共查询到20条相似文献，搜索用时 31 毫秒
1.
进化序列系统学是古生物学中研究物种间和类别间的系统发育关系为目的的学科, 包括研究物种或类别间的亲缘关系, 并确定它们形成的先后序列.表型-分支系统学是该系统学的基础.分支系统学的许多重要概念在该系统学中加入了时间的含义, 例如, 认为最亲近的姐妹种之间的时间间隔不会超过它们母种的生存期.姐妹群和性状镶嵌分析是进化序列研究的主要方法, 而理解性状镶嵌分布是关键.这些分析可由计算机程序实现.以二叠纪瓦岗珊瑚类作为研究进化序列系统学的实例, 该类在特提斯地区广泛分布.通过对瓦岗珊瑚类的特征分析确定了17个性状用于研究, 并且每一性状确定了几个变化状态.根据最广布的性状状态、化石记录和个体发生等原则分辨出近祖性状状态, 并根据性状在系统发育中的重要性确定性状分级.然后, 确定了姐妹群间的关系和物种间的进化序列.在姐妹群与进化序列分析相互检验中可发现性状退化、平行演化和多向分支等古生物学重要现象, 并分辨出物种的异常顺序.在检验生物地层学首次出现事件讨论中推测了一些化石首次出现的可能层位. 相似文献
2.
Samples from hazardous waste site investigations frequently come from two or more statistical populations. Assessment of background levels of contaminants can be a significant problem. This problem is being investigated at the U.S. Environmental Protection Agency's Environmental Monitoring Systems Laboratory in Las Vegas. This paper describes a statistical approach for assessing background levels from a dataset. The elevated values that may be associated with a plume or contaminated area of the site are separated from lower values that are assumed to represent background levels. It would be desirable to separate the two populations either spatially by Kriging the data or chronologically by a time series analysis, provided an adequate number of samples were properly collected in space and/or time. Unfortunately, quite often the data are too few in number or too improperly designed to support either spatial or time series analysis. Regulations typically call for nothing more than the mean and standard deviation of the background distribution. This paper provides a robust probabilistic approach for gaining this information from poorly collected data that are not suitable for above-mentioned alternative approaches. We assume that the site has some areas unaffected by the industrial activity, and that a subset of the given sample is from this clean part of the site. We can think of this multivariate data set as coming from two or more populations: the background population, and the contaminated populations (with varying degrees of contamination). Using robust M-estimators, we develop a procedure to classify the sample into component populations. We derive robust simultaneous confidence ellipsoids to establish background contamination levels. Some simulated as well as real examples from Superfund site investigations are included to illustrate these procedures. The method presented here is quite general and is suitable for many geological and biological applications. 相似文献
3.
On Evolutionary Sequence Systematics: Taking Permian Waagenophylloid Coral Fauna as an Example 总被引：2，自引：0，他引：2
INTRoDUCTIONEvolutionarysequencesystematicsisadisciplineinpale-ontologyandbiology,themainpurposeofwhichistostudyphylogeneticsystemoforganisms.Twojobsareincludedinthediscipline:(l)tounderstandkinshipamongspeciesortaxa,and(2)toshowtheirevolutionarysequence.Hennig(1966)definedtheconceptofphylogeneticrelationshipasthat:ThespeciesBandCcamefromasameancestor,butthespeciesAdidnotcomefromtheancestor,Therefore,there-lationshipbetweenspeciesBandCiscloserthanspeciesA.Thisdefinitioncontainsonlythef… 相似文献
4.
The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces. 相似文献
5.
Maureen G. Walsh Mark B. Bain Thomas Squiers John R. Waldman Isaac Wirgin 《Estuaries and Coasts》2001,24(1):41-48
Shortnose sturgeon,Acipenser brevirostrum, is a small, endangered species which occurs in 19 estuary systems along the east coast of North America. These populations are considered as separate entities by the U. S. National Marine Fisheries Service although evidence of morphologic or genetic differentiation among populations has not been documented. The purpose of this study was to compare morphological and genetic atributes among shortnose sturgeon collected from the Kennebec and Androscoggin Rivers, Maine, and the Hudson River, New York. Six morphometric and five meristic characteristics were quantified. Multivariate and univariate analyses of covariance and variance were used to assess differences among populations. Our analyses provided evidence for distinct populations in the Androscoggin and Kennebec Rivers, but character differentiation was greater between fish from these two locations and the Hudson River. Analysis of morphometric characters indicated significant differences in fish shape among the three rivers, with Hudson River sturgeon differing from the Maine rivers for the characters of head length, snout length, and mouth width. Significant differences were observed for meristic characters, but pairwise comparisons did not reflect a clear pattern of variability. Sequencing of a portion of the mitochondrial DNA control region revealed 15 haplotypes among 73 total specimens from the three rivers. Shortnose sturgeon from the Kennebec and Androscoggin Rivers were different from each other (p=0.0260); both differed significantly (p<0.0001) from the Hudson River collection. Gene flow was estimated at approximately 7 female migrants per generation between the two Maine populations and about 1 per generation between each of the Maine populations and the Hudson River population. Such strong stock structuring among presumably recently established post-Pleistocene (<10,000 yr) populations suggests that this species occurs in highly discrete units. Morphological and genetic variation observed in this study combined with current knowledge of life history attributes of shortnose sturgeon indicate that conservative management decisions are necessary until the patterns and extent of differentiation among populations species-wide can be investigated further. 相似文献
6.
岩石结构特征对岩爆的影响研究 总被引：2，自引：0，他引：2
岩爆是道及地下工程中常见的地质灾害，正确评价岩爆的烈度具有重要意义。以地岩爆烈度的研究侧重于岩爆岩石力学，而忽略了岩石结构特征的影响，从工程地质角度探讨了岩石原颗粒排列及颗粒的连接对岩爆裂度的影响，从断裂撂学角度分析了微裂隙的扩展规律及其对岩爆烈度影响的规律。 相似文献
7.
PETER NEUMANN-MAHLKAU 《Sedimentology》1967,9(3):245-261
Granulometric analysis of rudites on outcrop-photographs As it is impossible to determine the grain-size distribution of well-consolidated rudites by sieving, it has been attempted to use outcrop-photographs for their granulometric analysis. In order to assess the accuracy of this photo-method, nineteen samples of poorly consolidated rudites were subjected to analysis by both methods. It resulted that the two sets of data obtained could be correlated rather well, using a relatively simple formula. Although some broader experimental work would still seem advisable, it became quite clear that the photo-method is simpler as well as more accurate than the sieving method. It is therefore suggested to develop it as the standard method for granulometric studies of all rudites. 相似文献
8.
N. A. Ekimova P. A. Serov T. B. Bayanova I. R. Elizarova F. P. Mitrofanov 《Doklady Earth Sciences》2011,436(1):28-31
This paper presents data on the distribution of REEs in sulfide minerals from ore-bearing gabbronorites in the Penikat layered
intrusion and the results of their isotopic-geochronological Sm-Nd study. A new procedure for determination of REEs in the
samples without preliminary separating and concentrating was tested on standard samples to be further used for analysis of
sulfide minerals. Analysis of the spectra of the REE distribution in sulfides represents a distribution trend that is similar
to the already studied bulk rock and allows deducing that the character of the REE distribution in sulfide minerals from gabbronorites
in the Penikat layered intrusion was inherited from the parent magma melt; while the formation of sulfides took place at the
stage of rock crystallization. The performed complex studies allow considering that sulfides can be successfully used together
with the rock-forming minerals in Sm-Nd dating of ore-bearing mafite-ultramafite intrusions. 相似文献
9.
H. Ivert 《Cretaceous Research》1980,1(1):49-59
Six morphometrical characters are analyzed on each of 64-specimens of Gabonella elongata, de Klasz & Meijer (1960), picked out from the same level in the Upper Campanian part of a borehole core from western Nigeria. Multivariate statistical analyzes by means of standard methods, show the existence of trimorphism with one microspheric and two megalospheric generations, in this paper denoted Me1 and Me2. The generations are well separated by differences in size, morphological variability and ontogeny. There is a tendency for a reduction in size of the last chamber in the megalospheric populations, especially in Me1. 相似文献
10.
Here we report a new iguanodontian dentary found from the Lower Cretaceous Khok Kruat Formation, Nakhon Ratchasima, northeast Thailand. A unique character, which is an elongated and flat shape of the dentary ramus, makes it possible to assign the specimen to the new genus of non‐hadrosaurid iguanodontian, Ratchasimasaurus suranareae gen. et sp. nov. R. suranareae shows both primitive and derived characters, such as a caudally inclined coronoid process and alveolar trough with a primitive crown impression, and a derived buccal shelf between tooth row and coronoid process. The discovery of a new iguanodontian from the Indochina Terrene, considering that the previously reported “Probactrosaurus‐like” iguanodontian, points out a great diversity of this group in the late Early Cretaceous in Thailand, and corresponds to the Asian iguanodontian diversity at that time. 相似文献
11.
J. C. Gower 《Mathematical Geology》1970,2(1):39-45
Some of the problems of weighting characters and of eliminating correlational effects between characters are discussed. Many
different weighting schemes can be proposed for similarity coefficients even when, as in Burnaby’s coefficient, it is decided
to give high weight to matches between rare states. The rarity of a character state must be considered relative to the sampling
scheme used to select the sampling units. Similarities between all pairs of units may be analyzed to suggest groups among
the units. Groups having many correlated characters may be the most useful but are unlikely to be found by numerical methods
which eliminate correlational effects. 相似文献
12.
Application of bivariate extreme value distribution to flood frequency analysis: a case study of Northwestern Mexico 总被引：1，自引：0，他引：1
Carlos Escalante-Sandoval 《Natural Hazards》2007,42(1):37-46
In Mexico, poverty has forced people to live almost on the water of rivers. This situation along with the occurrence of floods
is a serious problem for the local governments. In order to protect their lives and goods, it is very important to account
with a mathematical tool that may reduce the uncertainties in computing the design events for different return periods.
In this paper, the Logistic model for bivariate extreme value distribution with Weibull-2 and Mixed Weibull marginals is proposed
for the case of flood frequency analysis. A procedure to estimate their parameters based on the maximum likelihood method
is developed. A region in Northwestern Mexico with 16 gauging stations has been selected to apply the model and regional at-site
quantiles were estimated. A significant improvement occurs, measured through the use of a goodness-of-fit test, when parameters
are estimated using the bivariate distribution instead of its univariate counterpart. Results suggest that it is very important
to consider the Mixed Weibull distribution and its bivariate option when analyzing floods generated by a␣mixture of two populations. 相似文献
13.
南沙西南海域万安盆地油气地质条件及其油气分布特征 总被引：3，自引：0，他引：3
通过收集南沙西南海域近几十年来的油气田（井）勘探资料和近年来的地球物理调查成果，在研究区域地质，沉积特征，油气地质条件与烃源岩演化关系的基础上，分析油气资源在整个盆地横向上和纵向上的分布特征，并总结其分布规律性。 相似文献
14.
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
15.
The cumulative distribution function (CDF) of magnitude of seismic events is one of the most important probabilistic characteristics in Probabilistic Seismic Hazard Analysis (PSHA). The magnitude distribution of mining induced seismicity is complex. Therefore, it is estimated using kernel nonparametric estimators. Because of its model-free character the nonparametric approach cannot, however, provide confidence interval estimates for CDF using the classical methods of mathematical statistics.To assess errors in the seismic events magnitude estimation, and thereby in the seismic hazard parameters evaluation in the nonparametric approach, we propose the use of the resampling methods. Resampling techniques applied to a one dataset provide many replicas of this sample, which preserve its probabilistic properties. In order to estimate the confidence intervals for the CDF of magnitude, we have developed an algorithm based on the bias corrected and accelerated method (BCa method). This procedure uses the smoothed bootstrap and second-order bootstrap samples. We refer to this algorithm as the iterated BCa method. The algorithm performance is illustrated through the analysis of Monte Carlo simulated seismic event catalogues and actual data from an underground copper mine in the Legnica–Głogów Copper District in Poland.The studies show that the iterated BCa technique provides satisfactory results regardless of the sample size and actual shape of the magnitude distribution. 相似文献
16.
A Bayesian procedure for Probabilistic Tsunami Hazard Assessment 总被引：1，自引：1，他引：0
In this paper, a Bayesian procedure is implemented for the Probability Tsunami Hazard Assessment (PTHA). The approach is general
and modular incorporating all significant information relevant for the hazard assessment, such as theoretical and empirical
background, analytical or numerical models, instrumental and historical data. The procedure provides the posterior probability distribution that integrates the prior probability distribution based on the physical knowledge of the process
and the likelihood based on the historical data. Also, the method deals with aleatory and epistemic uncertainties incorporating
in a formal way all sources of relevant uncertainty, from the tsunami generation process to the wave propagation and impact
on the coasts. The modular structure of the procedure is flexible and easy to modify and/or update as long as new models and/or
information are available. Finally, the procedure is applied to an hypothetical region, Neverland, to clarify the PTHA evaluation in a realistic case. 相似文献
17.
R. Bianchi A. Forni F. Cámara R. Oberti H. Ohashi 《Physics and Chemistry of Minerals》2007,34(8):519-527
The synthetic LiGaSi2O6 clinopyroxene is monoclinic C2/c at room-T. Its experimental electron density, ρ(r), has been derived starting from accurate room-T single-crystal diffraction data. Topological analysis confirms an intermediate ionic-covalent character for Si–O bonding,
as found by previous electron-density studies on other silicates such as diopside, coesite and stishovite. The non-bridging
Si–O bonds have more covalent character than the bridging ones. The Ga–O bonds have different bonding characters, the Ga–O2
bond being more covalent than the two Ga–O1 bonds. Li–O bonds are classified as pure closed-shell ionic interactions. Similar
to spodumene (LiAlSi2O6), Li has sixfold coordination, but the bond critical points associated to the two longest bonds are characterized by very
low electron density values. Similar to what previously found in spodumene and diopside, O···O interactions were detected
from the topological analysis of ρ(r), and indicate a cooperative interaction among the lone pairs of neighbouring oxygen atoms. In particular, this kind of interaction
has been obtained for the O1···O1 edge shared between two Ga octahedra. Integration over the atomic basins gives net charges
of −1.39(10), 2.82(10), 1.91(10) and 0.82(8) e for O (averaged), Si, Ga and Li atoms, respectively. Periodic Hartree–Fock
and DFT calculations confirm the results obtained by multipole refinement of the experimental data. Moreover, the theoretical
topological properties of the electron density distribution on the Si2O6 group are very similar to those calculated for spodumene.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Interpolation for geochemical surface reconstruction incorporating topographic catchment definitions
Geochemical surfaces are reconstructed by interpolating geochemical measurements obtained from stream-water and stream-sediment samples. The geographical region that influences (and therefore is represented by) the value of a geochemial sample is its topographic catchment area. However, standard convention is to treat and to record the stream sample in the database as a point location, and to reconstruct geochemical surfaces utilizing conventional point interpolation procedures. These interpolation procedures assume, generally, that a data point exerts geographical influence away from itself in all directions, and that influence declines with distance away from that data point. Conventional interpolation procedures are poorly suited for reconstructing geochemical surfaces from stream samples; they do not take into account the true geographic area that geochemical sample points represent (topographic catchments). In this paper we propose a method of interpolation which assumes that data points are representative of their topographic catchment areas. Experimental data indicates that a surface reconstruction procedure which preserves the areal character of geochemical samples provides results more meaningful than surfaces reconstructed using more conventional interpolation techniques. 相似文献
19.
Modeling soil variability as a random field 总被引：1，自引：0，他引：1
R. Baker 《Mathematical Geology》1984,16(5):435-448
The observed variability in the spatial distribution of soil properties suggests that it is natural to describe such distribution as a random field. One of the ways to study engineering problems in such a stochastic setting is by the use of the Monte-Carlo simulation procedure. Application of this technique requires the capability to generate a large number of realizations of a given random field. A numerical procedure for the generation of such realizations in two-dimensional space is introduced as a finite difference approximation of a stochastic differential equation. The equation used was that suggested by Heine (1955). The resulting procedure is essentially similar to other autoregressive procedures used for the same purpose (Whittle, 1954; Smith and Freeze, 1979). However, contrary to these procedures, the present one is defined in terms of physically significant parameters:r
0, the autocorrelation distance;, the discretization size; and the standard deviation, . Formulating the simulation procedure in terms of the physically significant parameters (r
0,, ) greatly simplifies the task of generating realizations that are compatable with a given soil deposit. 相似文献
20.
层状盐岩体三维Cosserat介质扩展本构模型的程序实现 总被引：3，自引：1，他引：2
对层状盐岩体内的油（气）储存硐室进行稳定性计算时,如何选用恰当的本构模型来反映层状盐岩体的特点是至关重要的。针对我国大多数盐矿为多层盐岩的地质构造特征,基于宏观平均意义下的考虑细观弯曲效应的三维Cosserat介质扩展本构模型,结合FLAC3D软件的主要计算思路,使用VC++平台开发了该模型的FLAC3D接口程序,并编译成动态链接库DLL文件。经算例验证,该程序的计算结果可靠,不仅可以考虑不同力学特性的岩层先后破坏引起复合体单元的渐进损伤破坏,而且引入了夹层体积含量等统计参数后可大大节省单元网格数量,为大型层状岩体内的地下硐室稳定性数值模拟计算奠定了基础。 相似文献