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1.
Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel and independent tool for estimating the Hubble constant (H0). This is very important given the recent discord in the value of H0) from two methods that probe different distance ranges. The success of this technique will rely of our ability to discover strongly lensed SNe with measurable time delays. Here, we present the magnifications and the time delays for the multiply-imaged galaxies behind the Hubble Frontier Fields (HFF) galaxy clusters, by using recently published lensing models. Continuing on our previous work done for Abell 1689 (A1689) and Abell 370, we also show the prospects of observing strongly lensed SNe behind the HFF clusters with the upcoming James Webb Space Telescope (JWST). With four 1-hour visits in one year, the summed expectations of all six HFF clusters are ~0.5 core-collapse (CC) SNe and 0.06 Type Ia SNe (SNe Ia) in F115W band, while with F150W the expectations are higher, ~0.9 CC SNe and ~0.06 SNe Ia. These estimates match those expected by only surveying A1689, proving that the performance of A1689 as gravitational telescope is superior. In the five HFF clusters presented here, we find that F150W will be able to detect SNe Ia (SNe IIP) exploding in 93 (80) pairsmultiply-imaged galaxies with time delays of less than 5 years.  相似文献   

2.
The task of discriminating between heterogeneity and complete spatial randomness (CSR) for a given point process can be divided into three subtasks: the identification of the point pattern; the determination of the sizes of clusters; and the estimation of the numbers of events in dominant clusters. Many studies have been performed regarding the first and second subtasks. However, limited work has been done on the third aspect; hence, the determination of the number of events in each dominant cluster is still an unsolved problem. In this paper, we provide a solution by constructing a new index which is defined as the ratio between the variance of the (k+1)th nearest distance and that of the kth nearest distance. Our method can be divided into two phases: the detection of point pattern and the estimation of the numbers of events in dominant clusters. These phases can be estimated by the values at which the index abruptly decreases to be less than 1. A comparative study between the existing indices and our index shows the following: (i) our index can indicate the numbers of events in dominant clusters in a relatively objective way, which is different from the K-function revealing the sizes of clustered patterns; (ii) it is a nonparametric index and is easy to implement; and (iii) it demonstrates the highest detection power for differentiating between heterogeneity and CSR. The simulations and two seismic case studies also confirmed the correctness of our method.  相似文献   

3.
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   

4.
The paper analyzes possible origins of stars located in intergalactic space that are not bound to specific galaxies, which comprise 15–50% of all stars in galaxy clusters. Some such stars can form in streams of intergalactic gas flowing around gas-rich disk galaxies moving in the cluster. Others may be the products of the decay of young, low-mass, spheroidal galaxies after the loss of their gaseous components during an initial burst of star formation. The decay of low-mass disk galaxies moving at high speeds after they have lost their gaseous components due to the pressure of the incident flow of dense intergalactic gas is possible in the cluster core. The largest fraction of intergalactic stars are probably produced by the partial disruption of galaxies as a result of close passages, collisions, or mergers. Collisions of low-mass, gas-rich galaxies are especially good suppliers of intergalactic stars. Both stars from decaying stellar components of galaxies and stars arising in the gaseous components of colliding galaxies can be supplied to the intergalactic medium. The merger of galaxies harboring supermassive black holes in their nuclei could lead to the partial or total disruption of these galaxies during the deceleration of the binary black hole that is formed during the merger. An enhanced density of intergalactic stars is observed in the cores of galaxy clusters, underscoring the role of galaxy collisions in the formation of the intergalactic stellar population, since the frequency of galaxy collisions grows with their density.  相似文献   

5.
Geographic profiling is a method that proved to be useful also in order to investigate the point of origin of a biological invasion. K-means clustering and Voronoi diagrams can partition a data set of geographic positions of populations invading a defined area and are, therefore, useful in cases in which an invasion had more introduction events as points of origin. One critical point of the method is to identify the right number of clusters in which to divide the starting data set formed by groups of points on a map. The Silhouette method proved to be capable of identifying the best number of subsets (clusters) of the general set of observations by providing different values for different subdivisions of the set of observations in clusters. For each cluster, the corresponding Voronoi tessellation was built on the starting map. To test the method, we did a simulation of clusters of data (points) on a map and we verified whether the proposed methods worked efficiently with the simulated data set with hundred repeats and using a varying number of clusters on the same map. The used techniques revealed to be efficient in finding the highest probability area of the map that would include the starting points for each cluster. A case study consisted in a known data set, that is, the spreading pattern of Caulerpa racemosa var. cylindracea (sea grapes), that was compatible (highest probability) with an original point of introduction in southern Italy and long distance (thousands of kilometers) secondary spreads via anthropic dispersal. The proposed techniques may also be applied to other kinds of data sets of biological data distributed on a map or in general on a geometrical surface.  相似文献   

6.
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   

7.
论述了 GIS支持下的一种基于“单元簇”概念和模糊逻辑推理的多元地学信息综合分析方法及其在区域矿产预测中的应用。针对以往矿产定量预测中的单元划分方法对空间信息利用不足的问题 ,用单元的空间组合 (“单元簇”)代替单元作为定量类比的基本单位 ,从而能较充分地利用地质变量的局部空间结构信息 ;将单元作为 GIS区图元 ,利用 GIS空间分析功能实现对单元及单元簇的管理和操作 ;建立两个层次即变量对单元和组成单元对单元簇的模糊推理规则 ,经两次模糊推理计算出所有未知单元的找矿有利度 ,为进一步圈定找矿远景区提供了基础 ,并以新疆康古尔塔格地区金矿预测实例说明了其应用效果  相似文献   

8.
A field study was conducted on two mountain streams in the Cascade Mountains of Washington State on the morphological characterization of cluster microforms. Morphological characterization of clusters is presented in terms of: (i) cluster shape; (ii) cluster geometric properties; and (iii) the spatial arrangement of clusters in the horizontal plane. Clusters were differentiated from other microtopography features such as reticulate structures and transverse ribs, and identified clusters were categorized by shape as being of pebble, line, comet, heap or ring type. The complex spatial arrangement of clusters at the sites was characterized by using a two‐dimensional correlation function, which allowed for measurement of the average cluster‐spacing properties. For the rivers examined, pebble‐shaped clusters were the most frequently observed cluster shape. Cluster geometric properties were found to be controlled by particles of the largest size fraction in the bed and the projected frontal width of the cluster – with cluster length being linearly related to cluster width for cluster width‐to‐height ratios <3·5. Results of the cluster‐spacing analysis suggest that cluster spacing increases with cluster size and decreases with local slope. Application of this principle to the available spacing data shows that cluster spacing λ scales with the ratio of S/d0 such that λS/d0 = constant, where S is the local slope and d0 the diameter of the largest particle in the cluster.  相似文献   

9.
Complexes of young clusters and high-luminosity stars in the shape of regular, circular arcs have been found in a number of galaxies, first and foremost the LMC, NGC 6946, and M83. These shapes are found even in strongly inclined galaxies, suggesting that the observed arcs are projections of partial spherical shells. Obviously, these stellar shells must have formed from gaseous shells swept up by some source of central pressure and become gravitationally unstable. The power of this source corresponds to several dozen supernova explosions; however, its nature remains unclear. A central cluster providing a source of O stars and supernovae is usually absent. The presence of multiple arcs located close to each other can be explained by the fall of a swarm of fragments or by the progenitor stars originating in a single peculiar star cluster, implying the existence of stellar objects capable of giving rise to explosions with energies an order of magnitude higher than those of individual supernovae. The same objects may be responsible for gamma-ray bursts. It may be that only the most massive clusters with frequent or especially powerful supernova explosions are capable of producing HI supershells. Otherwise, it is impossible to explain why no supershells have been found around numerous clusters that should be capable of producing them according to current theories. The presence of star clusters in shell-like structures provides extremely important information about the physical conditions in and the ages of the initial gaseous shells, making stellar arcs the best available laboratory for studies of triggered star formation.  相似文献   

10.
太阳原始星云原子团簇的初步研究   总被引：1，自引：1，他引：1  
选用Ａｌｌｅｎｄｅ和宁强两块ＣＶ３陨石，在分子团簇串级飞行时间质谱装置上。用激光溅射模拟太阳原始星云在高能环境下的Ｓｉ－０，Ｆｅ－０和Ｍｇ－０原子团簇的形成和分布，对模拟过程所产上的原子团簇系列的结构和稳定性，以及可能的天体化学意义进行了初步探讨。  相似文献   

11.
为了研究岩石张拉破坏的过程和机制,首先通过模拟计算,验证了加权反演法在进行巴西劈裂试验矩张量求解方面的优越性;其次基于花岗岩的巴西劈裂试验,进行声发射监测、事件定位及矩张量反演,并分析标准反演法和加权反演法对应矩张量结果的差别;使用聚类分析K均值算法对矩张量结果进行分簇研究。研究结果表明：模拟计算中加权反演法可以降低巴西劈裂试验矩张量反演误差;室内花岗岩巴西劈裂试验中,加权反演法较大程度地优化了声发射事件的剪切成分以及压/拉应力轴的分布,使得反演结果更加合理。针对加权反演结果,所有事件可分成3簇,同簇内事件的破裂类型、应力状态、破裂机制、辐射模式等均相近;不同簇中的事件在时空上交叉分布,试验后期在圆盘东?西方向上具有较为明显张拉特性的事件骤增,于圆盘中心附近聚集并占据主导,最终导致试样的宏观破裂。研究结果解释了花岗岩巴西劈裂试验的破裂过程和破裂机制,为岩石力学行为研究提供进一步指导。  相似文献   

12.
Summary. Studies of source mechanisms of mining-induced seismic events play an important role in understanding the various modes of failure observed around underground excavations and enable the geometry of likely planes of failure to be determined. These planes can be mapped using conventional techniques, for example, geological fracture mapping. However, such an approach is often problematical due to limited access to the site and/or poor exposures (if any) of the failure plane. An added difficulty is that planes of failure often do not follow faults of geological origin, but are related to the geometry of the advancing stope face. For example, the development of face-parallel shear zones ahead of deep-level stope faces. In such cases, the stresses induced by mining dominate over the geological structure in the critical region close to the stope face. Seismic methods therefore have the potential of being a practical method of studying the development of seismic shear zones underground.Slip on such a failure plane generates a three dimensional elastic wave that propagates through the rockmass, carrying a wealth of information regarding the source rupture process. The ground motions caused by the passage of the wave can be recorded by arrays of sensitive instruments called seismometers. These sets of recordings (seismograms) provide the basic data that seismologists use to study these elastic waves as they propagate through the Earth. Conventional seismic analyses provide scalar measurements of the rupture size and intensity. However, through a process known as moment tensor inversion (MTI), the seismograms recorded from a seismic event can be used to calculate a moment tensor that describes the three dimensional nature of the source mechanism. Interpretation of the moment tensor gives insight into whether the rockmass failed in tension, compression or shear and indicates the direction of movement and the failure plane.Moment tensor solutions computed using conventional MTI methods are sensitive to noise and may be biased due to systematic errors in the measurements. The primary objective of this study was to develop a robust MTI method to estimate the moment tensors of clusters of seismic events recorded in the underground environment. To achieve this, three hybrid MTI methods were developed by the author. These methods involve different iterative weighting schemes designed to enhance the accuracy of the computed moment tensors by decreasing the effect of outliers (data points whose residuals lie far from the mean or median error). The additional information required for hybrid methods is obtained by considering a spatial cluster of seismic events and assuming that the waves generated by each event in the cluster follow a similar path through the rockmass and allowing a common ray-path to be assumed. Hence the unknown effect of the heterogeneous rockmass on the waveform is similar for all the events in the cluster.The final objective was to determine whether the techniques developed could be successfully applied to real data. The hybrid MTI methods using the median and the weighted mean correction were applied to a cluster of 10 events, having remarkably similar waveforms, recorded at Oryx Gold Mine. For comparative purposes, the more conventional absolute method was also applied. The solutions computed using the hybrid MTI with a median correction displayed a distinct improvement after the iterative residual correction procedure was applied, in contrast to the solutions obtained from the absolute method. The radiation patterns and fault-plane solutions from the hybrid method showed a high degree of similarity, and were probably more accurate reflections of reality. These observations are very encouraging and point towards the potential for using the hybrid MTI method with a median correction as a standard processing tool for mine seismicity.The implications of this work are that a robust method for calculating the focal mechanisms of clusters of seismic events induced by mining activities has been developed. Regular application will lead to a better understanding of rock fracture processes and to improved safety underground.  相似文献   

13.
在研究和开发程度较低地区开展矿产预测，往往只能有很少矿产地用以建立定量预测模型，此时大多数统计分析方法不适用。一种GIS的基于“单元簇”概念的多源地学信息综合分析方法即Eigenface法，比较适合于只有一个模型单元时的建模。单元簇是相邻若干网格单元的空间定量组合Eigenface法先求出这种高维组合变量空间的某个低维特征子空间，然后计算未知单元簇和已知单元簇在特征子空间上投影点的距离来评价未知单元的的找矿有利性。Eigenface法与GIS集成是将单元作为区图元，利用GIS空间－属性分析功能提取预测信息并对单元和单元簇进行操作。以新疆乌斯拉台－亦格尔达坂地区铜铅锌银多金属矿产预测为例说明了其应用效果。  相似文献   

14.
A detailed study of the syndepositional Masada Fault Zone (MFZ) provides an example for fundamental characteristics of earthquakes, such as long term temporal clustering, repeated faulting on the same planes for a limited time of the order of a few thousands of years, and the formation of subaqueous breccia layers interpreted as seismites. The MFZ was studied in outcrops of 70–15 ka Lake Lisan sediments. Detailed columnar sections on both sides of well-exposed faults show that each individual fault exhibits a cluster, up to 4 ky long, with 3–5 slip events on the same plane. Each slip event is associated with the formation of widespread layers exhibiting soft sediment deformation, which are interpreted to be seismite layers. The uppermost part of the Lisan section, about 5 m, is not faulted, hence the last cluster of slip events ended about 25 ky ago. The clusters of activity of individual faults coalesce to form larger clusters. These are evident in the distribution of seismite layers throughout the entire Lisan section which shows earthquake clustering during periods of 10 ky. The clusters are separated by relatively quiescent periods of comparable duration.  相似文献   

15.
Disk clusters are developed to represent the shape of granular materials more precisely (compared to circular particles) and to minimise excessive rolling. Investigating the behaviour of dynamic disk-based discontinuous deformation analysis (DDA) with disk clusters is very important to evaluate the applicability of disk-based DDA to dynamic problems in geomechanics. In this paper, the accuracy of disk-based DDA under dynamic conditions is studied by a comprehensive sensitivity analysis. The results obtained by disk-based DDA are compared with the analytical solutions of a disk cluster on an incline subjected to gravitational force only, and three different accelerations of increasing complexity with sinusoidal input functions as well as gravitational load. In this research, the effects of time step size and interface friction angles on the results are studied. Overall, most of the error for both velocity and displacement occurs at the beginning of the solution. With increasing friction angle, the initial perturbation of the solution increases in the case of sliding under gravitational force only, and decreases in the case of sliding under dynamic loads. This study shows that disk-based DDA predicts accurately the velocities and displacements derived with respect to the frictional resistance offered by the inclines.  相似文献   

16.
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   

17.
We investigated moment tensors (MTs) of 70 events of the earthquake swarm which occurred in January 1997 in NW Bohemia. A refined location using the master-event procedure shows that all the foci clustered in a volume of less than 0.5 km3 comprising two compact clusters—the southern and northern ones. The results of single-source, absolute-moment tensor inversion of the P- and SH-peak amplitudes reveal two types of the source mechanisms, A and B in our denotation, which dominated in the swarm. Type A implies an oblique normal faulting with a nearly pure double-couple (DC) source. For the B type, an oblique-thrust faulting and a combined source [double-couple combined with the isotropic (ISO) and compensated linear-vector dipole (CLVD) components] are typical. Magnitudes of the non-double-couple components of MT appear unrelated to the ML magnitude of the event. The proximity of hypocentres of A and B events guarantees the non-double-couple source mechanisms of the B events not to be an artefact of a mismodelling of the medium. To exclude finiteness of the focus or station-site effects as possible causes of spurious non-double-couple components of MTs of the B events, the residuals of the peak amplitudes across the set of the B events were analysed and the jack-knife test was applied. The A and B events separate in time and space. Consequently, three major phases of swarm activity can be distinguished. In the first, only the southern cluster was active and A events prevailed, while B events dominated in the northern cluster in the third phase. Both A and B events occurred (the former in the southern cluster, the latter in the northern one) during the second phase. The initiation of the B events in the northern cluster are reflected in a pronounced increase in the non-double-couple components of the MTs, which points to tensile-source mechanisms as a consequence of a hypothesised fluid injection.  相似文献   

18.
Near-surface diffractors are one of the problems in land seismic exploration. They can scatter the surface wave energy emanating from the seismic source and contaminate the signal received by seismic receivers. The scattered energy from the near-surface diffractors manifests itself on seismic shot gathers as strong hyperbolic events, called diffractions, masking the weakly reflected body waves. Diffractions present complications to most of surface-wave suppression schemes, especially when they have been scattered by scatterers outside the receiver line. Different methods have been used to eliminate diffractions from seismic data, including geophone arrays, filtering, and inverse scattering. Each of those methods has its own limitations. In this study, we present processing algorithms to map and attenuate near-surface diffractors of surface waves in seismic shot gathers. The mapping algorithm is based on semblance measurements and time–offset relations, while the attenuation algorithm is based on the least-square fitting of a source wavelet. The algorithms are applied on synthetic data from two different models. The first model has three near-surface diffractors, while the second model has three clusters of near-surface diffractors. Each cluster consists of three near-surface diffractors with a different geometry for each cluster. The results show that the proposed algorithms are successful in locating and attenuating most near-surface diffractors, except when the separation between individual diffractors is below the wavelength of the diffracted surface wave.  相似文献   

19.
The aim of this paper is to contribute to an understanding of clusters, including both the material and discursive dynamism of cluster construction, and shed light on how clusters—once established—affect the actors, institutions and processes that constitute them. It does this by viewing clusters as an actant, i.e. something that acts or to which activity is granted by others. The empirical analysis examines two clusters in the public cluster programme Norwegian Centre of Expertise (NCE): the Møre maritime cluster and the Hordaland subsea cluster. It focuses on the type of development paths they are following and how the material and discursive processes are interweaved in these paths. The clusters are related to the concept of cluster construction, which is triggered by ideas, representations, policy and industry practice. The Møre maritime cluster is characterized by bottom-up clustering processes and illustrates how the material practices of firms can trigger clustering processes such as the establishment of a cluster and the identification of a prototype of best cluster practice. On the other hand, the Hordaland subsea cluster expresses a top-down process and how the ideal world of academics and policy-making can encourage processes of clustering among co-located firms. Based on these observations of material and discursive interweaved clustering processes and how they affect both those who are practicing and those who are promoting them, we find it reasonable to argue for a stronger awareness of such feedback loops in cluster studies.  相似文献   

20.
Instability of proper fluctuations of the phase density at the centers of six open clusters is demonstrated. The boundaries of the region of instability in terms of the mean mass densities of the cluster cores are determined. Estimates for a number of dynamical parameters (the potential, velocity dispersion of the stellar motions, mass density, phase-density fluctuation period, time for the development of instability of the fluctuations, etc.) are obtained for the central parts of these clusters, as well as for numerical dynamical models for open clusters. Equation that can be used to estimate the dynamical mass of a cluster taking into account the influence of the external field of the Galaxy and the non-stationarity of the cluster is derived. Allowance for these effects makes it possible to decrease the dynamical masses of clusters compared to the virial masses assuming isolated systems. Astrophysical applications of the results are discussed.  相似文献   

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