基于尺度空间的分层聚类方法及其在遥感影像分类中的应用   总被引：22，自引：3，他引：19  

骆剑承  梁怡  周成虎 《测绘学报》1999,28(4):319-324

基于尺度空间的分层聚类方法（ＳＳＨＣ）是一种以热力学非线性动力机制为理论基础的新型聚类算法,是视觉松驰化过程的模拟。与传统基于统计方法的聚类算法相比较,ＳＳＨＣ具有样本空间可服从自由分布、通过规则可获取最优聚类中心点及类别、可在聚类过程中融合后验知识等优点。本文从聚类和热力学运动机制和视觉模拟过程出发,对ＳＳＨＣ聚类算法进行综合分析,并对如何生成聚类树的过程进行详细描述邮通过融合点的部分自由能进行  相似文献   

Statistical framework for scale-up of dispersivity in multi-scale heterogeneous media     

Vikrant Vishal  Juliana Y. Leung 《Environmental Earth Sciences》2017,76(17):624

A hierarchical scale-up framework is formulated to study the scaling characteristics of reservoir attributes and input dispersivities at the transport modeling scale, where heterogeneity distribution exhibits both non-stationarity (trend) and sub-scale variability. The proposed method is flexible to handle heterogeneities occurring at multiple scales, without any explicit assumption regarding the multivariate distribution of the heterogeneity. This paper extends our previous work by incorporating the effects of non-stationarity into the modeling workflow. Rock property at a given location is modeled as a random variable, which is decomposed into the sum of a trend (available on the same resolution of the transport modeling scale) and a residual component (defined at a much smaller scale). First, to scale up the residual component to the transport modeling scale, the corresponding volume variance is computed; by sampling numerous sets of “conditioning data” via bootstrapping and constructing multiple realizations of the residual components at the transport modeling, uncertainty due to this scale-up process is captured. Next, to compute the input dispersivity at the transport modeling scale, a flow-based technique is adopted: multiple geostatistical realizations of the same physical size as the transport modeling scale are generated to describe the spatial heterogeneity below the modeling scale. Each realization is subjected to particle-tracking simulation. Effective longitudinal and transverse dispersivities are estimated by minimizing the difference in effluent history for each realization and that of an equivalent average medium. Probability distributions of effective dispersivities are established by aggregating results from all realizations. The results demonstrate that both large-scale non-stationarity and sub-scale variability are both contributing to anomalous non-Fickian behavior. In comparison with our previous work, which ignored large-scale non-stationarity, the non-Fickian characteristics observed in this study is dramatically more pronounced.  相似文献   

Acute hypoxic exposure affects gamete quality and subsequent fertilization success and embryonic development in a serpulid polychaete     

P.K.S. Shin  J.Y.S. Leung  J.W. Qiu  P.O. Ang  J.M.Y. Chiu  V. Thiyagarajan  S.G. Cheung 《Marine pollution bulletin》2014

Hypoxia likely compromises the reproductive success of those marine organisms carrying out external fertilization because their gametes and embryos are inevitably exposed to the external environment. Hydroides elegans, a dominant serpulid polychaete in Hong Kong waters, can spawn throughout the year but the number of recruits drops during summer when hypoxia commonly occurs. This study attempted to explain such observation by investigating the gamete quality, including sperm motility, egg size, complexity and viability, after 1-h hypoxic exposure (1 mg O₂ l⁻¹). In addition, how gamete quality affects fertilization success and embryonic development was examined. After 1-h hypoxic exposure, sperm motility was significantly reduced, compromising fertilization success. Although the eggs remained viable, more malformed embryos and retarded embryonic development were observed. We interpreted that the harmful effect of hypoxia on embryonic development was attributed to the teratogenicity and induced oxidative stress, ultimately causing the reduction in recruitment during summer.  相似文献   

Modelling the IDV Emissions of the BL Lac Objects with a Langevin Type Stochastic Differential Equation     

C. S. Leung  J. Y. Wei  T. Harko  Z. Kovacs 《Journal of Astrophysics and Astronomy》2011,32(1-2):189-192

In this paper, we introduce a simplified model for explaining the observations of optical intra-day variability (IDV) of the BL Lac Objects. We assume that the source of the IDV are the stochastic oscillations of an accretion disk around a supermassive black hole. The stochastic fluctuations on the vertical direction of the accretion disk are described by using a Langevin type equation with a damping term and a random, white noise type force. Furthermore, preliminary numerical simulation results are presented, which are based on the numerical analysis of the Langevin stochastic differential equation.  相似文献   

Fragility analysis of low‐rise masonry in‐filled reinforced concrete buildings by a coefficient‐based spectral acceleration method     

Chien‐Liang Lee  Ray Kai Leung Su 《地震工程与结构动力学》2012,41(4):697-713

This study presents a seismic fragility analysis of low‐rise masonry in‐filled (MI) reinforced concrete (RC) buildings using a proposed coefficient‐based spectral acceleration method. The coefficient‐based method, without requiring any complicated finite element analysis, is a simplified procedure for assessing the spectral acceleration demand (or capacity) of buildings subjected to earthquakes. This paper begins with a calibration of the proposed coefficient‐based method for low‐rise MI RC buildings using published experimental results obtained from shaking table tests. Spectral acceleration‐based fragility curves for low‐rise MI RC buildings under various inter‐story drift limits are then constructed using the calibrated coefficient‐based method. A comparison of the experimental and estimated results indicates that the simplified coefficient‐based method can provide good approximations of the spectral accelerations at peak loads of low‐rise MI RC buildings, if a proper set of drift‐related factors and initial fundamental periods of structures are used. Moreover, the fragility curves constructed using the coefficient‐based method can provide a satisfactory vulnerability evaluation for low‐rise MI RC buildings under a given performance level. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Distribution and source apportionments of polychlorinated biphenyls (PCBs) in mariculture sediments from the Pearl River Delta, South China   总被引：1，自引：0，他引：1  

Wang HS  Du J  Leung HM  Leung AO  Liang P  Giesy JP  Wong CK  Wong MH 《Marine pollution bulletin》2011,63(5-12):516-522

Surface and core sediments collected from six mariculture farms in the Pearl River Delta (PRD) were analyzed to evaluate contamination levels of polychlorinated biphenyls (PCBs). The ∑PCBs (37 congeners) concentrations ranged from 5.10 to 11.0 ng g(-1) (mean 7.96 ng g(-1)) in surface and 3.19 to 22.1 ng g(-1) (mean 7.75 ng g(-1)) in core sediments, respectively. The concentrations were significantly higher than that measured in the sediments of their corresponding reference sites, whereby the average enrichment percentages were 62.0% and 42.7% in surface and core sediments, respectively. Significant correlations (R2=0.77, p<0.05) of PCB homologue group proportions between fish feeds and surface mariculture sediments suggested that fish feed input was probably the main source for the enrichment of PCBs. Due to the fact that PCBs could be transferred along food chains, PCB contamination in fish feeds and mariculture sediments should not be overlooked.  相似文献   

Assessment of risk of PCDD/Fs and dioxin-like PCBs in marine and freshwater fish in Pearl River Delta, China     

Wei X  Leung KS  Wong MH  Giesy J  Cai ZW  Wong CK 《Marine pollution bulletin》2011,63(5-12):166-171

Fish consumption is known to be beneficial to human health. However since the age of industrialization, the released/disposed chemical pollutants into water systems make fish a source of various environmental toxicants to humans. In oceanic cities with heavy industrial activities, fish products contribute the greatest proportion of exposure to pollutants. In this study, risks and potential effects of dioxins to health of coastal populations in the Pearl River Delta were assessed. Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs) were measured in common fish species purchased at local markets. Concentrations of total dioxins in fish ranged from 0.481 to 9.05 pg TEQ/g wet weight were similar to the lesser concentrations reported for fish from other countries. The greatest concentrations of dioxins were measured in mandarin fish, a carnivorous freshwater fish. Exposure of murine primary leydig and ovarian cells to 2,3,7,8-tetrachlorinated dibenzo-p-dioxins (2,3,7,8-TCDD) reduced the synthesis of progesterone, testosterone and/or estrogen. The reductions were probably via inhibitory effects on the expression of the steroidogenic enzymes, steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc). Based on these reproductive parameters, the concentrations of dioxins and dioxin-like residues represent a moderate health risk due to consumption of fish.  相似文献   

Toxicities of antifouling biocide Irgarol 1051 and its major degraded product to marine primary producers     

Zhang AQ  Leung KM  Kwok KW  Bao VW  Lam MH 《Marine pollution bulletin》2008,57(6-12):575-586

Irgarol 1051 (2-methythiol-4-tert-butylamino-6-cyclopropylamino-s-triazine) is an algaecide commonly used in antifouling paints. It undergoes photodegradation which yields M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) as its major and most stable degradant. Elevated levels of both Irgarol and M1 have been detected in coastal waters worldwide; however, ecotoxicity effects of M1 to various marine autotrophs such as cyanobacteria are still largely unknown. This study firstly examined and compared the 96 h toxicities of Irgarol and M1 to the cyanobacterium Chroococcus minor and two marine diatom species, Skeletonema costatum and Thalassiosira pseudonana. Our results suggested that Irgarol was consistently more toxic to all of the three species than M1 (96 h EC50 values: C. minor, 7.71 microug L(-1) Irgarol vs. > 200 microg L(-1) M1; S. costatum, 0.29 microg L(-1) Irgarol vs. 11.32 microg L(-1)M1; and T. pseudonana, 0.41 microg L(-1) Irgarol vs. 16.50 microg L(-1)M1). Secondly, we conducted a meta-analysis of currently available data on toxicities of Irgarol and M1 to both freshwater and marine primary producers based on species sensitivity distributions (SSDs). Interestingly, freshwater autotrophs are more sensitive to Irgarol than their marine counterparts. For marine autotrophs, microalgae are generally more sensitive to Irgarol than macroalgae and cyanobacteria. With very limited available data on M1 (i.e. five species), M1 might be less toxic than Irgarol; nonetheless this finding warrants further confirmation with additional data on other autotrophic species.  相似文献   

Seasonal changes in imposex and tissue burden of butyltin compounds in Thais clavigera populations along the coastal area of Mirs Bay, China     

Ka Ming Chan  Kenneth Mei Yee Leung  Kwai Chung Cheung  Ming Hung Wong  Jian-Wen Qiu   《Marine pollution bulletin》2008,57(6-12):645

We assessed the current status of tributyltin (TBT) contamination of Thais clavigera (Gastropoda) along the coastal area of Mirs Bay, China for the first time. The snail samples were collected from 10 different sites in the summer (June) and winter (December) of 2006, respectively. They were analyzed for imposex status, i.e. relative penis size index (RPSI) and vas deferens sequence index (VDSI), followed by quantification of butyltins in their tissues. Most of the collected females suffered from imposex, but the level of butyltin contamination varied with the distance from Yantian Port, which is currently the fourth busiest container port in the world. The tissue concentration of TBT varied with season. For a particular site, the winter samples in general contained much higher concentration of TBT than the summer samples. RPSI, VDSI and organotin concentrations were higher in T. clavigera collected from sites closer to the Port, such as the Seafood Street and Kat O. Both RPSI and VDSI were positively correlated with the tissue burden of tributyltin. VDSI exhibited little seasonal variability, whereas RPSI showed marked seasonal variability, with lower values in the summer samples. The current results will serve as an important reference for long-term monitoring of butyltin contamination in this area.  相似文献   

近年中国夏季降水变化特征分析   总被引：1，自引：0，他引：1       下载免费PDF全文

赵宗慈  Leung Ruby  钱云 《气候变化研究进展》2005,1(1):29-31

利用台站观测资料和卫星观测换算资料,分析了近年（2002-2004年）中国夏季日内降水量变化统计学特征,其结果是较为一致的。对于东部大部分地区,日内最强降水易出现在下午到傍晚,对于西部大部分地区易出现在夜晚到清晨。夏季降水以对流降水为主,降水大的地区对应潜热通量也大。由于受观测资料的限制,计算结果有待更多的观测资料来验证。  相似文献