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131.
杜清运 《武汉大学学报(信息科学版)》1992,(1)
图形编辑系统是地理信息系统图形工作站上必不可少的一个组成部分,它对地理信息的获取,更新及其它处理都是至关重要的。在本文中,作者阐述了在微机地理信息系统上实现图形编辑系统时,地图数据的组织结构、系统的实现环境和交互设备等方面应具备的必要前提,并介绍了一个基于微机实现的系统设计。 相似文献
132.
This paper describes and tests two models for estimating net radiation(or the radiation balance)on sloping surfacesof alpine environments.They are an empirical method based on the linear relationship between net radiation and globalsolar radiation and a flux-by-flux method involving the estimation of all the individual components of radiation budgetindependently.The results show that the empirical method is capable of predicting hourly net radiation on sloping sur-faces to within about±53 W m~(-2) under all sky conditions.During clear sky conditions,it could predict net radiation onslopes to within±58 W m~(-2) or 16% of the measured values.The flux-by-flux method,although it did not perform aswell as the empirical method,performed adequately and could give estimates of net radiation on slopes with root meansquare error of less than 74 W m~(-2)(20%)and a mean bias error of 27 W m~(-2)(7%). 相似文献
133.
Jiangchuan Ni Yuntai Chen Ming Wang Mingxi Wu Jiayu Zhou Peide Wang Francis T. Wu 《地震学报(英文版)》1992,5(3):459-467
Based on the three component accelerograms, recorded at near-field distance by a temporary seismic network consisting of digital
cassette tape recording accelerographs, the focal mechanisms of three aftershocks of the April 18, 1985, Luquan, Yunnan Province,
China, earthquake ofM
S=6.1, are calculated using seismic moment tensor inversion technique. The phases of direct P, S and converted SP waves in
the displacement seismograms, produced by twice integrations of the observed accelerograms, are identified via forward calculation
using Green’s functions for homogeneous semi-infinite elastic medium, and used in the inversion. The results of inversion
show that a better fit of synthetic to the observed seismograms of direct as well as converted phases can be achieved if appropriate
weighting functions are used in solving the over definite linear equations. While these aftershocks are of different magnitudes
(M
L=4.8, 3.2 and 3.5, respectively) and hypocentral locations, their focal mechanisms are very similar and consistent with that
of the main shock. This feature demonstrates the intrinsic correlation between the occurrence of aftershocks and the seismogenic
fault of main shock. Our experimentations show that using the near field accelerogram obtained from the digital seismic network
with appropriate azimuthal coverage on the focal sphere, with the aid of even simple medium model, not only the shear dislocation
source, but also the isotropic part and CLVD (compensated linear vector dipole) can be retrieved by the technique of moment
tensor inversion.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 412–419, 1991.
This work is supported by the Chinese Joint Seismological Sciences Foundation and the Western Yunnan Earthquake Prediction
Test Site (WYEPTS), State Seismological Bureau. 相似文献
134.
Differential diatom dissolution in Late Quaternary sediments from Lake Manyara,Tanzania: an experimental approach 总被引:3,自引:0,他引:3
Philip Barker 《Journal of Paleolimnology》1992,7(3):235-251
Diatom dissolution in saline lakes represents an important obstacle to the quantitative reconstruction of water chemistry and climate from lake sediment archives. This problem is here approached experimentally by artificially dissolving diatom-bearing core sediment from Lake Manyara, Tanzania. Manyara holds one of the longest continuous palaeolimnological records from tropical Africa although its interpretation is based on a fragmentary diatom record due to frustule dissolution. These experiments have revealed clear changes in assemblage composition as dissolution operated differentially with respect to diatom taxa. Differential dissolution has considerable impact on the water chemistry estimates derived from transfer functions. Taphonomy, rather than environmental change, may have been responsible for minor fluctuations in the diatom assemblages from Manyara, although major palaeohydrological changes during the Late Pleistocene and Early Holocene can be identified. Particularly well represented by MANE-87 is a period of intermediate lake level between 27 500 and 23 000 14C yr BP which has regional palaeohydrological significance. 相似文献
135.
拉萨近地层风廓线模拟 总被引:1,自引:0,他引:1
本文利用1986年中美联合青藏高原大气科学试验期间的考察资料,研究了拉萨近郊风廊线的特征。从莫宁——奥布赫夫相似理论出发,建立了青藏高原近地层风廓线模拟的模式。 相似文献
136.
137.
The relationships between the diversity of invertebrate communities and the altitude of sampling sites were analysed in 438 benthic samples, collected between 1982 and 1991, in 56 rivers of western Switzerland. Diversity, estimated from total number of taxa (genus or family) and from number of taxa intolerant of pollution, was positively correlated with increasing altitude. In contrast, density of human population and the level of organic pollution were negatively correlated with increasing altitude. Therefore, the upstream increase of invertebrate diversity was attributed to the decrease of human population which is the main source of organic pollution. In this study, altitude was used, instead of organic pollution, to predict diversity. Empirical relationships between diversity and altitude were applied to surveys of water quality to describe the general altitudinal pattern characteristic for each region and to single out anomalous sites and rivers. In addition, changes in the altitudinal patterns of diversity can be used to monitor the recovery of rivers from pollution. 相似文献
138.
Knowledge-Driven and Data-Driven Fuzzy Models for Predictive Mineral Potential Mapping 总被引:5,自引:0,他引:5
In this paper, we describe new fuzzy models for predictive mineral potential mapping: (1) a knowledge-driven fuzzy model that uses a logistic membership function for deriving fuzzy membership values of input evidential maps and (2) a data-driven model, which uses a piecewise linear function based on quantified spatial associations between a set of evidential evidence features and a set of known mineral deposits for deriving fuzzy membership values of input evidential maps. We also describe a graphical defuzzification procedure for the interpretation of output fuzzy favorability maps. The models are demonstrated for mapping base metal deposit potential in an area in the south-central part of the Aravalli metallogenic province in the state of Rajasthan, western India. The data-driven and knowledge-driven models described in this paper predict potentially mineralized zones, which occupy less than 10% of the study area and contain at least 83% of the model and validation base metal deposits. A cross-validation of the favorability map derived from using one of the models with the favorability map derived from using the other model indicates a remarkable similarity in their results. Both models therefore are useful for predicting favorable zones to guide further exploration work. 相似文献
139.
Limitations associated with deterministic methods to quantify demands and develop rational acceptance criteria have led to the emergence of probabilistic procedures in performance‐based seismic engineering. The Pacific Earthquake Engineering Research performance‐based methodology is one such approach. In this paper, the impact of certain modelling decisions made at different stages of the evaluation process on the performance assessment of a typical multi‐bent viaduct is examined. Modelling, in the context of this paper, covers hazard modelling, structural modelling and loss modelling. The specific application considered in this study is a section of an existing viaduct in California: the I‐880 interstate highway. Several simulation models of the viaduct are developed, a series of nonlinear time‐history analyses are carried out to predict demands, measures of damage are evaluated and the probability of closure of the viaduct is estimated using the specified hazard for the site. It is concluded that the methodology offers several advantages over existing deterministic performance‐based procedures. Results of the investigation indicate that the assessment methodology is particularly sensitive to the reliability of decisions made by bridge inspectors following a seismic event, and to the dispersion in the demand estimation, which in turn is influenced by several factors including soil–structure interaction effects and ground motion scaling procedures. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
140.
The scaled boundary finite‐element method has been developed for the dynamic analysis of unbounded domains. In this method only the boundary is discretized resulting in a reduction of the spatial dimension by one. Like the finite‐element method no fundamental solution is required. This paper extends the scaled boundary finite‐element method to simulate the transient response of non‐homogeneous unbounded domains with the elasticity modulus and mass density varying as power functions of spatial coordinates. To reduce the number of degrees of freedom and the computational cost, the technique of reduced set of base functions is applied. The scaled boundary finite‐element equation for an unbounded domain is reformulated in generalized coordinates. The resulting acceleration unit‐impulse response matrix is obtained and assembled with the equation of motion of standard finite elements. Numerical examples of non‐homogeneous isotropic and transversely isotropic unbounded domains demonstrate the accuracy of the scaled boundary finite‐element method. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献