Seamount chains formed near the crest of Juan de Fuca Ridge,northeast Pacific Ocean     

Sandra M. Barr 《Marine Geology》1974,17(2):1-19

Heck and Heckle are seamount chains trending approximately northwest on the western flank of Juan de Fuca Ridge near its northern end. Evidence from magnetic anomalies and from chemistry and relative ages of dredged basalt suggests that the seamounts in these chains are produced near the spreading centre on Juan de Fuca Ridge and do not continue to grow as they are carried away by sea-floor spreading. Their development is possibly related to transverse fractures on Juan de Fuca Ridge resulting from reorientation of the ridge from north to north-northeast which began about 8 m.y. ago, combined with tension in the Pacific Plate. In contrast the Eickelberg Chain to the south may have been produced by a fixed-mantle plume now located near Juan de Fuca Ridge, as suggested by limited basalt geochemistry and by the long and productive life of that chain. The Pratt-Welker Chain may also have been produced by a mantle plume, but most other seamounts on the western flanks of Juan de Fuca and Explorer ridges are thought to have formed at crustal fractures near the spreading centres in the same way as the seamounts of the Heck and Heckle chains.  相似文献   

Melts of garnet lherzolite: experiments, models and comparison to melts of pyroxenite and carbonated lherzolite   总被引：2，自引：2，他引：0  

Timothy L. Grove  Eva S. Holbig  Jay A. Barr  Christy B. Till  Michael J. Krawczynski 《Contributions to Mineralogy and Petrology》2013,166(3):887-910

Phase equilibrium experiments on a compositionally modified olivine leucitite from the Tibetan plateau have been carried out from 2.2 to 2.8 GPa and 1,380–1,480 °C. The experiments-produced liquids multiply saturated with spinel and garnet lherzolite phase assemblages (olivine, orthopyroxene, clinopyroxene and spinel ± garnet) under nominally anhydrous conditions. These SiO₂-undersaturated liquids and published experimental data are utilized to develop a predictive model for garnet lherzolite melting of compositionally variable mantle under anhydrous conditions over the pressure range of 1.9–6 GPa. The model estimates the major element compositions of garnet-saturated melts for a range of mantle lherzolite compositions and predicts the conditions of the spinel to garnet lherzolite phase transition for natural peridotite compositions at above-solidus temperatures and pressures. We compare our predicted garnet lherzolite melts to those of pyroxenite and carbonated lherzolite and develop criteria for distinguishing among melts of these different source types. We also use the model in conjunction with a published predictive model for plagioclase and spinel lherzolite to characterize the differences in major element composition for melts in the plagioclase, spinel and garnet facies and develop tests to distinguish between melts of these three lherzolite facies based on major elements. The model is applied to understand the source materials and conditions of melting for high-K lavas erupted in the Tibetan plateau, basanite–nephelinite lavas erupted early in the evolution of Kilauea volcano, Hawaii, as well as younger tholeiitic to alkali lavas from Kilauea.  相似文献   

A reconstruction of extratropical Indo-Pacific sea-level pressure patterns during the Medieval Climate Anomaly     

Ian D. Goodwin  Stuart Browning  Andrew M. Lorrey  Paul A. Mayewski  Steven J. Phipps  Nancy A. N. Bertler  Ross P. Edwards  Tim J. Cohen  Tas van Ommen  Mark Curran  Cameron Barr  J. Curt Stager 《Climate Dynamics》2014,43(5-6):1197-1219

Subtropical and extratropical proxy records of wind field, sea level pressure (SLP), temperature and hydrological anomalies from South Africa, Australia/New Zealand, Patagonian South America and Antarctica were used to reconstruct the Indo-Pacific extratropical southern hemisphere sea-level pressure anomaly (SLPa) fields for the Medieval Climate Anomaly (MCA ~700–1350 CE) and transition to the Little Ice Age (LIA 1350–1450 CE). The multivariate array of proxy data were simultaneously evaluated against global climate model output in order to identify climate state analogues that are most consistent with the majority of proxy data. The mean SLP and SLP anomaly patterns derived from these analogues illustrate the evolution of low frequency changes in the extratropics. The Indo-Pacific extratropical mean climate state was dominated by a strong tropical interaction with Antarctica emanating from: (1) the eastern Indian and south-west Pacific regions prior to 1100 CE, then, (2) the eastern Pacific evolving to the central Pacific La Niña-like pattern interacting with a +ve SAM to 1300 CE. A relatively abrupt shift to –ve SAM and the central Pacific El Niño-like pattern occurred at ~1300. A poleward (equatorward) shift in the subtropical ridge occurred during the MCA (MCA–LIA transition). The Hadley Cell expansion in the Australian and Southwest Pacific, region together with the poleward shift of the zonal westerlies is contemporaneous with previously reported Hadley Cell expansion in the North Pacific and Atlantic regions, and suggests that bipolar climate symmetry was a feature of the MCA.  相似文献   

ELF and VLF radio waves     

R. Barr  D. Llanwyn Jones  C. J. Rodger 《Journal of Atmospheric and Solar》2000,62(17-18)

This review covers developments in ELF and VLF radio-wave propagation research over the last 50 years of the Journal of Atmospheric and Solar-Terrestrial Physics. A review of such a large field, over such a long period, cannot be fully comprehensive and the authors have therefore covered important areas which have they themselves have found interesting. The survey begins with a review of work on natural and man made sources of ELF and VLF radiation. This is followed by sections on experimental and theoretical studies of unperturbed (ambient) ELF and VLF radio propagation. Schumann resonance research, which is currently undergoing a renaissance, is then reviewed. A review of research into transient perturbations of ELF and VLF propagation follows, extending from the early work on nuclear explosions up to the current work on sprites. The review concludes with a brief summary of the VLF navigation systems of the USSR and USA, (Alpha and Omega) whose development and life-span covered most of the last 50 years.  相似文献   

Divergent/passive Margin Basins: Edwards, J. D. and Santogrossi, P. A. (editors) 1990. American Association of Petroleum Geologists Memoir 48. The American Association of Petroleum Geologists, Tulsa, Oklahoma, U.S.A. Price $102 hardcover. AAPG members $68     

David Barr 《Journal of Structural Geology》1991,13(10)

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Coefficient of permeability determined by measurable parameters   总被引：1，自引：0，他引：1  

Barr DW 《Ground water》2001,39(3):356-361

Selection of a coefficient of permeability or the hydraulic conductivity in practical situations has required a fair amount of judgment and the expectation of accuracy can range over an order of magnitude. A determination of the coefficient based on measurable characteristics would greatly reduce the judgment aspect. The coefficient of permeability of a porous media can be derived from the following measurable parameters: the density and viscosity of the permeating fluid, the porosity of the media, the average hydraulic radius of the pores, and the gravitation constant. The hydraulic radius is calculated from the grain size distribution analysis of the porous media assuming spherical particles and a factor to account for the shape of the particles. The shape factor ranges from 1.0 to 1.4 in the extreme but, for common porous media, ranges only from 1.0 to about 1.1. All of the variables, except the shape factor, are measurable by standard test procedures. An important advantage of using this procedure for determining permeability is that the factors can be visualized as part of the physical flow process. The procedure assumes laminar flow and applies equally to liquid or gas fluids.  相似文献   

Turbulent flow through porous media     

Barr DW 《Ground water》2001,39(5):646-650

The pressure driving flow through porous media must be equal to the viscous resistance plus the inertial resistance. Formulas are developed for both the viscous resistance and the inertial resistance. The expression for the coefficient of permeability consists of parameters which describe the characteristics of the porous medium and the permeating fluid and which, for unconsolidated isotropic granular media, are all measurable. A procedure is proposed for testing for the occurrence of turbulence and calculating the effective permeability when it occurs. The formulas are applied to a set of data from 588 permeameter runs ranging from laminar to highly turbulent. The equations fit the data from the permeameter closely through the laminar flow conditions and quite closely through the turbulent conditions. In the turbulent range, the plotting of the data separates into three distinct lines for each of the three shapes of particles used in the tests. For the porous medium and fluid of these tests, turbulence begins at a head gradient of about 0.1.  相似文献   

The planning of NOAO 8 m telescope enclosure and facilities     

Woon-Yin Wong  Lawrence D. Barr 《Astrophysics and Space Science》1989,160(1-2):87-101

The National Optical Astronomy Observatories (NOAO) proposes to build 8 m telescopes at two locations. The Northern Hemisphere location is on Mauna Kea, Hawaii, and the Southern Hemisphere location is within the existing boundary of the Cerro Tololo Inter-American Observatory. This paper describes the sites under consideration and the facilities that support the operation of each telescope, namely, the telescope enclosure, the control facility, and the recoating facility.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation.  相似文献   

Ecosystem metabolism and carbon fluxes of a tidally-dominated coastal lagoon   总被引：1，自引：0，他引：1  

Rui?SantosEmail author  Jo?o?Silva  Ana?Alexandre  Nuria?Navarro  Cristina?Barrón  Carlos?M.?Duarte 《Estuaries and Coasts》2004,27(6):977-985

The metabolism and carbon flux in the western sector of the highly dynamic coastal lagoon Ria Formosa (south Portugal) were assessed to elucidate the relative importance of the contribution of the main communities, the treated sewage inputs from the adjacent city of Faro, and the exchange with the adjacent coastal waters to the ecosystem metabolism. The results depict the Ria Formosa as being a highly productive ecosystem dominated by the seagrassZostera noltii. The community dominated by the seagrassCymodocea nodosa had half of the gross production ofZ. noltii, followed by bare sediments and phytoplankton. The net contribution of seagrasses to community metabolism was negligible, as bothZ. noltii andC. nodosa showed a production: respiration ratio close to 1. Benthic microalgae emerge as the most important components of the net metabolism. The western sector of Ria Formosa was in metabolic balance during the summer when the study was done. Even though the total net ecosystem production was 7.22 Kmol C d⁻¹, the error associated with this estimate was 8.38 Kmol C d⁻¹, so ecosystem net production was not significantly different from zero. The Ria Formosa ecosystem is shallow and rapidly flushed by the tides, which force an important exchange of dissolved organic carbon (DOC) and particulate organic carbon (POC) with the adjacent coastal waters. The daily net export rate to the adjacent coastal waters, 0.98 Kmol d⁻¹, represented 7.6% of the net ecosystem production, suggesting that the bulk of the net ecosystem production accumulates within the ecosystem. The organic carbon retention in the western sector of the Ria Formosa is higher than net production, because the allochthonous carbon inputs from urban sewage enter the carbon mass balance with about 40% of the autochthonous processes, at about 1.6 Kmol d⁻¹ of DOC and 2.8 Kmol d⁻¹ of POC. The western sector of Ria Formosa has an organic carbon sink of about 46.4 tons per year. Most of this is harvested in the form of molluscs (clams, cuttlefish, etc.) and fish (sea bream, sea bass, etc.). The total carbon harvested every year in the form of bivalves is about 40 tons, rendering the Ria Formosa the most productive seafood area in Portugal.  相似文献   

A decision support system for geotechnical applications     

D. G. Toll  R. J. Barr 《Computers and Geotechnics》2001,28(8):575-590

A knowledge-based system shell called ‘Confound’ has been developed for the production of decision support systems. It was initially used for developing a system for conceptual foundation design but has subsequently been used for retaining wall, expansive soil and ground investigation applications. It uses a hierarchical object-oriented knowledge base where each object represents a decision in the decision making process. A simple rule-based approach is used to provide advice on the suitability of each potential choice, based on project specific information that is provided by the user. Confound has the ability to work with incomplete information and uses a system of confidence levels so that the user is aware of the confidence with which each piece of advice is given. Conflicting information in areas where knowledge is poorly defined can also be handled. Confound is designed to leave the user in full control. It simply provides comments on suitability (with an indication of confidence) and leaves the final decision to the user.  相似文献