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1.
We have analyzed the spatial distribution of galaxies from the latest release of the Sloan Digital Sky Survey of galactic
redshifts (SDSS DR7), applying the complete correlation function (conditional density), two-point conditional density (cylinder),
and radial density methods. Our analysis demonstrates that the conditional density has a power-law form for scales lengths
0.5–30 Mpc/h, with the power-law corresponding to the fractal dimension D = 2.2 ± 0.2; for scale lengths in excess of 30 Mpc/h, it enters an essentially flat regime, as is expected for a uniform distribution of galaxies. However, in the analysis applying
the cylinder method, the power-law character with D = 2.0 ± 0.3 persists to scale lengths of 70 Mpc/h. The radial density method reveals inhomogeneities in the spatial distribution of galaxies on scales of 200 Mpc/h with a density contrast of two, confirming that translation invariance is violated in the distribution of galaxies to 300
Mpc/h, with the sampling depth of the SDSS galaxies being 600 Mpc/h. 相似文献
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S. V. Pilipenko 《Astronomy Reports》2007,51(10):820-829
The space distribution of quasars from the 2dF and SDSS DR5 catalogs in the redshift interval 0.3 < z < 1.9 is analyzed. The distributions of quasars in both catalogs are found to have the following common features: (1) when the distance between the nearest objects exceeds 35h ?1 Mpc (where h = H 0/100 km/s Mpc is the dimensionless Hubble constant), the distribution of quasars virtually coincides with a uniform three-dimensional distribution; (2) on scale lengths of (5–35)h ?1 Mpc, the fractal dimension of the quasar distribution is 2.3; (3) the amplitude of quasar clustering and the average distance between neighboring quasars increase slowly with z (at a significance level of about 1.5σ). Twenty large groups of quasars with sizes of (50–150)h ?1 Mpc can be identified in the 2dF catalog at the 4σ significance level. These groups are incipient superclusters (two earlier known groups are confirmed). The space density of these groups is of the order of 7h 3 Gpc?3. 相似文献
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LONG TERM HISTORY (DEXTRAL TO SINISTRAL AND DUCTILE TO BRITTLE) OF THE DAMXUNG—JIALI SHEAR ZONE IN SOUTHERN TIBET 相似文献
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Horton's hierarchical and fractal analysis of channel circumference reveals that tidal-channel systems in the Dutch Wadden Sea have similar branching patterns. Channel systems have the same characteristics as three- to four-times branching networks. The branch lengths of these channels decrease logarithmically. The channel systems can be regarded as statistical self-similar fractal networks, considering the natural variability in branch lengths and channel positions. Branching of channels does not continue below the 500 m scale. The channel-system circumference length is logarithmically related to the tidal prism and drainage area. The similarity of the channel systems, regardless of their size, relative amount of intertidal flats, and tidal amplitude, points to a self-organising nature. All processes depend on the feedback between morphology and hydrodynamics. At first sight, the channel systems can be regarded as an ebb-driven drainage network, governed by erosion. However, flood-dominated net sedimentation occurs in large parts of the drainage basins and modifies the ebb-driven network. The complex interaction of hydrodynamic and morphodynamic processes in tidal basins limits the applicability of process-based models. Behaviour-oriented modelling has a wide applicability and can be improved using the fractal geometry as the dynamical equilibrium morphology. The fractal-network geometry can also be used for stochastic reconstructions of fossil tidal-channel systems, when only limited observations are available. 相似文献
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为解决经典强度准则预测岩石破坏强度不准确的问题,本文使用交叉最小二乘支持向量机(DILSSVM)在单轴及三轴加载情况下对岩石强度进行预测。将现场和实验室试验得到的各种岩石相关数据划分成训练和验证子集。将抗压强度c和最小主应力3作为输入值,最大主应力值1f作为输出值训练DILSSVM。使用训练后的DILSSVM预测岩石破坏时的1f,同时使用训练子集反演Hoek-Brown经验公式的常数m。使用测试数据对训练后DILSSVM预测的目标岩石强度的准确性进行验证,同时将测试数据带入2类Hoek-Brown(m值的取值不同)经验公式预测目标岩石强度1f。比较DILSSVM和Hoek-Brown预测结果, 表明:DILSSVM预测结果的均方差减小了45% ～55%,决定系数增加了0.055～0.085,更接近于1。说明DILSSVM对岩石强度的预测范围较宽,且适合岩石种类多变的复杂非线性情况。 相似文献
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空间尺度转换是近年来区域生态水文研究领域的一个基本研究问题。其需要主要是源于模型的输入数据与所能提供的数据空间尺度不一致以及模型所代表的地表过程空间尺度与所观测的地表过程空间尺度不吻合。综述了目前区域生态水文模拟研究中常用的空间尺度转换研究方法,包括向上尺度转换和向下尺度转换。详细论述了2种向下尺度转换方法: 统计学经验模型和动态模型。前者是通过将GCM大尺度数据与长期的历史观测数据比较从而建立统计学相关模型, 然后利用这个统计学经验模型进行向下的空间尺度转换. 然而动态模型并不直接对GCM数据进行向下尺度的转换,而是对与GCM进行动态耦合的区域气候模型(RCM) 的输出数据进行空间尺度转换. 通常后者所获得的数据精度要比前者高,但是一个主要缺点就是并不是全球所有的研究区域都有对应的RCM。还详细论述了2种向上尺度转换方法: 统计学经验模型和斑块模型。前者是建立一个能代表小尺度信息在大尺度上分布的密度分布概率函数, 然后利用这个函数在所需的大尺度上进行积分而求得大尺度所需的信息。而后者是根据相似性最大化原则将大尺度划分为若干个可操作的小尺度斑块,然后将计算的每个小尺度斑块的信息平均化得到大尺度所需的信息。通常在计算这种斑块化的小尺度信息的时候,对每个小尺度也会采用统计学经验模型来计算代表整个斑块小尺度的信息。建议用斑块模型与统计学经验模型相集合的方法来实现向上的空间尺度转换 相似文献
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Ali Azdimousa Jacques Bourgois Gérard Poupeau Mercedes Vázquez Lahcen Asebriy Erika Labrin 《Arabian Journal of Geosciences》2014,7(5):1993-2005
The Beni Bousera peridotite massif and its metamorphic surrounding rocks have been analyzed by the fission track (FT) method. The aim was to determine the cooling and uplift history of these mantle and associated crustal rocks after the last major metamorphic event that dates back to the Lower Miocene–Upper Oligocene time (～22–24 Ma). The zircon FT analyses give an average cooling—i.e., below 320 °C—age of ～19.5 Ma. In addition, the apatite FT data give an average cooling—i.e., below 110 °C—age of ～15.5 Ma. Taking into account the thermal properties of the different thermochronological systems used in this work, we have estimated a rate of cooling close to 50 °C/Ma. This cooling rate constrains a denudation rate of about ～2 mm year?1 from 20 to 15 Ma. These results are similar to those determined in the Ronda peridotite massif of the Betic Cordilleras documenting that some ultrabasic massifs of the internal zones of the two segments of the Gibraltar Arc have a similar evolution. However, Burdigalian sediments occur along the Betic segment (Alozaina area, western Betic segment) unconformably overlying peridotite. At this site, ultramafic rock was exposed to weathering at ages ranging from 20.43 to 15.97 Ma. Since the Beni Bousera peridotite was still at depth until 15.5 Ma, we infer that no simple age projection from massif to massif is possible along the Gibraltar Arc. Moreover, the confined fission track lengths data reveal that a light warming (～100 °C) has reheated the massif during the Late Miocene before the Pliocene–Quaternary tectonic uplift. 相似文献
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Subsurface flow models can exhibit strong full-tensor anisotropy due to either permeability or grid nonorthogonality effects.
Upscaling procedures, for example, generate full-tensor effects on the coarse scale even for cases in which the underlying
fine-scale permeability is isotropic. A multipoint flux approximation (MPFA) is often needed to accurately simulate flow for
such systems. In this paper, we present and apply a different approach, nonlinear two-point flux approximation (NTPFA), for
modeling systems with full-tensor effects. In NTPFA, transmissibility (which provides interblock connections) is determined
from reference global flux and pressure fields for a specific flow problem. These fields can be generated using either fully
resolved or approximate global simulations. The use of fully resolved simulations leads to an NTPFA method that corresponds
to global upscaling procedures, while the use of approximate simulations gives a method corresponding to recently developed
local–global techniques. For both approaches, NTPFA algorithms applicable to both single-scale full-tensor permeability systems
and two-scale systems are described. A unified framework is introduced, which enables single-scale and two-scale problems
to be viewed in a consistent manner. Extensive numerical results demonstrate that the global and local–global NTPFA techniques
provide accurate flow predictions over wide parameter ranges for both single-scale and two-scale systems, though the global
procedure is more accurate overall. The applicability of NTPFA to the simulation of two-phase flow in upscaled models is also
demonstrated. 相似文献
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Precise statistical models are proposed for the distribution of paleocurrent directions in distributary systems. These models are based on a von Mises distribution for directions of paleocurrents in a system. The method of maximum likelihood is used to obtain an estimated position and confidence regions for the apex of the system. Both axial data (where only the trend of the paleocurrent is known) and directional data (where the direction of paleoflow is known) can be used. These models have been applied to two fluvial distributary systems in flat-lying Miocene deposits in the Ebro Basin, northern Spain. The estimate of the position of the apex of one of these systems is in good agreement with the position at the basin margin predicted from sedimentary facies information. The estimate of the position of the apex of the second system lies outside of the sedimentary basin; this result is considered to indicate that the distributary system had several feeder points along the basin margin, a situation which is predicted also from facies distributions. This statistical procedure can be used successfully on small data sets of around a hundred paleocurrent readings provided that they are scattered evenly across the area or lie in a wide arc. 相似文献
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Amanda Owen Adrian J. Hartley Alena Ebinghaus Gary S. Weissmann Maurício G. M. Santos 《Sedimentology》2019,66(2):736-763
Basin‐scale models are required to interpret ancient continental sedimentary successions, and reduce uncertainty in assessing geological resources in basins. Recently, modern studies show distributive fluvial systems to comprise a substantial proportion of modern sedimentary basins, but their role in ancient basin fills has yet to be quantitatively documented at the basin scale. This study analysed key fluvial characteristics to construct a detailed basin‐wide model of the Palaeogene Fort Union and Willwood formations (Bighorn Basin, Wyoming), using observations from modern studies, and ancient system scale studies of distributive fluvial systems, to guide interpretations. Mapping showed these formations to be highly heterogeneous with channel‐body proportion (from 12 to 81%) and geometry types (large amalgamated bodies to isolated channels), grain size (silt to conglomerate), average channel‐body thickness (4 to 20 m) and average storey thickness (3 to 10 m) varying significantly across the basin. Distributive fluvial systems in the form of alluvial and fluvial fans in transverse configurations were recognized as well as a wide axial system, with heterogeneity in the formations being closely aligned to these interpretations. Furthermore, numerous individual depositional systems were identified within the formations (Beartooth Absaroka, Washakie, Owl Creek and axial). Predicted downstream distributive fluvial system trends (i.e. downstream decrease in channel proportion, size and grain size) were identified in the Beartooth, Absaroka and Owl Creek systems. However, predicted trends were not identified in the Washakie system where intrabasinal thrusting disturbed the sequence. Importantly, a wide axial fluvial system was identified, where reverse downstream distributive fluvial system trends were present, interpreted to be the result of the input of transverse systems of variable size. This study provides a new level of detail in the application of basin‐scale models, demonstrating their usefulness in trying to understand and predict alluvial architecture distribution and heterogeneity, with important implications for economic resources and palaeogeographic reconstructions. 相似文献
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One widely used technique for the construction of equilibrium models of stellar disks is based on the Jeans equations and the moments of velocity distribution functions computed using these equations. Stellar disks constructed using this technique are shown to be “not entirely” in equilibrium. Our attempt to abandon the epicyclic approximation and the approximation of infinite isothermal layers, which are commonly adopted in this technique, failed to improve the situation substantially. We conclude that the main drawback of techniques based on the Jeans equations is that the system of equations employed is not closed and, therefore, requires adopting an essentially ad hoc additional closure condition. A new iterative approach to constructing equilibrium N-body models with a given density distribution is proposed. The main idea behind this approach is that a model is first constructed using some approximation method, and is then allowed to adjust to an equilibrium state with the specified density distribution—if necessary, with the required parameters of the velocity distribution remaining fixed in the process. This iterative approach was used to construct isotropic, spherically symmetric models and models of stellar disks embedded in an external potential. The numerical models constructed prove to be close to equilibrium. It is shown that the commonly adopted assumption that the profile of the radial-velocity dispersion is exponential may be wrong. The technique proposed can be applied to a wide range of problems involving the construction of models of stellar systems with various geometries. 相似文献
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在西藏罗布莎蛇绿岩块的豆荚状铬铁矿中，存在包裹体矿物镁橄榄石，这些镁橄榄石为无色透明多晶面形成的自形晶，Fo值可达到97－98，具富镁端员组分，选取一代表性颗粒的单晶进行X单晶和衍射分析，表明其为斜方晶系，空间群Pbnm，镁橄榄石晶胞参数,a,b,c以及M1－0和M2－0键长均小于地幔包裹体和一般地幔岩中橄缆中的对应值，测试出的晶胞参数与人工合成镁橄榄石的一致，镁橄榄石具有橄榄石族中已知最小的晶胞参数，据此推断它是在超高压环境下结晶的。 相似文献
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S. Uyeda 《International Journal of Earth Sciences》1981,70(2):552-569
In the framework of plate tectonics, the basic mechanism operating in the trencharc-back arc systems is believed to be the subduction of oceanic lithosphere. This model, however, was developed more or less as a logical consequence of sea-floor spreading. The question then is whether or not the subduction model can explain all the major features of the trench-arc-back arc systems. Many features, such as thrust type inter-plate earthquakes and deep earthquakes along Wadati-Benioff zones, are readily explained. But, the occurrences of extentional spreading and high heat flow in the back arc region and arc volcanism are difficult to explain. An approach to solve these problems may be found in what may be called “comparative subductology”: there seem to exist two basically different modes of subduction; one — Chilean type — causing compressional stress regime in the arc and back arc regions, the other — Mariana type — causing tensional. World's subduction zones are classified in terms of the postulated two modes, and some tectonic implications and causes of the two modes are discussed. 相似文献
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沉积盆地型与隆起山地型地热系统地表地球化学异常模式差异性分析 总被引：1，自引：0，他引：1
地球化学勘探技术作为地热资源综合勘查技术之一,在地热勘探开发中发挥了重要作用。沉积盆地型与隆起山地型地热系统由于自身地质特征的不同,必然造成它们的地球化学判识指标和异常模式存在差异。目前国内外尚缺乏对这两种类型地热系统判识指标和地球化学异常模式差异性进行地质地球化学分析,导致针对不同的勘探对象在方法选择和异常解释上依据不足。以典型沉积盆地型地热系统——河北雄县地热系统,隆起山地型地热系统——安徽巢湖半汤地热系统为例,开展地球化学方法试验,建立了两种类型地热系统的地表地球化学异常模式,并从地热系统的地质因素(热源、热水、热储、通道、盖层)出发,对其地表地球化学异常模式差异性进行分析,表明隆起山地型地热系统地表地球化学异常模式为受导水断层、破碎带控制的正异常;沉积盆地型地热系统气体地球化学异常模式为受热储构造控制的正异常,微量元素地球化学异常为受氧化还原环境控制的负异常;二者在有效地球化学指标组合和异常形态上均存在差异。研究结果为不同类型地热系统勘探提供方法和理论依据。 相似文献
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Hydrothermal mineralising systems are discussed as large, open flow chemical reactors held far from equilibrium during their life-time by deformation and the influx of heat, fluid and dissolved chemical species. As such they are nonlinear dynamical systems and need to be analysed using the tools that have been developed for such systems. Hydrothermal systems undergo a number of phase transitions during their evolution and this paper focuses on methods for characterising these transitions in a quantitative manner and establishing whether they resemble either abrupt or continuous (critical) phase transitions or whether they have some other kind of nature. Critical phase transitions are characterised by long range correlations for some parameter characteristic of the system, power-law probability distributions, so that there is no characteristic length scale, and a high sensitivity to perturbations. The transitions undergone in mineralised hydrothermal systems are: (i) widespread, non-localised mineral alteration involving exothermic mineral reactions that produce hydrous silicate phases, carbonates and iron-oxides, (ii) strongly localised veining, brecciation and/or stock-work formation, (iii) a series of localised endothermic mineral reactions involving the formation of non-hydrous silicates, sulphides and metals such as gold, (iv) multiple overprinting repetitions of transitions (ii) and (iii). We quantify aspects of these transitions in some gold deposits from the Yilgarn craton of Western Australia using wavelet transforms. This technique is convenient and fast. It enables one to establish if the transition is multifractal (and if so, quantify the multifractal, or singularity, spectrum) and to determine the scale dependence of long range correlations or anti-correlations. Other aspects of the spectrum enable quantitative distinctions between sub-critical, critical and super-critical systems. The availability of long drill holes with detailed chemical analyses and mineral abundances derived from hyperspectral data enables individual ore bodies to be characterised rapidly in a quantitative manner and constraints placed on whether the various transitions are possibly critical or of some other form. We also present some simple nonlinear models, including numerical simulation, self-organised branching and multiplicative cascade processes that produce the multifractal character and correlation scaling relations observed in these data sets. Distinctions between systems that are strongly and weakly mineralised are discussed. 相似文献
20.
A. D. Chernin P. Teerikorpi V. P. Dolgachev A. A. Kanter L. M. Domozhilova M. J. Valtonen G. G. Byrd 《Astronomy Reports》2012,56(9):653-663
Outward flows of galaxies are observed around groups of galaxies on spatial scales of about 1 Mpc, and around galaxy clusters on scales of 10 Mpc. Using recent data from the Hubble Space Telescope (HST), we have constructed two synthetic velocity-distance phase diagrams: one for four flows on galaxy-group scales and the other for two flows on cluster scales. It has been shown that, in both cases, the antigravity produced by the cosmic dark-energy background is stronger than the gravity produced by the matter in the outflow volume. The antigravity accelerates the flows and introduces a phase attractor that is common to all scales, corresponding to a linear velocity-distance relation (the local Hubble law). As a result, the bundle of outflow trajectories mostly follow the trajectory of the attractor. A comparison of the two diagrams reveals the universal self-similar nature of the outflows: their gross phase structure in dimensionless variables is essentially independent of their physical spatial scales, which differ by approximately a factor of 10 in the two diagrams. 相似文献