共查询到20条相似文献，搜索用时 31 毫秒
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This paper describes a proposed method for clustering attributes on the basis of their spatial variability and the uncertainty of cluster membership. The method is applied to geometallurgical domaining in mining applications. The main objective of geometallurgical clustering is to ensure consistent feed to a processing plant by minimising transitions between different types of feed coming from different domains (clusters). For this purpose, clusters should contain not only similar geometallurgical characteristics but also be located in as few contiguous and compact spatial locations as possible so as to maximise the homogeneity of ore delivered to the plant. Most existing clustering methods applied to geometallurgy have two problems. Firstly, they are unable to differentiate subsets of attributes at the cluster level and therefore cluster membership can only be assigned on the basis of exactly identical attributes, which may not be the case in practice. Secondly, as they do not take account of the spatial relationships they can produce clusters which may be spatially dispersed and/or overlapped. In the work described in this paper a new clustering method is introduced that integrates three distinct steps to ensure quality clustering. In the first step, fuzzy membership information is used to minimise compactness and maximise separation. In the second step, the best subsets of attributes are defined and applied for domaining purposes. These two steps are iterated to convergence. In the final step a graph-based labelling method, which takes spatial constraints into account, is used to produce the final clusters. Three examples are presented to illustrate the application of the proposed method. These examples demonstrate that the proposed method can reveal useful relationships among geometallurgical attributes within a clear and compact spatial structure. The resulting clusters can be used directly in mine planning to optimise the ore feed to be delivered to the processing plant. 相似文献
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Nir Cohen 《GeoJournal》2007,68(2-3):267-278
This paper deploys a critical discourse analysis methodology to examine the emergence of three (sometimes overlapping) discourses on emigration in Israel. It examines the linkages between the various discursive phases and processes of (trans-) national identity formation among emigrants. It argues that emigration discourses have often been strong predictors of subsequent changes in state policies—and other programmatic initiatives—aimed at Israeli citizens abroad. By juxtaposing the discursive construction of emigration (and its linkages to nation-forming political strategies in Israel) and the effects they have had on emigrant identities the paper contributes to the emerging literature on state-diaspora relations and transnational politics. 相似文献
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《Geoforum》2016
Legal processes shape how water resources are allocated, regulated, distributed, and governed. This paper examines the public trust doctrine, a legal principle that addresses the state’s role in governing natural resources by requiring states to manage certain bodies of water and their shorelines for the good of the public. The paper focuses on how the public trust doctrine has been used—with varying degrees of success—to protect water bodies by contesting the diversion and transfer of water in California. The paper compares how the doctrine was applied in two cases: Mono Lake and the Salton Sea, two California lakes that have been threatened by water diversions and transfers. Advocates at Mono Lake successfully used the public trust doctrine for environmental protection, while public trust was an unsuccessful strategy at the Salton Sea. The paper examines issues of nonequilibrium ecosystems, natural versus artificial ecosystems, and wasteful versus reasonable uses of water.By investigating why one case was deemed eligible for public trust protections while the other was not, this paper examines how discursive constructions of nature are embedded in and enacted by legal institutions and how these constructions of nature impact the implementation of legal protections of natural resources. In examining the use of the public trust doctrine in California, the paper examines both the potential and the limitations of the public trust in practice, showing how legal processes and institutions can be used to protect public interests in natural resources but also how particular environmental narratives are reinforced through these institutions. 相似文献
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This paper advances understanding of how unequal risks to environmental hazards are generated. Marginalization is the best known explanation for the production of risk. The concept of marginalization was elaborated through studies of hazards in the global South and connotes how social inequalities constrain livelihood options of less powerful social groups. Thus, marginal groups are pressured to degrade landscapes and occupy hazardous environments while they experience decreased capacities to cope with environmental change. This paper directs analytical attention beyond the material to include the discursive realm and demonstrates that the production of unequal risk is contingent upon how hazards are differentially perceived, represented, and contested in social spaces. Findings from a flood disaster case study in the El Paso (US)–Ciudad Juárez (Mexico) border metropolis highlight how hegemonic discourses reinforce material processes of marginalization in flood-prone social spaces. Findings also reveal how socially-powerful geographical groups of people have harnessed institutional resources in their efforts to externalize risks and capitalize on environmental opportunities in some flood-prone areas. The concept of facilitation is used to explain the material-discursive production of socially-elite, flood-prone spaces. Facilitation clarifies how powerful groups are provided privileged access to institutional resources in their pursuit of environmental rewards, contributing to unjust socioenvironmental outcomes. In conclusion, I outline key aspects of how unequal risks are materially and discursively (re)produced within hazardscapes through relational processes of marginalization/facilitation. 相似文献
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U. Kramar 《Journal of Geochemical Exploration》1995,55(1-3)
In stream sediment and soil surveys, samples represent mixtures of components from different geological environments. Such mixed samples are misclassified when using conventional “hard” cluster methods. In fuzzy clustering, each sample is allowed to belong to several clusters. Similar to element concentrations, these cluster contributions can be displayed in contour maps (e.g. kriging maps). The amount of an element that is explained by the cluster contribution and element residuals can be calculated. The modified fuzzy clustering algorithm called “limited fuzzy clusters” used in this paper avoids negative residuals.Stream sediment data of Sierra de San Carlos, Tamaulipas, Mexico are used to demonstrate the possibilities of limited fuzzy clustering in geochemical exploration and mapping. From the different drainage systems, 681 stream sediment samples were taken and analyzed for 24 elements. A nineteen-element data set was used to calculate limited fuzzy clusters and element residuals. The contribution values for the clusters and element residuals are displayed in contour maps. All geological units were outlined by the cluster contributions. Extended anomalies are characterized by their own cluster. Small anomalies are clearly identified from the element residuals. 相似文献
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Cluster analysis can be used to group samples and to develop ideas about the multivariate geochemistry of the data set at hand. Due to the complex nature of regional geochemical data (neither normal nor log-normal, strongly skewed, often multi-modal data distributions, data closure), cluster analysis results often strongly depend on the preparation of the data (e.g. choice of the transformation) and on the clustering algorithm selected. Different variants of cluster analysis can lead to surprisingly different cluster centroids, cluster sizes and classifications even when using exactly the same input data. Cluster analysis should not be misused as a statistical “proof” of certain relationships in the data. The use of cluster analysis as an exploratory data analysis tool requires a powerful program system to test different data preparation, processing and clustering methods, including the ability to present the results in a number of easy to grasp graphics. Such a tool has been developed as a package for the R statistical software. Two example data sets from geochemistry are used to demonstrate how the results change with different data preparation and clustering methods. A data set from S-Norway with a known number of clusters and cluster membership is used to test the performance of different clustering and data preparation techniques. For a complex data set from the Kola Peninsula, cluster analysis is applied to explore regional data structures. 相似文献
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The development of clusters of local growth is supported by different processes. Endogenous economic development produced by small and medium-sized enterprises (SMEs) is based on family firms in which local market characteristics influence the sectorial diversification that emerges within certain regions. In the Berguedà region (Catalonia, Spain), the formation of a successful network of SMEs in three main sectors (food, textile and machinery) in the 1990s demonstrated the importance of grass-roots prerequisites, including industrial tradition, social networks and a sense of spatial loyalty, one of the main concepts studied in this paper. The aim of this paper is to study how institutions, local economic networks and collective social agents generate a propitious economic space that constitutes favourable embedding in Berguedà. However, the key element in this industrial system is the loyalty that entrepreneurs and workers feel towards their industrial region. These two processes, territorial embeddedness and spatial loyalty, appear to be two of the major forces behind the economic dynamism of the region and have led to the formation of a new cluster of firms. 相似文献
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Interpretation of regional scale, multivariate geochemical data is aided by a statistical technique called “clustering.” We investigate a particular clustering procedure by applying it to geochemical data collected in the State of Colorado, United States of America. The clustering procedure partitions the field samples for the entire survey area into two clusters. The field samples in each cluster are partitioned again to create two subclusters, and so on. This manual procedure generates a hierarchy of clusters, and the different levels of the hierarchy show geochemical and geological processes occurring at different spatial scales. Although there are many different clustering methods, we use Bayesian finite mixture modeling with two probability distributions, which yields two clusters. The model parameters are estimated with Hamiltonian Monte Carlo sampling of the posterior probability density function, which usually has multiple modes. Each mode has its own set of model parameters; each set is checked to ensure that it is consistent both with the data and with independent geologic knowledge. The set of model parameters that is most consistent with the independent geologic knowledge is selected for detailed interpretation and partitioning of the field samples. 相似文献
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《Geoforum》2016
In this paper I offer a critical analysis of ‘sharing’ as a discursive formation in the emerging on-demand economy or, as its more commonly known, ‘sharing’ economy. The set of firms and digital platforms that constitute the on-demand economy evade precise definition, though in popular commentary include Uber, Lyft, Airbnb, Taskrabbit, Couchsurfing, and Yelp, among others. I argue that sharing is a discursive formation that is produced through neoliberal economic practices and contributes to their constitution and performance, connoting the embeddedness and inter-determination of the economic with the social. I analyze interview material with software developers and others working for on-demand economy firms in San Francisco to underscore how the sharing discourse is produced, and to examine the possible relationship between the sharing discourse and working practices in the on-demand economy. I explore how sharing, though a fragile and contested discourse, has been used by some proponents of the on-demand economy in an attempt to justify and normalize flexible and precarious work through an ambiguous association between capitalist exchange and altruistic social values. This ambiguity is productive insofar as sharing has become associated variously with transactional platforms, digital peer review via surveillant and punitive ratings systems, and algorithmically mediated, precarious, and ‘entrepreneurial’ contract work, while retaining affective associations with community, inclusion, and participation. 相似文献
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海底隧道涌水量数值计算的渗透系数确定方法 总被引：1，自引：0，他引：1
海底隧道的建设往往伴随着高风险,而水害则是海底隧道建设期间风险最主要的来源之一,隧道涌水对施工安全与建成后的运营成本控制有着重要影响,因此,对海底隧道进行涌水量预测便显得尤为重要。数值计算方法是当前涌水量预测中应用最广的方法之一,而计算涌水量过程中最关键的问题之一是渗透系数的确定。以青岛胶州湾海底隧道工程为背景,通过数值计算、模型试验与现场监测数据分析等手段相结合的方法,对海底隧道建设期涌水量的预测进行了研究。首先进行海底隧道开挖后涌水量现场监测,得到开挖后涌水量变化曲线;再采用数值计算方法对围岩渗透系数的取值进行反分析,对渗透系数进行不断修正,并在数值计算中成功拟合实测涌水量曲线,所得到的渗透系数即为数值计算中应采用的合理渗透系数。在结合试验段地质情况的基础上将合理渗透系数与前期地勘压水试验得到的渗透系数进行比对,得到两者之间的关系。并通过模型试验的手段对以上结论进行验证。将其应用到海底隧道的涌水量预测中,通过正演数值计算预测围岩相似洞段的涌水量,其结果对海底隧道涌水量预测有一定的参考意义。 相似文献
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Maysam Abedi Gholam Hossain Norouzi Seyed Ali Torabi 《Arabian Journal of Geosciences》2013,6(10):3601-3613
This paper describes the usage of clustering methods including self-organizing map (SOM) and fuzzy c-means (FCM) which are applied to prepare mineral prospectivity map. Different evidential layers, including geological, geophysical, and geochemical, to evaluate Now Chun copper deposit located in the Kerman province of Iran are used. Clustering approaches are used to reduce the dimension of 13 feature vectors derived from different layers. At first, Geospatial Information Systems (GIS) is employed to analyze and integrate different layers, and the area under study is prioritized to five classes. Then, the SOM as an unsupervised classification method is carried out to classify this area into five clusters. Produced clusters are compared with GIS prospect map, while the SOM results are matched with the GIS output. The main reason to use the FCM is that a vector belongs simultaneously to more than one cluster so that membership values of each cluster can be mapped. As a consequence, clusters generated by the SOM and FCM are considerably matched with five-class-map of the GIS approach. The chosen cluster as a high potential location to additional drilling is matched to the main alteration and faults zone. To validate generated clusters for mineral potential mapping, geological matching of study area and selected proper cluster can be a satisfactory way. Finally, clustering methods can be a very fast approach to interpret the area under study. 相似文献
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Evaluation of graphical and multivariate statistical methods for classification of water chemistry data 总被引：12，自引：2，他引：12
Cüneyt Güler Geoffrey D. Thyne John E. McCray Keith A. Turner 《Hydrogeology Journal》2002,10(4):455-474
A robust classification scheme for partitioning water chemistry samples into homogeneous groups is an important tool for the
characterization of hydrologic systems. In this paper we test the performance of the many available graphical and statistical
methodologies used to classify water samples including: Collins bar diagram, pie diagram, Stiff pattern diagram, Schoeller
plot, Piper diagram, Q-mode hierarchical cluster analysis, K-means clustering, principal components analysis, and fuzzy k-means
clustering. All the methods are discussed and compared as to their ability to cluster, ease of use, and ease of interpretation.
In addition, several issues related to data preparation, database editing, data-gap filling, data screening, and data quality
assurance are discussed and a database construction methodology is presented.
The use of graphical techniques proved to have limitations compared with the multivariate methods for large data sets. Principal
components analysis is useful for data reduction and to assess the continuity/overlap of clusters or clustering/similarities
in the data. The most efficient grouping was achieved by statistical clustering techniques. However, these techniques do not
provide information on the chemistry of the statistical groups. The combination of graphical and statistical techniques provides
a consistent and objective means to classify large numbers of samples while retaining the ease of classic graphical presentations.
Electronic Publication 相似文献
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E. Murad 《Physics and Chemistry of Minerals》1996,23(4-5):248-262
Iron (III) oxides are common constituents of geologic materials, they are products and by-products of many industrial processes, they are involved in biological processes, and they are the outcome of iron and steel corrosion. In many of these examples the iron oxides are — fortuitously or intentionally — of small particle size, and as a consequence difficult, if not impossible, to characterize by standard physicochemical techniques. 57Fe Mössbauer spectroscopy is suitable for this purpose because it can serve as a probe of the electric and magnetic conditions in the vicinity of iron nuclei in solid samples, no matter how the iron may be bound. Deviations of the magnetic properties of iron oxides of small particle size from those of their bulk counterparts lead to radical changes in the appearance of their Mössbauer spectra. Diverse models that have been put forward to account for such changes are discussed in this paper, including superparamagnetism, collective magnetic excitations, anomalous recoil-free fractions, superferromagnetism, spin canting and speromagnetism, reduced hyperfine field supertransfer, and Néel temperature reductions and distributions. Specific examples of microcrystalline iron (III) oxides and related minerals originating from different natural environments, resulting from technical processes, and being studied as planetary analogs are presented and discussed in the light of present-day knowledge on the properties of such materials. 相似文献
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Jef Caers 《Mathematical Geology》1996,28(5):601-624
The two-dimensional spatial distribution of precious stones, such as diamonds in alluvial and coastal deposits, shows a high degree of clustering. Usually, stones tend to gather in relatively small clusters or traps, made by potholes, gullies, or small depressions in the rough bedcock. Therefore, when taking samples of such deposits, discrete distributions of the number of stones counted in each sample yield an extreme skewness. Most samples have no stones, whereas samples containing a few hundred stones are not unusual. This paper constructs a model and a method for fitting a new and general family of counting distributions based on the Neyman-Scott cluster model and the mixed Poisson process, which can be used to model a differing degree of clustering. General recursion equations for the discrete probabilities of these distributions are derived. Application of this model to simulated data shows that information such as cluster size, number of point events per cluster, and number of clusters per measurement unit can be extracted easily from this model. Fitting the model to data of two real diamond deposits of a totally different nature—small rich clusters of Namibia versus larger but less rich clusters of Guinea—demonstrates its flexibility. 相似文献
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Kosuke Tamura Dustin T. Duncan Jessica Athens Marc Scott Michael RientiJr. Jared Aldstadt Laurie M. Brotman Brian Elbel 《GeoJournal》2018,83(4):775-782
Sedentary behavior and lack of physical activity are key modifiable behavioral risk factors for chronic health problems, such as obesity and diabetes. Little is known about how sedentary behavior and physical activity among adolescents spatially cluster. The objective was to detect spatial clustering of sedentary behavior and physical activity among Boston adolescents. Data were used from the 2008 Boston Youth Survey Geospatial Dataset, a sample of public high school students who responded to a sedentary behavior and physical activity questionnaire. Four binary variables were created: (1) TV watching (>2 h/day), (2) video games (>2 h/day), (3) total screen time (>2 h/day); and (4) 20 min/day of physical activity (≥5 days/week). A spatial scan statistic was utilized to detect clustering of sedentary behavior and physical activity. One statistically significant cluster of TV watching emerged among Boston adolescents in the unadjusted model. Students inside the cluster were more than twice as likely to report >2 h/day of TV watching compared to respondents outside the cluster. No significant clusters of sedentary behavior and physical activity emerged. Findings suggest that TV watching is spatially clustered among Boston adolescents. Such findings may serve to inform public health policy-makers by identifying specific locations in Boston that could provide opportunities for policy intervention. Future research should examine what is linked to the clusters, such as neighborhood environments and network effects. 相似文献
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为精确模拟海底盾构隧道掘进过程的施工力学效应,以厦门地铁2号线海底盾构段工程为依托,建立盾构机-注浆体-围岩-海水相互作用的三维数值模型,全面考虑施工影响因素,如开挖面泥水压力、千斤顶推力、盾构机超挖、机身与土体相互作用、注浆压力、海水压力、壁后注浆的时空变化性质等,通过计算结果与实测的验证后,对开挖面支护压力、地层损失率、注浆压力和千斤顶力等4种因素进行参数变化分析。结果表明:初期管片水土压力受到的施工扰动较为强烈,之后先大幅快速下降,降幅在100kPa左右,再缓慢降低,降幅在20kPa左右,最后趋于稳定;开挖面支护压力设为320kPa左右最为合理,增大支护压力,仅对开挖面前方一定范围内土体变形有影响,由于埋深较大,对地表竖向位移基本没有影响;地层损失率对地层沉降、管片上浮及管片内力的影响较大,随着地层损失率增大1%,地表沉降增大241.3%,管片上浮量降低38.2%,弯矩减少23.9%;注浆压力对管片上浮和管片内力有较大影响,注浆压力增大10%,管片上浮量增大32.1%,弯矩增大24.3%;千斤顶力主要对沿隧道轴向的管片轴力有一定影响,对管片上浮和管片弯矩影响很小。研究成果可为管片结构设计及海底盾构施工参数控制提供更加合理的参考建议。 相似文献