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41.
42.
海杂波微弱目标分形检测 总被引:1,自引:1,他引:0
The target on the sea surface is complex and difficult to detect due to the interference of backscattered returns from the sea surface illuminated by the radar pulse. Detrended fluctuation analysis (DFA) has been used successfully to extract the time-domain Hurst exponent of sea-clutter series. Since the frequency of the sea clutter mainly concentrates around Doppler center so that we consider to extract frequency-do- main fractal characterization and then detect a weak target within sea clutter by using the difference of frequency-domain fractal characterization. The generalized detrended fluctuation analysis (GDFA) is more flexible than traditional DFA owing to its smoothing action for the clutters. In this paper, we apply the GDFA to evaluate the generalized Hurst exponent of sea-clutter series in the frequency domain. The difference of generalized Hurst exponents between different sea-clutter range bins would be used to determine whether the target exists. Moreover, some simulations with the real IPIX radar data have also been demonstrated in order to suooort this conclusion. 相似文献
43.
井中磁测仪器距离场源近,磁测资料受到钻孔打穿磁性体产生的内磁场影响,往往存在强干扰压制有用信号,因此研究井中磁测资料预处理与弱信号识别方法具有重要意义。笔者将地面重磁资料边界识别中倾斜角总水平导数和解析信号振幅方法改进后应用于井中磁测资料预处理中,提出倾斜角垂向导数和均值归一解析信号振幅方法。通过模型分析证明了两种方法都可识别强弱不同的井旁磁性体位置,反映边界信息,且给出了计算均值归一解析信号振幅过程中窗口选择的依据。将两种方法应用于江苏某工区ZK002孔磁测资料预处理中,得出倾斜角垂向导数方法应用于实测资料中会放大干扰,而均值归一解析信号振幅方法增强了该钻孔弱异常信息,且压制了干扰信号,处理结果与磁化率测井和钻孔资料相对应。 相似文献
44.
Abstract Starting from the nonlinear shallow water equations of a homogeneous rotating fluid we derive the equation describing the evolution of vorticity by a fluctuating bottom topography of small amplitude, using a multiple scale expansion in a small parameter, which is the topographic length scale relative to the tidal wave length. The exact response functions of residual vorticity for a sinusoidal bottom topography are compared with those obtained by a primitive perturbation series and by harmonic truncation, showing the former to be invalid for small topographic length scales and the latter to be only a fair approximation for vorticity produced by planetary vortex stretching. In deriving the exact shape of the horizontal residual velocity profile at a step-like break in the bottom topography, it is shown that the Lagrangian profile only exists in a strip having the width of the amplitude of the tidal excursion at both sides of the break, and that it vanishes outside that interval. Moreover, in the limit of small amplitude topography at least, it vanishes altogether for the generation mechanism by means of planetary vortex stretching. The Eulerian profile is shown to extend over twice the interval of the Lagrangian profile both for production by vortex stretching and by differential bottom friction. These finite intervals over which the residual velocity profiles exist for a step-like topography are not reproduced by harmonic truncation of the basic equation. This method gives exponentially decaying profiles, indicating spurious horizontal diffusion of vorticity. In terms of orders of magnitude, the method of harmonic truncation is reliable for residual velocity produced by vortex stretching but it overestimates the residual velocity produced by differential bottom friction by a factor 2. 相似文献
45.
论弱势群体的法律保护 总被引:3,自引:0,他引:3
毛晓华 《广东海洋大学学报》2005,25(2):20-23
弱势群体是社会分层的结果,对其进行保护是法律追求正义与秩序的必然要求,具体途径为通过法律再分配社会性资源,缩小强弱差距,保护弱势群体的正当权益。完善我国的弱势群体法律保护制度,须遵循“一个协调,两个结合”的指导原则,即效率与公平相协调,长远措施与短期措施相结合,全面保护与重点保护相结合。 相似文献
46.
投弃式海流电场剖面仪(XCP)是利用海流切割地磁场产生感生电场的原理进行快速测量海流的观测仪器,在地磁场稳定的情况下,感生电场的大小主要取决于海流的速度。因此,通过测量海流产生的感生电场便可以研究海流的运动特征。本文研制了用于XCP中的模拟电路,实现了对XCP中电极信号、罗盘线圈信号及温度信号的采集预处理。所设计模拟电路主要实现以下功能:(1)通过INA128放大电路实现对电极信号与罗盘线圈信号的多级放大处理;(2)考虑到电极信号与罗盘线圈信号均为频率16 Hz左右的信号,在电路中加入中心频率点为16 Hz的二阶带通滤波电路以提取有效信号;(3)进行硬件电路补偿,在一定程度上克服XCP探头下沉引起感生电场的强干扰。实验测试结果表明,所设计模拟电路稳定可靠,可以实现滤除噪声,提取前端微弱信号并进行多级放大,满足实际应用需求。 相似文献
47.
岩土颗粒材料在达到Mohr-Coulomb塑性极限之前可能已经发生了没有明显局部损伤的全域准均匀破坏,即分散性失稳。近年来,网络科学工具在颗粒材料环境中的应用为研究其失稳破坏现象提供了有趣新颖的洞见。采用离散单元法对不同初始密实度的颗粒体系进行等体积应变加载路径的数值试验,发现初始状态越松散的颗粒体系越有可能发生分散性失稳;采用网络科学的理论和方法分析颗粒接触网络的拓扑结构特性和演化规律,发现颗粒材料分散性失稳的结构根源是颗粒接触网络完全崩塌。将颗粒体系划分为强、弱接触系统以构建强接触子网络、弱接触子网络和强−弱接触子网络,研究颗粒接触网络及其3个子网络的特征量演化,结果表明:当颗粒材料开始处于不稳定状态时,易受扰动的弱接触系统的部分接触先失效,导致强接触系统失去其稳定支撑作用而降低承载能力。随着加载的继续,系统通过非局部的自组织过程导致接触结构的全面崩塌,最终触发整体分散性失稳。因此,先于整体失稳的部分弱接触的失效,可视为颗粒材料分散性失稳的关键性临界征兆。 相似文献
48.
双口山荒漠、戈壁景观区位于我国柴北缘重要成矿带上。该景观区1∶5万水系沉积物测量发现"HS-9-4"综合异常弱小、零散、峰值低;元素空间套合性差,无规律性;多元素仅有1级异常分带。根据其本身自然地理景观,经"衬度异常法"与常规方法对比,发现"HS-9-4"弱小异常值得重视,对该异常开展了查证工作,最终在异常区发现了多处与金相关的矿(化)体及线索,为下一步地质工作提供了可靠依据。 相似文献
49.
Quasi-shear wave coupling in weakly anisotropic 3-D media 总被引:2,自引:0,他引:2
50.
The E24 profile slope analyzed belongs to a series of excavated slopes of the Haizhou Opencast Coal Mine. It seems to be divided into Downslope Part and Upslope Part. Its profile comprises two noticeable coal seams, called the 8# and 9# weak layers, considered as the potential failure surfaces. In consideration of the actual configuration as in the perspective of any modification, assessing the stability of this slope with various profile forms under given conditions, and assessing the risk of instability and quantifying the influence of earthworks or other modifications to the stability of this slope, have constituted the primordial objectives carried out. From assumed potential failure surfaces, any specific profiles and specified slip surfaces are defined. A factor of safety (FoS) is computed for each specified slip surface; the smallest FoS found corresponds to the least favorable slip surface. The safety factor values obtained are compared to the suggested safety factor. Limit equilibrium methods of vertical slices implemented in Slope/W, computer program for slope stability analyses, have been adopted to perform the E24 slope stability analysis. The safety factor values computed with 9# weak layer are lower than for 8#; the factors of safety obtained with Sarma's method are the smallest; more, without groundwater (long term) overall values are greater than those determined under groundwater condition (short term). The lowest safety factor value is found for a profile depending on an adopted earthwork sequence. The E24 profile slope stability analysis shows the instability risk for the deepest weak layer, and also shows the short and long term stability of this slope for the envisaged earth movements. However it demonstrates the existence of instability risk for any earthwork firstly affecting the downslope part. 相似文献