共查询到20条相似文献，搜索用时 31 毫秒
1.
Aneta Rozmarynowska 《Acta Geophysica》2009,57(2):311-329
Two methods of reconstruction of Ito equations on the basis of time series were analysed. The Sequin method appeared to be
completely inadequate in cases of considerable noise. The histogram method required some improvements; therefore, the procedure
of smoothing of joint distribution function was proposed and verified.
Ito equations may constitute some macroscopic models of phenomena in which microscopic interactions are averaged in an adequate
way. Analysis of two geophysical phenomena is presented. For these two examples, Ito equations are constructed and some physical
causes of resulting forms of the deterministic and stochastic force are deduced. 相似文献
2.
Corentin Faucher Antoine Saucier Denis Marcotte 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):253-273
We present a new stochastic simulation method that builds two-dimensional images by assembling together square image pieces called blocks. The blocks are taken from a reference image. Our method, called patchwork simulation method (PSM), enforces pattern continuity in the image. Moreover, PSM allows to control the image local-mean histogram. This histogram bin-frequencies can be set to user-defined target values that may differ from the reference image local-mean histogram. This flexibility enhances the PSM generality by enlarging the set of all possible simulations. The local-mean histogram control is achieved by adjusting suitably the transition probabilities that associate a new block to an existing neighborhood in the partly simulated image. For several types of synthetic images and one polymer blend image, we show that PSM reproduces faithfully the reference image visual appearance (i.e. patterns are correctly shaped) and that simulated images are statistically compatible with the target local-mean histogram. Moreover, we show that our method has the ability to produce simulations that respect conditional hard data as well as a target local-mean histogram. 相似文献
3.
使用高密度电法和电测深法,对内蒙古宝昌地震台地电阻率场地进行实地测量,获得该场地电性结构特征参数,判定该台地电测区结构属于KH型,并结合钻孔柱状图,获得该台地下介质水平层状电性结构模型,发现地层厚度呈不均匀分布,总体较为连续、完整,可为今后该台地电阻率异常提取、异常识别及观测精度提高等提供基础数据。 相似文献
4.
CT图像增强方法的研究 总被引：3，自引：1，他引：2
利用直方图均衡、中值滤波和小波变换对CT图像(512×512)增强处理的方法进行了研究,实验结果表明,小波变换增强方法可以减少噪声的放大,在增强图像微小细节和避免放大噪声两方面获得令人满意的结果,其处理结果优于直方图均衡和中值滤波的增强方法. 相似文献
5.
基于局部直方图规定化的相干体增强 总被引：2，自引：1，他引：1
Coherence analysis is a powerful tool in seismic interpretation for imaging geological discontinuities such as faults and
fractures. However, subtle faults or fractures of one stratum are difficult to be distinguished on coherence sections (time
slices or profiles) due to interferences from adjacent strata, especially these with strong reflectivity. In this paper, we
propose a coherence enhancement method which applies local histogram specification (LHS) techniques to enhance subtle faults
or fractures in the coherence cubes. Unlike the traditional histogram specification (HS) algorithm, our method processes 3D
coherence data without discretization. This method partitions a coherence cube into many sub-blocks and self-adaptively specifies
the target distribution in each block based on the whole distribution of the coherence cube. Furthermore, the neighboring
blocks are partially overlapped to reduce the edge effect. Applications to real datasets show that the new method enhances
the details of subtle faults and fractures noticeably. 相似文献
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根据材料内部真实结构建立数值计算模型是岩土力学研究的一个热点。本文针对不同材料内部结构特征,介绍了等效图形法与边缘矢量化两种建模方法,并以自制孔隙岩土材料和混凝土的CT图像为例,说明了两种建模步骤。分析表明:当图像的灰度直方图具有明显双峰或多峰结构时,特征区域易分割;而当灰度直方图为单峰结构时,可以通过数学形态学的top-hat方法进行图像增强,以方便特征区域的提取。对于孔隙结构,可以利用等效圆或等效椭圆表征,建立相应的数值模型;而当内部结构复杂时,可利用特征边缘矢量化方法进行建模。本研究为如何建立反映岩土材料内部真实结构数值模型提供了方法。 相似文献
9.
微米X射线计算机断层扫描作为一种数字岩心探测手段,被广泛应用于研究含天然气水合物沉积物赋存形态,但由于水合物与水对X射线的衰减系数相近,二者在CT图像中灰度区间存在交集,导致在从CT图像上对水合物与水进行分割时存在强非唯一性。为提高对CT图像中水合物与水阈值分割的准确性,本文通过分析天然气水合物生长过程中不同时刻CT图像直方图特征,提出归一化CT图像及其直方图的方法。首先选定甲烷气与石英砂的峰值灰度基准;然后用高斯函数分别对当前CT图像直方图中的甲烷气与石英砂曲线进行拟合,得到当前CT图像直方图中的甲烷气与石英砂峰值灰度;再将当前CT图像直方图中的甲烷气峰值灰度与石英砂峰值灰度归一化到选定的峰值灰度基准;进而用归一化的直方图对CT图像进行归一化;最后根据归一化灰度直方图的变化趋势,定量统计得到CT图像中水合物增加和气-水减少的灰度区间,完成图像中不同组分的阈值划分。实验结果表明,提出的阈值分割方法能够为天然气水合物CT图像中水合物与水边界的确定和水合物饱和度计算提供定量的依据,具有实际的工程应用价值。 相似文献
10.
Application of a deterministic geometric approach for the simulation of highly intermittent hydrologic data is presented. Specifically, adaptations of the fractal-multifractal (FM) method and a Cantorian extension are advanced in order to simulate rainfall records measured at the daily scale and encompassing a water year. It is shown, using as case studies 2 years of rainfall sets gathered in Laikakota, Bolivia and Tinkham, Washington, USA, that the FM approach, relying on only at most 8 parameters, is capable of closely preserving either the whole record’s histogram (therefore including moments), the whole data’s Rényi entropy function and/or the maximum number of consecutive zero values present in the sets, resulting in suitable rainfall simulations, whose overall features and textures are similar to those of the observed sets. The study hence establishes the possibility of simulating highly intermittent sets in time in a deterministic and holistic way as a novel parsimonious methodology to supplement available stochastic frameworks. 相似文献
11.
Corentin Faucher Antoine Saucier Denis Marcotte 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(8):2027-2050
This paper presents a new stochastic simulation method that improves on our unilateral patchwork simulation method (Faucher et al., Stoch Environ Res Risk Assess, 27:253–273, 2012) by eliminating anisotropy biases. As in our unilateral method, images are built by assembling patterns together while controlling the local-mean histogram. The patterns, which are square image-pieces, are picked in a reference image. The reference image is used as a data bank holding the statistical informations about the random field to simulate. In contrast with the unilateral method, the path followed by our new simulation is random and guided by local errors. The new method, called corrective pattern-matching simulation, proceeds iteratively by making local corrections to the simulated image. For several types of images, it is shown that our simulations respect conditioning data and reproduce faithfully the reference image visual appearance. It is shown that the control of the local-mean histogram allows to control one-point statistics and multi-point statistics. 相似文献
12.
本研究发展了结构地震反应性态的随机最优控制理论和方法。这一研究建立在物理随机系统思想的新理论框架下,突破了以I^to随机微分方程描述动力系统的经典随机最优控制的藩篱。提出了基于系统二阶统计量评价、单目标超越概率和多目标能量均衡的控制器参数设计准则,以及基于概率可控指标的控制器位置设计准则,并将它们统一为物理随机最优控制的广义最优控制律。数值算例分析表明,本文发展的物理随机最优控制方法能够实现结构地震反应性态的精细化控制。 相似文献
13.
基于小波分析的CT图像噪声类型识别 总被引：1，自引：0，他引：1
对CT图像噪声的类型进行识别,采用相适应的去噪方法提高图像去噪效果,减少去噪中的盲目性.分析小波高频子带系数的能量分布,利用直方图的信噪比和曲线拟合图的积分,对CT图像中最常见的两类噪声,即高斯噪声和椒盐噪声进行识别.直方图的信噪比R为0.2,曲线拟合图积分A为60,可作为高斯噪声和椒盐噪声分界线.对大量含噪CT图像的... 相似文献
14.
Dion Weatherley 《Pure and Applied Geophysics》2006,163(9):1933-1947
The recurrence interval statistics for regional seismicity follows a universal distribution function, independent of the tectonic
setting or average rate of activity (Corral, 2004). The universal function is a modified gamma distribution with power-law
scaling of recurrence intervals shorter than the average rate of activity and exponential decay for larger intervals. We employ
the method of Corral (2004) to examine the recurrence statistics of a range of cellular automaton earthquake models. The majority
of models has an exponential distribution of recurrence intervals, the same as that of a Poisson process. One model, the Olami-Feder-Christensen
automaton, has recurrence statistics consistent with regional seismicity for a certain range of the conservation parameter
of that model. For conservation parameters in this range, the event size statistics are also consistent with regional seismicity.
Models whose dynamics are dominated by characteristic earthquakes do not appear to display universality of recurrence statistics. 相似文献
15.
目的:探索直肠癌Mile’s术后局部复发与术后瘢痕CT灌注定量参数的优化测量方法。方法:连续入组因症状或复查怀疑直肠癌局部复发的直肠癌Mile’s术后患者10例,所有患者均行病变区CT灌注成像（对比剂70mL,延迟10s,扫描周期1s,扫描时间60s）,CT灌注后处理工作站进行不同方式感兴趣区（ROI）勾画,包括:固定面积ROI（24mm2）、热点（单体素）、热区（24mm2）及肿块整体。分别获得各自血流量（BF）,血容量（BV）,平均通过时间（MTT）,表面通透性（PS）及相应灌注图。通过工作站横断面直方图分析软件,分别获得各定量灌注参数最高5％、10％、20％、40％和60％平均值。相隔两周,对以上参数进行二次测量。CT灌注扫描后一周内对所有病灶进行CT引导下穿刺活检,并长期随访证实病灶性质。SPSS软件对不同测量方法测量值行单因素方差分析,对前后两次测量结果进行配对样本t检验。结果:10例患者,共11个病灶（复发组6个,瘢痕组5个）。不同测量方法的测量值差异大,肿块整体测量值最低,最高5％平均值最高。除固定ROI测量MTT、热点测量MTT和PS在复发组和瘢痕组的差异无统计学意义（P均>0.05）外,复发组的其余各测量方法的各灌注参数均高于对照组（P均<0.05）;除热区测量PS外（P<0.05）,其他方法前后两次测量值差异均无统计学意义（P均>0.05）。其中以肿块整体测量值及各项直方图最高百分比平均值稳定性最高（r≥0.960,P均<0.05）。结论:相较传统测量方法,利用横断面直方图分析软件获得最高百分数平均值对直肠癌术后骶前肿块灌注定量参数进行测量对直肠癌术后复发和瘢痕的鉴别更为客观、稳定,其中推荐使用最高5％平均值。 相似文献
16.
RESEARCH ON THE RELATIONSHIP BETWEEN FRACTAL FACTORS AND TECTONIC ACTIVITY——A CASE STUDY OF SOUTHWESTERN YUNNAN BLOCK 
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下载免费PDF全文 Geomorphology could record long-term accumulation of tectonic movement and quantify it by relevant parameters.But because the influences of other factors such as climate and lithology,how to use the relevant parameters to reveal the relationship between geomorphology and tectonics is a research hot spot.In this paper,we utilize the variogram method and the cellular fractal model to estimate parameters such as the fractal dimension (D) and ordinate intercept (γ) from the SRTM3 DEM using a moving window operation.We compare the distribution characteristics of the parameters in different climate and lithology.The results indicate that the correlation between the parameters and lithology or climate is very poor.The fractal dimension (D) reveals a very good correlation with tectonics,which is low in tectonically inactive areas and high in active areas.It implies that fractal dimension (D) may be a new method for research of regional tectonic movement. 相似文献
17.
基于VTK的医学图像系统研究 总被引：6，自引：0，他引：6
医学三维数据场可视化是当前科学计算可视化应用的重点。本文论述了可视化工具包VisualizationToolkit(VTK)的主要特点,介绍了三维医学可视化系统实现的原理和方法。根据一系列人体断面图像,应用VTK实现了三维医学图像重构,对重构后的三维图像进行解剖分析;并实现对人体的二维图像逐帧浏览及柱状统计。实验结果表明,VTK具有使用灵活,功能强大的优点,是医学三维数据场可视化的有力工具。 相似文献
18.
Histogram and variogram inference in the multigaussian model 总被引：1，自引：4，他引：1
Xavier Emery Julián M. Ortiz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(1):48-58
Several iterative algorithms are proposed to improve the histogram and variogram inference in the framework of the multigaussian model. The starting point is the variogram obtained after a traditional normal score transform. The subsequent step consists in simulating many sets of gaussian values with this variogram at the data locations, so that the ranking of the original values is honored. The expected gaussian transformation and the expected variogram are computed by an averaging operation over the simulated datasets. The variogram model is then updated and the procedure is repeated until convergence. Such an iterative algorithm can adapt to the case of tied data and despike the histogram. Two additional issues are also examined, referred to the modeling of the empirical transformation function and to the optimal pair weighting when computing the sample variogram. 相似文献
19.
《Journal of Atmospheric and Solar》2008,70(1):89-100
Sodars are useful devices in atmospheric research beyond the first tenths of metres, the management of their observations proving equally important as the data itself. In this paper, a 3-year database of wind direction and speed was used, although in this case both variables have been transformed. The lowest measurement level was considered as a reference and differences in wind direction, ratios in wind speed and the power law exponent were calculated up to the 500 m level. First, the Ekman spiral was considered in order to fix its range as well as daily and seasonal evolutions. Diurnal cycles were then determined to establish the sharp contrast between day and night, and the difference in transitions in morning and afternoon. Histograms of wind direction differences, ratios in wind speed and the power law exponent were also calculated. Their shape was similar, evidencing only one mode with a rapid decrease from it, though the histogram was right skewed for transformed wind speed whereas it was symmetrical for the other two variables. These histograms were fitted by an original three-parameter distribution function using simple linear regressions, considering the least root mean square error as fitting criterion. The cumulative distribution function was also theoretically obtained. A close-up expression for the interquartile range as a function of the distribution function parameters was proposed with satisfactory results. Robust kurtosis behaviour was also observed. A bivariate distribution was calculated and satisfactorily contrasted with experimental values. Finally, the influence of wind speed on the distribution parameters was considered. 相似文献
20.
《Advances in water resources》1999,22(6):577-584
A method is proposed to determine the phase-volume fractions in tomographic representations of two-phase systems. The method is applicable in cases where no independent mean values for the phase-characteristic property (α) are available, such as in standard X-ray computed tomography (CT) using a polychromatic source. The proposed procedure is based on fitting a sum of three parametric expressions to the histogram of α-values. The terms include two normal probability-density functions to account for noisy pure-phase values, and an analytical expression to account for intermediate values due to interface-containing voxels and blurring. To test the method, it was applied to several X-ray CT data sets of two-phase systems with known volume fractions and varying α-ranges, including a system with only about one standard deviation difference between the mean phase α-values, i.e., with substantial overlap between the noisy pure-phase distributions. The accuracy for the considered cases was found to be approximately 2 vol% or better. As an example, the proposed fitting procedure was used to determine the representative elementary volume needed for porosity estimation of a porous medium consisting of 0.5-mm glass beads. 相似文献