice and Action Research》2016,29(5):425-448
The Longmen Shan Fault area is one of the most active seismic zones in the world, has a relatively dense population and a low economic development level. Therefore, the provision of effective post-earthquake relief is very important for saving lives and restricting financial losses. However, providing urgent relief is a complex problem that requires efficient coordination between the organizations, and departments involved, and the specific environments, for the supply of urgent materials, energy and information. In practice, although there are sufficient relief supplies, because of the lack of systemic thinking, relief activities are often chaotic leading to inefficiencies and even increases in the damage and loss of life. In this study, a critical systems thinking approach is used to reflect on the system contexts, boundaries, structures and functions of the emergency relief systems. Using systems modeling we constructed simulations for different relief plans and their consequences, and a work shop of metasynthetic engineering was constructed to integrate the different views, knowledge and contexts. At the practical stage, after the model’s validity was verified from the 2008 Wenchuan earthquake data, based on the 2013 Lushan earthquake simulation results, some recommendations are made to improve future post-disaster relief operations. Finally, the significance of critical systems thinking is demonstrated to ensure effective and efficient of post-earthquake relief. Some limitations and future research also have been presented in conclusion. 相似文献
974.
王昌龄是唐代著名的边塞诗人,他对当时边塞战争的认识经历了一个不断深化的过程,从他的边塞诗中,我们可以清楚地看到其对当时边塞战争的态度。青年时代漫游边关,慷慨激昂,热情讴歌、积极支持保卫边关的战争;深入了解边塞和戍边士卒的现实情况后,他开始厌倦没完没了的开边战争;随着人生阅历的增加,他对边塞战争给人民带来的苦难有了更深的认识,到晚年他更是明确反对穷兵黩武的开边、扩边战争。 相似文献
975.
976.
Recurrent event data frequently occur in many longitudinal studies, and the observation on recurrent events could be stopped by a terminal event such as death. This paper considers joint modeling and analysis of recurrent event and terminal event data through a common subject-specific frailty, in which the proportional intensity model is used for modeling the recurrent event process and the additive hazards model is used for modeling the terminal event time. Estimating equation approaches are developed for parameter estimation and asymptotic properties of the resulting estimators are established. In addition, some procedures are presented for model checking. The finite sample behavior of the proposed estimators is evaluated through simulation studies, and an application to a heart failure study is provided. 相似文献
977.
戴建国 《湖南文理学院学报(自然科学版)》2017,29(2)
为构造最佳对数线性模型,通过λ系数构造λ相关系数矩阵,将其作为对数线性模型中交互项选择的方法,并用于分析肺癌治疗数据。结果表明,选出的交互项可以构造最佳的模型对数据进行准确的分析,因此在应用对数线性模型分析前,先用相关系数矩阵进行探索性研究分析是很有必要的。 相似文献
978.
Nitrogen and sulfur doped titanium dioxide photocatalysts were prepared by the sol-gel method. The products were characterized
by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-visible diffuse reflectance spectra (DRS). Photocatalytic
activities of the samples were investigated on the degradation of methyl orange (MO). The effect of the dopants on the electronic
structure of TiO2 was studied by the first-principles calculations based on the density functional theory (DFT). The orbital hybridization
resulted in energy gap narrowing and electronic delocalization in the crystal of doped TiO2. Mobile electrons of varied energetic states could offer enhanced electron transfer, together with optical absorption improvement.
The results show that the doping elements of N and S play a cooperative role in the modification of electronic structure,
which enhances the photocatalytic performance. The experimentally observed absorption edges of N-doped TiO2, S-doped TiO2, and N, S-codoped TiO2 are 420, 413, and 429 nm, respectively, which can be explained by the theoretical calculation results. 相似文献
979.
设计并实现了一个高扩展性、高可用性的数据网格系统RFGrid来处理海量的铁路货运数据.RFGrid提出一个虚拟化数据模型,集成全国各个铁路局所有的数据,提供全局统一的数据视图,支持灵活高效的构件化业务开发模式.RFGrid采用分布处理的模式,将任务分解到各个路局并行执行,所有处理细节对用户透明,降低了分布式数据处理的复杂性,提高了资源利用率.最后,利用真实的货运生产应用作为负载进行性能分析,结果显示RFGrid能显著提升货运数据处理的性能,提高了货运分析的效率,对提高运输组织水平有重要意义. 相似文献
980.
Reactive ion etching was used to etch barium strontium titanate thin films in a CHF3/Ar plasma.BST surfaces before and after etching were analyzed by X-ray photoelectron spectroscopy to investigate the reaction ion etching mechanism,and chemical reactions had occurred between the F plasma and the Ba,Sr and Ti metal species.Fluorides of these metals were formed and remained on the surface during the etching process.Ti was almost completely removed because the TiF4 by-product is volatile.Minor quantities of Ti?F could still be detected by narrow scan X-ray photoelectron spectra,and Ti?F was thought to be present in the form of a metal-oxy-fluoride.These species were investigated from O1s spectra,and a fluoride-rich surface was formed during etching.BaF2 and SrF2 residues were difficult to remove because of their high boiling point.The etching rate was limited to 12.86 nm/min.C?F polymers were not found on the surface,indicating that the removal of BaF2 and SrF2 was important for further etching.A 1-min Ar/15 plasma physical sputtering was carried out for every 4 min of surface etching,which effectively removed remaining surface residue.Sequential chemical reaction and sputtered etching is an effective etching method for barium strontium titanate films. 相似文献