Editorial: Three essays of remembrance on the life of Helmut Landsberg     

Stephen H. Schneider 《Climatic change》1986,9(3):259-259

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Vegetative physiographic analysis of a U.S. northern barrier system     

Robert E. Zaremba  Stephen P. Leatherman 《Environmental Geology》1986,8(4):193-207

A quantitative analysis of historical aerial photographs and maps coupled with detailed field surveys provided the data necessary to assess the importance of overwash processes and vegetative recovery on Nauset Spit, Cape Cod, Massachusetts Development of all plant communities and physiographic features is extremely rapid on the spit. Dunes are evident from aerial photographic analysis in as little as three years after overwash; salt marshes are apparent in only ten years. Classical ecological succession does not appear to occur on Nauset Spit, since environments are periodically altered by overwash processes. Most dominant species on the barrier can grow in bare sandy substrate. Migration of the Nauset Spit, system proceeds by a cyclic series of events, involving inlet dynamics, overwash processes, and dune building  相似文献   

The entrainment of high-viscosity magma into low-viscosity magma in eruption conduits     

Armin Freundt  Stephen R. Tait 《Bulletin of Volcanology》1986,48(6):325-339

We report experiments on the flow of two fluids of contrasting viscosity through a pipe in which low-viscosity fluid occupies the center of the pipe. The volume flux of the low-viscosity fluid in the pipe increased during an experiment but did not reach 100% in most cases. The transition from high- to low-viscosity-dominated outflow involved a drop in pressure gradient and an increase in flow rate due to reduced viscous resistance in the pipe. Initially, the central flow was thin and parallel-sided, but as its diameter increased the flow became unstable. A sequence of instabilities was observed during the course of each experiment, both in time and as a function of height in the pipe. In the most commonly observed instability the central flow adopted a helical geometry. The transition from parallel-sided to unstable flow first appeared at the top of the pipe and propagated downwards against the flow. Axisymmetric instabilities originating at the pipe entrance were also observed. All forms of instability exhibited entrainment of viscous fluid into the faster moving central flow. Entrainment was extensive early in the existence of the central flow, but later on the volume flux of lower-viscosity fluid in the central flow rose more rapidly than the rate of entrainment and the proportion of lower-viscosity fluid increased with time. These compositional changes determined the viscosity of the central flow which was found to control its diameter and velocity. In banded pumice deposits, silicic pumice without mafic component is commonly erupted alongside banded pumice blocks. We infer that banded pumice may correspond to the central flow in our experiments, i. e., that viscous magma has been incorporated into less viscous melt, and that pure acid pumice is derived from the outer flow. Changes in eruption style may be caused by variations in pressure gradient and flow rate due to changes in the viscosity of the melt in the conduit. Varied mafic/silicic proportions and degree of mixing in magmatic associations are controlled by the bulk volume erupted, discharge rate, initial temperature difference and aspect ratio of the conduit.  相似文献   

Elimination of spurious higher-mode response in pseudodynamic tests     

Pui-Shum B. Shing  Stephen A. Mahin 《地震工程与结构动力学》1987,15(4):425-445

In a pseudodynamic test, errors in restoring-force feedback are introduced into numerical computations. Some of these errors can excite the higher-frequency response of the specimen. In this paper, the use of viscous and numerical dampings to eliminate spurious higher-frequency effects is studied. Since the tangent stiffness of a non-linear specimen cannot be measured accurately, initial-stiffness-dependent viscous damping is considered. In addition, an explicit integration algorithm with desired numerical damping properties is proposed and examined. The analytical and numerical studies presented indicate that viscous-damping properties can be substantially changed by non-linear deformations. For this reason, the use of numerical damping appears to be more advantageous.  相似文献   

Bimodal magmatism and associated sedimentary facies with particular reference to the correlation between orogeny and regression     

Stephen Ayrton 《International Journal of Earth Sciences》1987,76(1):81-88

It is stressed that a thorough investigation of the subtle and still poorly understood relationships between orogeny, magmatism and associated sediments is warranted. Certain types of sediments appear to be commonly linked to specific magmatic contexts. This is especially true for the oceanic crust, but it may be equally valid for bimodal continental magmatism with the development of granite. Grand scale regression with the formation of continental detrital deposits could represent the response to mantle upwelling and/or plume activity.

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Zusammenfassung Zwischen Orogenese, Magmatismus und zugehörigen Sedimenten existiert ein enger Zusammenhang, der meist wenig verstanden ist und dringend eingehender Studien bedarf. Gewisse Sediment-Typen sind meist an einen ganz spezifischen, magmatischen Kontext gebunden. Dies ist insbesondere der Fall für die ozeanische Kruste, könnte aber auch für den bimodalen, kontinentalen magmatischen Zyklus mit der Bildung von Granit zutreffen. Die gro\räumigen Regressionen und die damit verbundene Entstehung von kontinentalen, detritischen Ablagerungen könnte die Antwort auf vertikale Mantel-Konvektion oder Plume-Aktivität sein.

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Résumé Il est important de mieux comprendre les relations subtiles existant entre orogenèse, magmatisme et sédiments associés. Certains types de sédiments sont systématiquement apparentés à un contexte magmatique spécifique. Ceci est particulièrement évident pour la croûte océanique, mais pourrait Être également valable dans le cadre du magmatisme continental bimodal avec développement de granite. Les régressions à grande échelle avec formation de sédiments détritiques continentaux pourraient représenter la conséquence d'une activité accrue et/ou de mouvements convectifs du manteau.

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The lattice dynamics and thermodynamics of the Mg2SiO4 polymorphs     

Geoffrey D. Price  Stephen C. Parker  Maurice Leslie 《Physics and Chemistry of Minerals》1987,15(2):181-190

We use an approach based upon the Born model of solids, in which potential functions represent the interactions between atoms in a structure, to calculate the phonon dispersion of forsterite and the lattice dynamical behaviour of the beta-phase and spinel polymorphs of Mg₂SiO₄. The potential used (THB1) was derived largely empirically using data from simple binary oxides, and has previously been successfully used to model the infrared and Raman behaviour of forsterite. It includes ‘bond bending’ terms, that model the directionality of the Si-O bond, in addition to the pair-wise additive Coulombic and short range terms. The phonon dispersion relationships of the Mg₂SiO₄ polymorphs predicted by THB1 were used to calculate the heat capacities, entropies, thermal expansion coefficients and Gruneisen parameters of these phases. The predicted heat capacities and entropies are in outstandingly good agreement with those determined experimentally. The predicted thermodynamic data of these phases were used to construct a phase diagram for this system, which has Clausius-Clapeyron slopes in very close agreement with those found by experiment, but which has predicted transformation pressures that show less close agreement with those inferred from experiment. The overall success, however, that we have in predicting the lattice dynamical and thermodynamic properties of the Mg₂SiO₄ polymorphs shows that our potential THB1 represents a significant step towards finding the elusive quantitative link between the microscopic or atomistic behaviour of minerals and their macroscopic properties.  相似文献   

Book review     

John M. Cubitt  Stephen R. Hunt 《Mathematical Geosciences》1987,19(4):361-364

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Kriging—Blue or pink?     

Stephen Henley 《Mathematical Geosciences》1987,19(2):155-158

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KARST OF CHINA     

J. Stephen Schindler 《Ground water》1982,20(2):226-230

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Cyclic Storage: A Preliminary Assessment     

Dennis P. Lettenmaier  Stephen J. Burges 《Ground water》1982,20(3):278-288

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