Jumps in deformation gradients and particle velocities across propagating coherent boundaries     

P.R. Cobbold  W.D. Means  M.B. Bayly 《Tectonophysics》1984,108(3-4)

Grain boundaries and axial surfaces of folds are geological examples of thin transition zones, which can be modelled mathematically as surfaces of discontinuity. Here we consider coherent boundaries, across which no material lines are ever discontinuous, but deformation gradients and particle velocities can be so. A discontinuity in particle velocity requires that a coherent boundary propagate (migrate) through the material.The geometry and kinematics of coherent boundaries were studied by Hadamard (1903) and reviewed by Truesdell and Toupin (1960). Here, we rederive their results in a geological context, using modern notation and simple coordinates. We conclude that velocity gradient, stretching and spin can all be discontinuous. Applied to ideal kink bands in non-dilatant foliated materials, the theory predicts that kink boundaries rotate through the material at exactly the rate needed to maintain fold symmetry. In a polycrystalline aggregate, easily migrating coherent grain boundaries are mechanically analogous to slippery incoherent boundaries: both kinds support little shear stress.  相似文献   

Comprehensive chemical analyses of natural cordierites: implications for exchange mechanisms     

Christian Bertoldi  Alexander Proyer  Dieter Garbe-Schnberg  Harald Behrens  Edgar Dachs 《Lithos》2004,78(4):389-409

Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H₂O and CO₂ (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg₋₁ and MnMg₋₁ on the octahedral site, some minor KNa₋₁ on the Ch0 channel site, and Fe³⁺Al₋₁ on the T₁1 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□₋₁Mg₋₁), and of Be and other divalent cations on the tetrahedral T₁1 site (NaBe□₋₁Al₋₁ and Na(Mg,Fe²⁺)□₋₁Al₋₁). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: ^Ch(Na,K)_0–1 ^VI(Mg,Fe²⁺,Mn,Li)₂ ^IVSi₅ ^IVAl₃ ^IV(Al, Be, Mg, Fe²⁺, Fe³⁺)O₁₈ *x^Ch(H₂O, CO₂…). Our results show that the population of (Mg, Fe²⁺) on the T₁1-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M²⁺–Na.  相似文献   

Nonlinear numerical assessment of the seismic response of hillside RC buildings     

Miguel A.Gómez  Edgar Giovanny Díaz-Segura  Juan Carlos Vielma 《地震工程与工程振动(英文版)》2021,20(2):423-440

Major damage has been reported in hilly areas after major earthquakes,primarily because of two special conditions:the variation in the seismic ground motion due to the inclined ground surface and the irregularities caused by a stepped base level in the structure.The aim of this study is to evaluate possible differences in the responses of Chilean hillside buildings through numerical linear-elastic and nonlinear analyses.In the first step,a set of response-spectrum analyses were performed on four simplified 2D structures with mean base inclination angles of 0°,15°,30°,and 45°.The structures were designed to comply with Chilean seismic codes and standards,and the primary response parameters were compared.To assess the seismic performance of the buildings,nonlinear static(pushover)and dynamic(time-history)analyses were performed with SeismoStruct software.Pushover analyses were used to compare the nonlinear response at the maximum roof displacement and the damage patterns.Time-history analyses were performed to assess the nonlinear dynamic response of the structures subjected to seismic ground motions modified by topographic effects.To consider the topographic modification,acceleration records were obtained from numerical models of soil,which were calculated using the rock acceleration record of the Mw 8.01985 Chilean earthquake.Minor differences in the structure responses(roof displacements and maximum element forces and moments)were caused by the topographic effects in the seismic input motion,with the highly predominant ones being the differences caused by the step-back configuration at the base of the structures.High concentrations of shear forces in short walls were observed,corresponding to the walls located in the upper zone of the foundation system.The response of the structures with higher angles was observed to be more prone to fragile failures due to the accumulation of shear forces.Even though hillside buildings gain stiffness in the lower stories,resulting in lower design roof displacement,maximum roof displacements for nonlinear time-history analyses remained very close for all the models that were primarily affected by the drifts of the lower stories.Additionally,vertical parasitic accelerations were considered for half the time-history analyses performed here.The vertical component seems to considerably modify the axial load levels in the shear walls on all stories.  相似文献   

Physical models of magmatic intrusion during thrusting     

Olivier Galland  Jean de Bremond d'Ars  Peter R. Cobbold  Erwan Hallot 《地学学报》2003,15(6):405-409

To investigate how magma rises through the brittle upper crust in a context of compressional tectonics, we have performed experiments on scaled physical models. Powdered silica (having a cohesion of 300 Pa and an angle of internal friction of 38°) was used to represent brittle crust. A vegetable oil (with a Newtonian viscosity of 10^?2 Pa·s at 50 °C) was used to represent magma. A moving piston shortened the models in a box, while oil was injected steadily at the base. On cooling to room temperature, the oil solidified. The resulting intrusions were thin sills, dykes and laccoliths. Their shapes and emplacement modes depended on the ratio R between rates of shortening and injection. From shapes and orientations of intrusions, we infer that hydraulic fracturing was one mechanism of emplacement. Unconsolidated intrusions strongly influenced thrust formation. On the basis of our experiments, we suggest that magmas in orogenic belts can rise along thrust faults.  相似文献   

The Helmeth Grits of the Caradoc Range,church stretton; their bearing on part of the Pre-Cambrian succesion of Shropshire     

Edgar Sterling Cobbold  Walter Frederick Whittard 《Proceedings of the Geologists' Association. Geologists' Association》1935,46(3):348-IN13

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SHEBA flux–profile relationships in the stable atmospheric boundary layer     

Andrey A. Grachev  Edgar L Andreas  Christopher W. Fairall  Peter S. Guest  P. Ola G. Persson 《Boundary-Layer Meteorology》2007,124(3):315-333

Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used to examine the profile stability functions of momentum, φ _m , and sensible heat, φ _h , in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φ _m and φ _h in detail and includes ample data for the very stable case. New parameterizations for φ _m (ζ) and φ _h (ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ _m follows a ζ ^1/3 dependence, whereas φ _h initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects of self-correlation, which occur in plots of φ _m and φ _h versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging.  相似文献   

Effect of moisture content on ammonia emissions from broiler litter: A laboratory study   总被引：3，自引：0，他引：3  

Zifei Liu  Lingjuan Wang  David Beasley  Edgar Oviedo 《Journal of Atmospheric Chemistry》2007,58(1):41-53

A dynamic flow-through chamber system was designed to measure ammonia emissions from broiler litter and to investigate the responses of ammonia emissions to litter moisture content under laboratory-controlled conditions. It was observed that ammonia emissions from litter were very sensitive to litter moisture content. As water was added to the litter, the total ammoniac nitrogen content (TAN) in the litter increased, and can potentially increase ammonia emissions. However, measurements of ammonia concentrations in the chamber and total nitrogen losses from litter samples all suggested that water applied to the litter also had an effect of suppressing ammonia emissions for a short time. After enough time (1 to 2 weeks) was allowed, higher moisture content in litter eventually resulted in higher ammonia emissions. It was also noticed that, at very high litter moisture content, even when more time was allowed, ammonia concentrations began to decrease as moisture content further increased.  相似文献   

Progress in NTHMP Hazard Assessment     

Frank I. González  Vasily V. Titov  Harold O. Mofjeld  Angie J. Venturato  R. Scott Simmons  Roger Hansen  Rodney Combellick  Richard K. Eisner  Don F. Hoirup  Brian S. Yanagi  Sterling Yong  Mark Darienzo  George R. Priest  George L. Crawford  Timothy J. Walsh 《Natural Hazards》2005,35(1):89-110

The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers.  相似文献   

Pumping of a planetesimal disc by a rapidly migrating planet     

Richard Edgar  Pawel Artymowicz 《Monthly notices of the Royal Astronomical Society》2004,354(3):769-772

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Exploration for a Buried Valley by Resistivity and Thermal Probe Surveys     

Edgar M. Smith 《Ground water》1974,12(2):78-83

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