Discrete models for vertical vibrations of surface and embedded foundations     

Francisco C. P. De Barros  J. Enrique Luco 《地震工程与结构动力学》1990,19(2):289-303

A five-parameter discrete model that approximates the dynamic force4isplacement relationship for rigid foundations undergoing vertical vibrations on a uniform elastic half-space is presented. The model involves a combination of two springs, two viscous dampers and a mass. Values of the parameters for circular, square and rectangular foundations placed on the surface or embedded in an elastic half-space are listed. The parameters are obtained by minimizing the discrepancy between the force4isplacement relation for the model and that obtained by solution of the mixed boundary-value problem of the rigid foundation on an elastic half-space. The definition of an appropriate input motion to represent wave excitation is also discussed. The input motion to the discrete model differs from the input motion that should be used in a continuum model.  相似文献   

Fractal properties of simulated bed profiles in coarse-grained channels   总被引：2，自引：0，他引：2  

André Robert 《Mathematical Geology》1991,23(3):367-382

Bed roughness characteristics in coarse-grained channels are fairly complex. A hierarchy of roughness elements can be observed, ranging from variable particle sizes and shapes and small-scale sedimentary structures, to large-scale bedforms such as riffle-pool sequences. The effects of these scales of roughness on the flow geometry still remain to be thoroughly investigated. The semivariogram has been suggested in the past as a means of quantifying bed roughness effects on streamflow, as well as for distinguishing between scales of roughness. However, field measurements are rather time-consuming. The low number of bed profiles measured in the field precludes the identification of generally applicable relationships between the statistical properties derived from the semivariograms (such as the Hausdorff dimensions and the scale of autocorrelation corresponding to each fractal band) and the bed configuration itself (geometrical and sedimentological properties). Simulation results of gravel-bed profiles are, therefore, presented in order to complement the original investigation of Robert (1988a). The simulation experiments, based on grain characteristics of sizes and shapes and on morphological properties of small-scale bedforms, yield very significant information on boundary roughness at the microscale and give insight into the interpretation of empirical semivariograms (derived from field measurements). Bed-material sorting, variable grain shapes, and height and spacing of cluster bedforms control the fractal dimensions obtained from the semivariograms, as well as the location of the break of slope and the range of the process.  相似文献   

Mixture of populations     

Hua Zhu  André G. Journel 《Mathematical Geosciences》1991,23(4):647-671

A simple example simulating a mixture of two normal populations results in some important observations, nonnormality and nonsymmetry of the mixture conditional pdf, nonlinearity of the conditional mean as a function of the conditioning data, heteroscedasticity of the conditional variance and its nonmonotonicity as a function of distance of the unknown to the conditioning data. A comparison of the mixture statistics with those predicted by traditional models ignoring the mixture reveals the inadequacy and inappropriateness of these traditional approaches. A mixture of two multivariate normal populations is illustrated through the analytical expressions of its conditional distribution and moments.  相似文献   

Size of earthquakes in southern Mexico from indirect methods     

José A. Canas 《Pure and Applied Geophysics》1991,136(4):479-498

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Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano,Panama   总被引：3，自引：0，他引：3  

Mare J. Defant  Lee F. Clark  Robert H. Stewart  Mark S. Drummond  Jelle Z. de Boer  René C. Maury  Hervé Bellon  Thomas E. Jackson  Juan F. Restrepo 《Contributions to Mineralogy and Petrology》1991,106(3):309-324

The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites. The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics. We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano is related to the subduction of relatively hot lithosphere.  相似文献   

Diabatic wind and temperature profiles obtained from a 100 m tower: A statistical comparison of model performances     

R. San José  J. Regueroa  J. Casanova 《Boundary-Layer Meteorology》1986,37(1-2):1-15

More than 8000 10-min profiles of wind and temperature obtained during an extensive field experiment have been analyzed. The study was carried out in the environs of Valladolid (Spain) where a 100-m and a 6-m meteorological tower are located. Less than 20% of data were discarded due to equipment failure. Because of its exceptional flatness, the site is almost ideal for model performance comparisons.Predicted profiles of wind speed and potential temperature at 12, 26, 51, and 100 m heights were obtained using the methods proposed by Berkowicz and Prahm (1982) and San José (1983) based on values observed on a 6 m tower. Statistical t, F, and R tests were used to determine bias, scatter and correlation. The data were classified according to atmospheric stratification and height above ground. Finally, a determination was made of the predicted wind speeds and potential temperatures that fell within the 1 and 20% confidence ranges centered at the measured value. San José's method performed better than did that of Berkowicz and Prahm for the temperature profiles in both unstable and stable conditions. However, no significant differences were found for the wind speed profiles.  相似文献   

A modified parameterization of flux-profile relationships in the surface layer using different roughness length values for heat and momentum   总被引：1，自引：0，他引：1  

Patrick Mascart  Joel Noilhan  Hervé Giordani 《Boundary-Layer Meteorology》1995,72(4):331-344

The surface-layer flux-profile formulae of Louis (1979), used in many atmospheric models, are modified in a simple way to allow for different values of the roughness lengths for heat and momentum. The modified set of formulae simplifies the calculation of surface-layer fluxes over most natural land surfaces, where the roughness length for momentum can be almost an order of magnitude greater than that for heat.  相似文献   

Observed dependence of the water vapor and clear-sky greenhouse effect on sea surface temperature: comparison with climate warming experiments     

Sandrine Bony  Jean-Philippe Duvel  Hervé Le Trent 《Climate Dynamics》1995,11(5):307-320

This study presents a comparison of the water vapor and clear-sky greenhouse effect dependence on sea surface temperature for climate variations of different types. Firstly, coincident satellite observations and meteorological analyses are used to examine seasonal and interannual variations and to evaluate the performance of a general circulation model. Then, this model is used to compare the results inferred from the analysis of observed climate variability with those derived from global climate warming experiments. One part of the coupling between the surface temperature, the water vapor and the clear-sky greenhouse effect is explained by the dependence of the saturation water vapor pressure on the atmospheric temperature. However, the analysis of observed and simulated fields shows that the coupling is very different according to the type of region under consideration and the type of climate forcing that is applied to the Earth-atmosphere system. This difference, due to the variability of the vertical structure of the atmosphere, is analyzed in detail by considering the temperature lapse rate and the vertical profile of relative humidity. Our results suggest that extrapolating the feedbacks inferred from seasonal and short-term interannual climate variability to longer-term climate changes requires great caution. It is argued that our confidence in climate models' predictions would be increased significantly if the basic physical processes that govern the variability of the vertical structure of the atmosphere, and its relation to the large-scale circulation, were better understood and simulated. For this purpose, combined observational and numerical studies focusing on physical processes are needed.  相似文献   

Roof-rock contamination of magma along the top of the reservoir for the Bishop Tuff     

Wendell A. Duffield  Joaquin Ruiz  James D. Webster 《Journal of Volcanology and Geothermal Research》1995,69(3-4)

The Bishop Tuff, a well known Quaternary high-silica rhyolite in east-central California, is widely considered the type example of a vertically and monotonically zoned pyroclastic deposit that represents zoning in the source magma reservoir, inverted during the process of pyroclastic emplacement. However, the deposit of plinian pumice, which forms the base of the Bishop Tuff and represents the initial 10% or so of all magma erupted during the event that produced the Bishop Tuff, contains features at odds with monotonie zoning for the reservoir. Relative to overlying ignimbrite, the plinian deposit contains a reversal in trace-element zoning. Moreover, the ⁸⁷Sr/⁸⁶Sr is significantly higher than that in overlying ignimbrite (about 0.7084 vs 0.7064), and melt inclusions trapped in quartz phenocrysts exhibit notable variability of trace-element concentrations, even within a single host crystal (e.g., U: 10.77 to 8.91 ppm).These data have been previously interpreted as due to processes of chemical fractionation and evolution operating within a magma system closed to chemical interactions with its roof rocks. For example, the reversal in trace-element zoning has been explained by the first-erupted magma being erupted from somewhat below the top of a monotonically zoned reservoir. However, we submit that the reversed zoning and other above-noted features can be explained equally well as consequences of minor assimilation of roof rocks into a magma reservoir that was erupted from the top down.The basal part of the Bishop Tuff exhibits extreme concentrations and depletions of trace elements, relative to the average composition of crustal rocks. For example, the upward decrease of Sr in the Bishop magma reservoir (downward decrease in the ignimbrite) results in concentrations as low as 2–4 ppm. Because of the attendant ‘chemical leverage’, assimilation of < 1 wt.% of Sierra Nevada batholith rocks typical of the area could readily reverse an ‘uncontaminated’ Sr (and other trace elements) trend of zoning and could also substantially raise ⁸⁷Sr/⁸⁶Sr. Small-scale trace-element variability in the uppermost part of the Bishop magma reservoir, as recorded by the above-mentioned melt inclusions, may simply reflect melt heterogeneity produced by the process of assimilation.  相似文献   

Evolution estivale de la turbidité dans le lac de Neuchâtel     

Par André Bapst  Bernard Kübler 《Aquatic Sciences - Research Across Boundaries》1987,49(1):1-15

Some turbiditic measures carried out by a limnological diffusiometer along with the physico-chemical determinations of the Lake of Neuchatel have permitted to subdivide the water column in 4 distinct layers: the Epilimnium, the Clear Water Layer, the Pelagic Nepheloid Layer and the Benthic Nepheloid Layer.   相似文献