Variations in the velocities of the major plates since the late cretaceous     

Daniel M. Davis  Sean C. Solomon 《Tectonophysics》1981,74(1-2)

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Finite strain theories and comparisons with seismological data     

F. D. Stacey  B. J. Brennan  R. D. Irvine 《Surveys in Geophysics》1981,4(3):189-232

All the finite strain equations that we are aware of that are worth considering in connection with the interior of the Earth are given, with the assumptions on which they are based and corresponding relationships for incompressibility and its pressure derivatives in terms of density. In several cases, equations which have been presented as new or independent are shown to be particular examples of more general equations that are already familiar. Relationships for deriving finite strain equations from atomic potential functions or vice versa are given and, in particular it is pointed out that the Birch-Murnaghan formulation implies a sum of power law potentials with even powers. All the equations that survive simple plausibility tests are fitted to the lower mantle and outer core data for the PEM earth model. For this purpose the model data are extrapolated to zero temperature, using the Mie-Grüneisen equation to subtract the thermal pressure (at fixed density) and the pressure derivative of this equation to substract the thermal component of incompressibility. Fitting of finite strain equations to such zero temperature data is less ambiguous than fitting raw earth model data and leads immediately to estimates of the low temperature zero pressure parameters of earth materials. On this basis, using the best fitting equations and constraining core temperature to give an extrapolated incompressibilityK ₀=1.6×10¹¹Pa, compatible with a plausible iron alloy, the following numerical data are obtained: Core-mantle boundary temperature 3770 K Zero pressure, zero temperature densities: lower mantle 4190 kg m^–3 outer core (solidified) 7500 kg m^–3 Zero pressure, zero temperature incompressibility of the lower mantle 2.36×10¹¹PaHowever, an inconsistency is apparent betweenP() andK() data, indicating that, even in the PEM model, in which the lower mantle is represented by a single set of parameters, it is not perfectly homogeneous with respect to composition and phase.  相似文献   

Piezomagnetic effect of ground loading by Lake Gordon, Tasmania     

B.J. Brennan  L.M. Hastie 《Tectonophysics》1979,56(3-4)

A series of precisely repeated magnetic surveys has been carried out over a five year period, during the filling of Lake Gordon, Tasmania, following construction of a dam. After subtraction of the secular variation gradient over the region, a mean decrease of 1.6 nT in total field intensity is found over the survey area, which exceeds 600 km², corresponding to the expected form of a tectonomagnetic anomaly due to ground loading. During the survey period there were several local magnetic events, coinciding with more rapid, local changes in benchmark levels, that may be attributed to aseismic movements on faults in the area.  相似文献   

Atmospheric Disturbances that Generate Intermittent Turbulence in Nocturnal Boundary Layers     

Jielun Sun  Donald H. Lenschow  Sean P. Burns  Robert M. Banta  Rob K. Newsom  Richard Coulter  Stephen Frasier  Turker Ince  Carmen Nappo  Ben B. Balsley  Michael Jensen  Larry Mahrt  David Miller  Brian Skelly 《Boundary-Layer Meteorology》2004,110(2):255-279

Using the unprecedented observational facilities deployed duringthe 1999 Cooperative Atmosphere-Surface Exchange Study (CASES-99),we found three distinct turbulent events on the night of 18October 1999. These events resulted from a density current,solitary wave, and internal gravity wave, respectively. Our studyfocuses on the turbulence intermittency generated by the solitarywave and internal gravity wave, and intermittent turbulenceepisodes associated with pressure change and wind direction shiftsadjacent to the ground. Both the solitary and internal gravitywaves propagated horizontally and downward. During the passage ofboth the solitary and internal gravity waves, local thermal andshear instabilities were generated as cold air was pushed abovewarm air and wind gusts reached to the ground. These thermal andshear instabilities triggered turbulent mixing events. Inaddition, strong vertical acceleration associated with thesolitary wave led to large non-hydrostatic pressure perturbationsthat were positively correlated with temperature. The directionaldifference between the propagation of the internal gravity waveand the ambient flow led to lateral rolls. These episodic studiesdemonstrate that non-local disturbances are responsible for localthermal and shear instabilities, leading to intermittentturbulence in nocturnal boundary layers. The origin of thesenon-local disturbances needs to be understood to improve mesoscalenumerical model performance.  相似文献   

Geostatistical interpolation of object counts collected from multiple strip transects: Ordinary kriging versus finite domain kriging   总被引：2，自引：0，他引：2  

Hirotaka Saito  Sean A. McKenna  D. A. Zimmerman  Timothy C. Coburn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(1):71-85

Data collected along transects are becoming more common in environmental studies as indirect measurement devices, such as geophysical sensors, that can be attached to mobile platforms become more prevalent. Because exhaustive sampling is not always possible under constraints of time and costs, geostatistical interpolation techniques are used to estimate unknown values at unsampled locations from transect data. It is known that outlying observations can receive significantly greater ordinary kriging weights than centrally located observations when the data are contiguously aligned along a transect within a finite search window. Deutsch (1994) proposed a kriging algorithm, finite domain kriging, that uses a redundancy measure in place of the covariance function in the data-to-data kriging matrix to address the problem of overweighting the outlying observations. This paper compares the performances of two kriging techniques, ordinary kriging (OK) and finite domain kriging (FDK), on examining unexploded ordnance (UXO) densities by comparing prediction errors at unsampled locations. The impact of sampling design on object count prediction is also investigated using data collected from transects and at random locations. The Poisson process is used to model the spatial distribution of UXO for three 5000 × 5000 m fields; one of which does not have any ordnance target (homogeneous field), while the other two sites have an ordnance target in the center of the site (isotropic and anisotropic fields). In general, for a given sampling transects width, the differences between OK and FDK in terms of the mean error and the mean square error are not significant regardless of the sampled area and the choice of the field. When 20% or more of the site is sampled, the estimation of object counts is unbiased on average for all three fields regardless of the choice of the transect width and the choice of the kriging algorithm. However, for non-homogeneous fields (isotropic and anisotropic fields), the mean error fluctuates considerably when a small number of transects are sampled. The difference between the transect sampling and the random sampling in terms of prediction errors becomes almost negligible if more than 20% of the site is sampled. Overall, FDK is no better than OK in terms of the prediction performances when the transect sampling procedure is used.  相似文献   

Specific Storage Volumes: A Useful Tool for CO2 Storage Capacity Assessment   总被引：1，自引：0，他引：1  

Sean T. Brennan  Robert C. Burruss 《Natural Resources Research》2006,15(3):165-182

Subsurface geologic strata have the potential to store billions of tons of anthropogenic CO₂; therefore, geologic carbon sequestration can be an effective mitigation tool used to slow the rate at which levels of atmospheric CO₂ are increasing. Oil and gas reservoirs, coal beds, and saline reservoirs can be used for CO₂ storage; however, it is difficult to assess and compare the relative storage capacities of these different settings. Typically, CO₂ emissions are reported in units of mass, which are not directly applicable to comparing the CO₂ storage capacities of the various storage targets. However, if the emission values are recalculated to volumes per unit mass (specific volume) then the volumes of geologic reservoirs necessary to store CO₂ emissions from large point sources can be estimated. The factors necessary to convert the mass of CO₂ emissions to geologic storage volume (referred to here as Specific Storage Volume or ‘SSV’) can be reported in units of cubic meters, cubic feet, and petroleum barrels. The SSVs can be used to estimate the reservoir volume needed to store CO₂ produced over the lifetime of an individual point source, and to identify CO₂ storage targets of sufficient size to meet the demand from that given point source. These storage volumes also can then be projected onto the land surface to outline a representative “footprint,” which marks the areal extent of storage. This footprint can be compared with the terrestrial carbon sequestration capacity of the same land area. The overall utility of this application is that the total storage capacity of any given parcel of land (from surface to basement) can be determined, and may assist in making land management decisions.  相似文献   

Late Quaternary secular variation of geomagnetic declination in western New York     

William J. Brennan  Mark J. Hamilton  Richard K. Kilbury  Richard L. Reeves  Laura J. Covert 《Earth and Planetary Science Letters》1984,70(2):363-372

A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (¹⁴C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated.  相似文献   

Chemical beneficiation of zircon concentrates in Western Australia     

L.J. Brennan  R.V. Field  T.J. George  R.E. Marshall 《International Journal of Mineral Processing》1984,13(4):251-258

Western Australian zircons are typically brown-strained and inherently tinged with colour so that production of premium grade zircon has required special attention. The brown coating interferes with the separation of zircon from other minerals and adds to the level of impurities, particularly iron, in the product. Even when the stain is removed the zircon's pink-purple hue detracts from its market appeal. Two separate processes for the beneficiation of zircon to premium grade have been evaluated for three typical Western Australian zircon concentrates. One of the processes has been successfully implemented on a commercial scale.  相似文献   

Geo-historical Trajectories of Democratic Transition: The Case of Nigeria     

Brennan Kraxberger 《GeoJournal》2004,60(1):81-92

There has been a long-term, halting diffusion of the liberal democratic state. The literature on democratization, however, tends to underplay issues of geo-historical context. This paper addresses the relationship between geo-historical context and democratization through a case study of Nigeria. Key contextual factors of transition discussed include: international pressure for democratization, geo-political dynamics of pro-democracy coalitions, and local and trans-local political economic relationships. Nigeria under the military governments of Babangida and Abacha (1985–1998) was in a perpetual half-hearted state of transition to democracy. The country's status as a major oil exporter allowed it relative immunity from international pressure for democratization. Beyond repression and neo-patrimonialism, both governments deployed a distinctly spatial resistance strategy, that of state creation. The generals tried to shift attention away from regime failures and excesses, notably the illegitimacy of military rule and economic decline. Mobilization for state creation served to divide opposition to military government because it focused attention at the local scale, as new state movements competed for access to centrally controlled resources and political recognition of their ethno-regional group(s). This transition period produced several legacies for Nigeria's Fourth Republic (1999-). These include: a dysfunctional national state apparatus; problems of national disunity; and a stagnant economy. These legacies of transition present major obstacles to national development and the consolidation of a liberal democratic state. The Nigerian case points to a broader need for an understanding of geo-historical context in assessing prospects for the spread of democracy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Nucleosynthesis and early chemical evolution in galaxies     

Stelios A Tsangarides  Enrico Arnone  Sean G Ryan 《Astronomy& Geophysics》2003,44(2):2.28-2.29

Nucleosynthesis and galactic chemical evolution are inter-linked topics that merge various fields in astronomy and physics. Speakers at the RAS discussion meeting of January 2003 combined theory and observation in understanding these fields. Stelios A Tsangarides, Enrico Arnone and Sean G Ryan report.  相似文献