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1.
Large cokriging systems arise in many situations and are difficult to handle in practice. Simplifications such as simple kriging,
strictly collocated and multicollocated cokriging are often used and models under which such simplifications are, in fact,
equivalent to cokriging have recently received attention. In this paper, a two-dimensional second-order stationary random
process with known mean is considered and the redundancy of certain components of the data at certain locations vis-à-vis
the solution to the simple cokriging system is examined. Conditions for the simple cokriging weights of these components at
these locations are set to zero. The conditions generalise the notion of the autokrigeability coefficient and can, in principle,
be applied to any data configuration. In specific sampling situations such as the isotopic and certain heterotropic configurations,
models under which simple kriging, strictly collocated, multicollocated and dislocated cokriging are equivalent to simple
cokriging are readily identified and results already available in the literature are obtained. These are readily identified
and the results are already available in the literature. The advantage of the approach presented here is that it can be applied
to any data configuration for analysis of permissible simplifications in simple cokriging. 相似文献
2.
Walter Leimgruber 《GeoJournal》2005,64(3):239-248
Boundaries can be seen as barriers or as places of contact. It has been suggested that we are “prisoners of borders”, of all
kinds of borders (political, religious, social, cultural, linguistic etc.). While this statement appears to be somewhat exaggerated,
it holds some truth. Boundaries are elements in spatial organization, and they influence daily life in many ways (not only
for people living right along them). The paper addresses the question if we must call ourselves “prisoners” or if we simply
have to live with all kinds of borders. Departing from theoretical observations, the paper discusses the various aspects boundaries
assume in the European context before looking at a few concrete Swiss examples. They reveal that even regions at a certain
distance of the state border will feel its effects (the case of Zurich airport), but the most important benefit can been drawn
by people living in the border area itself (through price differences between the two countries, as exemplified by the Swiss-Italian
border). There may be asymmetry on state borders, but this asymmetry can also swing around: the advantages often lie on both
sides. The paper concludes by pointing to the persistence of the boundary concept. They are a necessity for the organization
of space and society, but they are not absolute. There are always holes in these prison walls, and the examples where boundaries
were impermeable are probably rare. 相似文献
3.
Ryan Holifield 《Geoforum》2009,40(3):363-372
A common source of conflict at hazardous waste sites in the US Environmental Protection Agency’s Superfund program is the accuracy of scientific investigations and representations produced to inform cleanup decisions. Liable firms often produce these technical representations themselves, and communities surrounding sites frequently argue that such “voluntary” investigations are compromised by conflicts of interest. In order to challenge the representations of powerful firms, locally situated actors often develop trans-local connections with expertise and equipment concentrated at distant centers of calculation. Although some interpret the spatial politics of such connecting in terms of “jumping scales,” another important spatial dimension of this network construction is differential positioning. In a conflict over groundwater models at the St. Regis Superfund Site in Minnesota, the counter-network that emerged to challenge the owner’s representations of the site positioned some actors as “outsiders” and others as “insiders.” This differential positioning enabled the counter-network to balance the need to demonstrate the reliability and impartiality of its claims with the requirement to maintain its accountability to local public interests. I argue that these requirements result from the prevalent view of the science-policy interface, which assumes a rigid separation between science and politics. Nonetheless, the conflict over groundwater at St. Regis reveals how at the science-policy interface, speaking for things and speaking for people are thoroughly entangled. 相似文献
4.
《Journal of Structural Geology》1999,21(8-9):917-921
This note poses two related questions about structural evolution in rocks. How easy is it to recognize structural features that have reversed their sense of development over time? Are there circumstances in rock deformation where early intensification of structure sows the seeds for a later, more or less inevitable, diminution of intensity? It is suggested, as a partial answer to the first question, that there is an irreversibility principle inherent to most structural development, such that even if bulk strain is reversed, the structural changes that accompanied `forward' structural development will not be completely reversed when the strain is reversed. Where this principle applies, it should always be possible to recognize structural reversals, by sufficiently close observation of the final state. It is suggested, as a partial answer to the second question, that where energy is stored by forward structural changes, this energy can often be expected to drive further structural changes, and these further changes may sometimes cause the original structure to `bounce' back to a less intense state. These questions may have some bearing on developing a firmer basis for kinematic analysis, and for understanding overprinting structures in orogens. 相似文献
5.
Physical phenomena are observed in many fields (science and engineering) and are often studied by time-consuming computer codes. These codes are analyzed with statistical models, often called emulators. In many situations, the physical system (computer model output) may be known to satisfy inequality constraints with respect to some or all input variables. The aim is to build a model capable of incorporating both data interpolation and inequality constraints into a Gaussian process emulator. By using a functional decomposition, a finite-dimensional approximation of Gaussian processes such that all conditional simulations satisfy the inequality constraints in the entire domain is proposed. To show the performance of the proposed model, some conditional simulations with inequality constraints such as boundedness, monotonicity or convexity conditions in one and two dimensions are given. A simulation study to investigate the efficiency of the method in terms of prediction is included. 相似文献
6.
V. I. Shcheglov 《Mathematical Geology》1991,23(1):77-85
Possible changes of mineralization area seem to be a transformation of hypergeometric distribution of a model within possible maximum boundaries of the ore body. As a model of subboundary misrepresentation of the investigated area, normally distributed random values can be used as variation limits which are determined by dimensions of subboundary zones of uncertainty. A new method for determining boundaries of stratified deposits is suggested (applying polar coordinates). 相似文献
7.
土壤多样性理论方法的新近发展与应用 总被引：20，自引：0，他引：20
与建议也陆续出现 ,按此势头发展下去 ,极有可能使传统土壤学发扬光大 ,对拓宽环境管理与评价的途径具有重要意义。在国家自然科学基金的资助下 ,我们已经将土壤多样性的理论方法介绍到中国[3 4,3 5] ,并且在山东省 1∶10 0万SOTER数据库支持下 ,进行了探索性研究①[3 6 ] 。目前正着手在海南SOTER数据库的支持下 ,对海南省土壤多样性进行多方位、多层次的分析研究 ,相信不久将会有相关研究报告发表土壤多样性理论方法的新近发展与应用@张学雷$中国科学院南京土壤研究所!江苏南京210008
@陈杰$中国科学院南京土壤研究所!江苏南京210… 相似文献
8.
The geotechnical engineer is often faced with the problem of how to assess the statistical properties of a soil parameter on the basis of a sample measured in-situ or in the laboratory with the defect that some values have been replaced by interval bounds because the corresponding soil parameter values have turned out to exceed the capacity of the measuring instrument. Given such a censored sample the problem is to estimate the mean value, variance and certain fractiles of the distribution of the soil parameter as it would be measured by an instrument of unrestricted range. In many situations only a small censored sample is given. To estimate the characteristic value defined as a lower fractile value corresponding to a codified probability value, the geotechnical engineer is thus urged to supplement the information from the measurements at the actual location by considering whatever prior knowledge is available about the soil parameter distribution. The present paper shows how a characteristic value by computer calculations can be assessed systematically from the actual sample of censored data supplemented with prior information from a soil parameter data base. 相似文献
9.
Some current methods to represent the heterogeneity of natural media in hydrogeology 总被引：4，自引：0，他引：4
We have known for a long time that the material properties of the subsurface are highly variable in space. We have learned that this variability is due to the extreme complexity and variation with time of processes responsible for the formation of the earth's crust, from plate tectonics to erosion, sediment transport, and deposition, as well as to mechanical, climatic, and diagenetic effects. As geologists, we learned how to "read" this complex history in the rocks and how to try to extrapolate in space what we have understood. As physicists, we then learned that to study flow processes in such media we must apply the laws of continuum mechanics. As mathematicians using analytical methods, we learned that we must simplify by dividing this complex continuum into a small number of units, such as aquifers and aquitards, and describe their properties by (constant) equivalent values. In recent years, as numerical modelers, we learned that we now have the freedom to "discretize" this complex reality and describe it as an ensemble of small homogeneous boxes of continuous media, each of which can have different properties. How do we use this freedom? Is there a need for it? If the answer is "yes," how can we assign different rock-property values to thousands or even millions of such little boxes in our models, to best represent reality, and include confidence levels for each selected rock property? As a tribute to Professor Eugene S. Simpson, with whom the first author of this paper often discussed these questions, we present an overview of three techniques that focus on one property, the rock permeability. We explain the motivation for describing spatial variability and illustrate how to do so by the geostatistical method, the Boolean method, and the genetic method. We discuss their advantages and disadvantages and indicate their present state of development. This is an active field of research and space is limited, so the review is certain to be incomplete, but we hope that it will encourage the development of new ideas and approaches. 相似文献
10.
The method by Broms for the evaluation of lateral load capacity of piles and shafts is well known to every geotechnical engineer and still used nowadays, at least in some simple situations. It applies to piles with a restrained head at the ground level, or a free head at or above the ground, both for cohesive and cohesionless soils. In this paper the Broms theory for cohesionless soils is extended to account for an arbitrary position of the pile head, considering embedded as well as over-ground restrained and free pile head. Explicit analytic expressions for the collapse load and the geometrical parameters of the problem are given, making use of the geometric approach by Nickalls to the solution of the cubic equation. The relationships between embedding and over-ground situations on one hand, and restrained and free head cases on the other are discussed, some simplified calculation procedures being suggested. 相似文献
11.
Andrej Gosar 《Natural Hazards》2012,62(3):1059-1079
Site effects studies using microtremor free-field measurements were performed recently in five Slovenian towns characterized by increased seismic hazard to determine resonance frequency of soft sediments. In this study, microtremor investigations were extended to the measurements inside buildings to determine their fundamental frequencies and to assess the possible occurrence of soil-structure resonance. Measurements were performed in 66 buildings, and by spectral analysis, it was possible to determine reliably fundamental frequencies (longitudinal and transverse) for 58 buildings. Residential masonry houses with two or three floors prevail, but some buildings of up to six-floor height were also surveyed. Microtremor measurements have proved to be an effective tool for assessment of fundamental frequencies of buildings. Such experimental approach is very valuable, as analytical seismic evaluation of an existing building is usually very difficult. Statistical analysis of the fundamental frequency versus number of floors (height) was performed to generalize identification of potential soil-structure resonance. The difference in average fundamental frequency is very clear between buildings with two and three floors. The average value of both horizontal components for two-floor buildings is 9.11?±?1.94?Hz, and for three-floor buildings, 7.03?±?1.46?Hz. On the other hand, the difference in frequencies between three- and four-floor buildings (average for later is 6.52?±?0.80?Hz) is very small. The average fundamental frequencies for five- and six-floor buildings are lower, 4.62?±?0.64?Hz and 5.30?±?0.70?Hz, respectively, with no statistically significant difference between both types. Most Slovenian towns are located in shallow sedimentary basins where the free-field soft covers frequencies are in the range 2?C20?Hz. On the other hand, houses with two and three floors represent the large majority of the building stock. To assess the possible occurrence of soil-structure resonance in general, an average fundamental frequency?±?one standard deviation interval is obtained for these two building heights, which gives the range 5.6?C11.1?Hz. The free-field data show that this frequency range occupies from 22?% of the surveyed area in the Kobarid basin to up to 59?% in the Bovec basin and is in between for other three basins. This leads to the conclusion that the possible occurrence of soil-structure resonance is a serious issue for typical geological situations, in which towns are located. 相似文献
12.
Keith Beven 《Comptes Rendus Geoscience》2012,344(2):77-88
The environmental modeller faces a dilemma. Science often demands that more and more process representations are incorporated into models (particularly to avoid the possibility of making missing process errors in predicting future response). Testing the causal representations in environmental models (as multiple working hypotheses about the functioning of environmental systems) then depends on specifying boundary conditions and model parameters adequately. This will always be difficult in applications to a real system because of the heterogeneities, non-stationarities, complexities and epistemic uncertainties inherent in environmental prediction. Thus, it can be difficult to define the information content of a data set used in model evaluation and any consequent measures of belief or verisimilitude. A limit of acceptability approach to model evaluation is suggested as a way of testing models, implying that thought is required to define critical experiments that will allow models as hypotheses to be adequately differentiated. 相似文献
13.
Coastal aquifers of Europe: an overview 总被引：8，自引：3，他引：5
Emilio Custodio 《Hydrogeology Journal》2010,18(1):269-280
Europe has a long coastline along which many human activities are concentrated. Coastal aquifer development is often intensive and subject to salinity problems as a result of seawater intrusion, upconing of deep saline water, and residual salinity in aquitards. Studies have been carried out since the end of the nineteenth century, and have set the basic principles of freshwater/marine-water relations. Some aquifers are carefully studied, monitored and managed; examples can be found in The Netherlands, Belgium, southern Italy and northeastern Spain. Often important coastal aquifers are of relatively small size but crucial to supply human needs, which vary from mostly urban and industrial in mid to high latitudes, to dominantly seasonal for irrigation in the Mediterranean area and the archipelagos. The different situations can be grouped into: recent deltas, other coastal detritic formations, carbonate formations, and the special situations in small islands. Comments on these situations are provided and some examples are introduced, just for illustration. 相似文献
14.
Trond Mannseth 《Computational Geosciences》2007,11(1):59-72
We consider discretization on quadrilateral grids of an elliptic operator occurring, for example, in the pressure equation
for porous-media flow. In a realistic setting – with non-orthogonal grid, and anisotropic, heterogeneous permeability – special
discretization techniques are required. Mixed finite element (MFE) and multipoint flux approximation (MPFA) are two methods
that can handle such situations. Previously, a framework for analytical comparison of MFE and MPFA in special cases has been
suggested. A comparison of MFE and MPFA-O (one of two main variants of MPFA) for isotropic, homogeneous permeability on a
uniformly distorted grid was also performed. In the current paper, we utilize the suggested framework in a slightly different
manner to analyze and compare MFE, MPFA-O and MPFA-U (the second main variant of MPFA). We reconsider the case previously
analyzed. We also consider the case of generally anisotropic, homogeneous permeability on an orthogonal grid. 相似文献
15.
Yılmaz Mahmutoğlu 《Environmental Earth Sciences》2017,76(12):435
Engineering properties of building stones can vary because of degradation by weathering agents. Thermal fluctuation is one of the most important agents on deteriorations such as sugaring, bowing, cracking and spalling of marble. As a result, physical and mechanical properties of marble used in the construction of old and/or modern structures are adversely affected by time. On the other hand, some properties of building stones are always required for decision of rehabilitation works. Several kinds of conventional tests have been suggested for characterization of stones, to measure their properties or to evaluate conservation or repair works. However, in most cases, sampling from historical buildings is not possible. Therefore, nondestructive testing methods are often suggested for the prediction of weathering grade of building stones. One of the most practical methods for similar purposes is ultrasonic pulse velocity measurement, which can be performed easily. The main goal of this study is attainment of sound empirical correlations between the ultrasonic pulse velocity and engineering properties of previously deteriorated marble. Experimental works were conducted on seven different specimen categories of a coarse-grained marble having different micro-crack frequencies induced by both cyclical heating–cooling and freeze–thaw actions. The experimental results indicated that physical and mechanical properties of Mu?la marble can be reliably estimated for different environmental cases by ultrasonic pulse velocities. P-wave velocities in dry and saturated cases are two sound indicators of both the apparent porosity and the coefficient of capillary absorption, and whereby the sugaring type of deterioration for coarse-grained marbles. 相似文献
16.
Water reservoirs, lakes, and larger basins, including their drainage areas, represent sedimentologically closed to semi-closed denudation-accumulation systems. The mean rates of mechanical denudation, DRme, and clastic sedimentation, SRme, are related by the ratio of the drainage/lake area, Ad/Al. If the latter is known, DRme (or the specific sediment yield SY in t per km2/a) can be calculated from SRme, or vice versa. The best data for modern SY mainly come from the sediment fills of artificial reservoirs. Small drainage areas of mountainous regions show SY values up to two orders of magnitude higher than lowlands and approximately one order higher than larger regions of mixed relief. This is also true of arid to semi-arid zones which often provide approximately as much sediment (SY) as humid temperate and even tropical zones of comparable relief. Lithology and climate (river runoff) also may play some role for SY from catchments of limited size. The importance of these factors is exemplified by perialpine lakes and two East African lakes. Sediment yields gained from some large reservoirs compare well with long-term denudation rates derived from geological studies (e.g., the Tarbela dam reservoir along the Indus River). In many other cases, human activities have raised SY by factors of 2–10, locally up to >100. Artificial reservoirs in mountainous regions with SY in the range of 300–2000?t?per?km2/a tend to become filled within several tens to hundreds of years; some have even shorter lifetimes. Perialpine lakes of the Alps and British Columbia are strongly affected by delta prograding and have lifetimes mostly between 15 and 40?ka. Closed lake systems in deep morphological depressions (Lake Bonneville, Aral Sea, northern Caspian Sea) have a high potential for sediment storage up to the level of spillover and therefore can persist over long time periods. Basins with markedly subsiding basin floors (lakes of the East African rift zone, the southern Caspian Sea, and the Black Sea, both on oceanic crust) can survive for many Ma in the future, despite relatively high terrigenous input. 相似文献
17.
Resistivity inverse problems are routinely solved in order to characterize hydrocarbon bearing formations. They often require a large number of forward problems simulations. When considering a one dimensional (1D) planarly layered media, semi-analytical methods can be employed in order to solve a single forward problem in a fraction of a second. However, in some situations, a large number of (over one million) simulations is required, preventing this method to be used as a real time (logging) alternative. In this paper, we propose a novel semi-analytical method that dramatically reduces the total computational time, so it can be employed for real time inversion. In our proposed method, we select an ad hoc basis representation for the spectral solution such that its inverse Hankel transform can be computed analytically. The proposed method requires a pre-process that is expensive when compared with a single evaluation in classical semi-analytical methods. However, subsequent evaluations can be rapidly obtained, decreasing thus the total computational time by orders of magnitude when the number of required forward simulations is large. 相似文献
18.
洪水浸泡和水位骤降情况下黄河下游堤防堤岸稳定性分析 总被引：1，自引：0，他引：1
水库库岸边坡稳定在水位骤降工况下的研究目前已比较成熟,但对黄河下游堤防在水位骤降工况下的堤坡稳定状态却研究甚少。通过选取黄河下游标准化堤防某段堤岸边坡为研究对象,建立有限元渗流模型,提出黄河下游堤防的水位骤降速度标准,同时分析了在水位骤降速度为2、4、5 m/d时的坡内浸润线变化、堤岸稳定性变化,以及在水位骤降组合洪水浸泡最不利工况下的堤岸稳定状态。通过分析,给出水位下降情况、水位下降组合浸泡情况下的堤岸稳定状态图,并从图中可以查出在某一水位下降速度、洪水水位降至某一高程处的堤岸稳定状态,为工程人员在堤防建设中运用和推广提供了便利。 相似文献
19.
A liquefaction severity index suggested for engineering practice 总被引：4，自引：0，他引：4
One of the major tasks in earthquake geotechnical engineering is the preparation of liquefaction susceptibility maps. For this purpose, some indices associated with liquefaction susceptibility are used. However, the currently used indices have some limitations. In this study, a liquefaction severity index, which can be used in preparation of susceptibility maps, is suggested. The suggested severity index is applied to two sites selected from Taiwan (Yuanlin) and Turkey (Inegol) to examine performance. The application indicated that the suggested index shows a good performance for the selected sites, and can be considered as a tool for further studies. 相似文献
20.
Marine overwash from the north a few centuries ago transported hundreds of angular cobbles and boulders tens to hundreds of meters southward from limestone outcrops in the interior of Anegada, 140?km east?Cnortheast of Puerto Rico. We examined two of several cobble and boulder fields as part of an effort to interpret whether the overwash resulted from a tsunami or a storm in a location where both events are known to occur. One of the cobble and boulder field extends 200?m southward from limestone outcrops that are 300?m inland from the island??s north shore. The other field extends 100?m southward from a limestone knoll located 800?m from the nearest shore. In the two fields, we measured the size, orientation, and spatial distribution of a total of 161 clasts and determined their stratigraphic positions with respect to an overwash sand and shell sheet deposit. In both fields, we found the spacing between clasts increased southward and that clast long-axis orientations are consistent with a transport trending north?Csouth. Almost half the clasts are partially buried in a landward thinning and fining overwash sand and none were found embedded in the shelly mud of a pre-overwash marine pond. The two cobble and boulder fields resemble modern tsunami deposits in which dispersed clasts extend inland as a single layer. The fields contrast with coarse clast storm deposits that often form wedge-shaped shore-parallel ridges. These comparisons suggest that the overwash resulted from a tsunami and not from a storm. 相似文献